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Atomic-absorption determination of beryllium in liquid environmental samples
Tthntn,
Vol. 23, pp. 289-294. Pergamon Press, 1976. Printed in Great Britam
ATOMIC-ABSORPTION DETERMINATION OF BERYLLIUM IN LIQUID ENVIRONMENTAL SAMPLES J. KORKISCH,A. SORIOand 1. STEFFAN T...: . ... 1.. *..rl-~‘__l ~nermsrry, -3 .:_. nna~ysm I ._I- -(- of Nuciear Raiv Materiais Division, Uiliversiiji I~SLIIUL~: wr nndyuca~ 38, A-1090 Vienna, Austria (Received
Of Vkiiiia, WlhiiiigKStidk
19 June 1975. Accepted 19 October 1975)
Summary-A method is described for the atomic-absorption determination of beryllium in liquid environmental samples after separation by solvent extraction and cation-exchange. The beryllium is first isolated from natural waters and beverages by chloroform extraction of its acetylacetonate from a solution at pH 7 and containing EDTA. The chloroform extract is then mixed in the ratio of 3: 6: 1 with tetrahydrofuran and methanol containing nitric acid, and passed through a column of Dowex 50 X8 (H+-form). After removal of acetylacetone, chloroform and tetrahydrofuran by washing the resin bed with methanol-HNO,. is eluted acid and determined by ________.___ ___ _ =, bervllium __ .,.. __~~~~. _~. ~~ with 6M hydrochloric atomic-absorption spectroscopy. The method was successfully applied to determine beryllium in tap-, river- and sea-water samples, mineral waters and wines. Beryllium contents in the range from co.01 to 2.3 &l. were found in these materials.
Determinations of trace quantities of beryllium in liquid environmental samples, e.g., natural waters and beverages, are gaining increased importance with the growing interest in pollution of the environment with this toxic element. Analytical techniques based on atomic-absorption spectrophotometry,“’ emission spectroscopy, ‘-lo fluorimetry’ l-l’ and spectrophotometry’“can be employed. To avoid interference by matrix elements and to increase the sensitivity, suitable preconcentration techniques are often used to separate beryllium before its quantitative determination. Especially suitable for quantitative isolation of trace amounts of beiyllium from natural waters are separation methods based on the chloroform (or carbon tetrachloride) extraction of beryllium acetylacetonate3*‘3.‘8,‘g or co-precipitation with suitable collectors such as the hydrous oxides of iron(III), 6, “3 1k16*20 aluminium’5~ l6 and manganese,20 or titanium phosphate. I7 Other techniques are based on the adsorption of beryllium on various sorbents such as a 1: 1 mixture of activated charcoal and chlorinated lignin,’ silica gel” and the strong-acid cationexchanger Dowex 50 X8 (in the Fe3 ’ or MnZf form and treated with excess of ammonia solution).*’ Combinations of these methods may also be employed, e.g., co-precipitation of beryllium with ferric hydroxide and subsequent separation by anion-exchange.15 In the present paper, a combination of separation techniques is described, which utilizes chloroform extraction of hervllium 2s the --__, ----____ -__ , ------- acetvlacetnnate2’~22 first preconcentration step, followed by cationexchange enrichment of beryllium directly from the organic extract. 289
EXPERIMENTAL Solurions and reagents Ion-exchange resin. Dowex 50 X8 (lW200 mesh; H+-form) was used. For purification, 500 g of the resin were treated successively with 2 litres of 6M nitric acid, 500 ml of O.lM nitric acid, 2 litres of distilled water and 500 ml of reagent-grade methanol. The purified resin was airdried. Before use 4 g of the cation-exchanger were slurried with a few ml of CHC13PTHF-MeOH solution and transferred to the ion-exchange column as completely as possible with the same solution. Standard beryllium solutions. An exactly weighed amount of beryllium nitrate tetrahydrate was dissolved in 1M nitric acid to obtain a stock solution containing 630 ppm of beryllium. From this solution, standard solutions O.lM in nitric acid and 0.6M in hydrochloric acid were prepared, which contained from 0.006 to 630 nom and from 0003 to 630 ppm of beryllium respectively. I CHCI,-THF-MeOH solution. This solution, of @lM overall acidity, is prepared by mixing 30 ml of chloroform with 60 ml of tetrahydrofuran (THF) and 10 ml of \Ioc\U
Lvl~“lrllL.“g
UhTn
..A,+..,., IIII*LuI~
,,A ,“I
1 \I 11”1
A..n..“ll
““c;LLLLI
-“:A:+..,
auurrJ,.
MeOH-HNO% mixture. A mixture with 1M overall acidity is prepared by dilution of 69 ml of concentrated nitric acid to 1 litre with methanol. To obtain the MeOH-HNO, mixture of O.lM overall acidity which is used for the ionexchange separation of beryllium, 10 ml of this solution are diluted to 100 ml with methanol. THF-MeOH solution. This consists of a 9 : 1 v/v mixture of tetrahydrofuran and MeOH-HNO, mixture (of 1M overall acidity). The overall acidity of this THF-MeOH solution is O.lM. Other reagents. Acetylacetone, 5% aqueous acetylacetone solution, chloroform, solid EDTA (disodium salt). lo”/, and O.lM aqueous EDTA solutions, 5% and 20% sbluti& of sodium hydroxide, O.lM, 06M, 6M and concentrated hydrochloric acid, 1% methanolic solution of arsenazo 1, 2M sodium acetate, tetrahydrofuran, methanol and concentrated nitric, sulphuric, perchloric, and hydrobromic acids. The reagents used were all stable for at least 6 months
290
J. KORKISCH, A. SORIO and I. ST~FAN
Apparatus und operating conditions
A Perkin-Elmer
303 atomic-absorption spectrophotometer (equipped with a Hitachi-Perkin-Elmer Recorder 56 connected to a read-out accessory) was used with the following instrumental settings. Grating: .,,-..-1-..-rL.
ultraviolet m-1A nm ~34’~ up to 30x 5 (3 mm; 2 nm bandpass) beryllium hollow-cathode lamp
w a”cleIlgrrl:
Scale expansion Slit: Source :
:
Lamp current: Burner : Acetylene Nitrous
pressure: oxide-pressure:
Noise suppression
:
30 mA one-slit burner for the acetylene-nitrous oxide flame 8 psig; 14 on flowmeter (arbitrary scale) 30 psig; 6 on flowmeter (arbitrary scale) up to 5
Under these conditions the sensitivity for 1% absorption was found to be 0.015 ppm of beryllium in @6M hydrochloric acid. The detection limit for beryllium was OQOl ppm. The calibration curve was linear up to 0.5 pg of beryllium per ml. The spectrophotomctric calibration curve (Beckman DB-GT instrument, 1 cm cells) was linear up to a berylhum concentration of 1.0 pg/ml. The separations of beryllium \N~!F performed in ion-exchange columns of the type atid dimCnsions described earlier.23 Determination of distribution coefficients The weight distribution coefficients (&-values Dowex 50) of beryllium were determined by using batch equilibrium method.”
on the
Pretreatment of samples and solvent extraction of beryllium Natural waters and mineral waters. To 1 litre of the water sample (saline or non-saline), in the polyethylene bottle in which it was collected, 10 ml of concentrated hydrochloric acid are added and after filtration the sample is let stand for about 24 hr (degassing of the sample; mainly for removal of CO,). Then 3 ,a of EDTA are added and dissolved, the pH is-adjusted toabout 7 with 20% sodium hydroxide solution (about 20-25 ml are required) and after addition of 2 ml of acetylacetone the mixture is shaken thoroughly until complete homogeneity is attained. Finally the pH of the solution is adjusted to 7 by careful addition of 20% and 5% sodium hydroxide solutions and let stand for at least 2 hr (preferably overnight) so that beryllium can react quantitatively with the acetylacetone. Then the sample solution is transferred to a 2-litre separatory funnel, 20 ml of chloroform are added and beryllium acetylacetonate is extracted by vigorous shaking for 1 min. After phase separation the organic extract is passed through a dry filter paper to remove aqueous droplets adhering to the organic layer. The extraction of the sample solution is repeated twice with 10 ml of chloroform each time and a shaking period of 30 sec. After filtration through dry filter paper these last two extracts are combined with the first and thus about 30 ml of chloroform-acetylacetone solution are obtained (“beryllium extract”). From this organic mixture beryllium is isolated by the cation-ex“l.“_,.” _.._“,.?l ..r_ A,.“,...:l.-A l--I _..I ~l,‘l,lg,r; ~‘“C’;““‘L; U~>~II”.Z” v=,vw. Wines. To the wine sample (1 We) concentrated hydrochloric acid is added to make it 0.6M in this acid and
*To prepare the sorption solution from the beryllium extract (about 20 ml) obtained from a wine sample, mix the extract with about 40 ml of tetrahydrofuran and 7 ml of MeOHpHNOj mixture (overall acidity 1M).
after about 24 hr the acidified wine is filtered and 250 ml of it, in a 600-ml beaker, are evaporated to about onethird of the original volume. Subsequently 50 ml of concentrated nitric acid are added (preferably after the concentrated wine sample has been allowed to cool to room temperature) and the mixture is evaporated to dryness on a steam-bath. The residue is taken up in 100 ml of a 3: 1: I mixture of concentrated nitric, sulphuric and perchloric acids and the solution is first heated on a steam-bath (until its volume is reduced to about 50 ml) and then evaporated to dryness on a sand-bath. To destroy perchlorate, 25 ml of concentrated hydrobromic acid are added and after evaporation of the solution to dryness on the steam-bath the residue is dissolved in about 20 ml of O.lM hydrochloric acid or water. Then 20 ml of 10% EDTA solution are added, the pH is adjusted to about 7 with sodium hydroxide, 2 ml of 5% aqueous acetylacetone solution are added, and then the same extraction procedure is followed as described above for the analysis of waters except that only half the volume of chloroform is used, i.e., 10 ml for the first and 5 ml each for the two subsequent extractions. Ion-exchange
separation
The beryllium extract (about 30 ml)* is mixed with 60 ml of tetrahydrofuran and 10 ml of MeOH-HNO, mixture (overall acidity 1M) and the resulting solution (the sorption solution, overall acidity 0.W) is passed through a 4-g column of the cation-exchanger (pretreated with 10 ml of CHCI,-THF-MeOH solution) at a flowrate of about 60 ml/hr. The resin bed is then washed with about 5 ml of THF-MeOH solution, followed by about 10 ml of MeOHHNOj mixture (overall acidity O.IM) and finally beryllium is eluted with 50 ml of 6M hydrochloric acid (beryllium eluate). Quantitative determination of beryllium Atomic-absorption spectroscopy. The beryllium eiuate is evaporated under an infrared lamp, the residue is dissolved in 1 ml of 6M hydrochloric acid, and after dilution with water to 10 ml the solution is aspirated into the acetylenenitrous oxide flame. A calibration curve is constructed by aspirating suitable beryllium standard solutions before and after each batch of samples. A reagent blank is run through the whole procedure (starting with addition of the first reagent) and finally deducted from the beryllium found in the sample. Spectrophotometry. The beryllium eluate is evaporated and the residue is taken up in 1 ml of 6M hydrochloric acid; then 1 ml of arsenazo I solution and 1 ml of 0.1 M EDTA solution are added. and the solution is diluted to 10 ml with 2M sodium acetate. The absorbance is measured at 580 nm against a reagent blank. The absorbance is 0.350 for 1 ppm of beryllium in the solution measured.
RESULTS AND DISCUSSION
Acidification of the samples with concentrated hydrochloric acid prevents the adsorption of beryllium on the walls of the sample container and co-precipitation of beryllium with hydroxides and phosphates of iron etc. which may occasionally be present in relativelv, ~..~__ large _.____ amounts (r ___ in ~0117~ minera! ____I) c-‘D.’
waters
and
especially in wine samples. The chloroform extraction of beryllium acetylacetonate is carried out in the presence of EDTA to prevent the co-extraction of most of the main and trace constituents of liquid environmental samples. Thus, a beryllium extract is obtained which is virtually free from elements interfering with the assay of beryllium.
291
Beryllium in liquid environmental samples
Unfortunately the assay cannot be done directly on the chloroform extract by atomic-absorption spectroscopy. Therefore, an attempt was made to determine beryllium in aqueous medium after removal of chloroform by evaporation. However, the volatility of beryllium acetylacetonate caused considerable losses of the element (especially when only submicrogram amounts were present) even when the evaporation was carried out at very low heat and with 4-5 ml of concentrated hydrochloric acid and 2.5ml of methanol added to the chloroform extract. The hydrochloric acid was added to liberate beryllium from its acetylacetone chelate and methanol was added to obtain a homogeneous mixture with the chloroform. Therefore a means was sought for separating beryllium from both the chelating agent and the chloroform without the application of heat. As a result, the nnt;, ‘?.YnLnnrm -,+i.,Pr n,ln*-+:,V. “1 ACIm...,, raLL”~l-~nL,1aJ,l;r IIILLIIW..+;l:,:..” ur,,,nu,g aua”ltJL,“L, uXy,lium on Dowex 50 from the mixed CHCla-THFMeOH medium containing nitric acid was developed. In this mixture the presence of tetrahydrofuran is necessary to obtain a homogeneous solution, and the methanol is the component regulating the flow-rate through the ion-exchange column. In the absence of methanol the viscosity of the sorption solution is extremely low, so that a flow-rate is attained at which complete adsorption of beryllium is not guaranteed. Nitric acid has to be present in the mixture SO that beryllium is in the ionic form which is adsorbed on the cation-exchanger during the sorption process, after which residual chloroform and acetylacetone are removed by washing the resin bed with THF-MeOH solution and MeOH-HNO~ mixture. Thus, after the elution of beryllium with 6M hydrochloric acid an eluate is obtained which does not contain organic substances which could give rise to the formation of beryllium compounds that are volatile during evaporation of the eluate. Through the combination of this ion-exchange separation step with the extraction of beryllium acetylacetonate from the water sample it is possible to isolate submicrogram and microgram amounts of this eleTable 1. Effect of concentration Amount of Be added to 1 litre of the water sample, fig 063 1.26 6.30 12.6 63.0 0-T 110 630
ment from both saline and non-saline waters. Table 1 shows that beryllium recoveries are in the range 93403%. That the separation of beryllium is not affected by large quantities of foreign ions (which are usually only trace constituents of natural waters) is demonstrated by the results presented in Table 2. The only two elements which are co-extracted with beryllium to a considerable extent are iron and copper, and then only from sea-water (see footnote to Table 2) because the dissolved salts act as salting-out agents during the extraction. In the ~tion-exch~ge separation of beryllium these co-extracted elements are co-adsorbed with the beryllium irrespective of the acidity used (the beryllium adsorption was found to decrease only slightly with increasing nitric acid concentration in the CHC13-THF-MeOH-HNO, mix*....2, LUl(riT,LL \lla”lG J,. In the absence of the organic solvents, distribution coefficients for beryllium of 255 and 900 were measured in 0.184 hydrochloric and O.lh4 nitric acid media respectively. Under the conditions of elution, i.e., in 6M hydrochloric acid, the distribution coeficient for beryllium was < 1. Iron and copper are coeluted with the beryllium but do not interfere with the atomic-absorption determination nor with the spectrophotometric method (because of the masking action of the EDTA added). However, the spectrophotometric results often showed a positive bias of - -0; this is most probably due to the elfect about j-5/,,; of small amounts of coloured organic matter in the residue obtained after evaporation of the beryllium efuate. Another di~dv~tage of the spectrophotometric method is its low sensitivity: beryllium concentrations below 0.06 fig/ml in the final solution measured cannot be determined with sufficient accuracy. Since this con~ntration is rarely reached in beryllium eluates obtained from I-litre samples, the arsenazo I method was not used for most of the liquid environmental samples. The much more sensitive atomic-absorption spectroscopy technique (in which, contrary to recent information,’ sodium was not
on beryllium recovery from tap- and sea-water
Tap-water* Beryllium found 1((1/1. % 0.62 1.19 5.90 11.9 60.5 *_(n IL” 611
98 94 93 94.5 96 _r c YJ’3 97
Sea-water? Beryllium found % w/l. 065 I .25 5.95 11.8 60.8
‘,.. IL5
621
103 99.5 94.5 94.0 96-5
___ Y i'l(
98.5
* Vienna tap-water was taken and found to contain 0.02, Mg of beryllium per litre. This concentration was subtracted from those found. 7 Artificial sea-water was prepared by dissolving the following chemicals in one litre of tap-water: NaCl (28 g), KC1 (O-8 g), MgC1,.6H,O (1 g), MgS04.7HZ0 (6.96 g) and CaCl,.2H,O (l-325 g). Its beryllium concentration was 0.026 pg/l, which was subtracted from the values found.
292
J. KORKISCH,A. SORIOand I. STEFFAN Table 2. Effect of foreign ions on beryflium recovery from artificial sea-water (1.26 fig of beryllium were added to each litre sample) Foreign ion added to I-litre sample of artificial sea-water, W Cr(III) 0.8 Fe(II1) 2.0* Co(II) I.05 Ni(I1) 0.95 Cu(rr) 1.13* Mn(I1) 0.7 UO@) 0.01 All metal ions listed above (_ 7 mg)
Beryllium recovered,
Foreign ion present in beryllium eluate,
II/
/”
PS
!4l
1.23 1.23 1.25 1.23 1.23 1.25 1.24 1.24
98 9s 99 98 98 99 98.5 98.5
1.24
985
%
3.5 1 x lo3 I.0 1.5 150 1.8 0.04
0.4 50 0.1 o-2 13 0.25 0.4
not determined
* When the same amounts of these elements were added to corresponding samples of tap-water the concentrations of iron and copper in the beryiiium eiuates were found to be considerably lower, 40 and 3 pg respectively.
* This is the acidity at which beryllium is adsorbed on Dowex 50 when applying the separation procedure described.
Numerous samples of Austrian waters were analysed by the methods described above. Good agreement was obtained between results for spiked and unspiked samples. For sea-water (Adriatic Sea and Pacific Ocean) rest&s ranging from
found to interfere) being preferred. Sometimes even the atomic-abso~tion method is not sensitive enough to determine beryllium accurately. Thus, in certain samples it was possible to detect beryllium (detection limit = 0.001 ppm) but the signals were not sufficiently strong to give reliable results.
the weathering process beryllium is concentrated in hydrolysates, and like aluminium does not go into solution to any appreciable degree. On the other hand, some mineralwaters were found to have ~ryllium con~ntrations higher by several orders of magnitude than those found for most saline and non-saline waters (Table 4). Measurements of the pH-values and calcium contents (as a
Table 3. Distribution coefficients of beryllium at varying overall acidities of the CHCI,THF-MeOH mixture (sorption solution) Overall acidity O.lM HNO,* 0.W HNO, l.OM HN03
580 560 540
Table 4. Results of determinations
of beryllium in samples of bottled mineral waters Beryllium contents, pg//.
Trade name and geographical origin of sample Viislauer, Bad VGslau, Lower Austria Riimerquelle, Bad Vzisiau, Lower Austria Hunyadi Janos, Saxlehner’s Bitterquelle, Budapest, Hungary Radenska, Radenska Slatina, Yugoslavia Giissinger, Burg G&sing, Burgenland Gasteiner, Bad Gastein, Salzburg ~1.1.1_.~.1._~._ ~‘-1-~-..~--_-.. ionanmsorunntm, T-1.-.. .:-L _.._.. TI-1 vleznenocrger aau ulezcnenoerg, Styria Donat, Rogaska Slatina, Yugoslavia Thalheimer, Thalheim/Judenburg, Styria Preblauer, Preblau, Carinthia
A
B
- 0,005 (0.063) - 0.007 (0.063) < 0.01 (0.063)
0.025 0.05s 0% ,? t* V’II
0.03 0.06 0.055 ,..A U’IU
(0@63) (0.063) (0.063) ,,,..-.I\ (U’ILO)
0.75 1.02 2.30
0.85 1.07 2.25
(0.630) (1.260) (3.150)
A = Beryllium contents determined by atomic-absorption spectrophotometry following solvent extraction and cationexchange of beryllium. B = Same as for A but after deduction of a spike (the figure in parentheses).
Beryllium in liquid environmental samples
293
Table 5. Beryllium in wine samples (vintage 1974). Beryllium contents, /+7/l.
Trade name and geographical origin Red wines
St. Laurent, LoibenWachau,
Lower Austria Poisdorfer, Poisdorf, Lower Austria Burgunder, Kirchberg a. Wagram, Lower Austria Rotwein, Sonnenberg/Baden, Lower Austria
0.07 0.07 0.08 0.09
Rntrnrarht ‘\“‘yy.,.,A~.,
0.11
White
l?,,rtmhs=to A...“.-.““m,
R,,ro~nlnnrl ‘“-O1..-......
wines
RLuschl, LoibenWachau, Lower Austria Neuburger, Baden, Lower Austria Neuburger, Kirchberg am Wagram, Lower Austria Weinzierlberg (Griiner-Veltliner), Drasenhofen, Lower Austria Neusiedler Seekonig, Rusterberg, Burgenland
measure of the carbonate concentrations) showed that the mineral waters with extremely high beryllium contents are considerably more alkaline than the others in which l~vds ___ RTCcnmnarahlc= to those _._ . . . .._.. the .___ hervllimn ---.‘______ * __._-1 -‘----~--I--of the non-saline waters. For instance, the calcium concentration in the Thalheimer and Preblauer samples was 450 and 34Omg/l. respectively, while in the samples of Vijslauer and Romerquelle it was 100 and 140 mg/l. The pH-values for the last two mineral waters were found to be lower by about 2 and 3.5 pH units than those of Thalheimer and Preblauer respectively. In an oil-field water from a deep oil-well, (Litzelsdorf 1) containing appreciable amounts of dissolved carbonates, a beryllium content of about O.lOpg/l. ._.^^ p_..__l DeCUlSe n___..._ “1 _r rl_ --^^^_^_ “1 _A-1_--_ _.._-r:r:__ was ,““rKl. UK p,reaence rarge qUiUlrlrlCb of organic substances the isolation of beryllium from this oil-field water was most probably not quite quantitative (it was very difficult to obtain two distinct phases during the extraction of beryllium acetylacctonate with chloroform) so the beryllium concentration may actually be higher. According to previous experience” beryllium is regarded as one of the trace elements which is either not contained in wines under normal conditions or cannot be detected with certainty. That this is not the case, however, is illustrated by the results shown in Table 5 from which it is seen that in only one out of ten different wine samples (collected at random) was the beryllium content below the limit for accurate determination. It is also evident that wines originating from the same locality contain very similar beryllium concentrations. Before separation of beryllium the wine samples have to be wet-ashed by the method described. Direct extraction of beryllium from wine is not possible because of the presence of the alcohol. In conclusion it should be mentioned that in place of the solvent extraction procedure beryllium can also be concentrated quantitatively on a 4-g column of the cation-exchanger Dowex 50 from one litre of nonsaline water which is 0.M in nitric acid. However, this cation-exchange method was abandoned in
favour of the extraction method because the latter can be performed much more rapidly and is also applicable to natural waters of high salinity such as sea-water and minera!-waters. Acknowledgement-This research was sponsored by the Fonds zur Forderung der wissenschaftlichen Forschung, Vienna, Austria. The generous support from this Fund is gratefully acknowledged. REFERENCES
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Environmental
Protection
Agency
Manual,
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294
J. KORKISCH. A. SORIO and I. STEFFAN
19. T. G. Kornienko and A. I. Samchuk, Ukr. Khim. Zh., 1972, 38, 914. 20. J. R. Merrill, M. Honda and J. R. Arnold, Anal. Chem., 101* JL) ** I-PA”. 1“ln I7W,
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an” “. JKI‘IUW (C”b., pp. +I I, ‘++I),‘tit,. nca”eullLI
Vol. 23, pp. 289-294. Pergamon Press, 1976. Printed in Great Britam
ATOMIC-ABSORPTION DETERMINATION OF BERYLLIUM IN LIQUID ENVIRONMENTAL SAMPLES J. KORKISCH,A. SORIOand 1. STEFFAN T...: . ... 1.. *..rl-~‘__l ~nermsrry, -3 .:_. nna~ysm I ._I- -(- of Nuciear Raiv Materiais Division, Uiliversiiji I~SLIIUL~: wr nndyuca~ 38, A-1090 Vienna, Austria (Received
Of Vkiiiia, WlhiiiigKStidk
19 June 1975. Accepted 19 October 1975)
Summary-A method is described for the atomic-absorption determination of beryllium in liquid environmental samples after separation by solvent extraction and cation-exchange. The beryllium is first isolated from natural waters and beverages by chloroform extraction of its acetylacetonate from a solution at pH 7 and containing EDTA. The chloroform extract is then mixed in the ratio of 3: 6: 1 with tetrahydrofuran and methanol containing nitric acid, and passed through a column of Dowex 50 X8 (H+-form). After removal of acetylacetone, chloroform and tetrahydrofuran by washing the resin bed with methanol-HNO,. is eluted acid and determined by ________.___ ___ _ =, bervllium __ .,.. __~~~~. _~. ~~ with 6M hydrochloric atomic-absorption spectroscopy. The method was successfully applied to determine beryllium in tap-, river- and sea-water samples, mineral waters and wines. Beryllium contents in the range from co.01 to 2.3 &l. were found in these materials.
Determinations of trace quantities of beryllium in liquid environmental samples, e.g., natural waters and beverages, are gaining increased importance with the growing interest in pollution of the environment with this toxic element. Analytical techniques based on atomic-absorption spectrophotometry,“’ emission spectroscopy, ‘-lo fluorimetry’ l-l’ and spectrophotometry’“can be employed. To avoid interference by matrix elements and to increase the sensitivity, suitable preconcentration techniques are often used to separate beryllium before its quantitative determination. Especially suitable for quantitative isolation of trace amounts of beiyllium from natural waters are separation methods based on the chloroform (or carbon tetrachloride) extraction of beryllium acetylacetonate3*‘3.‘8,‘g or co-precipitation with suitable collectors such as the hydrous oxides of iron(III), 6, “3 1k16*20 aluminium’5~ l6 and manganese,20 or titanium phosphate. I7 Other techniques are based on the adsorption of beryllium on various sorbents such as a 1: 1 mixture of activated charcoal and chlorinated lignin,’ silica gel” and the strong-acid cationexchanger Dowex 50 X8 (in the Fe3 ’ or MnZf form and treated with excess of ammonia solution).*’ Combinations of these methods may also be employed, e.g., co-precipitation of beryllium with ferric hydroxide and subsequent separation by anion-exchange.15 In the present paper, a combination of separation techniques is described, which utilizes chloroform extraction of hervllium 2s the --__, ----____ -__ , ------- acetvlacetnnate2’~22 first preconcentration step, followed by cationexchange enrichment of beryllium directly from the organic extract. 289
EXPERIMENTAL Solurions and reagents Ion-exchange resin. Dowex 50 X8 (lW200 mesh; H+-form) was used. For purification, 500 g of the resin were treated successively with 2 litres of 6M nitric acid, 500 ml of O.lM nitric acid, 2 litres of distilled water and 500 ml of reagent-grade methanol. The purified resin was airdried. Before use 4 g of the cation-exchanger were slurried with a few ml of CHC13PTHF-MeOH solution and transferred to the ion-exchange column as completely as possible with the same solution. Standard beryllium solutions. An exactly weighed amount of beryllium nitrate tetrahydrate was dissolved in 1M nitric acid to obtain a stock solution containing 630 ppm of beryllium. From this solution, standard solutions O.lM in nitric acid and 0.6M in hydrochloric acid were prepared, which contained from 0.006 to 630 nom and from 0003 to 630 ppm of beryllium respectively. I CHCI,-THF-MeOH solution. This solution, of @lM overall acidity, is prepared by mixing 30 ml of chloroform with 60 ml of tetrahydrofuran (THF) and 10 ml of \Ioc\U
Lvl~“lrllL.“g
UhTn
..A,+..,., IIII*LuI~
,,A ,“I
1 \I 11”1
A..n..“ll
““c;LLLLI
-“:A:+..,
auurrJ,.
MeOH-HNO% mixture. A mixture with 1M overall acidity is prepared by dilution of 69 ml of concentrated nitric acid to 1 litre with methanol. To obtain the MeOH-HNO, mixture of O.lM overall acidity which is used for the ionexchange separation of beryllium, 10 ml of this solution are diluted to 100 ml with methanol. THF-MeOH solution. This consists of a 9 : 1 v/v mixture of tetrahydrofuran and MeOH-HNO, mixture (of 1M overall acidity). The overall acidity of this THF-MeOH solution is O.lM. Other reagents. Acetylacetone, 5% aqueous acetylacetone solution, chloroform, solid EDTA (disodium salt). lo”/, and O.lM aqueous EDTA solutions, 5% and 20% sbluti& of sodium hydroxide, O.lM, 06M, 6M and concentrated hydrochloric acid, 1% methanolic solution of arsenazo 1, 2M sodium acetate, tetrahydrofuran, methanol and concentrated nitric, sulphuric, perchloric, and hydrobromic acids. The reagents used were all stable for at least 6 months
290
J. KORKISCH, A. SORIO and I. ST~FAN
Apparatus und operating conditions
A Perkin-Elmer
303 atomic-absorption spectrophotometer (equipped with a Hitachi-Perkin-Elmer Recorder 56 connected to a read-out accessory) was used with the following instrumental settings. Grating: .,,-..-1-..-rL.
ultraviolet m-1A nm ~34’~ up to 30x 5 (3 mm; 2 nm bandpass) beryllium hollow-cathode lamp
w a”cleIlgrrl:
Scale expansion Slit: Source :
:
Lamp current: Burner : Acetylene Nitrous
pressure: oxide-pressure:
Noise suppression
:
30 mA one-slit burner for the acetylene-nitrous oxide flame 8 psig; 14 on flowmeter (arbitrary scale) 30 psig; 6 on flowmeter (arbitrary scale) up to 5
Under these conditions the sensitivity for 1% absorption was found to be 0.015 ppm of beryllium in @6M hydrochloric acid. The detection limit for beryllium was OQOl ppm. The calibration curve was linear up to 0.5 pg of beryllium per ml. The spectrophotomctric calibration curve (Beckman DB-GT instrument, 1 cm cells) was linear up to a berylhum concentration of 1.0 pg/ml. The separations of beryllium \N~!F performed in ion-exchange columns of the type atid dimCnsions described earlier.23 Determination of distribution coefficients The weight distribution coefficients (&-values Dowex 50) of beryllium were determined by using batch equilibrium method.”
on the
Pretreatment of samples and solvent extraction of beryllium Natural waters and mineral waters. To 1 litre of the water sample (saline or non-saline), in the polyethylene bottle in which it was collected, 10 ml of concentrated hydrochloric acid are added and after filtration the sample is let stand for about 24 hr (degassing of the sample; mainly for removal of CO,). Then 3 ,a of EDTA are added and dissolved, the pH is-adjusted toabout 7 with 20% sodium hydroxide solution (about 20-25 ml are required) and after addition of 2 ml of acetylacetone the mixture is shaken thoroughly until complete homogeneity is attained. Finally the pH of the solution is adjusted to 7 by careful addition of 20% and 5% sodium hydroxide solutions and let stand for at least 2 hr (preferably overnight) so that beryllium can react quantitatively with the acetylacetone. Then the sample solution is transferred to a 2-litre separatory funnel, 20 ml of chloroform are added and beryllium acetylacetonate is extracted by vigorous shaking for 1 min. After phase separation the organic extract is passed through a dry filter paper to remove aqueous droplets adhering to the organic layer. The extraction of the sample solution is repeated twice with 10 ml of chloroform each time and a shaking period of 30 sec. After filtration through dry filter paper these last two extracts are combined with the first and thus about 30 ml of chloroform-acetylacetone solution are obtained (“beryllium extract”). From this organic mixture beryllium is isolated by the cation-ex“l.“_,.” _.._“,.?l ..r_ A,.“,...:l.-A l--I _..I ~l,‘l,lg,r; ~‘“C’;““‘L; U~>~II”.Z” v=,vw. Wines. To the wine sample (1 We) concentrated hydrochloric acid is added to make it 0.6M in this acid and
*To prepare the sorption solution from the beryllium extract (about 20 ml) obtained from a wine sample, mix the extract with about 40 ml of tetrahydrofuran and 7 ml of MeOHpHNOj mixture (overall acidity 1M).
after about 24 hr the acidified wine is filtered and 250 ml of it, in a 600-ml beaker, are evaporated to about onethird of the original volume. Subsequently 50 ml of concentrated nitric acid are added (preferably after the concentrated wine sample has been allowed to cool to room temperature) and the mixture is evaporated to dryness on a steam-bath. The residue is taken up in 100 ml of a 3: 1: I mixture of concentrated nitric, sulphuric and perchloric acids and the solution is first heated on a steam-bath (until its volume is reduced to about 50 ml) and then evaporated to dryness on a sand-bath. To destroy perchlorate, 25 ml of concentrated hydrobromic acid are added and after evaporation of the solution to dryness on the steam-bath the residue is dissolved in about 20 ml of O.lM hydrochloric acid or water. Then 20 ml of 10% EDTA solution are added, the pH is adjusted to about 7 with sodium hydroxide, 2 ml of 5% aqueous acetylacetone solution are added, and then the same extraction procedure is followed as described above for the analysis of waters except that only half the volume of chloroform is used, i.e., 10 ml for the first and 5 ml each for the two subsequent extractions. Ion-exchange
separation
The beryllium extract (about 30 ml)* is mixed with 60 ml of tetrahydrofuran and 10 ml of MeOH-HNO, mixture (overall acidity 1M) and the resulting solution (the sorption solution, overall acidity 0.W) is passed through a 4-g column of the cation-exchanger (pretreated with 10 ml of CHCI,-THF-MeOH solution) at a flowrate of about 60 ml/hr. The resin bed is then washed with about 5 ml of THF-MeOH solution, followed by about 10 ml of MeOHHNOj mixture (overall acidity O.IM) and finally beryllium is eluted with 50 ml of 6M hydrochloric acid (beryllium eluate). Quantitative determination of beryllium Atomic-absorption spectroscopy. The beryllium eiuate is evaporated under an infrared lamp, the residue is dissolved in 1 ml of 6M hydrochloric acid, and after dilution with water to 10 ml the solution is aspirated into the acetylenenitrous oxide flame. A calibration curve is constructed by aspirating suitable beryllium standard solutions before and after each batch of samples. A reagent blank is run through the whole procedure (starting with addition of the first reagent) and finally deducted from the beryllium found in the sample. Spectrophotometry. The beryllium eluate is evaporated and the residue is taken up in 1 ml of 6M hydrochloric acid; then 1 ml of arsenazo I solution and 1 ml of 0.1 M EDTA solution are added. and the solution is diluted to 10 ml with 2M sodium acetate. The absorbance is measured at 580 nm against a reagent blank. The absorbance is 0.350 for 1 ppm of beryllium in the solution measured.
RESULTS AND DISCUSSION
Acidification of the samples with concentrated hydrochloric acid prevents the adsorption of beryllium on the walls of the sample container and co-precipitation of beryllium with hydroxides and phosphates of iron etc. which may occasionally be present in relativelv, ~..~__ large _.____ amounts (r ___ in ~0117~ minera! ____I) c-‘D.’
waters
and
especially in wine samples. The chloroform extraction of beryllium acetylacetonate is carried out in the presence of EDTA to prevent the co-extraction of most of the main and trace constituents of liquid environmental samples. Thus, a beryllium extract is obtained which is virtually free from elements interfering with the assay of beryllium.
291
Beryllium in liquid environmental samples
Unfortunately the assay cannot be done directly on the chloroform extract by atomic-absorption spectroscopy. Therefore, an attempt was made to determine beryllium in aqueous medium after removal of chloroform by evaporation. However, the volatility of beryllium acetylacetonate caused considerable losses of the element (especially when only submicrogram amounts were present) even when the evaporation was carried out at very low heat and with 4-5 ml of concentrated hydrochloric acid and 2.5ml of methanol added to the chloroform extract. The hydrochloric acid was added to liberate beryllium from its acetylacetone chelate and methanol was added to obtain a homogeneous mixture with the chloroform. Therefore a means was sought for separating beryllium from both the chelating agent and the chloroform without the application of heat. As a result, the nnt;, ‘?.YnLnnrm -,+i.,Pr n,ln*-+:,V. “1 ACIm...,, raLL”~l-~nL,1aJ,l;r IIILLIIW..+;l:,:..” ur,,,nu,g aua”ltJL,“L, uXy,lium on Dowex 50 from the mixed CHCla-THFMeOH medium containing nitric acid was developed. In this mixture the presence of tetrahydrofuran is necessary to obtain a homogeneous solution, and the methanol is the component regulating the flow-rate through the ion-exchange column. In the absence of methanol the viscosity of the sorption solution is extremely low, so that a flow-rate is attained at which complete adsorption of beryllium is not guaranteed. Nitric acid has to be present in the mixture SO that beryllium is in the ionic form which is adsorbed on the cation-exchanger during the sorption process, after which residual chloroform and acetylacetone are removed by washing the resin bed with THF-MeOH solution and MeOH-HNO~ mixture. Thus, after the elution of beryllium with 6M hydrochloric acid an eluate is obtained which does not contain organic substances which could give rise to the formation of beryllium compounds that are volatile during evaporation of the eluate. Through the combination of this ion-exchange separation step with the extraction of beryllium acetylacetonate from the water sample it is possible to isolate submicrogram and microgram amounts of this eleTable 1. Effect of concentration Amount of Be added to 1 litre of the water sample, fig 063 1.26 6.30 12.6 63.0 0-T 110 630
ment from both saline and non-saline waters. Table 1 shows that beryllium recoveries are in the range 93403%. That the separation of beryllium is not affected by large quantities of foreign ions (which are usually only trace constituents of natural waters) is demonstrated by the results presented in Table 2. The only two elements which are co-extracted with beryllium to a considerable extent are iron and copper, and then only from sea-water (see footnote to Table 2) because the dissolved salts act as salting-out agents during the extraction. In the ~tion-exch~ge separation of beryllium these co-extracted elements are co-adsorbed with the beryllium irrespective of the acidity used (the beryllium adsorption was found to decrease only slightly with increasing nitric acid concentration in the CHC13-THF-MeOH-HNO, mix*....2, LUl(riT,LL \lla”lG J,. In the absence of the organic solvents, distribution coefficients for beryllium of 255 and 900 were measured in 0.184 hydrochloric and O.lh4 nitric acid media respectively. Under the conditions of elution, i.e., in 6M hydrochloric acid, the distribution coeficient for beryllium was < 1. Iron and copper are coeluted with the beryllium but do not interfere with the atomic-absorption determination nor with the spectrophotometric method (because of the masking action of the EDTA added). However, the spectrophotometric results often showed a positive bias of - -0; this is most probably due to the elfect about j-5/,,; of small amounts of coloured organic matter in the residue obtained after evaporation of the beryllium efuate. Another di~dv~tage of the spectrophotometric method is its low sensitivity: beryllium concentrations below 0.06 fig/ml in the final solution measured cannot be determined with sufficient accuracy. Since this con~ntration is rarely reached in beryllium eluates obtained from I-litre samples, the arsenazo I method was not used for most of the liquid environmental samples. The much more sensitive atomic-absorption spectroscopy technique (in which, contrary to recent information,’ sodium was not
on beryllium recovery from tap- and sea-water
Tap-water* Beryllium found 1((1/1. % 0.62 1.19 5.90 11.9 60.5 *_(n IL” 611
98 94 93 94.5 96 _r c YJ’3 97
Sea-water? Beryllium found % w/l. 065 I .25 5.95 11.8 60.8
‘,.. IL5
621
103 99.5 94.5 94.0 96-5
___ Y i'l(
98.5
* Vienna tap-water was taken and found to contain 0.02, Mg of beryllium per litre. This concentration was subtracted from those found. 7 Artificial sea-water was prepared by dissolving the following chemicals in one litre of tap-water: NaCl (28 g), KC1 (O-8 g), MgC1,.6H,O (1 g), MgS04.7HZ0 (6.96 g) and CaCl,.2H,O (l-325 g). Its beryllium concentration was 0.026 pg/l, which was subtracted from the values found.
292
J. KORKISCH,A. SORIOand I. STEFFAN Table 2. Effect of foreign ions on beryflium recovery from artificial sea-water (1.26 fig of beryllium were added to each litre sample) Foreign ion added to I-litre sample of artificial sea-water, W Cr(III) 0.8 Fe(II1) 2.0* Co(II) I.05 Ni(I1) 0.95 Cu(rr) 1.13* Mn(I1) 0.7 UO@) 0.01 All metal ions listed above (_ 7 mg)
Beryllium recovered,
Foreign ion present in beryllium eluate,
II/
/”
PS
!4l
1.23 1.23 1.25 1.23 1.23 1.25 1.24 1.24
98 9s 99 98 98 99 98.5 98.5
1.24
985
%
3.5 1 x lo3 I.0 1.5 150 1.8 0.04
0.4 50 0.1 o-2 13 0.25 0.4
not determined
* When the same amounts of these elements were added to corresponding samples of tap-water the concentrations of iron and copper in the beryiiium eiuates were found to be considerably lower, 40 and 3 pg respectively.
* This is the acidity at which beryllium is adsorbed on Dowex 50 when applying the separation procedure described.
Numerous samples of Austrian waters were analysed by the methods described above. Good agreement was obtained between results for spiked and unspiked samples. For sea-water (Adriatic Sea and Pacific Ocean) rest&s ranging from
found to interfere) being preferred. Sometimes even the atomic-abso~tion method is not sensitive enough to determine beryllium accurately. Thus, in certain samples it was possible to detect beryllium (detection limit = 0.001 ppm) but the signals were not sufficiently strong to give reliable results.
the weathering process beryllium is concentrated in hydrolysates, and like aluminium does not go into solution to any appreciable degree. On the other hand, some mineralwaters were found to have ~ryllium con~ntrations higher by several orders of magnitude than those found for most saline and non-saline waters (Table 4). Measurements of the pH-values and calcium contents (as a
Table 3. Distribution coefficients of beryllium at varying overall acidities of the CHCI,THF-MeOH mixture (sorption solution) Overall acidity O.lM HNO,* 0.W HNO, l.OM HN03
580 560 540
Table 4. Results of determinations
of beryllium in samples of bottled mineral waters Beryllium contents, pg//.
Trade name and geographical origin of sample Viislauer, Bad VGslau, Lower Austria Riimerquelle, Bad Vzisiau, Lower Austria Hunyadi Janos, Saxlehner’s Bitterquelle, Budapest, Hungary Radenska, Radenska Slatina, Yugoslavia Giissinger, Burg G&sing, Burgenland Gasteiner, Bad Gastein, Salzburg ~1.1.1_.~.1._~._ ~‘-1-~-..~--_-.. ionanmsorunntm, T-1.-.. .:-L _.._.. TI-1 vleznenocrger aau ulezcnenoerg, Styria Donat, Rogaska Slatina, Yugoslavia Thalheimer, Thalheim/Judenburg, Styria Preblauer, Preblau, Carinthia
A
B
- 0,005 (0.063) - 0.007 (0.063) < 0.01 (0.063)
0.025 0.05s 0% ,? t* V’II
0.03 0.06 0.055 ,..A U’IU
(0@63) (0.063) (0.063) ,,,..-.I\ (U’ILO)
0.75 1.02 2.30
0.85 1.07 2.25
(0.630) (1.260) (3.150)
A = Beryllium contents determined by atomic-absorption spectrophotometry following solvent extraction and cationexchange of beryllium. B = Same as for A but after deduction of a spike (the figure in parentheses).
Beryllium in liquid environmental samples
293
Table 5. Beryllium in wine samples (vintage 1974). Beryllium contents, /+7/l.
Trade name and geographical origin Red wines
St. Laurent, LoibenWachau,
Lower Austria Poisdorfer, Poisdorf, Lower Austria Burgunder, Kirchberg a. Wagram, Lower Austria Rotwein, Sonnenberg/Baden, Lower Austria
0.07 0.07 0.08 0.09
Rntrnrarht ‘\“‘yy.,.,A~.,
0.11
White
l?,,rtmhs=to A...“.-.““m,
R,,ro~nlnnrl ‘“-O1..-......
wines
RLuschl, LoibenWachau, Lower Austria Neuburger, Baden, Lower Austria Neuburger, Kirchberg am Wagram, Lower Austria Weinzierlberg (Griiner-Veltliner), Drasenhofen, Lower Austria Neusiedler Seekonig, Rusterberg, Burgenland
measure of the carbonate concentrations) showed that the mineral waters with extremely high beryllium contents are considerably more alkaline than the others in which l~vds ___ RTCcnmnarahlc= to those _._ . . . .._.. the .___ hervllimn ---.‘______ * __._-1 -‘----~--I--of the non-saline waters. For instance, the calcium concentration in the Thalheimer and Preblauer samples was 450 and 34Omg/l. respectively, while in the samples of Vijslauer and Romerquelle it was 100 and 140 mg/l. The pH-values for the last two mineral waters were found to be lower by about 2 and 3.5 pH units than those of Thalheimer and Preblauer respectively. In an oil-field water from a deep oil-well, (Litzelsdorf 1) containing appreciable amounts of dissolved carbonates, a beryllium content of about O.lOpg/l. ._.^^ p_..__l DeCUlSe n___..._ “1 _r rl_ --^^^_^_ “1 _A-1_--_ _.._-r:r:__ was ,““rKl. UK p,reaence rarge qUiUlrlrlCb of organic substances the isolation of beryllium from this oil-field water was most probably not quite quantitative (it was very difficult to obtain two distinct phases during the extraction of beryllium acetylacctonate with chloroform) so the beryllium concentration may actually be higher. According to previous experience” beryllium is regarded as one of the trace elements which is either not contained in wines under normal conditions or cannot be detected with certainty. That this is not the case, however, is illustrated by the results shown in Table 5 from which it is seen that in only one out of ten different wine samples (collected at random) was the beryllium content below the limit for accurate determination. It is also evident that wines originating from the same locality contain very similar beryllium concentrations. Before separation of beryllium the wine samples have to be wet-ashed by the method described. Direct extraction of beryllium from wine is not possible because of the presence of the alcohol. In conclusion it should be mentioned that in place of the solvent extraction procedure beryllium can also be concentrated quantitatively on a 4-g column of the cation-exchanger Dowex 50 from one litre of nonsaline water which is 0.M in nitric acid. However, this cation-exchange method was abandoned in
favour of the extraction method because the latter can be performed much more rapidly and is also applicable to natural waters of high salinity such as sea-water and minera!-waters. Acknowledgement-This research was sponsored by the Fonds zur Forderung der wissenschaftlichen Forschung, Vienna, Austria. The generous support from this Fund is gratefully acknowledged. REFERENCES
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294
J. KORKISCH. A. SORIO and I. STEFFAN
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an” “. JKI‘IUW (C”b., pp. +I I, ‘++I),‘tit,. nca”eullLI