Paulette Maxwell

Headspace single-drop microextration for the detection of organotin compounds

The performance of single-drop microextraction (SDME), coupled with gas chromatography/mass spectrometry, was assessed for the determination of tributyltin compounds in water and solid samples. Experimental parameters impacting the performance of SDME, such as microextraction solvent and sampling and stirring time, were investigated. Analytical results obtained by SDME were compared with those generated by conventional solid phase microextraction (SPME) and liquid-liquid extraction (LLE) for the determination of TBT in PACS-2 sediment certified reference material (CRM).

Application of isotope dilution to the determination of methylmercury in fish tissue by solid-phase microextraction gas chromatography-mass spectrometry

Species-specific isotope dilution (ID) calibration using solid-phase microextraction (SPME) in combination with gas chromatography-mass spectrometry (GC-MS) for separation and detection of methylmercury (MeHg) in fish tissue is described. Samples were digested with methanolic potassium hydroxide. Analytes were propylated and headspace sampled with a polydimethylsiloxane-coated SPME fused-silica fiber. ID analysis was performed using a laboratory-synthesized 198Hg-enriched methylmercury (Me 198Hg) spike. Using selective ion monitoring (SIM) mode, the intensities of Me 202HgPr+ at m/z 260 and Me 198HgPr+ at m/z 256 were used to calculate the m/z ratio at 260/256, which was used to quantify MeHg in NRCC CRM DORM-2 fish tissue. A MeHg concentration of 4.336 +/- 0.091 microg g(-1) (one standard deviation, n = 4) as Hg was obtained in DORM-2, in good agreement with the certified value of 4.47 +/- 0.32 microg g(-1) (95% confidence interval). A concentration of 4.58 +/- 0.31 microg g(-1) was determined by standard additions calibration using ethylmercury (EtHg) as an internal standard. The three-fold improvement in the precision of measured MeHg concentrations using ID highlights its superiority in providing more precise results compared to the method of standard additions. A method detection limit (3 S.D.) of 0.037 microg g(-1) was estimated based on a 0.25 g subsample of DORM-2.

Extraction of butyltin species and their gas chromatographic determination as chlorides in a sediment certified reference material for trace metals, PACS-1☆

Abstract A gas chromatographic method has been developed for the determination of butyltin species in sediments. The butyltin species are separated as chlorides by using a DB-608 open tubular column after their extraction from the sediment using a combination of sonication in methanolic HCl and solvent extraction. Two extractants are possible: toluene—isobutyl acetate—tropolone and hexane—isobutyl acetate. The efficiencies for the first extractant are: tributyltin, 94.4 ± 4.7%; dibutyltin, 94.9 ± 2.2%; and monobutyltin, 86.3 ± 4.2%. The absolute detection limits are about 30 pg tin. Using a 1-g sample, the relative detection limits are about 30 ng tin per g sediment. These may be lowered to 3 ng tin per g by starting with a 4-g sample and adding a concentration step. The reference material PACS-1 was found to contain 1.08 ± 0.31 μg tin per g of tributyltin and 1.13 ± 0.30 μg tin per g of dibutyltin.

Speciation without chromatography : Part I. Determination of tributyltin in aqueous samples by chloride generation, headspace solid-phase microextraction and inductively coupled plasma time of flight mass spectrometry

An analytical procedure was developed for the determination of tributyltin in aqueous samples. The relatively high volatility of the organometal halide species confers suitability for their headspace sampling from the vapour phase above natural waters or leached solid samples. Tributyltin was collected from the sample headspace above various chloride-containing matrices, including HCl, sodium chloride solution and sea-water, by passive sampling using a polydimethylsiloxane/divinylbenzene (PDMS/DVB)-coated solid-phase microextraction (SPME) fiber. Inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) was used for detection following thermal desorption of analytes from the fiber. A detection limit of 5.8 pg ml–1(as tin) was realized in aqueous samples. Method validation was achieved using NRCC PACS-2 (Sediment) certified reference material, for which reasonable agreement between certified and measured values for tributyltin content was obtained.

Determination of Arsenobetaine in Fish Tissue by Species Specific Isotope Dilution LC-LTQ-Orbitrap-MS and Standard Addition LC-ICPMS

An accurate and precise method for the determination of arsenobetaine (AsB, (CH(3))(3)(+)AsCH(2)COO(-)) in fish samples using exact matching species specific isotope dilution (ID) liquid chromatography LTQ-Orbitrap mass spectrometry (LC-LTQ-Orbitrap-MS) and standard addition LC inductively coupled plasma mass spectrometry (LC-ICPMS) is described. Samples were extracted by sonication for 30 min with high purity deionized water. An in-house synthesized (13)C enriched AsB spike was used for species specific ID analysis whereas natural abundance AsB, synthesized and characterized by quantitative (1)H NMR (nuclear magnetic resonance spectroscopy), was used for reverse ID and standard addition LC-ICPMS. With the LTQ-Orbitrap-MS instrument in scan mode (m/z 170-190) and resolution set at 7500, the intensities of [M + H](+) ions at m/z of 179.0053 and 180.0087 were used to calculate the 179.0053/180.0087 ion ratio for quantification of AsB in fish tissues. To circumvent potential difficulty in mass bias correction, an exact matching approach was applied. A quantitatively prepared mixture of the natural abundance AsB standard and the enriched spike to give a ratio near one was used for mass bias correction. Concentrations of 9.65 ± 0.24 and 11.39 ± 0.39 mg kg(-1) (expanded uncertainty, k = 2) for AsB in two fish samples of fish1 and fish2, respectively, were obtained by ID LC-LTQ-Orbitrap-MS. These results are in good agreement with those obtained by standard addition LC-ICPMS, 9.56 ± 0.32 and 11.26 ± 0.44 mg kg(-1) (expanded uncertainty, k = 2), respectively. Fish CRM DORM-2 was used for method validation and measured results of 37.9 ± 1.8 and 38.7 ± 0.66 mg kg(-1) (expanded uncertainty, k = 2) for AsB obtained by standard addition LC-ICPMS and ID LC-LTQ-Orbitrap-MS, respectively, are in good agreement with the certified value of 39.0 ± 2.6 mg kg(-1) (expanded uncertainty, k = 2). Detection limits of 0.011 and 0.033 mg kg(-1) for AsB with LC-ICPMS and ID LC-LTQ-Orbitrap-MS, respectively, were obtained demonstrating that the technique is well suited to the determination AsB in fish samples. To the best of our knowledge, this is first application of species specific isotope dilution for the accurate and precise determination of AsB in biological tissues.

Microwave-assisted acid digestion protocol for the determination of methionine and selenomethionine in selenium-enriched yeast by species specific isotope dilution GC-MS

A quantitative and fast microwave assisted protein digestion method is described for the simultaneous determination of methionine (Met) and selenomethionine (SeMet) in yeast. Extraction of Met and SeMet from the selenized yeast was performed in a focused microwave system using methanesulfonic acid (MSA). The effects of parameters such as extraction time, temperature, power and sample mass on the extraction efficiencies of Met and SeMet were investigated. Species specific isotope dilution (ID) calibration using 13C enriched Met and SeMet spikes was employed to obtain accurate results. Analytes were derivatized with methyl chloroformate and extracted into chloroform prior to species specific ID GC-MS analysis. Using a 20 minute extraction time at 165 °C and 6 ml of 4 M MSA was found to be efficient for both analytes based on a 50 mg sample mass. Under these conditions, concentrations of 5862 ± 32 and 3366 ± 60 μg g−1 (one standard deviation, n = 3) for Met and SeMet, respectively, were obtained in SELM-1 yeast certified reference material (CRM). The obtained results are in good agreement with the certified values of 5758 ± 277 and 3448 ± 146 μg g−1 (expanded uncertainty, k = 2). Compared to previous MSA reflux digestion, this newly proposed method offers dramatic reduction in extraction time from 8–16 hours of the conventional MSA reflux to 20 minutes by microwave extraction, significantly improving the sample throughput. Additionally, the microwave extraction is fully automated and uses 75% less reagent (MSA) than the conventional acid reflux setup. The developed method is suitable for quasi real time production monitoring of Met and SeMet in Se enriched yeast and other food products.

Gas phase detection of tributyltin chloride arising from aqueous and solid matrices

The vapour phase above water spiked with tributyltin chloride (TBTCl) and PACS-2 sediment certified reference material was sampled with a solid phase microextraction fiber. The collected volatile compounds were analysed by GC-MS using a HBr–methanol-treated capillary column. Two ion sources were used for this study and their performance characteristics compared. These were electron impact (EI) and negative chemical ionisation (NCI), which allowed both detection of trace amounts of analytes (NCI source) and their identification. This approach provides structural information on the sampled species; at this stage no quantitation was attempted. TBTCl can be detected in the vapour phase above saline water or PACS 2 sediment after one night of passive sampling without any stirring or heating of the sample. This work indicates the need to consider evaporation of TBT as the chloride as a mechanism of loss of this analyte from water or sediment. This may take place from natural settings and contributes to the global biogeochemical cycle of tin; hydride or methyl forms of trace metals are not the only compounds capable of volatilising into the atmosphere.

CHEMOMETRIC OPTIMIZATION OF AN EXTRACTION PROCEDURE USING TARTARIC ACID FOR BUTYLTIN COMPOUNDS FROM SEDIMENT SAMPLES BY GC-PFPD

In this study a simple extraction procedure was developed to minimize the sulfur interferences on the determination of butyltin in sediment samples based on extraction with tartaric acid solution. The optimal conditions were determined using an experimental design methodology and these were achieved using a solution of tartaric acid (0.5 M) with methanol (30 % v/v) for 12 hours in an orbital shaker. This protocol could be followed by a liquid-liquid extraction and this organic phase can be analyzed directly by gas chromatography with pulsed flame photometric detection (GC-PFPD) without any further cleanup due to interferences from elemental sulfur were completely eliminated. The accuracy of the procedure was verified analyzing two reference materials (CRM) (BCR-646, freshwater sediment and PACS-2, marine sediment) and comparing the results to the certified values, the optimized method produced satisfactory results certified values in the CRMs. Finally, harbour sediment samples were analyzed in order to evaluate the suitability of the method for organotin control in complex environmental samples containing high concentrations of sulfur compounds.