Evaluation of sample preparation methods for organotin speciation analysis in sediments — focus on monobutyltin extraction

ANALmcA CHIMICA ACIA ELSEVIER

Analytica Chimica Acta 317 (1995) 161-170

Evaluation of sample preparation methods for organotim speciation analysis in sediments - focus on monobutyltin extraction Michiel Ceulemans, Freddy C. Adams Department

of Chemistry,

University of Antwerp @IA), Universiteitsplein

*

1, B-26lOAntwerp,

Belgium

Received 24 April 1995; revised 3 July 1995; accepted 20 July 1995

Abstract Two sample preparation procedures, based on different leaching, extraction, complexing and derivatization conditions, for the analysis of butyltin compounds in sediment samples are evaluated and compared. Particular emphasis is given to factors affecting monobutyltin extraction efficiency. The validity of both methods is demonstrated by the analysis of the available reference materials. Two independent hyphenated techniques, gas chromatography interfaced with atomic emission spectrometry and atomic absorption spectrometry, are used for independent confirmation of analytical results. Applications for the analysis of sediments, sampled from Belgian harbours and drydocks are shown. Gas chromatography; Atomic absorption spectrometry; Organotin speciation; Environmental analysis; Sediments! Monobutyltin extraction; Reference materials

Keywords:

1. Introduction The toxic effects of tributyltin (TBT), released from antifouling paints, on aquatic life are well understood by now and have resulted in environmental legislation in many countries, restricting the use of this compound [l-3]. This has stimulated many laboratories to develop analytical methods, and at present methods are available which allow for routine monitoring of this compound in the different matrices of the marine environment. TBT half-life in

* Corresponding

author.

0003-2670/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDI 0003-2670(95)00386-X

the water column is short, ranging from days to several weeks dependent on the study [4-61. Sediments however, may act as a sink for any organotin released in the water and half-lives here lare reported to be up to several years [6-81. In this way contaminated sediments may remain a source of TBT long after the actual source has been removed and thus create a long term problem as was confirmed in a recent study where TBT concentrations in Dutch marine waters were partly attributed to desorption from contaminated sediments, apart from illegal usage of TBT-containing paints [9]. Analytical methods should allow for the determination of the individual organotin compdunds thereby providing sufficient sensitivity (1 ng g- ’ for dry

162

M. Ceulemans, F.C. Adams /Analytica

solid materials). The presently available techniques combine a separation technique such as gas chromatography (GC), liquid chromatography (LC) or supercritical fluid chromatography (SFC) with element selective detection like atomic absorption spectrometry (AAS), atomic emission spectrometry @ES), mass spectrometry (MS) or flame photometric detection (FPD) [lo-131. A commonly used sample preparation approach to release the organotin compounds from the sediment involves acid leaching in aqueous or methanolic media by sonification, stirring, shaking or Soxhlet extraction with an organic solvent [14]. Complexing agents (tropolone, diethyldithiocarbamate (DDTC)) are often added to increase extraction yields. More recently supercritical fluids have been used to extract organotins from sediments, offering the advantages of the reduction in handling steps and the omittance of use of hazardous organic solvents [15-191. Once extracted from the sediment, ionic or complexed organotins need to be derivatized into gas chromatographable species. The methods used involve hydride generation with sodium borohydride (NaBH,) or alkylation by Grignard reagents or sodium tetraethylborate (NaBEt,). Studies on methods using hydride generation have revealed that poor organotin recoveries are obtained in matrices displaying high sulphur and hydrocarbon contents due to an inhibition of the hydridization reaction [20,21]. In a recent study, however, it was stated that organic compounds only account for a small part of the signal suppression but that the major responsible is the presence of interfering inorganic metals [22]. Grignard alkylation and NaBEt, ethylation are not prone to such interferences and proceed quantitatively leading to stable derivatives. Alkylation with Grignard reagents, however, can only be performed in completely dry or non aqueous media requiring extraction into an apolar organic phase prior to the derivatization. NaBEt, does not suffer from this drawback as it may act as an aqueous phase ethylating reagent able to derivatize organotin in aqueous and methanolic extracts [23-261. To evaluate the performance of the plethora of existing sample preparation procedures and instrumental setups used among the different laboratories, certified reference materials (CRMS) were prepared by different standardization organizations which al-

Chimica Acta 317 (I 995) I61 -I 70 Table 1 Comparison of literature reported (certified) reference materials

Certified Determined

MBT

values

determined

PACS- 1 a

CRM 462 b

RM 424 b

0.28 + 0.17 0.52 + 0.15 [30] 0.36+0.17[31]

n.c. ’ 13-244 [28] 102+38[30]

(257 + 54) d 16.7&4.6 [17] 85.6f20.1 [this work]

0.03 kO.01 [17] 1.03 + 0.01 [19]

14.1 k5.6 [17] 125 f 16 [this work]

in

0.41 f 0.04 1191 0.94 -f 0.06 [this work] a b ’ d

Concentrations expressed Concentrations expressed n.c.: not certified. (1: indicative value.

in pg g-’ as Sn. in ng g-’ as compound.

low for the quality control of analytical results. Analysis results of CRMs presented in some reports show that reliability of sample preparation is often not sufficient proving that several limitations still remain. Especially the accurate determination of MBT remains doubtful as, according to some reports on certification experiments [27-291, no reliable method for determination of this compound has been reported up to now as is apparent from Table 1. This paper presents a critical evaluation and comparison of two sample preparation procedures for organotin speciation analysis in sediments, using different leaching, extraction, complexing and derivatization conditions. A comprehensive study on parameters affecting MBT extraction is presented. The accuracy of both procedures was verified by the analysis of certified reference materials. Examples for the analysis of sediments, sampled from Belgian harbours and drydocks are also presented.

2. Experimental

2.1. Apparatus 2.1.1. GC-AES Organotin species were separated on an HP-l capillary column (25m X 0.32 mm i.d. X 0.17 pm film thickness) using a Model 5890 Series II gas chromatograph and detected by means of an HP

M. Ceulemans, F.C. Adams/Analytics

Model 5921 A atomic emission detector (HewlettPackard, Avondale, PA). The gas chromatograph was equipped with a KAS 503 (Gerstel, Miilheim, Germany) programmable temperature vaporization (PTV) injector. Injections were made using a Hamilton 701 RN syringe through the septumless injection head in a smooth finished glass vaporization liner filled with a 2 cm plug of Tenax (80-100 mesh). 2.1.2. GC-AAS A Varian Model 3700 gas chromatograph (Varian, Sunnyvale, CA) fitted with a RSL-150 (RSL, Eke, Belgium) megabore column (15 m X 0.53 mm i.d. X 1.2 ,um), or an HP Model 5890 Series II gas chromatograph fitted with an HP-l capillary column were used to separate the analytes prior to the detection by quartz furnace atomic absorption spectrometry (QFAAS); PE Model 2380 (Perkin Elmer, Norwalk, CT). For megabore column GC, samples were introduced on-column through a septum in a wide bore hot on-column liner. Injections on the capillary column were done using PTV as described above. Injector, gas chromatograph, interface and detector operating conditions have been described in detail earlier for GC-AAS 1321 and GC-AES 1331. 2.2. Reagents Analytical reagent grade chemicals obtained from Merck (Darmstadt, Germany) were used unless otherwise stated. Deionised water, further purified in a Milli-Q system (Millipore, El Paso, TX) system was used throughout. Pentylmagnesiumbromide (2 M in diethyl ether) was obtained from Aldrich (Milwaukee, WI>. Sodium tetraethylborate was obtained from Strem Chemicals (Bischheim, France). A 0.3% (w/v> aqueous solution was prepared daily. Diethyldithiocarbamic acid was prepared by dissolving 2.25 g of sodium diethyldithiocarbamate (NaDDTC) salt in water. The solution of DDTC in pentane was obtained by shaking the aqueous solution with 20 ml of 0.5 M of H,SO, and extracting with 10 ml of pentane for 5 min. Acetate buffer (pH 5; 0.1 M) was prepared by dissolving 13.6 g of sodium acetate trihydrate in 1 1 of water, followed by pH adjustment with concentrated acetic acid. A 0.05% tropolone solution was prepared by dissolving the appropriate amount in hexane-ethyl acetate (1:l). The sources,

Chimica Acta 317 (1995) 161-170

163

purity and synthesis of organotin standards have been described in detail earlier [25,34]. Certified reference materials were obtained from the National Research Council of Canada (NRCC, Ottawa, Canada): PACS-1 marine sediment and the Community Bureau of Reference (BCR, CommissCon of the European Communities, Brussels, Belgium): CRM462 coastal sediment and RM 424 harbourlsediment. 2.3. Method I (MZ: tropolone extraction ethyl acetate; NaBEt, derivatization)

ih hexane-

Circa 1 g of sediment was accurately weighed and placed in a centrifugation vessel with glass stopper together with 2 ml of hydrochloric acid (32%) and 8 ml of water; 25 ml of the hexane-ethyl acetate mixture (l:l), containing 0.05% tropolone were added and the mixture was sonicated for 1 h, followed by centrifugation at 3000 rpm for 5 min. The organic phase was transferred into an extraction vessel and evaporated to dryness using rotary evaporation. Then, 0.5 ml of hexane, containing Pe,SnEt as an internal standard, were added and the complexes were derivatized by addition of 1 ml of the NaBEt, solution together with 50 ml of acetate buffer solution. The mixture was shaken manually for 5 min and after phase separation the hexane phase was sampled for clean up/analysis. 2.4. Method ZZ (MZZ: DDTC extraction Grignard (n-PeMgBr) derivatization)

in hexane;

This method has been described in dttail earlier [35]. Briefly, 1 g of sediment was placed in a 100 ml Erlenmeyer flask, together with 4 ml of water, 1 ml of acetic acid (96%), 1 ml of DDTC in pentane and 25 ml of hexane. The mixture was then sonicated for 30 min, the organic phase was decanted into a 100 ml beaker and the sediment was extracted again with 25 ml of hexane stirring magnetically for 30 min. The mixture was then centrifuged for 5 min at 3000 rpm. The combined hexane extracts were dried over Na,SO, and evaporated to dryness on a rotary evaporator. Subsequently 250 ~1 of n-octane, containing Pr,SnPe as internal standard, were added, after which pentylation with 1 ml of 1 M n-PeMgBrl was carried out. Excess Grignard reagent was destroyed by the

164

M. Ceulemans, F. C. Adams /Analytica

addition of 10 ml of 0.5 M H,SO,. was sampled for clean-up/analysis.

Chimica Acta 317 (I 995) 161-l 70

The octane layer

2.5. Clean-up A detailed description and discussion of extract clean-up has been presented previously [26]. A Pasteur pipette was filled with basic alumina to form a plug of 5 cm. The sediment extract was introduced onto the clean-up column. After elution of the original extract volume, an additional volume of 1 ml diethyl ether was brought onto the clean-up column. The diethyl ether was evaporated from the combined eluate using a gentle stream of nitrogen.

3. Results and discussion

3.1. Comparison of sample preparation procedures 3.1.1. Acid As organotin compounds are not involved in mineralogical processes and bind only onto the surface of the sediment, a complete dissolution of the matrix was not considered necessary. Therefore acid leaching forms the basic approach to release organotin compounds from sediments. Hydrochloric, acetic and hydrobromic acid are most commonly used for leaching organotin compounds from sediments. All three acids were investigated for this purpose using Method I and it was found that, whereas for DBT and TBT no significant difference in performance was observed, for MBT hydrochloric acid gave by far the highest removal efficiency. Hydrobromic and acetic acid gave efficiencies of 82% and 60%, respectively, relative to hydrochloric acid. 3.1.2. Solvent A suitable organic solvent or mixture of organic solvents must be used to simultaneously extract all analyte species. Apolar solvents are most popular for extracting organotin, as they enable easy phase separation after the leaching/extraction step. Method II, using only hexane as solvent, proved to be inefficient for extracting MBT (recovery < 10%) and it was found that polar solvents such as ethyl acetate were necessary for the extraction of this compound. Chau et al. 1191, reported the use of toluene as the extrac-

0 & 60 ._ WI

“A0

IB Ethylacetate

in

Solvent

Mixture

Fig. 1. Effect of the ethyl acetate-hexane ratio on the extraction efficiency of butyltin compounds from sediments. 0 = MBT, A =DBT; O=TBT.

tion solvent for sediment analysis. It was found that the use of the polar toluene, in combination with a chelating agent, improved the extraction efficiency of MBT substantially. The use of polar solvents creates the effect however that it dissolves part of the aqueous/acid phase, which prevents evaporation of the organic phase to dryness. This causes difficulties when Grignard reagents are used for the derivatization as is discussed further. Fig. 1 shows the influence of the composition of the ethyl acetate-hexane mixture on the extraction of butyltin compounds using Method I. It can be seen that the extraction of MBT strongly increases when the ethyl acetate fraction in the solvent mixture increases, while for DBT and TBT no such effect is observed. The decrease in recovery observed for all butyltins after the ethyl acetate fraction exceeds 65% of the total composition of the organic phase was found to be due to derivatization problems and will be discussed later. 3.1.3. Complexing agent The addition of complexing agents (tropolone, diethyl dithiocarbamic acid (DDTC)) is mandatory in order to increase extraction yields, especially for diand mono-substituted alkyltins. Tropolone has the advantage over DDTC that it has good stability in organic solvents while the DDTC solution has to be prepared prior to its use. A drawback of tropolone is that during the reaction of the organotin-tropolone complexes with NaBEt, byproducts are formed which were coextracted in the final extract. A cleanup step is therefore mandatory in order to prevent

165

M. Ceulemans, F.C. Adams / Analytica Chimica Acta 317 (1995) 161-l 70 70

60i

carried out without problems. Using Method I however, after evaporation of the ethyl acetate-hexane phase a small volume of water-acid remained, which makes it impossible to use Grignard reagents for derivatization. NaBEt, was found to derivatize the complexes quantitatively in the remaining extract after pH adjustment to 4.5-5 with acetate buffer. When too high ethyl acetate-hexane ratios are used large amounts of acid remained present after evaporation of the extract which most probably negatively affects the ethylation and/or complexation reaction and explains the decrease in recovery for all butyltins for higher ethyl acetate-hexane ratios as can be seen from Fig. 1.

I

TIME (mln)

Fig. 2. Chromatogram for a sample of RM 424 after sample preparation (Method I) and GC-AES measurement: Sn’” = inorganic tin; 1 = MBT; 2 = DBT, 3 = TBT; is. = internal standard (Pe,SnEt).

rapid column contamination and/or background interferences as were sometimes observed during GCAES analysis. This can be seen in Fig. 2 which represents a chromatogram of RM 424 after extraction using Method I and GC-AES analysis. The baseline distortion at retention time 7.5 min. is caused by coeluting compounds, giving high carbon emission and resulting in background overcorrection at the Sn-channel [26].

3.2. Influence of the sediment composition recovery

In general, when a method is proposed and recovery figures are given to indicate the performance of the method, the results reflect experiments done on one sediment only and little or no attention is given to the composition of the sediment. During1 this study however, it was found that extraction effiaiency was strongly dependent on the sediment analyzed. In earlier work it was shown already that using Method II, DBT and TBT recoveries could differ up to 15% depending on the sediment [35]. Here a similar study was done using Method I on 9 different sediments. The origin of all investigated sediments can be seen from Table 2. The recovery of butyltin aompounds was evaluated by analysing organotin spiked sediments and, after substraction of the organotin concentrations naturally present in the sediment, com-

3.1.4. Derivatization agent Apart from hydride generation, which according to several reports, often gives problems in derivatization of sediment extracts, two other methods are available to convert the ionic or complexed organotins in gas chromatographable species: Grignard alkylation and ethylation using NaBEt,. A Grignard reaction proceeds quantitatively when carried out in a suitable solvent. Using Method II, hexane extracts can be evaporated completely to dryness and after redissolvation in octane the pentylation reaction is Table 2 Elemental

composition

of sediments

(o/o), MBT recovery

on butyltin

(%) with application

of Method I

Sample

Na

Mg

Al

Si

P

S

Cl

K

Ca

Fe

Cu

Zn

TOC

MBT recovery

PACS-1 CRM 462 RM 424 LM-L ANT-L OST-H SCH-R ANT-DD LlM-DD

0.98 0.97 1.37 0.00 0.00 1.09 0.00 0.24 0.00

1.86 1.11 0.77 1.09 0.33 1.06 1.06 1.70 0.90

7.48 5.16 9.23 9.26 3.55 6.03 2.89 12.6 8.08

27.3 35.6 28.0 22.3 39.7 23.7 38.4 2.4 23.4

0.05 0.00 0.00 1.25 0.11 0.29 0.11 0.00 0.80

1.50 1.00 1.44 1.94 0.06 2.10 0.03 0.17 0.94

4.01 1.69 4.10 0.06 0.00 5.24 0.59 0.17 0.06

1.89 1.35 3.02 2.51 2.21 1.83 1.02 3.61 1.72

1.81 0.33 0.44 6.08 0.07 9.88 2.80 4.14 4.23

7.31 3.16 5.39 9.53 3.38 5.30 3.05 9.01 14.4

0.12 0.02 0.00 0.04 0.00 0.04 0.09 0.83 0.00

0.09 0.10 0.04 0.14 0.00 0.00 0.09 0.36 1.33

5.30 2.78 6.39 36.2 0.41 9.18 0.60 8.91 10.1

67 80 38 27 93 78 88 79 69

L = lake; R = river; H = harbor; DD = drydock;

LM = Lago Maggiore;

ANT = Antwerp:

+ 4 * 9 + 8 & 10 f 5 &7 * 5 + 4 + 6

OST = Ostend; SCH = Scheldt; LlM = Limburg.

M. Ceulemans, F.C. Adams/Analytics

166 1000

1

10

10

100 GC-AES

Fig. 3. Correlation the determination (r = 0.9990).

1000 (ng

g-‘)

obtained between GC-AAS and GC-AES for of butyltin compounds in sediment extracts

paring the results with those obtained from the analysis of organotin standards. TBT and DBT recoveries were ranging from 85-93% and 88-97%, respectively, for all sediments. For MBT recovery however, large discrepancies were found, as can be seen in Table 2 with recoveries ranging between 27-93%. The reason for this large scattering of extraction efficiencies can result from: (i) inhibition of the derivatization reaction, (ii) interferences in the atomization step during measurement and (iii) incomplete desorption from the sediment. Experiments were set up to investigate all three possibilities: (i) inhibition of th e d erivatization reaction. The poor recoveries observed in hydride generation of some sediment extracts have been attributed to an inhibition of the hydridization reaction. To test the possibility of a similar effect on the ethylation reaction all sediments were extracted as described in Method 1. After evaporation of the collected organic phase and redissolvation in hexane, ionic butyltins were added and derivatized in the presence of the coextracted compounds and the organotin naturally present in the sediment. The results were compared with an identical butyltin spike in 1 ml of hexane followed by derivatization. Recovery values for MBT

Table 3 Correlation

between MBT recovery

MBT recovery

Chimica Acta 317 (1995) 161-170

found in this way ranged between 87-104% indicating that the ethylation reaction was not inhibited by the presence of coextracted organic and inorganic compounds. (ii) detector interferences. A possible detector interference in the form of signal quenching, as was suggested by some authors [36,37] to occur during measurement of sediment extracts was investigated by analysing a number of sediment extracts (CRM 462, RM 424, OST-1) displaying different recoveries, using both AAS and AES detection. Butyltin concentrations calculated from the results of both techniques are presented in Fig. 3 as a correlation graph. The deviations from perfect correlation (straight line in Fig. 31, which were observed for the lowest values are due to the fact that the measured concentrations are close to the limit of determination of the AAS detector and hence do not result from interferences generated during detection. Detection limits range between 0.01 and 2.5 ng g-’ (as Sn> for AES and AAS detection, respectively. The excellent correlation between the two independent detection techniques indicate that interferences during detection are most probably not the reason for the poor MBT recoveries in some sediments. Coextracted compounds may however cause chromatographic interferences as was shown in earlier work, an effect which can be eliminated to a great extent using clean-up methods 1261. (iii) Desorption from the sediment. Studies on the adsorptive behaviour of organotin compounds have indicated that the strength of adsorption is in the order: MBT > TBT > DBT where TBT adsorption is favoured by hydrophobicity and MBT adsorption favoured by polarity which might explain the high adsorption affinity of MBT towards particulate matter [38]. A further indication for the strong adsorption of MBT was found in the fact that its removal from the sediment was strongly influenced by the acid used, whereas for DBT and TBT no significant difference between all tested acids (HCl,

and sediment composition

Na

Mg

Al

Si

P

S

Cl

K

Ca

Fe

Cu

Zn

TOC

-0.20

-0.05

-0.55

0.59

-0.57

-0.66

-0.14

-0.40

-0.13

-0.38

-0.19

-0.01

-0.77

M. Ceulemans, F.C. Adams/Analytics Table 4 Results of the determination

of butyltins

in (certified)

PACS-1 a

MBT DBT TBT

reference

materials

CRM 462 b

RM 424 b

Certified value

MI

MI1

Certified value

MI

MI1

Reference value

MI

MI1

0.28 + 0.17 1.16 + 0.18 1.27 + 0.22

0.94 + 0.06 1.13 + 0.04 1.10 f 0.05

1.53 f 0.17 1.24 + 0.09

n.c. ’ 128 + 16 70 + 14

125 + 16 114+9 64.2 f 5.8

128k7 64.8 + 7.7

(257 + 54) d (53 +_ 19) 20 * 5

85.6 + 20.1 42.1 + 4.6 21.5 f 4.1

28.4: + 2.8 12.1 * 3.9

a Concentrations expressed b Concentrations expressed c nc.: not certified. d 0: indicative values.

in pg gg ’ as Sn. in ng g-’ as compound.

acetic acid, HBr) was observed. Further, polar solvents were found mandatory for extracting the polar MBT compound. It was concluded that the combination of a strong acid and a polar solvent was necessary for effective extraction of MBT from sediments. An attempt was made to find the parameters affecting the variations in MBT adsorption affinity towards the different sediments. Therefore the elemental composition of all sediments was determined using X-ray fluorescence and the total organic carbon content (TOC) was determined using the method of Walkley and Black [39]. The results are shown in Table 2. Further, all sediment extracts were analyzed by GC-MS in order to identify coextracted compounds from the sediment. GC-MS analysis of sediment extracts did not lead to any conclusion, as no similar pattern in compounds coextracted from sediments displaying low MBT recoveries could be found. Application of multivariate methods such as correlation and factor analysis to the data presented in Table 2 did not lead to a firm conclusion because, as no explicit trends

Table 5 Results of the determination Concentration

of butyltin compounds f 95% confidence

OST-1

MBT DBT TBT

167

Chimica Acta 317 (1995) 161-l 70

influencing MBT recovery were present, the1 number of sediments investigated was too low for statistical conclusions. The correlations obtained between MBT recovery and elemental and TOC composition are presented in Table 3 and show only the trend that high sulphur and organic carbon contents could negatively affect MBT extraction from sediments. 3.3. Analysis of reference materials Reference materials are the most powerful tools for quality control of measurements. Two certified reference materials (CRMS) are available fot butyltin analysis in sediments: PACS-1 marine harbour sediment (NRCC) and CRM 462 coastal sediment (BCR). Further, a research material has been recently made available by the BCR: RM 424 industrial harbour sediment with low butyltin concentration and a difficult matrix composition. In this study we have applied the two sample preparation procedures using different leaching, complexing, extraction and derivatization conditions to all the available refer-

in environmental

interval a ( pg g-

sediment samples

’ as compound)

OST-2

ANT-DD

LIM-DD

MI

MI1

MI

MI1

MI

MI

0.14 f 0.02 0.44 + 0.03 0.29 f 0.02

0.43 5 0.02 0.31 f 0.03

0.36 f 0.02 1.11 * 0.12 2.33 + 0.14

_ 1.39 + 0.06 2.67 f 0.08

8.13 zh 0.33 10.0 + 0.6 26.4 f 1.8

1.55 + 0.09 1.67 f 0.20 6.60 + 0.18

Mean value of 4 independent

replicates

(n = 4) expressed

in micrograms

per gram of dry mass.

168

M. Ceulemans,

F.C. Adams/Analytics

ence materials. The mean results of 5 independent replicates for each sediment are presented in Table 4. PACS-1. As can be seen from Table 4, both methods show good agreement within the confidence interval for TBT. For DBT, Method II gives slightly higher values. The value found for MBT using Method I is completely out of range with the value certified. Concentration values for MBT presented by other workers for this sediment range from 0.03 to 1.03 j_&gg-r as can be seen from Table 1. Zhang et al. [27] have evaluated 10 different extraction techniques through the analysis of the PACS-1 sediment. None of the methods, however, was able to quantitatively extract MBT from the sediment, showing erratic and non reproducible MBT recoveries, which proves the difficulty of accurate MBT determination in sediments and poses some questions on the reliability of certified values given for this compound. CRM-462. Sediments originating from remote and less contaminated areas often have concentrations at 3

(6 2

II& SrP

1

02468

TIME imm)

3

W

2

Chimica Acra 317 (1995) 161-I 70

sub pug g-’ level. A CRM is available at this concentration level in the form of a coastal sediment prepared by the BCR. Table 4 shows excellent agreement with the certified values for the two methods both for DBT and TBT. Application of Method I led to a MBT value of 125 f 16 ng g-l. However, no concentration was specified for this sediment, due to the large scattering of individual results (13-244 ng g-l> during the certification [28]. Values presented by other workers are rare, so the relevance of the figure presented here may not be verified. m-424. A sediment rich in organic material containing low levels of TBT was prepared in order to test the performance of analytical methods under extreme conditions. Owing to obscurities in the results by individual participants of the standardization exercise, this sediment was not certified but made available as a research material [29]. The value given for TBT is a reference value, while the values for DBT and MBT are only indicative. Table 4 shows that differences are obtained between the two investigated methods, even for TBT. Comparison with the reference value shows that application of both methods leads to concentrations at the level specified and the same is true for the DBT value. The MBT value found using Method I differs by a factor 3 from the value specified. A chromatogram of RM 424 after GC-AES measurement is shown in Fig. 2. The fact that no (CRM 462) or only indicative values (RM 424) are given for MBT plus the observation that large differences in comparison with the certified value are obtained (PACS-1) using Method I, proves the difficulty of analysing MBT in sediments. DBT and TBT values agree well with the certified values for both methods. As can be seen from the results of RM 424 care should be taken when sediments with complex matrices and low concentrations are analyzed. 3.4. Application to real samples

1

I 0

2

4 6 8 10 12 TIME (mid

Fig. 4. Chromatogram for a sample of Ostend harbour sediment after sample preparation using (a) Method I, (b) Method II and GC-AAS measurement: Sn’” = inorganic tin; 1 = MBT, 2 = DBT; 3=TE%T.

Both methods were applied to the analysis of sediment samples collected in the environment. Two sediments were collected at different sites in the harbour of Ostend (Belgium), which is characterized by intense shipping activities from pleasure craft and ferry ships. The detected concentrations are presented in Table 5. Comparison with the Environmen-

M. Ceulemans, F.C. Adams/Analytics

tal Quality Target for TBT in sediments, set at l-2 ng g -’ [40] and implemented now in most European countries, indicates severe TBT contamination in the harbour, especially in sample OST-2 ( pg g-’ level). TBT degradation accounts for the detection of DBT and MBT in the sediments. Fig. 4 shows chromatograms of the OST-2 sediment after application of (a) Method I and (b) Method II. It can be seen from the chromatograms that Method I is able to extract also inorganic tin (Sri’“) from the sediment. However, the extraction was found to be irreproducible and not quantitative. The use of pentylation instead of ethylation for derivatization accounts for the reversed order of elution of the different compounds, while the lower boiling points of the ethylated derivatives explain the shorter elution times. AAS detection was used in both analyses. Both chromatograms were recorded under different chromatographic conditions. The chromatogram in Fig. 4b is the result of separation on a RSL-150 megabore column with temperature programming: 100°C -+ 10”C/min + 270°C. In Fig. 4a separation was done on an HP-l capillary column with temperature program: 80°C (1 min) -+ 20”C/min + 270°C. The excellent separating power of a capillary column allows higher ramp rates to be used in comparison with a megabore column, thereby considerably speeding up the analysis. Two sediments were sampled in drydocks, one in an industrial ship repair facility located in the harbour of Antwerp, another in a maintenance place for pleasure craft located in the province of Limburg. They were analyzed using Method I only and the results are presented in Table 5. Extremely high concentrations were found in the Antwerp drydock (ANT-DD) sediment as could be expected due to maintenance operations (washing, blasting and painting) of seaships. The high concentrations found in the Limburg drydock (LIM-DD) sediment indicate the illegal usage of TBT-containing antifouling paint, as following EC directives the usage of these paints is forbidden on ships < 25 m and/or the long-time persistence of TBT in sediments.

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ments has to be related to the strong adsorption affinity of this compound onto the sediment. Further it was found that polar solvents and strong acidic conditions, in combination with a suitable complexing agent are required to favourise MBT extraction from the sediment, though recoveries were shown to be strongly affected by the composition of the sediment. An attempt to find the parameters affecting adsorption strength of MBT to sediments did not lead to firm conclusions. Analysis of certified reference materials proved that the two presented methods, based on different leaching, complexing, extraction and derivatization conditions, are able to accurately determine TBT and DBT in sediments, while MBT determination in general still remains doubtful due to the absence of reliable, or no or only indicative values for this compound in reference materials. However, Method I was shown to be suitable for MBT determination in certain sediments, where care should be taken to evaluate the MBT recovery in all the individual sediments. Analysis of sediments sampled from harbours and drydocks in Belgium have shown high butyltin concentrations (> pg g-l), indicating that the problem of contamination of the marine environment with TBT is far from solved, despite recent alternative antifoulants and legislation and EC directives towards the use of this compound.

Acknowledgements A research grant by the N.F.W.O. Belgium to M. Ceulemans is gratefully acknowledged. Further, the authors would like to thank C. Brenkers for her assistance with sample preparation, R. Nullens for carrying out the XRF measurements and B. Spanoghe, W. Van Dongen for assistance with the GC-MS measurements. R. Ma and W. Vain Mol, are acknowledged for helpful discussions during preparation of the manuscript.

References 4. Conclusions In this study it was shown that the difficulty of efficient MBT extraction and determination in sedi-

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