Evaluation of comprehensive two-dimensional gas chromatography with flame photometric detection: Potential application for sulfur speciation in shale oil

Flame photometric detection in the sulfur channel has been evaluated for sulfur speciation and quantification in comprehensive two-dimensional gas chromatography [GC × GC-FPD(S)] for S-compound speciation in shale extracts. Signal non-linearity and potential quenching effects were reportedly major limitations of this detector for analysis of sulfur in complex matrices. However, reliable linear relationships with correlation coefficient >0.99 can be obtained if the sum of the square root of each modulation slice in GC × GC is plotted vs. sulfur concentration. Furthermore, the quenching effects are reduced due to essentially complete separation of S-containing components from the hydrocarbon matrix. An increase of S/N of up to 150 times has been recorded for benzothiophene and dibenzothiophene in GC × GC-FPD when compared to GC-FPD due to the modulation process. As a consequence, 10 times lower detection limits were observed in the former mode. The applicability of the method was demonstrated using shale oil sample extracts. Three sulfur classes were completely separated and the target class (thiophenes) was successfully quantified after the rest of the sample was diverted to the second detector by using a heart-cut strategy. Based on the proposed method, 70% of the sulfur in the shale oil was assigned to the thiophenes, 24% to benzothiophenes, and 5% to dibenzothiophene compounds.     

Speciation of butyltins in fish and sediment by means of gas chromatography with flame photometric detection

A modified method for the determination of tributyl-, dibutyl-, and monobutyl-tin in fish and sediment samples is proposed. The samples are digested with hydrochloric acid and the butyltin compounds are extracted into a tropolone solution in pentane and pentylated by a Grignard reaction. The products are cleaned up by washing with a sodium hyrdoxide solution, dried over sodium sulphate, concentrated by evaporation and analysed by gas chromatography with flame photometric detection, using an interence filter at 610 nm. Problems peculiar to the fish and sediment samples are overcome by this improved clean-up procedure. The limit of detection for tributyltin in fish is 0.04 m?g g^?1 and the reproducibility at 0.06 μg g^?1, expressed as the relative standard deviation, is 6.8%. Contaminated sediment samples were found to contain the mixed methylbutyl-tin compounds Me₂BuSn⁺ and MeBu₂Sn⁺.     

Determination of methylmercury in biological samples by capillary gas chromatography with electron capture detection

A precise and accurate method has been developed for the determination of methylmercury in biological material using capillary gas chromatography with electron-capture detection. Homogenized fish or mussel samples were digested with acid, spiked with ethylmercury chloride as an internal standard and extracted with toluene. After treatment of the solvent extract with sodium thiosulphate and cupric bromide the alkylmercurials were extracted into benzene as their bromide derivatives and analyzed using an OV-275 coated glass capillary column. The detection limit of the method for methylmercury was 5 g/kg tissue.     

Organotin speciation analyses in marine biota using sodium tetraethylborate ethylation and gas chromatography with flame photometric detection

The analysis of organotin compounds based on the in situ simultaneous derivatization and extraction with sodium tetraethylborate has been optimized to overcome the most common matrix effect problems with biological samples. To obtain a complete dissolution of the samples, free of colloidal interfaces problems, mechanical agitation has been coupled with stirring in a warmed ultrasonic bath. A strict quality control system using three internal standards was implemented. Tripropyltin chloride was used as internal standard to assess the derivatization reaction and tetraoctyltin was used to check the overall extraction efficiency. Tetrabutyltin was used to verify the gas chromatography (with flame photometric detector) performance of the analyses. The technique was validated using Certified Reference Materials (NIES‐11 and BCR‐477) and has been applied successfully to different biological matrices (fish, mussels, oyster and barnacles). Copyright © 2002 John Wiley & Sons, Ltd.     

Method for analysis of heavy sulphur compounds using gas chromatography with flame photometric detection

A method for analysis of heavy sulphur compounds in wines, based on gas chromatography (GC) with flame photometric detection, is reported. Wine samples preparation includes a dichloromethane liquid-liquid extraction followed by concentration under a nitrogen atmosphere. The extracted fraction was also analysed by GC-mass spectrometry. The method enables high recovery of sulphur compounds in wine and satisfies the requirements of repeatability and sensitivity. Applications of the method to red, white and Port wines are reported.     

Determination of organotin compounds (OTC) at low levels in seawater by solid-phase extraction (SPE) and gas chromatography-pulsed flame photometric detection (GC-PFPD)

In this work, a simple, sensitive and affordable analytical method for the simultaneous determination of nine organotin compounds (butyltins, phenyltins and methyltins) in seawater using solid-phase extraction (SPE) and gas chromatography-pulsed flame photometric detection was developed and validated. The performance of three different SPE cartridges (Envi C₁₈, Oasis HLB and Oasis MCX) and three elution solvents of different polarity (hexane, methanol and acetonitrile) was evaluated. The extraction parameters, such as solvent volume, presence of complexing and ion-pairing reagents, sample volume and pH and breakthrough volume, were also investigated. Tributyltin, as the organotin compound of special interest, was efficiently extracted using any of the cartridges and solvents tested. However, the simultaneous extraction of all nine organotin compounds was the most efficient using reversed-phase Envi C₁₈ cartridge and 0.1% (w/v) tropolone in methanol as eluent. The optimised method resulted in good recovery, precision and linearity for all compounds, particularly for tri- and disubstituted species. Method detection limits ranged from 0.22 to 1.27 ng(Sn) L^?1 for butyltins, 0.37 to 4.91 ng(Sn) L^?1 for phenyltins and 0.45 to 1.16 ng(Sn) L^?1 for methyltins. The accuracy of butyltins determination was further verified by the comparison with purchased derivatised standards. The developed method was successfully applied to the environmental samples.     

The potential of on-line flame photometric detection in microcolumn liquid chromatography

The potential of an interface for the on-line coupling of microcolumn liquid chromatography (LC)and a flame photometric detector (FPD) has been further investigated. With the micro-LC/FPD system, relatively high-molecular-weight polar compounds such as cyclic adenosine monophosphate, guanosine monophos- phate, glucose monophosphate, fructose monophosphate, and phytic acid were separated and selectively detected. In order to increase the sensitivity, on-line preconcentration with a microprecolumn inserted in the rotorof a Valcovalve has been applied. Preliminary results have shown that an injection volume of at least 500 1-11 water containing organophosphorus acids at a 5–50 ng/rnl concentration level is possible.     

The fundamental properties of the direct injection method in the analysis of gaseous reduced sulfur by gas chromatography with a pulsed flame photometric detector

In this study, the fundamental aspects of gas chromatography with a pulsed flame photometric detector were investigated through the calibration of gaseous reduced sulfur compounds based on the direct injection method. Gaseous standards of five reduced sulfur compounds (hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide) were calibrated as a function of injection volume and concentration level. The results were evaluated by means of two contrasting calibration approaches: fixed standard concentration method (variable volumetric injection of standard gases prepared at a given concentration) and fixed standard volume method (injection of multiple standards with varying concentrations at a given volume). The optimum detection limit values of reduced sulfur compounds, when estimated at 100 μL of injection volume, ranged from 2.37 pg (carbon disulfide) to 4.89 pg (dimethyl sulfide). Although these detection limit values improved gradually with decreasing injection volume, the minimum detectable concentration (e.g., in nmol mol⁻¹ scale) remained constant due to a balance by the sample volume reduction. The linearity property of pulsed flame photometric detector also appeared to vary dynamically with changes in its sensitivity. According to this study, the performance of pulsed flame photometric detector, when tested by direct injection method, is highly reliable to precisely describe the behavior of reduced sulfur compounds above ∼20 nmol mol⁻¹.     

Organolead speciation in environmental samples: a review

The speciation of organolead in some environmental samples is reviewed. Sampling, storage and pretreatment methods for water, soil, sediment and air samples are discussed before an assessment of recent developments in analytical methods.     

Mercury speciation in environmental solid samples using thermal release technique with atomic absorption detection

A sensitive and very simple method for determination of mercury species in solid samples has been developed involving thermal release analysis in combination with atomic absorption (AAS) detection. The method allows determination of mercury(II) chloride, methylmercury and mercury sulfide at the level of 0.70, 0.35 and 0.20 ng with a reproducibility of the results of 14, 25 and 18%, respectively. The accuracy of the developed assay has been estimated using certified reference materials and by comparison of the results with those of an independent method. The method has been applied for Hg species determination in original samples of lake sediments and plankton.     

双气相色谱-双脉冲火焰光度法高通量检测动物性食品中有机磷农药残留及其代谢产物

建立了动物性食品中包括代谢产物在内的54种有机磷农药残留及其代谢产物的双气相色谱-双脉冲火焰光度检测器(GC-PFPD)检测方法。动物组织样品经丙酮提取后以二氯甲烷进行液-液萃取,经凝胶渗透色谱净化后采用配有双脉冲火焰光度检测器的气相色谱仪测定。采用外标法定量,有机磷农药的响应与其浓度在线性范围内均呈良好的线性关系,相关系数在0.9905～0.9999之间。分别在空白鸡肉、羊肉、牛肉和猪肉样品中添加低、中和高3个加标水平的标准品进行了回收试验,回收率在50.5%～128.1%之间,相对标准偏差(n=6)在1.1%～25.5%之间,证明该方法的精密度和准确度良好。各有机磷农药的检出限在0.001～0.170 mg/kg之间,定量限在0.002～0.455 mg/kg之间。对从市场采集的动物组织样品进行了测定,检出敌敌畏、乙拌磷亚砜等有机磷农药残留。本方法灵敏度高、特异性强,且能同时检测有机磷农药多残留及其代谢产物,能够更加真实地反映动物性食品中有机磷农药的残留水平。     

Potential of microcolumn liquid chromatography and capillary electrophoresis with flame photometric detection for determination of polar phosphorus-containing pesticides

Summary The potential of microcolumn liquid chromatography (μlC) and capillary electrophoresis (CE) with on-line, flame photometric detection (FPD) in the P-selective mode has been studied for determination of polar P-containing pesticides, glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA), ethephon, fosetyl-aluminium and acephate. Acephate was determined by reversed-phase μLLC-FPD using large-volume injections with peak compression, the other compounds were determined by μLC-FPD and CE-FPD using simple, large-volume injection procedures to obtain limits of detection of 7.5-500 ng·mL⁻¹ and 1.0 μ·mL⁻¹, respectively. The methods showed acceptable repeatability and robustness and were successfully applied for rapid and selective determination of pesticides in fruit, vegetable and water samples.     

Quantitative determination of taurine in real samples by high-performance anion-exchange chromatography with integrated pulsed amperometric detection

As taurine is a very important compound involved in a large number of metabolic processes, it is naturally present in the mammal tissues and is often deliberately added in some foods as a fortifying component. A detailed knowledge of taurine metabolic roles in biological systems can be obtained only if a sensitive, reliable and rapid analytical method is available. This article describes the successful application of high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection (HPAEC-IPAD) for taurine determination in egg white and yolk samples, as well extracts of human serum and urine. Applications are shown for determination of taurine in soft drinks and pharmaceutical preparations where the taurine content was evaluated by standard additions. These results were achieved without prior derivatization of taurine.     

Development of a simple desulfurization procedure for the determination of butyltins in complex sediment samples using gas chromatography-pulsed flame photometric detection

In this study a rapid solid phase extraction (SPE) procedure was developed to minimize the effect of different sulfur species for the determination of butyltin in sediments. The organosulfur species and organotins were firstly retained on C8 cartridges and then organotins were selectively eluted and analyzed by gas chromatography-pulsed flame photometric detection (GC-PFPD). Optimal conditions for the SPE procedure were obtained using an experimental design approach. The method's accuracy was established by analyzing a certified reference material (CRM), BCR-646 freshwater sediment. The experimental values were found to be in agreement with the assigned values for butyltins. Finally, complex sediment samples collected from a Chilean harbor were analyzed using this methodology to demonstrate its analytical potential for the determination of butyltin in environmental samples.     

鱼贝类水产品中有机锡的气相色谱-脉冲火焰光度法测定研究

采用振荡萃取法,以凝胶渗透色谱净化浓缩液,用戊基溴化镁衍生;衍生物经弗罗里硅土净化后,用气相色谱-脉冲火焰光度法（GC-PFPD）测定,以内标法定量,建立了鱼贝类水产品中8种有机锡的分析方法。方法的线性范围在10-500μg/mL之间,检出限为1.0μg/kg左右。以牡蛎干粉为基质,在10和40μg/kg水平下加标,各有机锡的平均回收率在82.0%-104%之间,相对标准差（RSD）为1.4%-13.3%,牡蛎标准参考物测定结果落在定值范围内。     

Tributyltin analysis in seawater by GC FPD after direct aqueous-phase ethylation using sodium tetrathylborate

Using sodium tetraethylborate as an alkylation reagent, one-step ethylation and extraction of organotin compounds in seawater was performed directly in the aqueous phase to obtain optimal rection conditions. No further purification or concentration of the extract was required before GC FPD analysis. The detection limit for monobutyl-dibutyl-and tributyl-tin was approximately 0.4 ng dm^?3, which is adequate for any currently know toxicity effect. The linearity range (0–200 ng dm^?3) was solely dependent on the detector response curve. Compared with the Grignard reaction after extraction in an organic solvent, this new ethylation procedure reduces the number of analytical steps, thus saving time and improving reliability.     

Application of liquid phase microextraction based on solidification of floating organic drop for the determination of triazine herbicides in soil samples by gas chromatography with flame photometric detection

A simple and efficient liquid phase microextraction based on solidification of floating organic drop coupled with gas chromatography–flame photometric detection was developed for the extraction and determination of some triazine herbicides (metribuzin, simetryn, ametryn and prometryn) in soil samples. The type and volume of the extraction solvent, sample solution temperature, salt addition, stirring rate, and the extraction time were optimized. Under the optimal conditions, the linear response was observed over the range of 10–2000?µg?kg^?1 for metribuzin and 2–500?µg?kg^?1 for simetryn, ametryn, and prometryn, respectively, with the correlation coefficients (r) varying from 0.9990 to 0.9992. The limits of detection were in the range between 0.2 and 1.0?µg?kg^?1 (S/N?=?3?:?1). The recoveries of the target analytes for the spiked soil samples ranged from 75.5% to 97.3%, with the relative standard deviation values less than 7.2% (n?=?5). The enrichment factors were achieved ranging from 122 to 336. The developed method was applied for the preconcentration and determination of triazine herbicides in real soil samples and a satisfactory result was obtained.     

Organotin speciation in French brandies and wines by solid-phase microextraction and gas chromatography--pulsed flame photometric detection

An analytical method devoted to organotin compounds (OTC) determination in brandy and wine was developed. It is based on solid-phase microextraction (SPME) of ethylated organotins. The following operating factors were examined: SPME mode/nature of fibre coating, sample volume/dilution, and sampling time. The optimisation work led to dilute the sample in an aqueous buffer (1/11, v/v ratio) in order to satisfactorily decrease the matrix effects due to competitive sorption of non-OTC species onto/into fibre coating. The optimised operating conditions consist of polydimethylsiloxane (PDMS) coated fibre used in headspace mode for 30 min. In wines, the limits of detection (LOD) and quantification (LOQ) ranged from 1 to 40 and 3 to 80 ng(Sn)L(-1) respectively, according to the species. The analytical validation was made by evaluating the accuracy of OTC determination in spiked samples with various concentrations over the whole calibration range, i.e. from LOQ to 1000 ng(Sn)L(-1). Recovery was around 80-110% and precision (relative standard deviation, RSD) was between 12% and 25%. Despite the presence of two chromatographic peaks corresponding to sulphur compounds during brandy analysis, the selectivity of the method is adequate. The analysis confirmed the analytical performances and applicability of the method to wine and brandy samples. The obtained results emphasise the contamination of brandy and wine by organotins, the storage in plastic container seeming to be confirmed as the main OTC source.     

Interferences in ultratrace speciation of organolead and organotin by gas chromatography with atomic spectrometric detection

Interferences in trace and ultratrace speciation analysis of organotin and organolead compounds in various samples by gas chromatography coupled with atomic absorption spectrometry (AAS) and/or microwave induced plasma atomic emission spectrometry (MIP AES) are investigated. Particular attention is given to the effects of matrix co-extractives and reagents impurities introduced during sample preparation. Their influence on the detection limits is discussed in terms of baseline noise level, blank value, formation of artefacts and signal suppression. Loss of column resolution during the analysis of some matrices is observed.     

Headspace solid‐phase microextraction and gas chromatographic analysis of low‐molecular‐weight sulfur volatiles with pulsed flame photometric detection and quantification by a stable isotope dilution assay

Low‐molecular‐weight volatile sulfur compounds such as thiols, sulfides, disulfides as well as thioacetates cause a sulfidic off‐flavor in wines even at low concentration levels. The proposed analytical method for quantification of these compounds in wine is based on headspace solid‐phase microextraction, followed by gas chromatographic analysis with sulfur‐specific detection using a pulsed flame photometric detector. Robust quantification was achieved via a stable isotope dilution assay using commercial and synthesized deuterated isotopic standards. The necessary chromatographic separation of analytes and isotopic standards benefits from the inverse isotope effect realized on an apolar polydimethylsiloxane stationary phase of increased film thickness. Interferences with sulfur‐specific detection in wine caused by sulfur dioxide were minimized by addition of propanal. The method provides adequate validation data, with good repeatability and limits of detection and quantification. It suits the requirements of wine quality management, allowing the control of oenological treatments to counteract an eventual formation of excessively high concentration of such malodorous compounds.