Investigating the potential of high-performance liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry as an alternative method for the speciation analysis of organotin compounds

Liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) was applied for the determination of butyl- and phenyltin compounds. Chromatography was performed on a 30 ׶2 mm, 3 μm C18 column, enabling the separation of mono-, di- and trisubstituted butyl- and phenyltin compounds in less than 10 min using a water/1% trifluoroacetic acid/¶methanol gradient. While satisfactory retention and resolution is achieved for the di- and trisubstituted butyl- and phenyltin compounds, monobutyltin and monophenyltin cannot be resolved chromatographically. Depending on the parameter values of the interface, APCI-MS detection allows both specific detection of the molecular ion or cluster ion at low to intermediate fragmentor voltages or quasi-element specific detection of the Sn⁺ ion released from the organotin compounds at high fragmentor voltages. The sensitivity of MS detection is similar for butyl- and phenyltin compounds, but varies largely from mono- to trisubstituted organotin compounds with tributyl- and triphenyltin being the most sensitively detectable compounds. Detection limits are in the 20–65 pg (abs.) range in SIM mode and in the 750–2000 pg (abs.) range in the scan mode for tributyl- and triphenyltin and for dibutyl- and diphenyltin, respectively. Monobutyl- and monophenyltin can be detected with much lower sensitivity which, together with their unfavorable chromatographic behavior, accounts for the fact that they cannot be analyzed at environmentally relevant concentrations. Although LC-APCI-MS is generally less sensitive than comparable GC methods, it is applicable to the analysis of environmental samples as demonstrated by the analysis of the PACS-2 sediment certified reference material. Although the derivatization of the ionic organotin compounds, which particularly in real samples is a potential source of error, is circumvented when LC-APCI-MS is used, the extraction step is still critical and may lead to underestimation when quantitation is not done by the method of standard addition.     

Comparison of sulphur-mode and tin-mode flame photometric detectors for the gas chromatographic determination of organotin compounds

A comparison of sulphur-mode (393 nm) and tin-mode (610 nm) flame photometric detectors for the gas chromatographic determination of butyl- and phenyltin compounds is described. The chromatographic peaks of the butyl- and phenyltin compounds were well separated, and high sensitivity was achieved in both modes; however, the tin-mode was more specific for tin compounds than the sulphur-mode. The absolute detection limits with the sulphur-mode and the tin-mode were 3.9-7.6 pg and 2.6-5.1 pg as tin, respectively. The application of the tin-mode gas chromatographic method to the determination of organotin compounds in fish is presented. For this application, organotins are extracted (as chloride) with hydrochloric acid and n-hexane-benzene (3:2, containing 0.05% tropolone) and the extracts are pentylated by a Grignard reagent prior to gas chromatography. The absolute recoveries of butyl- and phenyltin compounds added to fish samples ranged from 68.5 to 84.4% (the coefficients of variation were less than 6.6% for all substances, n = 8). Significant amounts of three organotin compounds (di- and tributyltin and triphenyltin) in fish samples were detected by this method. This technique may have application for other organotin compounds and the monitoring of butyl- and phenyltin compounds in the environment.     

Simultaneous determination of butyltin and phenyltin compounds in oysters by capillary gas chromatography

A method is described for the simultaneous determination of butyl- and phenyltin compounds in oyster samples. The organotin compounds were extracted (as chlorides) from oyster homogenates with hydrochloric acid and benzene in the presence of 0.05% tropolone. These compounds were converted into pentyl derivatives with pentyl Grignard reagent and then analysed by capillary gas chromatography with a flame photometric detector equipped with a 393-nm filter. The recoveries of six organotin compounds added to oyster samples ranged from 71 to 74%. The detection limits of butyl- and phenyltin compounds were in the 5-9 pg range as tin. We detected significant amounts of three organotin compounds (di- and tributyltin and triphenyltin) in oyster samples.     

Different Behavior of Organotin Compounds by Anodic Stripping Voltammetry and their Quantification after Partial Ion Exchange Separation

 The electrochemical behavior and the analytical performance of the organotin compounds mono-, di- and tributyltin, as well as, mono-, di- and triphenyltin were investigated by various voltammetric techniques, such as alternating current polarography of the first harmonic (ACP1), square wave polarography at a hanging mercury drop electrode (SQW) and anodic stripping voltammetry (ASV). Differences could be observed in the sensitivity, the detection limit and the reproducibility of the organotins by the techniques used and in some cases their simultaneously determination was difficult, as the half-wave potentials were very close together. However, by ASV double peaks were observed only for the monophenyltin and dibutyltin species, distinguishing them from the overlapping peaks of diphenyltin and triphenyltin, respectively. This different electrochemical behavior, is due to the formation of intermediate products during the electrolysis of these compounds with other half wave potentials and was successfully utilized for the separation and determination of monophenyltin in the presence of diphenyltin. In the case of dibutyltin, where no linear calibration curves for the two peaks were obtained, a prior suitable ion exchange procedure was developed for its separation and determination from the interfering triphenyltin. The successful application of this technique could be proved on a CRM freshwater sediment of BCR.     

Determination of mono-, di- and tri-substituted butyltin,phenyltin and methyltin compounds as free halides using gas chromatography with flame photometric detection

A simple chromatographic procedure has been developed for the sensitive determination of mono-, di- and tri-substituted butyltin, phenyltin, and methyltin compounds as halides. The organotin compounds were separated on a DB-1 capillary column and detected by flame photometric detection (FPD) equipped with a 611.5 nm filter. Pretreatment of the capillary column with an ethyl acetate solution of hydrobromic acid, or doping of standard solutions with hydrobromic acid, was found to be necessary if reproducibly sharp peaks of organotin halides were to be obtained. Column treatment and acid doping did not cause any background problems or undesirable degradation of the organotin compounds. Three different standard solutions in ethyl acetate had to be Jrepared, because undesirable degradation of the organotin halides was observed when all the compounds were dissolved in the same solution. The first, standard solution I, contained tri-n-butyltin chloride (TBTCI) and trimethyltin chloride (TMTCI), the second, standard solution II, contained triphenyltin chloride (TPTCI), and the third, standard solution III, contained hydrogen bromide and the other organotin compounds: di-n-butyltin chloride (DBTCI), mono-n-butyltin chloride (MBTCI), dimethyltin chloride (DMTCI), monomethyltin chloride (MMTCI), diphenyltin chloride (DPTCI), and monophenyltin chloride (MPTCI). An ethyl acetate solution containing hydrobromic acid (20 × 10^?3 mol/I) was used for column treatment.     

Analysis of organotin compounds by grignard derivatization and gas chromatography-ion trap tandem mass spectrometry

The determination of organotin compounds in water using gas chromatography-tandem mass spectrometry (GC-MS-MS) is described. Several organotin derivatives were synthesized by the reaction of organotin chlorides with Grignard reagents such as methyl-, propyl- and pentylmagnesium halides. After the optimization of the GC-MS-MS conditions, several derivatizations with the Grignard reagents were compared by evaluating the molar responses and volatilities of the derivatives and derivatization yields. As a result, the derivatizing reagent of choice is pentylmagnesium bromide. Calibration curves for the mono-, di- and tributyltins and mono-, di- and triphenyltins with pentylmagnesium bromide were linear in the range of 0.5-100 pg of Sn. The instrumental detection limits of six organotins ranged from 0.20 to 0.35 pg of Sn. The recovery tests from water samples (500 ml) were performed by using sodium diethyldithiocarbamate (DDTC) as a complexing reagent. Except for monophenyltin, the absolute recoveries of organotins from pure water at 200 ng of Sn/l were satisfactory. The recoveries calibrated by surrogate compounds (perdeuterated organotin chlorides) ranged from 71 to 109%. The method detection limits ranged from 0.26 to 0.84 pg of Sn (500-ml sample). This method was applied to the recovery of organotins from river water and seawater. The calibrated recoveries were between 90 and 122%.     

Determination of organotins in aquatic plants by headspace SPME followed by GC-PFPD determination

Optimal conditions of headspace solid-phase microextraction followed by gas chromatography coupled to pulsed flame photometric detection (SPME–GC–PFPD) have been investigated to validate the analysis of 11 organotin compounds in plant matrices including methyl-, butyl-, and phenyltin compounds. The extraction of organotin compounds from vegetal matrices has been carried out using optimized conditions of HCl-based extraction. The use of headspace SPME to preconcentrate the analytes allowed most of the detection limits to be obtained sub-0.5?ng(Sn)?g^?1. The precision evaluated using RSD with six replicates ranges between 5 and 10% (except for triphenyltin: 17%). The accuracy of the method was validated on spiked or polluted vegetal samples taken from Bizerte Lagoon (Tunisia) and by comparison with classical liquid–liquid extraction (LLE). These results highlight the suitability of the selected method for organotin control in complex environmental matrices such as aquatic plants.     

Determination of butyl- and phenyltin compounds in human urine by HS-SPME after derivatization with tetraethylborate and subsequent determination by capillary GC with microwave-induced plasma atomic emission and mass spectrometric detection

A headspace solid-phase micro-extraction (HS-SPME) method was developed and optimized for gas chromatographic separation and determination of commonly found organotin compounds in human urine after potential exposure. Butyl- and phenyltin compounds were in situ derivatized to ethylated derivatives by sodium tetraethylborate (NaBEt₄) directly in the urine matrix. The relevant parameters affecting the yield of the SPME procedure were examined using tetrabutyltin as internal standard. The method was optimized for direct use in the analysis of undiluted human urine samples and mono-, di- and tri-substituted butyl- and phenyltin compounds could be determined after a 15-min headspace extraction time at room temperature. The selectivity of the microwave-induced plasma atomic emission detector (MIP-AED) as an element specific detector in combination with the relatively selective sample preparation technique of HS-SPME allowed the interference-free detection of the organotin compounds in all cases. A quadrupole mass spectrometer was used in parallel experiments as a detector for the confirmation of the identity molecular structure of the eluted compounds. The performance characteristics of the developed method are given for the determination of mixtures of these compounds. Finally the proposed method was applied to the analysis of several human urine samples.     

Speciation of organotin compounds in waters and marine sediments using purge-and-trap capillary gas chromatography with atomic emission detection

A procedure for the simultaneous determination of six organotin compounds, including methyl-, butyl- and phenyltins, in waters and marine sediments is developed. The analytes were leached from the solid samples into an acetic acid:methanol mixture by using an ultrasonic probe. The organotins were derivatized with sodium tetraethylborate (NaBEt₄) in the aqueous phase, stripped by a flow of helium, pre-concentrated in a trap and thermally desorbed. This was followed by capillary gas chromatography with microwave-induced plasma atomic emission spectrometry as the detection system (GC-AED). Each chromatographic run took 22 min, including the purge time. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were at least 0.9991. Detection limits ranged from 11 to 50 ng Sn l⁻¹ for tributyltin and tetramethyltin, respectively. The seawater samples analyzed contained variable concentrations of mono-, di- and tributyl- and monophenyltin, ranging from 0.05 to 0.48 μg Sn l⁻¹, depending on the compound. Some of the sediments analyzed contained concentrations of dibutyl- and tributyltin of between 6.0 and 13.0 ng Sn g⁻¹. Analysis of the certified reference material PACS-2, as well as of spiked water and sediment samples showed the accuracy of the method. The proposed method is selective and reproducible, and is considered suitable for monitoring organotin compounds in water and sediment samples.     

Speciation of butyl- and phenyltin compounds in sediments using pressurized liquid extraction and liquid chromatography-inductively coupled plasma mass spectrometry

A liquid chromatographic method with inductively coupled plasma mass spectrometry is proposed for the speciation of butyl- (monobutyltin, dibutyltin, tributyltin) and phenyl- (monophenyltin, diphenyltin, triphenyltin) tin compounds in sediments. After evaluation of different additives in the mobile phase, the use of 0.075% (w/v) of tropolone and 0.1% (v/v) of triethylamine in a mobile phase of methanol-acetic acid-water (72.5:6:21.5) allowed the best chromatographic separation of the six compounds. Pressurized liquid extraction (PLE) with a methanolic mixture of 0.5 M acetic acid and 0.2% (w/v) of tropolone was suitable for the quantitative extraction of butyl- and phenyltin compounds with recovery values ranging from 72 to 102%. This analytical approach was compared to conventional solvent extraction methods making use of acids and/or organic solvent of medium polarity. The main advantages of PLE over conventional solvent extraction are: (i) the possibility to extract quantitatively DPhT and MPhT from sediments, which could not be done by a solvent extraction approach; (ii) to preserve the structural integrity of the organotin compounds; (iii) to reduce the extraction time from several hours in case of solvent extraction techniques to just 30 min. For spiked sediments, limits of detection ranged from 0.7 to 2 ng/g of tin according to the compound. The relative standard deviations were found to be between 8 and 15%. The developed analytical procedure was validated using a reference material and was applied to various environmental samples.     

A Simple Method for the Speciation of Organotin Compounds in Water Samples Using Ethylation and GC-QFAAS

 A simple method for the extraction of organotin compounds from water samples was developed in which both the instrumental parameters and the extraction/derivatization step were optimized. Organotin compounds (butyl-, phenyl- and octyl-) in tap water samples were ethylated with the addition of 2.5 ml of 0.4% w/v NaBEt₄ at pH 5.00 and subsequently extracted two times, for 10 min, with 3 and 2 ml of hexane. The combined extracts were analyzed with on-column capillary GC-QFAAS. The recoveries were quantitative for di- and tri- alkyltin compounds, whereas between 67 and 86% of the monoalkyltin compounds were recovered. The detection limits obtained ranged from 110 pg for monobutyltin to 500 pg for triphenyltin, as sensitivities were found to be compound dependent. The preparation of ethylated standards was also optimized. It was found that two subsequent extractions, with 1.0 and 0.5 ml of hexane were necessary for the quantitative recovery of the ethylated organotin compounds.     

GC FPD method for the simultaneous speciation of butyltin and phenyltin compounds in waters

A method is described for the simultaneous determination of nanogram amounts of mono-, di- and tri-butyltin compounds in water. The procedure is based on the conversion of tin compounds to volatile species by Grignard pentylation and analysis using GC with flame photometric detection (GC FPD). The ionic compounds are extracted from diluted acidified (HBr) aqueous solutions by using a pentane-tropolone solution. The extracted organotin compounds are pentylated by a Grignard reagent and purified on a Fluorisil column before analysis by GC FPD. The detection limits are 20 ng dm^?3 for butyltin compounds and 50 ng dm^?3 for phenyltin compounds. Recoveries from spiking experiments in tap-water and natural seawater matrices, in which no organotin compounds were detected, were greater than 90% for most of the alkyltin compounds.     

Determination of Butyltin and Phenyltin by GC–FPD Following Ethylation by NaBEt4

An organotin speciation method was optimized for the simultaneous determination of mono-, di- and tri-butyltin compounds and mono-, di- and tri-phenyltin compounds in water. The procedure was based on a one-step simultaneous ethylation and extraction using the sodium tetraethylborate reagent directly in the aqueous phase in the presence of an iso-octane layer. Direct extract analysis was performed using capillary gas chromatography and flame photometric detection (GC–FPD). This derivatization procedure reduces drastically the number of analytical steps, thus saving time and improving reliability. Relative detection limits range from 0.4 to 0.8 ng dm⁻³ for butyltin species and from 0.7 to 2.1 ng dm⁻³ for phenyltin species; the linearity ranges from 0 to 400 ng dm⁻³. Analysis of environmental aqueous samples and a Certified Reference Material (CRM) demonstrates the accuracy of the analytical method.     

Speciation of organotin in sediments by multicapillary gas chromatography with atomic emission detection after microwave-assisted leaching and solvent extraction-derivatization

Microwave-assisted leaching of organotin compounds from sediment samples followed by the simultaneous extraction-derivatization of the extracted species was revisited with the goal to compare the existing procedures, improve their recoveries and extend them to phenyltin compounds. The stability of butyl- and phenyltin compounds under microwave field, real recoveries of the whole analytical procedure, effect of the extraction solvent, and the necessity for an internal standard were evaluated using two candidate reference sediments. The combination of the optimized sample preparation procedure with multicapillary chromatography resulted in a rapid (2 min leaching + 5 min extraction-derivatization + 3 min chromatographic separation) and efficient analytical procedure for speciation analysis of organotin compounds in sediment samples. The detection limit achieved with a microwave-induced plasma atomic emission detector was 2 ng g^–1. Received: 27 July 1998 / Revised: 31 August 1998 / Accepted: 4 September 1998     

Preparation of pentylated organotin standards for use in trace analysis with gas chromatography

A method for the preparation and purification of pentylated derivatives is described for nine organotin compounds that are relevant in environmental analysis (tributyltin acetate, dibutyltin dichloride, butyltin trichloride, triphenyltin chloride, diphenyltin dichloride, phenyltin trichloride, tricyclohexyltin hydroxide (cyhexatin), dicyclohexyltin dibromide and bis (trineophyltin) oxide (fenbutatinoxide)). The compounds are synthesized on a 100 mg scale and purified by column chromatography. Purity checks were performed with gas chromatography with mass selective detection. The mass spectrum of pentyltrineophyltin is presented.     

Optimization of a Sample Preparation Procedure for the Speciation of Organotin Compounds in Sediment Samples Using GC-AED

Abstract

Results of a comprehensive study of all analytical steps involved in the sample preparation procedure for the speciation of butyl- and phenyltin compounds in sediments are presented. The proposed method is based on acid leaching (using aqueous acetic acid) and simultaneous extraction of the ionic species into an organic solvent (n-hexane/ethyl acetate) with the addition of a complexing agent (diethyl dithiocarbamic acid). After evaporation to dryness, the residue is derivatized with sodium tetraethylborate in an aqueous buffer solution (acetate buffer, 0.1 M, pH 5) and extracted into n-hexane. Cleanup is performed over basic alumina and the ethylated organotin species are analyzed with a gas chromatograph coupled to a microwave-induced helium plasma atomic emission detector (GC-AED). The optimized method was validated within an interlaboratory study for the certification of tributyltin, triphenyltin and their degradation products in a freshwater sediment, the BCR candidate reference material 646.     

Influence of the soil matrices on the analytical performance of headspace solid-phase microextraction for organotin analysis by gas chromatography-pulsed flame photometric detection

Organotin compounds (OTCs) have been identified in a variety of environmental media (air, surface water, groundwater, soil and sediments). In the past, much attention was assigned to the study of the OTCs content in biological samples, water and sediments. Little information about OTCs in soil is available. In this work, a procedure for butyl and phenyltin determination in soils by headspace-solid-phase microextraction (HS-SPME) gas chromatography-pulsed flame photometric detection (GC-PFPD) was investigated. For SPME analysis, a polydimethylsiloxane (PDMS) coating was applied. Peat soil rich in organic matter and with a high cation-exchange capacity (CEC), and clay soil low in organic matter and with a low CEC were analysed. The influence of these different soil matrices on HS-SPME analysis was evaluated by spiking of samples. In general, the recoveries for the two spiked soils exceeded 80%. The repeatability of the method was better than 10%. The limits of detection (LODs) and limits of quantification (LOQs) were in the ng S ng(-1) range. The technique may be reliably applied for the determination of butyltins and monophenyltin in soils, while it shows some limitations for the analysis of di- and triphenyltin (TPhT).     

Separation of butyltin and phenyltin species by ion-exchange chromatography with complexing mobile phases

Summary Butyltin and phenyltin species have been separated by ion-exchange chromatography using silica-based and polymer-based columns. Mobile phases consisted of methanol-water mixtures containing polyfunctional carboxylic acids, which can act as complexing agents for organotin species. The best results were achieved with a system based on a methanol mobile phase containing malic and oxalic acids and a polymer-based column, which allowed the separation of tri- and diorganotin compounds and some resolution between monobutyltin and monophenyltin.     

Determination of triphenyltin hydroxide derivatives by capillary GC and tin-selective FPD

A new method for the determination of triphenyltin hydroxide using capillary column gas chromatography with a tin-selective flame photometric detector has been developed. Triphenyltin hydroxide and its potential metabolites are converted to methyl derivatives and separated on glass capillary columns coated with OV-101. Derivatization of triphenyltin hydroxide, triphenyltin chloride, diphenyltin dichloride, phenyltin trichloride, and bis-triphenyltin oxide is nearly quantitative with a minimum of redistribution products. The selectivity of the flame photometric detector is cearly demonstrated by the comparison of chromatographic profiles obtained from using both the flame photometric and flame ionization detectors. The use of this chromatographic system in the analysis of triphenyltin hydroxide in a fortified water sample demonstrates the potential use of this system in organotin residue chemistry.     

Speciation of organotin compounds in marine sediments by capillary column gas chromatography-atomic absorption spectrometry coupled with hydride generation

A method for speciation of organotin compounds in marine sediments by solvent extraction combined with hydride generation gas chromatography-atomic absorption spectrometry has been developed. Sediment samples spiked with tributyltin and triphenyltin chlorides were homogenized in hydrochloric acid. The chlorides were extracted twice into toluene. Recoveries of the organotin compounds from the spiked sediment samples were improved by the addition of 8-quinolinol. Tributyltin and triphenyltin chlorides form ion-associates with 8-quinolinol in aqueous hydrochloric acid. The method was optimized with respect to derivatization reactions and extraction conditions. Interferences from Sn(II/IV) and additional 13 ions were investigated. Recoveries of 84-100% for tributyltin and 86-100% for triphenyltin were achieved using this method. The detection limits obtained for tributyltin and triphenyltin chlorides were 95 and 145 pg, respectively, corresponding to a relative detection limit of 95 and 145 ng kg(-1) in the sediment.