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Preparation and assessment of a candidate reference sample of Lake Baikal deep water
Spectrochimica Acta Part B 58 (2003) 277–288
Preparation and assessment of a candidate reference sample of Lake Baikal deep water夞 A.N. Suturina, L.F. Paradinaa,*, V.N. Epova, A.R. Semenova, V.I. Lozhkina, L.L. Petrovb a
Limnological Institute, Siberian Branch, Russian Academy of Sciences, Ulan-Batorskaya, 3, Irkutsk 664033, Russia b Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Favorsky, 1-a, Irkutsk 664033, Russia Received 1 October 2001; accepted 15 July 2002
Abstract The possibility of the creation of a multi-element reference sample of Lake Baikal deep-water composition is justified. This is a new type of reference sample composed of natural water with a wide range of macro- and microelements. This candidate reference sample has a matrix composition consisting of hydrocarbonate and calcium water, a composition that is typical of many rivers and lakes of the world, as well as rain water. The creation of a candidate reference sample of Lake Baikal water is possible due to the stable water composition at a depth of 500 m, and to the use of water sampling technology which results in the preservation of the initial composition of water and its absolute sterility. Trial batches of Baikal water collected annually and stored in special polyethylenetereftalate bottles for a period of 9 years remained stable and homogenous for most elements. Preliminary data for a range of elements and compounds are presented. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: Lake Baikal water; Reference sample; Analytical data quality; Homogeneity; Interlaboratory analytical program
1. Introduction Systems of scientific management of the environment state, which are formed in contemporary world, include both observation and assessment of the water ecosystems as an important initial factor. Information on the chemical composition of water 夞 This paper was presented at the INTERSIBGEOCHEM 01 Conference held in Irkutsk, Siberia, Russia, 24–27 July 2001 and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference. *Corresponding author. Tel.: q3952-42-29-51; fax: q395242-54-05. E-mail address: [email protected] (L.F. Paradina).
is of great importance for chemical and ecological monitoring of reservoirs and for predicting the quality of drinking water sources. Commonly used synthetic reference samples (RS) cannot completely reflect the specific character of matrix water composition, which may lead to errors in the results of analysis. Reference samples of natural freshwater composition with intact natural chemical matrix are still not available in Russia. The idea of using Baikal water for standardization of chemical investigations has been previously suggested w1,2x. The attempt to create an RS of Baikal water was undertaken by Institute of Physico-technical and Radiotechnical Measurements
0584-8547/03/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 8 4 - 8 5 4 7 Ž 0 2 . 0 0 1 5 7 - X
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Fig. 1. Ratio between the content of cations and ions in environment objects: 1, Baikal water; 2, lake water w4x; 3, river water w5,6x; 4, rain water w4x; 5, snow water w4,6x.
(Irkutsk) in 1993, but unfortunately this project did not come to fruition. The creation of reference samples of Lake Baikal water composition according to international requirements to reference samples of environment objects was initiated by M.A. Grachev, Director of Limnological Institute of Siberian Branch, Russian Academy of Sciences (SB, RAS). A Baikal reference water is required, principally for investigations of Lake Baikal itself w3x. Differences in the results of analysis of Baikal water composition for some elements (for example, mercury) by various authors varies by as much as 3 orders. This lack of agreement precludes an accurate assessment of changes in water composition and the role of anthropogenic factors in these changes.
The chemical matrix of freshwater reservoirs and rivers w4–6x, as well as atmospheric precipitation, is close to that of Lake Baikal waters (Fig. 1). Therefore, a multi-element reference sample of Baikal water would be a useful tool particularly for monitoring surveys. Changes to water quality standards (Fig. 2) are moving towards a composition similar to that of Lake Baikal water. Hence, a Baikal reference sample water will be of particular importance for the analysis of drinking water supplies and of bottled water. During the development of this candidate reference material, long-term hydrophysical, hydrochemical and hydrobiological measurements were made by the Limnological Institute SB of RAS w3–5,7,8x, and procedures were employed similar
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to those used for the preparation of other reference materials w2,9–15x. 2. Characteristics of Lake Baikal water
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composition of the main part of Lake Baikal water (over 17 000 km3). 3. Experimental 3.1. Water preparation
The water of Lake Baikal has pH 7.6, and it belongs to the category ultra-fresh, hydrocarbonate and calcium water with low mineralization. The total content of dissolved salts in Baikal water does not exceed 100 mgyl. Therefore, it follows the laws of ideal solutions w16x. Hence, there is no index of saturation for the majority of compounds. The element leaching from the dissolved state is only accomplished as a result of adsorption, colloid processes and consumption of elements by vital substances. Because of the water non-saturation, its ionic composition depends on the life activity of hydrobionts. Besides low mineralization, there are high concentrations of dissolved gases, particularly oxygen, which determines its chemical activity. The water column of Lake Baikal is divided into three zones w17x. Of special stability is the water of Baikal ‘nucleus’ — the zone at a depth from 300 m under the surface to 100 m above the bottom w18x. The surface water reaches the bottom of Lake Baikal on the average in 7–8 years. The ‘nucleus’ water, however, is exchanged more slowly, on average the surface water penetrates into the ‘nucleus’ only once in 10–14 years w17,19x. It means that aquatic organisms purify the water in the ‘nucleus’ zone for longer and more effectively. Turbid flows appearing near the shores, also pass by the ‘nucleus’ zone. In this zone, there are almost no diatoms, which are in abundance near the surface and are ‘pressed’ to the slope of the depression w20x. In the ‘nucleus’ zone, the temperature stays 3.5 8C all the year round w17,19x. According to published data w7,17,21–26x, there are changes of chemical composition (Fig. 3) (especially anions) in near-surface and near-bottom zones, in contrast to the water of the ‘nucleus’ zone which is stable in most elements. Thus, the sampling water from the deep zone provides a stable composition, and allows us to get a representative water sample, which demonstrates the
A permanent water sampling point was chosen in Listvenichny Bay at a depth of 500 m, 1.7 km off the shore. The sampling site is 200 m above the bottom of the lake. A permanent pipeline was laid from the sampling point to the shore. From the sampling point, the water is transported, via this pipeline, to an onshore works for processing. To avoid water contamination by alien elements while transporting samples to the shore, experimental surveys were performed to select the appropriate water-pipe material. They showed that even a short-term interaction of water with stainless steel and zinccoated tubes significantly increased the content of iron, zinc, nickel, vanadium, chrome, manganese and other metals in the water. The best result was achieved for polyethylene tubes. To purify the water from biota and suspended sediment, a stepwise water filtration and sterilization system was developed for the onshore processing works (Fig. 4). The material of an ultra-thin filter considerably influences filtrate composition. The investigations showed that the concentration of nickel in water increased up to 95 mgyl (before filtration 0.17 mgyl) and iron from 0.5 to 7.8 mgy l. Therefore, in the filtration system used, polypropylene filter-holders, which do not affect water composition were employed. Deep-water samples passed through 5-, 1- and 0.45-mm filters, were then ozonized and processed by ultraviolet radiation, and finally bottled. The element composition of water at the permanent sampling-point has been studied for 7 years w24–26x. Water sampling was performed at different seasons of a year following the above technique. The analytical method used was inductively coupled plasma mass-spectrometry (ICP-MS). 3.2. Package and storage of a reference sample Research was conducted to assess the best storage media w26x. In 1993, the water was placed
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Fig. 2. Norms of quality of drinking water: a, major components; b, microelements; 1, EEC, 2, Russia GOST; 3, WHO; 4, EPA USA; 5, Switzerland; 6, Lake Baikal water.
into glass and polyethylentereftalate (PET) bottles. In 1999, the bottles were opened and the water was analyzed. Simultaneously some more fresh samples from Lake Baikal were analyzed. Our investigations (Table 1) showed that during the storage of samples in glass vessels, sorption of cobalt on the vessel walls was observed as well as desorption of manganese, copper, zinc, sodium, barium cations and sulfates from glass. No sorption of macro- and microelements on the walls of PET package have been found. Thus, polyethylenteref-
talate bottles were chosen for packing. This material, unlike other plastics, is impervious to gases and does not isolate significant quantity of organic ingredients (acitaldegid and ftalates) into the water. In order to determine the conditions of storage and transportation of the water, subsamples were exposed to extremes of temperature. Freezing and subsequent thawing of a test sample caused partial deposition of organic compounds dissolved in the water: their quantity decreasing from 0.4 to 0.2–
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0.3 mgyl. There were also slight changes in microelement composition. Changes in pH were also observed. The value of pH remained constant to a temperature of 40 8C. Within the range of 40–70 8C, dissolved CO2 was removed and pH increased to 7.8–7.9. Boiling and heating to 137 8C at higher pressure caused the increase of pH to 8.0–8.2 and affected the ion ratio in the solution. Thus, during the storage and transportation of the sample, the temperature should be maintained between 1 and 40 8C. 3.3. Estimation of homogeneity and stability of reference sample material A fundamental requirement of a reference material is that it is homogenous with respect to chemical composition and stability during storage w9x. Recommended methods for estimating homogeneity and stability of water samples have not formally been made in Russia. However, following the principals detailed in references w10x and w11x and considering also principals outlined in references w13–15x, an estimation of homogeneity was made. Samples were analyzed by ICP-MS (Thermo Elemental PlasmaQuad PQ2q) The homogeneity of a candidate reference material may be quantitatively expressed as an inhomogeneity parameter. The parameter of inhomogeneity is the root mean square deviation of the concentration in individual samples of a given mass from the mean content of the same component in total mass of the sample. The number of samples (k) and the number of measurements (n) necessary for a reliable conclusion on the degree of homogeneity were calculated with the help of table given in w11x. In June 2001, a trial batch (2000 bottles) of water was bottled. The number of sub-samples chosen for analysis was 80 (20 bottles, four replicate measurements per bottles). According to w11x, the stability of a reference sample can be estimated by comparison of the content of analytes of interest of a sample, which is kept in a hermetically sealed package for several years under ordinary conditions. The object of this investigation was to examine deepwater samples collected in March 1992 and September 1994, placed in PET bottles, and freshly collected sam-
Fig. 3. Distribution of components within the depth according to the data of different authors. (a) Anions: 1, NOy 3 w7x; 2, 2y NOy w7x; 4, SO2y w4x; 5, SO2y w22x; 6, 3 (LIN); 3, SO4 4 4 y y SO2y (LIN); 7, HCOy 4 3 w7x; 8, HCO3 w4x; 9, HCO3 w22x. (b) Cations: 1, K (LIN); 2, Kq w22x; 3, Na (LIN); 4, Naq w22x; 5, sum of cations NaqqKq w4x; 6, Ca2q w4x; 7, Ca2q w22x; 8, Ca (LIN). (c) Microelements: 1, Cu w23x; 2, Rb w22x; 3, Rb (LIN); 4, Ba w23x; 5, Ba (LIN); 6, Sr w22x; 7, Sr (LIN).
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Fig. 4. Workshop of water preparation: 1, filter of rough purification (100 mm); 2, storage tank (500 l); 3, pump Wilo Jet 301; 4, filter for air treatment; 5, filter 5 mm; 6, filter 1 mm; 7, Manometer; 8, UV-device with lamp DRT 1000; 9, storage tank (1000 l); 10, injector ventury; 11, oxygen container; 12, ozonizer; 13, filter 0.45 mm; and 14, ozone measuring instrument.
ples taken in June 2001. To obtain representative sub-samples, five bottles were taken from each of the three batches, and four replicate measurements were performed for each bottle. The analysis of the whole set was carried out by one analyst. 3.4. Interlaboratory analytical program Compositional data for Baikal water were obtained from an interlaboratory analytical program (IAP). The components to be certified were stipulated and a set of analytical methods were chosen to support this program. A total of 22 laboratories (11 Russian and 11 foreign) were involved in this IAP. Analytical organization in Australia, Canada, France, Germany, Israel, Japan and the USA took part in the interlaboratory program. The largest amount of data was obtained for the major components. Considerably fewer data were obtained for microelements. Approximately 400 independent results were received, each being an average value of several (three to seven) replicate measurements. A summary of the data obtained are listed in Table 2 along with the analytical procedures used.
4. Results The changes of microelement concentrations in the water collected at the permanent samplingpoint in the course of 7 years and treated according to the technique, we have developed, did not exceed 5% w24–26x. Thus, thanks to the stationary character of the water sampling point and the presence of a water treatment works, it is possible to obtain material retaining all the certified characteristics, whenever a new batch of water is bottled. For the estimation of homogeneity of RS material on the basis of experimental data, there were calculated estimated variance characterizing the repeatability of the method (s21), total variance (s22), and inhomogeneity of the distribution of the element studied in RS mass (s2inhom). The value of variance difference was calculated according to Fisher’s criterion. Depending on the ratio between the experimental vs. table F values, the evaluation of the inhomogeneity parameter relied either on both s1 and s2 or s1 only, analogously to that in Ref. w11x. The resulting inhomogeneity errors are given in Table 3. For all the elements to be
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Table 1 Comparison of the results of element analysis of fresh Baikal water (1999) and bottled Baikal water (1993) (ns3, Ps0.95) Element Na Mg K S Ca Sr Al Li B V Cr Mn Co Cu Zn Se Rb Mo Cd Ba Pb U
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
Water sampled in 1999
Water bottled in 1993 Glass
PET
3.26"0.21 (0.05) 2.56"0.17 (0.05) 1.02"0.06 (0.04) 1.84"0.11 (0.03) 15.7"1.0 (0.04) 0.105"0.002 (0.01) 3.07"0.57 (0.13) 2.06"0.19 (0.07) 10.6"0.4 (0.03) 0.60"0.09 (0.11) 5.47"0.37 (0.04) 0.44"0.04 (0.07) 0.11"0.01 (0.08) 0.87"0.11 (0.09) 1.94"0.20 (0.07) 1.53"0.22 (0.11) 0.84"0.05 (0.04) 1.54"0.05 (0.02) 0.010"0.009 (0.22) 10.8"0.6 (0.04) 0.064"0.005 (0.06) 0.56"0.03 (0.04)
4.83"0.22 2.85"0.07 1.11"0.10 1.71"0.15 15.7"0.5 0.099"0.005 3.64"0.01 2.22"0.11 11.1"1.4 0.63"0.04 5.21"0.19 1.72"0.52 0.088"0.015 1.11"0.04 6.77"0.79 1.64"0.62 0.99"0.11 1.59"0.08 0.029"0.008 76.7"5.2 0.095"0.012 0.58"0.12
3.23"0.05 2.53"0.02 1.01"0.06 1.79"0.17 16.1"0.4 0.107"0.003 2.87"0.75 2.21"0.17 10.3"0.7 0.61"0.08 5.37"0.39 0.47"0.09 0.10"0.01 0.86"0.07 2.13"0.21 1.51"0.50 0.87"0.04 1.57"0.03 0.010"0.008 11.1"0.5 0.065"0.012 0.53"0.10
Parentheses enclose relative standard deviation (R.S.D.).
certified, estimated relative value of inhomogeneity parameter sinhom,r was less than third of the maximum permissible error, DD, for the certified value. The value of DD was calculated from the error standards of indices measurements of the composition of natural waters w27x. Hence, according to w11x, RS material can be considered as homogeneous in these components, and it is possible to ignore sinhom in establishing the overall uncertainty DRS of the certified value. Results of evaluation of stability of Baikal deep water composition are shown in Table 4. As is seen from Table 4, the condition texp.-t0.95,f, is observed for the majority of the elements studied, i.e. according to Student’s criterion, the value of mean difference on all the observations (d¯ ) is insignificantly different from zero. Hence, the concentration of these elements is constant. In case of texp.Gt0.95,f, the estimation of statistic value was calculated according to the criterion of insignificant error, i.e. value d¯ was compared with that of admissible root mean square deviation DD calcu-
lated from w27x. In this case the composition of a reference sample is stable in these elements as d¯ F1y3 DD. Thus, Baikal deep water processed according to the offered technology and bottled in PET bottles can be stored at ambient temperature up to 9 years preserving its initial chemical composition. The interpretation of the data obtained through the interlaboratory experiment was done in three stages, according to w28x. The preliminary interpretation (stage 1) is aimed preliminarily at eliminating accidental errors. All submitted data were checked for completeness, including identification of the analytical methods used and the conditions under which they were performed and identification of the analysts. The initial data interpretation (stage 2) includes a number of graphical operations on the data to aid in selecting the acceptable data for each element. One such operation involves compiling histograms at different scales to identify modes and other specific features of the data examined in stage 2. Fig. 5a,b illustrate the inter-
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Table 2 Results of interlaboratory experiment Component PH HCOy 3 NOy 3 SO2y 4 PO3y 4 Fy Cly Na Mg
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
K Ca
mgyl mgyl
Si Li B Al V Cr Mn Co Ni Cu Zn As Rb Sr Mo Cd Sb Ba Pb U
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
Methods
N
Cmin –Cmax
Electrode TM, IC FM, CM, IC TD, GM, IC CM, IC CM, IC MM, AMT, TM, IC FFM, AAS, ICP-MS, ICP-AES Titration with EDTA, TM, AAS, ICP-MS, ICP-AES FFM, AAS, ICP-MS, ICP-AES Titration with EDTA, TM, AAS, ICP-MS, ICP-AES CM, ICP-AES AAS, ICP-MS, ICP-AES ICP-MS, ICP-AES ICP-MS, ICP-AES ICP-MS, ICP-AES AAS, ICP-MS AAS, ICP-MS, ICP-AES ICP-MS AAS, ICP-MS AAS, ICP-MS, ICP-AES AAS, ICP-MS, ICP-AES AAS, ICP-MS ICP-MS AAS, ICP-MS, ICP-AES AAS, ICP-MS AAS, ICP-MS AAS, ICP-MS ICP-MS, ICP-AES ICP-MS ICP-MS, LLM
7 10 11 20 4 10 15 34 33
7.6–7.8 58.4–68.4 0.10–0.54 4.8–5.8 0.02–0.03 0.16–0.23 0.35–0.87 2.8–3.8 2.6–3.6
29 28
0.77–1.12 14.8–16.6
9 8 6 5 8 6 9 7 6 8 14 8 9 15 8 6 6 17 6 7
300–1040 1.49–2.35 3.4–20.0 0.20–0.67 0.30–0.72 0.034–0.062 0.05–0.33 0.02–0.07 0.31–0.96 0.54–1.11 0.64–6.48 0.30–0.63 0.40–0.58 87–112 1.0–1.5 0.003–0.01 0.08–0.22 8.0–13.3 0.028–0.064 0.28–0.89
N: number of individual determinations used for the evaluation of RS composition. Analytical method codes: TM, titrimetry; CM, coulometry; TD, turbidimetry; GM, gravimetry; MM, mercurymetry; FFM, flame photometry; AMT, argentometric titration; IC, ion chromatography; AAS, atomic absorption spectrometry; ICP-MS, inductively coupled plasma mass-spectrometry; ICP-AES, inductively coupled plasma atomic emission spectrometry; LLM, laser-luminescent method.
pretation of data for Na and Sr in RS. The most reliable data for Na are between 3 and 3.6 ppm, for Sr from 90 to 120. Therefore, the values of 4.7 for Na and 171 for Sr should not be used. Consequently, only data below 3.6 and 110 for Na and Sr, respectively, were used in the final statistical evaluation to establish the proposed certified value. The procedure for statistical evaluation (stage 3) is detailed in the State Standards Document w12x. First all initial data was recorded in order of increasing concentration. Second, data distribution
was examined. If 15-N-50, the proximity of data distribution to a normal one is evaluated using composite criteria. If N-15, the distribution symmetry was examined using Wilcoxon criteria. With normal distribution, the arithmetic mean of an ordered series is accepted as the value of a ˆ Interlaboratory cercertification characteristic (A). tification error (DRS) corresponds to the confidence level about the mean for an ordered series. With asymmetrical distribution of results, the median of the ordered series of results is taken as a certifi-
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Table 3 Results of inhomogeneity error estimates of elements of Baikal water reference sample (ks20, ns4, Ps0.95) Element
Fexp
sinhom,r%
sinhom,ryDD
Element
Fexp
sinhom,r%
sinhom,ryDD
Li B Na Mg Al Si P S K Ca Sc Ti V Cr Mn Co
0.42 1.32 2.60 1.08 1.51 2.12 1.38 1.47 0.75 1.02 2.35 2.49 8.60 1.85 9.94 0.63
5.63 3.10 1.2 2.15 8.21 16.5 3.56 1.63 6.69 1.77 7.3 15.5 12.9 4.42 16.4 12.7
0.11 0.06 0.08 0.09 0.16 0.32 0.14 0.06 0.32 0.18 0.15 0.31 0.26 0.04 0.32 0.25
Ni Cu Zn As Br Rb Sr Mo Cd Sn Sb I Ba W Pb U
2.97 12.9 8.13 1.11 16.0 2.86 1.01 1.40 1.43 2.00 4.05 8.00 1.27 2.00 2.96 1.48
11.1 13.6 8.4 5.38 13.5 3.1 1.50 5.11 6.80 8.8 11.3 12.0 2.10 8.4 18.3 3.26
0.22 0.27 0.17 0.11 0.27 0.06 0.07 0.10 0.14 0.18 0.23 0.24 0.04 0.17 0.18 0.06
The table value of Fisher’s coefficient F19,
60, 0.95
s1.8.
cation characteristic. Half-width of the confidence interval for the median is taken as the error. With symmetrical distribution of results, the median of ˆ The terms of the new ordered series is taken as A. this series are all possible half-sums of the initial series. Half-width of the confidence interval for
the median of the second series is taken as interlaboratory certification error. The IAP data allowed for the certification of 15 selected components, to be used as an institutional standard, and 16 components were determined more approximately as information values. The results of these calcula-
Table 4 Estimated composition stability of Baikal deep water, when stored in PET bottles Element
texp
Samples bottled in March Li 1.96 Na 0.12 Al 1.14 Si 1.18 P 0.62 S 0.32 K 1.11 Ca 1.24
Element 1992 Ti V Cr Mn Co As Br Cd
Samples bottled in September 1994 Li 2.00 Mn Na 1.88 Ni Mg 0.44 As Al 1.41 Sr Si 1.83 Cd K 1.94 Sn Ca 1.96 Pb Ti 1.94
texp
Element
texp.
0.16 2.02 1.39 1.76 0.80 0.39 1.20 0.96
Sn Sb I W Pb B Mg Sc
0.44 0.37 1.26 0.90 1.43 3.00 2.16 4.44
0.13 0.29 0.24
1.30 1.18 1.24 1.30 2.00 1.23 2.04
B P S Sc V Cr Co Br
7.61 2.30 2.91 2.80 8.61 3.22 4.67 2.32
0.28 0.29 0.18 0.17 0.29 0.22 0.24 0.12
The table value of Student’s coefficient t0.95,
20
s2.09.
d¯ yDD
Element
texp
d¯ yDD
Ni Rb Sr Mo Ba U
2.53 3.00 5.79 4.91 8.63 4.93
0.29 0.11 0.22 0.13 0.19 0.11
Rb Mo Sb I Ba W U
12.34 4.33 4.09 3.48 3.07 6.06 8.48
0.30 0.12 0.21 0.29 0.06 0.32 0.21
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Fig. 5. Data from interlaboratory experiment. Bar charts of sodium and strontium in RS.
tions are given in Table 5. The extension of the number of certified components requires additional analytical investigations. 5. Conclusion Our investigations have proved that it is possible to create a candidate reference sample of natural water with a constant chemical composition at least over a period of 9 years. Scientific research and experimental work have been performed to develop and create an RS. During the preparation of this candidate RS, international requirements were met. The stationary system of water sampling and preparation allows us to maintain water quality. The results of analyses of water samples taken
from any part of the ‘global’ sample, coincide within the range of error of measurement technique. The stability of elements in Baikal water RS to be certified has been proved by long-term analytical investigations of water samples from this water-sampling point. During long storage of the sample in polyethylenetereftalate package, there are no changes of its composition and no measurable contamination. The estimated cost of the RS is 1 order less than the price of other multicomponent water RS’s listed in available catalogues. According to the Russian classification w9x, the certified sample meets the requirements of an institutional standard. To attain the rank of a State
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Table 5 Major metrological characteristics of reference sample of Baikal deep-water composition Component
Units
Certified value
DRS
Institutional standard PH HCOy 3 SO2y 4 Fy Cly Na K Mg Ca Li As Rb Sr Mo Ba
Component
Units
Certified value
DC
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
0.34 0.024 718 11.2 0.52 0.44 0.048 0.14 0.034 0.57 0.87 3.0 0.006 0.18 0.046 0.50
0.09 0.005 175 8.3 0.24 0.14 0.014 0.08 0.018 0.33 0.20 1.3 0.004 0.07 0.018 0.12
Approximate data
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
7.66 66.6 5.35 0.21 0.55 3.37 0.92 3.08 15.8 1.93 0.41 0.47 104 1.28 10.3
0.06 2.2 0.11 0.01 0.08 0.08 0.03 0.09 0.3 0.23 0.10 0.06 3 0.18 0.8
NOy 3 PO3y 4 Si B Al V Cr Mn Co Ni Cu Zn Cd Sb Pb U
DRS: Uncertainty of certified concentration at 95% confidence interval (95% CI). DC : interlaboratory certification error at 95% CI.
Reference Sample, the interlaboratory experiment should involve a greater number of laboratories. Acknowledgments Many people were involved in the preparation and characterization of this Baikal candidate reference sample. We thank all those who have contributed to the extensive research work. Special thanks we should like to express to Phil Robinson, Conrad Gregoire, Peter Hoffmann and Irena Segal for analytical work they performed. References w1x K.K. Votintsev, I.B. Mizandrontsev, On project of indices standard of quality of Lake Baikal waters, in circulation of substance and energy in reservoirs, Geochem. Bottom Sediments 5 (1981) 26–28, Irkutsk. w2x S.V. Lontshikh, L.L. Petrov, Reference Samples of Natural Media Composition, Nauka, Novosibirsk, 1988. w3x M.A. Grachev, On Recent State of Ecological System of Lake Baikal, Irkutsk, 1999. w4x K.K. Votintsev, Hydrochemistry of Lake Baikal, Izd-vo AN SSSR, Moscow, 1961.
w5x K.K. Votintsev, I.V. Glazunov, A.P. Tolmacheva, Hydrochemistry of Rivers of Lake Baikal Basin, Izd-vo Nauka, Moscow, 1965. w6x P.V. Koval, V.I. Grebenshchikova, N.A. Kitaev, A.M. Koveshnikov, E.E. Lustenberg, V.A. Romanov, A.N. Falileev, Geochemistry of the environment of Prebaikalia, Geol. Geophys. 41 (4) (2000) 571–577. w7x G.Yu. Vereshchagin, Baikal, Gos, izd-vo geographicheskoy lit., Moscow, 1949. w8x P.P. Sherstyankin, Baikal, drinking water, sustainable development: today and in the XXI century, Chem. Interests Sustainable Development 5 (4) (1997) 443–451. w9x GOST 8.315–97 State system for ensuring the uniformity of measurement. Reference samples of composition and properties of substances and materials. Basic principles, Minsk, 1997. w10x GOST 8.531–85 Homogeneity of reference samples of dispersion material composition, Moscow, 1985. w11x OST 41-08-252-85 Reference samples of enterprise. Elaboration, certification and ratification, Moscow, 1985. w12x GOST 8.532-85 Reference samples of substance and materials composition. The order of the interlaboratory certification, Moscow, 1985. w13x The certification of the contents of Cd, Cu, Pb, Mo, Ni and Zn in sea water CRM 403, Commission of the European Communities, Community Bureau of Refer-
288
w14x
w15x
w16x w17x
w18x
w19x
w20x
w21x
A.N. Suturin et al. / Spectrochimica Acta Part B 58 (2003) 277–288 ence, Directorate-General Science, Research and Development, 1992. P. Quevauviller, K. Andersen, J. Merry, H. van der Jagt, Certified reference materials for the quality control of trace element determination in ground water, Sci. Total Environ. 220 (2–3) (1998) 223–234. P. Quevauviller, K.J.M. Kramer, T. Vinhas, A programme to improve the quality of trace element determination in estuarine water, Mar. Pollut. Bull. 28 (8) (1994) 506–511. A.I. Perelman, Geochemistry of Landscapes, Vysshaya shkola, Moscow, 1966. G.I. Galazy, K.K. Votintsev (Eds.), Hydrochemical investigations of Lake Baikal: Proceedings of Limnological Institute, III (XXIII), Izd-vo AN SSSR, Moscow, 1963. M.A. Grachev, A.N. Suturin, V.V. Avdeev, V.V. Dryukker, V.L. Zorin, G.P. Ivanov, A.R. Semenov, P.P. Sherstyankin, G.I. Galasiy, Patent No. 20455478 Russia, 1995. R.F. Weiss, E.C. Carmack, V.M. Koropalov, Deep-water renewal and biological production in Lake Baikal, Nature 349 (1991) 665–669. Y.V. Likhoshway, A.E. Kuzmina, T.G. Potyemkina, V.L. Potyemkin, M.N. Shimaraev, The distribution of diatoms near a thermal bar in Lake Baikal, J. Great Lakes Res. 1 (1996) 5–14. V.A. Vetrov, A.I. Kuznetsova, Microelements in Environment Media of Lake Baikal, Izd-vo SO RAN, NITS OIGGM, Novosibirsk, 1997.
w22x K.K. Falkner, C.I. Measures, S.E. Herbelin, J.M. Edmond, The major and minor element geochemistry of Lake Baikal, Limnol. Oceanogr. 3 (1991) 413–423. w23x K.K. Falkner, M. Church, C.I. Measures, G. LeBaron, D. Thouron, C. Jeandel, M.C. Stordal, G.A. Gill, R. Mortlock, P. Froelich, L.-H. Chan, Minor and trace element chemistry of Lake Baikal, its tributaries, and surrounding hot springs, Limnol. Oceanogr. 2 (1997) 329–345. w24x V.N. Epov, I.E. Vasiljeva, A.N. Suturin, V.I. Lozhkin, E.N. Epova, Determination of microelements in Baikal water by inductively coupled plasma mass spectrometry, J. Anal. Chem. 54 (11) (1999) 1170–1175. w25x V.N. Epov, I.E. Vasiljeva, V.I. Lozhkin, E.N. Epova, L.F. Paradina, A.N. Suturin, Determination of macroelements in Baikal water using inductively coupled plasma mass spectrometry, J. Anal. Chem. 54 (9) (1999) 943–948. w26x V.N. Epov, E.N. Epova, A.N. Suturin, A.R. Semenov, Inductively coupled plasma mass spectrometry applied to element analysis of Baikal deep water, Part I. Sustainability of element composition, Analytics Control 2 (2000) 202–208. w27x GOST 27384-87 Water. Norms of error in measurements of indices of composition and properties, Moscow, 1987. w28x L.L. Petrov, Regularities in the distribution of results in analytical intervals of measurements techniques in quantitative methods of element analyses, Industrial Laboratory. (Diagnostics of Materials) 67 (12) (2001) 49–58.
Preparation and assessment of a candidate reference sample of Lake Baikal deep water夞 A.N. Suturina, L.F. Paradinaa,*, V.N. Epova, A.R. Semenova, V.I. Lozhkina, L.L. Petrovb a
Limnological Institute, Siberian Branch, Russian Academy of Sciences, Ulan-Batorskaya, 3, Irkutsk 664033, Russia b Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Favorsky, 1-a, Irkutsk 664033, Russia Received 1 October 2001; accepted 15 July 2002
Abstract The possibility of the creation of a multi-element reference sample of Lake Baikal deep-water composition is justified. This is a new type of reference sample composed of natural water with a wide range of macro- and microelements. This candidate reference sample has a matrix composition consisting of hydrocarbonate and calcium water, a composition that is typical of many rivers and lakes of the world, as well as rain water. The creation of a candidate reference sample of Lake Baikal water is possible due to the stable water composition at a depth of 500 m, and to the use of water sampling technology which results in the preservation of the initial composition of water and its absolute sterility. Trial batches of Baikal water collected annually and stored in special polyethylenetereftalate bottles for a period of 9 years remained stable and homogenous for most elements. Preliminary data for a range of elements and compounds are presented. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: Lake Baikal water; Reference sample; Analytical data quality; Homogeneity; Interlaboratory analytical program
1. Introduction Systems of scientific management of the environment state, which are formed in contemporary world, include both observation and assessment of the water ecosystems as an important initial factor. Information on the chemical composition of water 夞 This paper was presented at the INTERSIBGEOCHEM 01 Conference held in Irkutsk, Siberia, Russia, 24–27 July 2001 and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference. *Corresponding author. Tel.: q3952-42-29-51; fax: q395242-54-05. E-mail address: [email protected] (L.F. Paradina).
is of great importance for chemical and ecological monitoring of reservoirs and for predicting the quality of drinking water sources. Commonly used synthetic reference samples (RS) cannot completely reflect the specific character of matrix water composition, which may lead to errors in the results of analysis. Reference samples of natural freshwater composition with intact natural chemical matrix are still not available in Russia. The idea of using Baikal water for standardization of chemical investigations has been previously suggested w1,2x. The attempt to create an RS of Baikal water was undertaken by Institute of Physico-technical and Radiotechnical Measurements
0584-8547/03/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 8 4 - 8 5 4 7 Ž 0 2 . 0 0 1 5 7 - X
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Fig. 1. Ratio between the content of cations and ions in environment objects: 1, Baikal water; 2, lake water w4x; 3, river water w5,6x; 4, rain water w4x; 5, snow water w4,6x.
(Irkutsk) in 1993, but unfortunately this project did not come to fruition. The creation of reference samples of Lake Baikal water composition according to international requirements to reference samples of environment objects was initiated by M.A. Grachev, Director of Limnological Institute of Siberian Branch, Russian Academy of Sciences (SB, RAS). A Baikal reference water is required, principally for investigations of Lake Baikal itself w3x. Differences in the results of analysis of Baikal water composition for some elements (for example, mercury) by various authors varies by as much as 3 orders. This lack of agreement precludes an accurate assessment of changes in water composition and the role of anthropogenic factors in these changes.
The chemical matrix of freshwater reservoirs and rivers w4–6x, as well as atmospheric precipitation, is close to that of Lake Baikal waters (Fig. 1). Therefore, a multi-element reference sample of Baikal water would be a useful tool particularly for monitoring surveys. Changes to water quality standards (Fig. 2) are moving towards a composition similar to that of Lake Baikal water. Hence, a Baikal reference sample water will be of particular importance for the analysis of drinking water supplies and of bottled water. During the development of this candidate reference material, long-term hydrophysical, hydrochemical and hydrobiological measurements were made by the Limnological Institute SB of RAS w3–5,7,8x, and procedures were employed similar
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to those used for the preparation of other reference materials w2,9–15x. 2. Characteristics of Lake Baikal water
279
composition of the main part of Lake Baikal water (over 17 000 km3). 3. Experimental 3.1. Water preparation
The water of Lake Baikal has pH 7.6, and it belongs to the category ultra-fresh, hydrocarbonate and calcium water with low mineralization. The total content of dissolved salts in Baikal water does not exceed 100 mgyl. Therefore, it follows the laws of ideal solutions w16x. Hence, there is no index of saturation for the majority of compounds. The element leaching from the dissolved state is only accomplished as a result of adsorption, colloid processes and consumption of elements by vital substances. Because of the water non-saturation, its ionic composition depends on the life activity of hydrobionts. Besides low mineralization, there are high concentrations of dissolved gases, particularly oxygen, which determines its chemical activity. The water column of Lake Baikal is divided into three zones w17x. Of special stability is the water of Baikal ‘nucleus’ — the zone at a depth from 300 m under the surface to 100 m above the bottom w18x. The surface water reaches the bottom of Lake Baikal on the average in 7–8 years. The ‘nucleus’ water, however, is exchanged more slowly, on average the surface water penetrates into the ‘nucleus’ only once in 10–14 years w17,19x. It means that aquatic organisms purify the water in the ‘nucleus’ zone for longer and more effectively. Turbid flows appearing near the shores, also pass by the ‘nucleus’ zone. In this zone, there are almost no diatoms, which are in abundance near the surface and are ‘pressed’ to the slope of the depression w20x. In the ‘nucleus’ zone, the temperature stays 3.5 8C all the year round w17,19x. According to published data w7,17,21–26x, there are changes of chemical composition (Fig. 3) (especially anions) in near-surface and near-bottom zones, in contrast to the water of the ‘nucleus’ zone which is stable in most elements. Thus, the sampling water from the deep zone provides a stable composition, and allows us to get a representative water sample, which demonstrates the
A permanent water sampling point was chosen in Listvenichny Bay at a depth of 500 m, 1.7 km off the shore. The sampling site is 200 m above the bottom of the lake. A permanent pipeline was laid from the sampling point to the shore. From the sampling point, the water is transported, via this pipeline, to an onshore works for processing. To avoid water contamination by alien elements while transporting samples to the shore, experimental surveys were performed to select the appropriate water-pipe material. They showed that even a short-term interaction of water with stainless steel and zinccoated tubes significantly increased the content of iron, zinc, nickel, vanadium, chrome, manganese and other metals in the water. The best result was achieved for polyethylene tubes. To purify the water from biota and suspended sediment, a stepwise water filtration and sterilization system was developed for the onshore processing works (Fig. 4). The material of an ultra-thin filter considerably influences filtrate composition. The investigations showed that the concentration of nickel in water increased up to 95 mgyl (before filtration 0.17 mgyl) and iron from 0.5 to 7.8 mgy l. Therefore, in the filtration system used, polypropylene filter-holders, which do not affect water composition were employed. Deep-water samples passed through 5-, 1- and 0.45-mm filters, were then ozonized and processed by ultraviolet radiation, and finally bottled. The element composition of water at the permanent sampling-point has been studied for 7 years w24–26x. Water sampling was performed at different seasons of a year following the above technique. The analytical method used was inductively coupled plasma mass-spectrometry (ICP-MS). 3.2. Package and storage of a reference sample Research was conducted to assess the best storage media w26x. In 1993, the water was placed
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Fig. 2. Norms of quality of drinking water: a, major components; b, microelements; 1, EEC, 2, Russia GOST; 3, WHO; 4, EPA USA; 5, Switzerland; 6, Lake Baikal water.
into glass and polyethylentereftalate (PET) bottles. In 1999, the bottles were opened and the water was analyzed. Simultaneously some more fresh samples from Lake Baikal were analyzed. Our investigations (Table 1) showed that during the storage of samples in glass vessels, sorption of cobalt on the vessel walls was observed as well as desorption of manganese, copper, zinc, sodium, barium cations and sulfates from glass. No sorption of macro- and microelements on the walls of PET package have been found. Thus, polyethylenteref-
talate bottles were chosen for packing. This material, unlike other plastics, is impervious to gases and does not isolate significant quantity of organic ingredients (acitaldegid and ftalates) into the water. In order to determine the conditions of storage and transportation of the water, subsamples were exposed to extremes of temperature. Freezing and subsequent thawing of a test sample caused partial deposition of organic compounds dissolved in the water: their quantity decreasing from 0.4 to 0.2–
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0.3 mgyl. There were also slight changes in microelement composition. Changes in pH were also observed. The value of pH remained constant to a temperature of 40 8C. Within the range of 40–70 8C, dissolved CO2 was removed and pH increased to 7.8–7.9. Boiling and heating to 137 8C at higher pressure caused the increase of pH to 8.0–8.2 and affected the ion ratio in the solution. Thus, during the storage and transportation of the sample, the temperature should be maintained between 1 and 40 8C. 3.3. Estimation of homogeneity and stability of reference sample material A fundamental requirement of a reference material is that it is homogenous with respect to chemical composition and stability during storage w9x. Recommended methods for estimating homogeneity and stability of water samples have not formally been made in Russia. However, following the principals detailed in references w10x and w11x and considering also principals outlined in references w13–15x, an estimation of homogeneity was made. Samples were analyzed by ICP-MS (Thermo Elemental PlasmaQuad PQ2q) The homogeneity of a candidate reference material may be quantitatively expressed as an inhomogeneity parameter. The parameter of inhomogeneity is the root mean square deviation of the concentration in individual samples of a given mass from the mean content of the same component in total mass of the sample. The number of samples (k) and the number of measurements (n) necessary for a reliable conclusion on the degree of homogeneity were calculated with the help of table given in w11x. In June 2001, a trial batch (2000 bottles) of water was bottled. The number of sub-samples chosen for analysis was 80 (20 bottles, four replicate measurements per bottles). According to w11x, the stability of a reference sample can be estimated by comparison of the content of analytes of interest of a sample, which is kept in a hermetically sealed package for several years under ordinary conditions. The object of this investigation was to examine deepwater samples collected in March 1992 and September 1994, placed in PET bottles, and freshly collected sam-
Fig. 3. Distribution of components within the depth according to the data of different authors. (a) Anions: 1, NOy 3 w7x; 2, 2y NOy w7x; 4, SO2y w4x; 5, SO2y w22x; 6, 3 (LIN); 3, SO4 4 4 y y SO2y (LIN); 7, HCOy 4 3 w7x; 8, HCO3 w4x; 9, HCO3 w22x. (b) Cations: 1, K (LIN); 2, Kq w22x; 3, Na (LIN); 4, Naq w22x; 5, sum of cations NaqqKq w4x; 6, Ca2q w4x; 7, Ca2q w22x; 8, Ca (LIN). (c) Microelements: 1, Cu w23x; 2, Rb w22x; 3, Rb (LIN); 4, Ba w23x; 5, Ba (LIN); 6, Sr w22x; 7, Sr (LIN).
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Fig. 4. Workshop of water preparation: 1, filter of rough purification (100 mm); 2, storage tank (500 l); 3, pump Wilo Jet 301; 4, filter for air treatment; 5, filter 5 mm; 6, filter 1 mm; 7, Manometer; 8, UV-device with lamp DRT 1000; 9, storage tank (1000 l); 10, injector ventury; 11, oxygen container; 12, ozonizer; 13, filter 0.45 mm; and 14, ozone measuring instrument.
ples taken in June 2001. To obtain representative sub-samples, five bottles were taken from each of the three batches, and four replicate measurements were performed for each bottle. The analysis of the whole set was carried out by one analyst. 3.4. Interlaboratory analytical program Compositional data for Baikal water were obtained from an interlaboratory analytical program (IAP). The components to be certified were stipulated and a set of analytical methods were chosen to support this program. A total of 22 laboratories (11 Russian and 11 foreign) were involved in this IAP. Analytical organization in Australia, Canada, France, Germany, Israel, Japan and the USA took part in the interlaboratory program. The largest amount of data was obtained for the major components. Considerably fewer data were obtained for microelements. Approximately 400 independent results were received, each being an average value of several (three to seven) replicate measurements. A summary of the data obtained are listed in Table 2 along with the analytical procedures used.
4. Results The changes of microelement concentrations in the water collected at the permanent samplingpoint in the course of 7 years and treated according to the technique, we have developed, did not exceed 5% w24–26x. Thus, thanks to the stationary character of the water sampling point and the presence of a water treatment works, it is possible to obtain material retaining all the certified characteristics, whenever a new batch of water is bottled. For the estimation of homogeneity of RS material on the basis of experimental data, there were calculated estimated variance characterizing the repeatability of the method (s21), total variance (s22), and inhomogeneity of the distribution of the element studied in RS mass (s2inhom). The value of variance difference was calculated according to Fisher’s criterion. Depending on the ratio between the experimental vs. table F values, the evaluation of the inhomogeneity parameter relied either on both s1 and s2 or s1 only, analogously to that in Ref. w11x. The resulting inhomogeneity errors are given in Table 3. For all the elements to be
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Table 1 Comparison of the results of element analysis of fresh Baikal water (1999) and bottled Baikal water (1993) (ns3, Ps0.95) Element Na Mg K S Ca Sr Al Li B V Cr Mn Co Cu Zn Se Rb Mo Cd Ba Pb U
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
Water sampled in 1999
Water bottled in 1993 Glass
PET
3.26"0.21 (0.05) 2.56"0.17 (0.05) 1.02"0.06 (0.04) 1.84"0.11 (0.03) 15.7"1.0 (0.04) 0.105"0.002 (0.01) 3.07"0.57 (0.13) 2.06"0.19 (0.07) 10.6"0.4 (0.03) 0.60"0.09 (0.11) 5.47"0.37 (0.04) 0.44"0.04 (0.07) 0.11"0.01 (0.08) 0.87"0.11 (0.09) 1.94"0.20 (0.07) 1.53"0.22 (0.11) 0.84"0.05 (0.04) 1.54"0.05 (0.02) 0.010"0.009 (0.22) 10.8"0.6 (0.04) 0.064"0.005 (0.06) 0.56"0.03 (0.04)
4.83"0.22 2.85"0.07 1.11"0.10 1.71"0.15 15.7"0.5 0.099"0.005 3.64"0.01 2.22"0.11 11.1"1.4 0.63"0.04 5.21"0.19 1.72"0.52 0.088"0.015 1.11"0.04 6.77"0.79 1.64"0.62 0.99"0.11 1.59"0.08 0.029"0.008 76.7"5.2 0.095"0.012 0.58"0.12
3.23"0.05 2.53"0.02 1.01"0.06 1.79"0.17 16.1"0.4 0.107"0.003 2.87"0.75 2.21"0.17 10.3"0.7 0.61"0.08 5.37"0.39 0.47"0.09 0.10"0.01 0.86"0.07 2.13"0.21 1.51"0.50 0.87"0.04 1.57"0.03 0.010"0.008 11.1"0.5 0.065"0.012 0.53"0.10
Parentheses enclose relative standard deviation (R.S.D.).
certified, estimated relative value of inhomogeneity parameter sinhom,r was less than third of the maximum permissible error, DD, for the certified value. The value of DD was calculated from the error standards of indices measurements of the composition of natural waters w27x. Hence, according to w11x, RS material can be considered as homogeneous in these components, and it is possible to ignore sinhom in establishing the overall uncertainty DRS of the certified value. Results of evaluation of stability of Baikal deep water composition are shown in Table 4. As is seen from Table 4, the condition texp.-t0.95,f, is observed for the majority of the elements studied, i.e. according to Student’s criterion, the value of mean difference on all the observations (d¯ ) is insignificantly different from zero. Hence, the concentration of these elements is constant. In case of texp.Gt0.95,f, the estimation of statistic value was calculated according to the criterion of insignificant error, i.e. value d¯ was compared with that of admissible root mean square deviation DD calcu-
lated from w27x. In this case the composition of a reference sample is stable in these elements as d¯ F1y3 DD. Thus, Baikal deep water processed according to the offered technology and bottled in PET bottles can be stored at ambient temperature up to 9 years preserving its initial chemical composition. The interpretation of the data obtained through the interlaboratory experiment was done in three stages, according to w28x. The preliminary interpretation (stage 1) is aimed preliminarily at eliminating accidental errors. All submitted data were checked for completeness, including identification of the analytical methods used and the conditions under which they were performed and identification of the analysts. The initial data interpretation (stage 2) includes a number of graphical operations on the data to aid in selecting the acceptable data for each element. One such operation involves compiling histograms at different scales to identify modes and other specific features of the data examined in stage 2. Fig. 5a,b illustrate the inter-
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Table 2 Results of interlaboratory experiment Component PH HCOy 3 NOy 3 SO2y 4 PO3y 4 Fy Cly Na Mg
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
K Ca
mgyl mgyl
Si Li B Al V Cr Mn Co Ni Cu Zn As Rb Sr Mo Cd Sb Ba Pb U
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
Methods
N
Cmin –Cmax
Electrode TM, IC FM, CM, IC TD, GM, IC CM, IC CM, IC MM, AMT, TM, IC FFM, AAS, ICP-MS, ICP-AES Titration with EDTA, TM, AAS, ICP-MS, ICP-AES FFM, AAS, ICP-MS, ICP-AES Titration with EDTA, TM, AAS, ICP-MS, ICP-AES CM, ICP-AES AAS, ICP-MS, ICP-AES ICP-MS, ICP-AES ICP-MS, ICP-AES ICP-MS, ICP-AES AAS, ICP-MS AAS, ICP-MS, ICP-AES ICP-MS AAS, ICP-MS AAS, ICP-MS, ICP-AES AAS, ICP-MS, ICP-AES AAS, ICP-MS ICP-MS AAS, ICP-MS, ICP-AES AAS, ICP-MS AAS, ICP-MS AAS, ICP-MS ICP-MS, ICP-AES ICP-MS ICP-MS, LLM
7 10 11 20 4 10 15 34 33
7.6–7.8 58.4–68.4 0.10–0.54 4.8–5.8 0.02–0.03 0.16–0.23 0.35–0.87 2.8–3.8 2.6–3.6
29 28
0.77–1.12 14.8–16.6
9 8 6 5 8 6 9 7 6 8 14 8 9 15 8 6 6 17 6 7
300–1040 1.49–2.35 3.4–20.0 0.20–0.67 0.30–0.72 0.034–0.062 0.05–0.33 0.02–0.07 0.31–0.96 0.54–1.11 0.64–6.48 0.30–0.63 0.40–0.58 87–112 1.0–1.5 0.003–0.01 0.08–0.22 8.0–13.3 0.028–0.064 0.28–0.89
N: number of individual determinations used for the evaluation of RS composition. Analytical method codes: TM, titrimetry; CM, coulometry; TD, turbidimetry; GM, gravimetry; MM, mercurymetry; FFM, flame photometry; AMT, argentometric titration; IC, ion chromatography; AAS, atomic absorption spectrometry; ICP-MS, inductively coupled plasma mass-spectrometry; ICP-AES, inductively coupled plasma atomic emission spectrometry; LLM, laser-luminescent method.
pretation of data for Na and Sr in RS. The most reliable data for Na are between 3 and 3.6 ppm, for Sr from 90 to 120. Therefore, the values of 4.7 for Na and 171 for Sr should not be used. Consequently, only data below 3.6 and 110 for Na and Sr, respectively, were used in the final statistical evaluation to establish the proposed certified value. The procedure for statistical evaluation (stage 3) is detailed in the State Standards Document w12x. First all initial data was recorded in order of increasing concentration. Second, data distribution
was examined. If 15-N-50, the proximity of data distribution to a normal one is evaluated using composite criteria. If N-15, the distribution symmetry was examined using Wilcoxon criteria. With normal distribution, the arithmetic mean of an ordered series is accepted as the value of a ˆ Interlaboratory cercertification characteristic (A). tification error (DRS) corresponds to the confidence level about the mean for an ordered series. With asymmetrical distribution of results, the median of the ordered series of results is taken as a certifi-
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Table 3 Results of inhomogeneity error estimates of elements of Baikal water reference sample (ks20, ns4, Ps0.95) Element
Fexp
sinhom,r%
sinhom,ryDD
Element
Fexp
sinhom,r%
sinhom,ryDD
Li B Na Mg Al Si P S K Ca Sc Ti V Cr Mn Co
0.42 1.32 2.60 1.08 1.51 2.12 1.38 1.47 0.75 1.02 2.35 2.49 8.60 1.85 9.94 0.63
5.63 3.10 1.2 2.15 8.21 16.5 3.56 1.63 6.69 1.77 7.3 15.5 12.9 4.42 16.4 12.7
0.11 0.06 0.08 0.09 0.16 0.32 0.14 0.06 0.32 0.18 0.15 0.31 0.26 0.04 0.32 0.25
Ni Cu Zn As Br Rb Sr Mo Cd Sn Sb I Ba W Pb U
2.97 12.9 8.13 1.11 16.0 2.86 1.01 1.40 1.43 2.00 4.05 8.00 1.27 2.00 2.96 1.48
11.1 13.6 8.4 5.38 13.5 3.1 1.50 5.11 6.80 8.8 11.3 12.0 2.10 8.4 18.3 3.26
0.22 0.27 0.17 0.11 0.27 0.06 0.07 0.10 0.14 0.18 0.23 0.24 0.04 0.17 0.18 0.06
The table value of Fisher’s coefficient F19,
60, 0.95
s1.8.
cation characteristic. Half-width of the confidence interval for the median is taken as the error. With symmetrical distribution of results, the median of ˆ The terms of the new ordered series is taken as A. this series are all possible half-sums of the initial series. Half-width of the confidence interval for
the median of the second series is taken as interlaboratory certification error. The IAP data allowed for the certification of 15 selected components, to be used as an institutional standard, and 16 components were determined more approximately as information values. The results of these calcula-
Table 4 Estimated composition stability of Baikal deep water, when stored in PET bottles Element
texp
Samples bottled in March Li 1.96 Na 0.12 Al 1.14 Si 1.18 P 0.62 S 0.32 K 1.11 Ca 1.24
Element 1992 Ti V Cr Mn Co As Br Cd
Samples bottled in September 1994 Li 2.00 Mn Na 1.88 Ni Mg 0.44 As Al 1.41 Sr Si 1.83 Cd K 1.94 Sn Ca 1.96 Pb Ti 1.94
texp
Element
texp.
0.16 2.02 1.39 1.76 0.80 0.39 1.20 0.96
Sn Sb I W Pb B Mg Sc
0.44 0.37 1.26 0.90 1.43 3.00 2.16 4.44
0.13 0.29 0.24
1.30 1.18 1.24 1.30 2.00 1.23 2.04
B P S Sc V Cr Co Br
7.61 2.30 2.91 2.80 8.61 3.22 4.67 2.32
0.28 0.29 0.18 0.17 0.29 0.22 0.24 0.12
The table value of Student’s coefficient t0.95,
20
s2.09.
d¯ yDD
Element
texp
d¯ yDD
Ni Rb Sr Mo Ba U
2.53 3.00 5.79 4.91 8.63 4.93
0.29 0.11 0.22 0.13 0.19 0.11
Rb Mo Sb I Ba W U
12.34 4.33 4.09 3.48 3.07 6.06 8.48
0.30 0.12 0.21 0.29 0.06 0.32 0.21
286
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Fig. 5. Data from interlaboratory experiment. Bar charts of sodium and strontium in RS.
tions are given in Table 5. The extension of the number of certified components requires additional analytical investigations. 5. Conclusion Our investigations have proved that it is possible to create a candidate reference sample of natural water with a constant chemical composition at least over a period of 9 years. Scientific research and experimental work have been performed to develop and create an RS. During the preparation of this candidate RS, international requirements were met. The stationary system of water sampling and preparation allows us to maintain water quality. The results of analyses of water samples taken
from any part of the ‘global’ sample, coincide within the range of error of measurement technique. The stability of elements in Baikal water RS to be certified has been proved by long-term analytical investigations of water samples from this water-sampling point. During long storage of the sample in polyethylenetereftalate package, there are no changes of its composition and no measurable contamination. The estimated cost of the RS is 1 order less than the price of other multicomponent water RS’s listed in available catalogues. According to the Russian classification w9x, the certified sample meets the requirements of an institutional standard. To attain the rank of a State
A.N. Suturin et al. / Spectrochimica Acta Part B 58 (2003) 277–288
287
Table 5 Major metrological characteristics of reference sample of Baikal deep-water composition Component
Units
Certified value
DRS
Institutional standard PH HCOy 3 SO2y 4 Fy Cly Na K Mg Ca Li As Rb Sr Mo Ba
Component
Units
Certified value
DC
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
0.34 0.024 718 11.2 0.52 0.44 0.048 0.14 0.034 0.57 0.87 3.0 0.006 0.18 0.046 0.50
0.09 0.005 175 8.3 0.24 0.14 0.014 0.08 0.018 0.33 0.20 1.3 0.004 0.07 0.018 0.12
Approximate data
mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl mgyl
7.66 66.6 5.35 0.21 0.55 3.37 0.92 3.08 15.8 1.93 0.41 0.47 104 1.28 10.3
0.06 2.2 0.11 0.01 0.08 0.08 0.03 0.09 0.3 0.23 0.10 0.06 3 0.18 0.8
NOy 3 PO3y 4 Si B Al V Cr Mn Co Ni Cu Zn Cd Sb Pb U
DRS: Uncertainty of certified concentration at 95% confidence interval (95% CI). DC : interlaboratory certification error at 95% CI.
Reference Sample, the interlaboratory experiment should involve a greater number of laboratories. Acknowledgments Many people were involved in the preparation and characterization of this Baikal candidate reference sample. We thank all those who have contributed to the extensive research work. Special thanks we should like to express to Phil Robinson, Conrad Gregoire, Peter Hoffmann and Irena Segal for analytical work they performed. References w1x K.K. Votintsev, I.B. Mizandrontsev, On project of indices standard of quality of Lake Baikal waters, in circulation of substance and energy in reservoirs, Geochem. Bottom Sediments 5 (1981) 26–28, Irkutsk. w2x S.V. Lontshikh, L.L. Petrov, Reference Samples of Natural Media Composition, Nauka, Novosibirsk, 1988. w3x M.A. Grachev, On Recent State of Ecological System of Lake Baikal, Irkutsk, 1999. w4x K.K. Votintsev, Hydrochemistry of Lake Baikal, Izd-vo AN SSSR, Moscow, 1961.
w5x K.K. Votintsev, I.V. Glazunov, A.P. Tolmacheva, Hydrochemistry of Rivers of Lake Baikal Basin, Izd-vo Nauka, Moscow, 1965. w6x P.V. Koval, V.I. Grebenshchikova, N.A. Kitaev, A.M. Koveshnikov, E.E. Lustenberg, V.A. Romanov, A.N. Falileev, Geochemistry of the environment of Prebaikalia, Geol. Geophys. 41 (4) (2000) 571–577. w7x G.Yu. Vereshchagin, Baikal, Gos, izd-vo geographicheskoy lit., Moscow, 1949. w8x P.P. Sherstyankin, Baikal, drinking water, sustainable development: today and in the XXI century, Chem. Interests Sustainable Development 5 (4) (1997) 443–451. w9x GOST 8.315–97 State system for ensuring the uniformity of measurement. Reference samples of composition and properties of substances and materials. Basic principles, Minsk, 1997. w10x GOST 8.531–85 Homogeneity of reference samples of dispersion material composition, Moscow, 1985. w11x OST 41-08-252-85 Reference samples of enterprise. Elaboration, certification and ratification, Moscow, 1985. w12x GOST 8.532-85 Reference samples of substance and materials composition. The order of the interlaboratory certification, Moscow, 1985. w13x The certification of the contents of Cd, Cu, Pb, Mo, Ni and Zn in sea water CRM 403, Commission of the European Communities, Community Bureau of Refer-
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w22x K.K. Falkner, C.I. Measures, S.E. Herbelin, J.M. Edmond, The major and minor element geochemistry of Lake Baikal, Limnol. Oceanogr. 3 (1991) 413–423. w23x K.K. Falkner, M. Church, C.I. Measures, G. LeBaron, D. Thouron, C. Jeandel, M.C. Stordal, G.A. Gill, R. Mortlock, P. Froelich, L.-H. Chan, Minor and trace element chemistry of Lake Baikal, its tributaries, and surrounding hot springs, Limnol. Oceanogr. 2 (1997) 329–345. w24x V.N. Epov, I.E. Vasiljeva, A.N. Suturin, V.I. Lozhkin, E.N. Epova, Determination of microelements in Baikal water by inductively coupled plasma mass spectrometry, J. Anal. Chem. 54 (11) (1999) 1170–1175. w25x V.N. Epov, I.E. Vasiljeva, V.I. Lozhkin, E.N. Epova, L.F. Paradina, A.N. Suturin, Determination of macroelements in Baikal water using inductively coupled plasma mass spectrometry, J. Anal. Chem. 54 (9) (1999) 943–948. w26x V.N. Epov, E.N. Epova, A.N. Suturin, A.R. Semenov, Inductively coupled plasma mass spectrometry applied to element analysis of Baikal deep water, Part I. Sustainability of element composition, Analytics Control 2 (2000) 202–208. w27x GOST 27384-87 Water. Norms of error in measurements of indices of composition and properties, Moscow, 1987. w28x L.L. Petrov, Regularities in the distribution of results in analytical intervals of measurements techniques in quantitative methods of element analyses, Industrial Laboratory. (Diagnostics of Materials) 67 (12) (2001) 49–58.