大体积进样技术在环境分析中的应用

在毛细管气相色谱法(CGC)中,采用大体积进样技术(LVI),即使用能够容纳大体积样品的进样装置以及增加可控时间的溶剂蒸汽放空装置,可以满足环境样品中超痕量组分的分析要求,简化样品浓缩步骤以及实现液相色谱(LC)与CGC的在线联用。针对分析物的性质、毛细管柱的规格和分析的目的已发展了多种LVI。本文总结了几种常见的LVI,包括柱头进样(OCI)和程序升温进样(PTV),以及近年来发展的一些新技术,如在柱同时溶剂浓缩进样、样品直接引入进样/复杂基质进样和同时溶剂冷凝无分流进样,阐述了各种进样技术的基本原理及其与样品提取、LC纯化在线联用的方法在环境分析应用中的一些最新研究进展。     

Simultaneous determination of planar chlorobiphenyls and polychlorinated dibenzo-p-dioxins and -furans in Dutch milk using isotope dilution and gas chromatography—high-resolution mass spectrometry

A method is described for the simultaneous determination of planar chlorobiphenyls and dioxins in milk using isotope dilution and gas chromatography—high-resolution mass spectrometry (GC-MS). The method is based on gel permeation chromatography, alumina clean-up and carbon chromatography and is highly automated, making a high sample throughput possible. Data on recovery, accuracy and reproducibility of results obtained with quality control samples are presented. Data for both dioxins and planar chlorbiphenyls from the analysis of samples of Dutch milk from several areas in the Netherlands are also presented. Possible interference of the chlorobiphenyls in the determination of the dioxins in the GC-MS method is discussed.     

Determination of curcumol in rat plasma by capillary gas chromatography with a hydrogen flame ionization detector

A simple and sensitive capillary gas chromatography with a hydrogen flame ionization detector (GC‐FID) method was developed for the determination of curcumol in rat plasma. From a variety of compounds and solvents tested, buagafuran was selected as the internal standard (IS) and acetonitrile was found to be the best protein precipitation agent and solvent for extracting curcumol from plasma and tissues samples. (Buagafuran was used as an internal standard. Curcumol was extracted by a protein precipitation with acetonitrile.) The samples were determined by GC on an HP‐5 column (30.0 m × 0.32 mm, 0.25 μm); inlet volume 2 μL; split ratio 10 : 1; inlet temperature 250°C; oven temperature 180°C; flow 1.0 mL/·min; FID 250°C; carrier gas N₂. The resulting retention times of curcumol and IS were 6.0 and 9.5 min. There was good linearity over the range 0.133–133.3 μg/mL (r = 0.9999) in plasma samples. The method recoveries were 97.7–102.0% in plasma, and the intra‐ and inter‐day variances (RSD) were less than 15% in all cases. The GC method was applied to develop a pharmacokinetics study in which experimental rats received a single administration of curcumol by intravenous injection. Copyright © 2009 John Wiley & Sons, Ltd.     

Book reviews

This work is a thorough investigation on the major operating parameters of the programmable temperature vaporisation (PTV) inlet used for gas chromatographic injection, including injection mode and volume, inlet temperature, vent and purge flow rates. The results clearly demonstrate the advantage of large volume injection in enhancing the detection of polybrominated diphenyl ethers (PBDEs). Partial loss of injected PBDEs occurred during solvent venting and due to incomplete sample transfer. Such loss was minimised by lowering the initial inlet temperature and vent flow and elevating the final inlet temperature. The results show that 50 mL/min vent flow, as low as 0°C initial and higher than 300°C final inlet temperatures produced the relatively high responses. Two mass spectrometric parameters were also evaluated. Indoor dust, lake sediment and human placenta tissue samples were analysed to demonstrate reliability and sensitivity improvement of the PTV large volume injection.     

Large volume injection techniques in capillary gas chromatography

Large volume injection (LVI) is a prerequisite of modern gas chromatographic (GC) analysis, especially when trace sample components have to be determined at very low concentration levels. Injection of larger than usual sample volumes increases sensitivity and/or reduces (or even eliminates) the need for extract concentration steps. Also, an LVI technique can serve as an interface for on-line connection of GC with a sample preparation step or with liquid chromatography. This article reviews the currently available LVI techniques, including basic approaches to their optimization and important real-world applications. The most common LVI methods are on-column and programmed temperature vaporization (PTV) in solvent split mode. Newer techniques discussed in this article include direct sample introduction (DSI), splitless overflow, at-column, and "through oven transfer adsorption desorption" (TOTAD).     

Determination by coupled high-performance liquid chromatography-gas chromatography of the beta-blocker levomoprolol in plasma following ophthalmic administration

Levomoprolol is a beta-blocking agent used in the topical treatment of glaucoma. The necessity for comparing the plasma levels of a drug administered by the ophthalmic route with those obtained following systemic treatment requires increasingly sensitive methods in order to determine the low plasma concentrations produced by the administration of eye drops. On-line high-performance liquid chromatography-gas chromatography and concurrent solvent evaporation proved to be advantageous in the determination of levomoprolol in human plasma. Levomoprolol was determined by capillary gas chromatography (GC) with electron-capture detection (ECD) after solid-phase extraction from plasma and derivatization. Quantitation was based on the internal standard method. The detection limit of 0.2 ng/ml is 50 times lower than that obtained with previous GC methods involving on-column injection and ECD.     

Multi-Pesticide Analysis in Sediment by GC-EI-MS/MS Using Programmed Temperature Vaporization–Large Volume Injection Technique

A sensitive, selective and high throughput gas chromatography–tandem mass spectrometry method using programmable temperature vaporization–large volume injection mode (PTV-LVI-GC-MS/MS) for the analysis of 30 organochlorine pesticides (OCPs) including toxaphenes in sediments was developed. The PTV-LV injection settings, viz. inlet temperature, split flow, injection phase time, and injection speed were optimized for 50 µL injection. A significant increase in sensitivity was accomplished as compared with that obtained by the conventional 1 µL cold splitless injection. Average LVI recoveries for OCPs were in the range 58–133 % with low % RSD in instrument precision (<12 %). The method detection limits achieved were 0.04–0.92 µg kg^?1. The method recovery ranged from 80 to 120 % with <10 % RSD for more than 83 % of targeted analytes fortified at 10 µg kg^?1 in sediments. The PTV-LVI-GC-MS/MS allows simultaneous determination and unambiguous confirmation of trace OCPs and toxaphene congeners, which significantly streamlines and improves the trace organic analysis in the environmental surveillance and monitoring.     

Analysis of β‐blockers in groundwater using large‐volume injection coupled‐column reversed‐phase liquid chromatography with fluorescence detection and liquid chromatography time‐of‐flight mass spectrometry

Atenolol, nadolol, metoprolol, bisoprolol and betaxolol were simultaneously determined in groundwater samples by large‐volume injection coupled‐column reversed‐phase liquid chromatography with fluorescence detection (LVI‐LC‐LC‐FD) and liquid chromatography‐time‐of‐flight mass spectrometry (LC‐TOF‐MS). The LVI‐LC‐LC‐FD method combines analyte isolation, preconcentration and determination into a single step. Significant reductions in costs for sample pre‐treatment (solvent and solid phases for clean up) and method development times are also achieved. Using LC‐TOF‐MS, accurate mass measurements within 3 ppm error were obtained for all of the β‐blockers studied. Empirical formula information can be obtained by this method, allowing the unequivocal identification of the target compounds in the samples. To increase the sensitivity, a solid‐phase extraction step with Oasis MCX cartridge was carried out yielding recoveries of 79–114% (n=5) with RSD 2–7% for the LC‐TOF‐MS method. SPE gives a high purification of β‐blockers compared with the existing methods. A 100% methanol wash was allowed for these compounds with no loss of analytes. Limit of quantification was 1–7 ng/L for LVI‐LC‐LC‐FD and 0.25–5 ng/L for LC‐TOF‐MS. As a result of selective extraction and effective removal of coextractives, no matrix effect was observed in LVI‐LC‐LC‐FD and LC‐TOF‐MS analyses. The methods were applied to detect and quantify β‐blockers in groundwater samples of Almería (Spain).     

Determination of 3-MCPD by GC-MS/MS with PTV-LV injector used for a survey of Spanish foodstuffs

3-Monochloropropane-1,2-diol (3-MCPD) is the most common chemical contaminant of the group of chloropropanols. It can occur in foods and food ingredients at low levels as a result of processing, migration from packaging materials during storage and domestic cooking. A sensitive method for determination of 3-MCPD in foodstuffs using programmable temperature vaporization (PTV) with large-volume injection (LVI) gas chromatography (GC) with tandem mass spectrometry detection (MS/MS) has been developed and optimized. The optimization of the injection and detection parameters was carried out using statistical experimental design. A Plackett-Burman design was used to estimate the influence of resonance excitation voltage (REV), isolation time (IT), excitation time (ET), ion source temperature (IST), and electron energy (EE) on the analytical response in the ion trap mass spectrometer (ITMS). Only REV was found to have a statically significant effect. On the other hand, a central composite design was used to optimize the settings of injection temperature (T(inlet)), vaporization temperature (T(vap)), vaporization time (t(vap)) and flow (Flow). The optimized method has an instrumental limit of detection (signal-to-noise ratio 3:1) of 0.044 ng mL(-1). From Valencian, Spain, supermarkets 94 samples of foods were surveyed for 3-MCPD. Using the optimized method levels higher than the limit established for soy sauce by the European Union were found in some samples. The estimated daily intake of 3-MCPD throughout the investigated foodstuffs for adults and children was found about 0.005 and 0.01%, respectively, of the established provisional tolerable daily intake.     

Determination of organophosphate esters in air samples by dynamic sonication-assisted solvent extraction coupled on-line with large-volume injection gas chromatography utilizing a programmed-temperature vaporizer

An on-line method for the determination of airborne organophosphate esters based on dynamic sonication-assisted solvent extraction and large-volume injection (LVI) gas chromatography with nitrogen-phosphorous detection is introduced. The LVI is performed with a programmed-temperature vaporizer. The entire extracted fraction of 800 microl (hexane-methyl-tert.-butyl ether, 7:3, v/v) is introduced directly into the GC system without any clean-up step following extraction. The extraction and analysis step were completed in less than 15 min. The limit of detection of the investigated organophosphate esters was established to be in the range of 5-32 pg/filter. The correlation coefficients (r2) were investigated in the linear range study of the entire system and established to be approximately 0.9900 for all the investigated organophosphates esters. Applications of the method was demonstrated with the extraction of air samples collected onto glass fiber filters from different indoor environments. Six organophosphate esters were found at the levels 0.4-138 ng/m3.     

Determination of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans,and dioxin‐like polychlorinated biphenyls in human serum using programmable‐temperature vaporization gas chromatography with high‐resolution mass spectrometry

The determination of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans, and dioxin‐like polychlorinated biphenyls in blood from a non‐occupational population is essential for the investigation of adverse health effects from these pollutants. In this study, a sensitive method based on programmable‐temperature vaporization with large‐volume injection coupled with gas chromatography with high‐resolution mass spectrometry was developed to determine these pollutants in 1–2 mL of human serum samples. Various key parameters of programmable‐temperature vaporization injector, including vent temperature, vent time, vent flow, transfer temperature and transfer time were optimized by factorial design. The accuracy and precision as well as applicability were assessed by determining polychlorinated dibenzo‐p‐dioxins, polychlorinated dibenzofurans, and dioxin‐like polychlorinated biphenyls in calibration standard solutions, standard reference materials and real human serum samples from non‐occupational population. The method detection limits of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans, and dioxin‐like polychlorinated biphenyls were 1.5–9.0 and 0.005–0.02 ng/kg wet weight, respectively. By comparing with typically splitless injection, the application of programmable‐temperature vaporization injector could effectively lead to higher detectable rate of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans, and dioxin‐like polychlorinated biphenyls in 1–2 mL of human serum samples.     

Optimization of a method for determining dioxin in whole blood samples based on solvent extraction and simplified cleanup

Dioxins, including polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/Fs) and coplanar polychlorinated biphenyls (Co-PCBs), such as mono-ortho-PCBs and non-ortho-PCBs, are environmental pollutants that have deleterious effects on human health. Although screening of blood samples for dioxins is necessary, the current methods are time-, reagent- and labor-intensive. To optimize the extraction and cleanup of dioxins, we have designed a column chromatography method, coupled with a water washing step. We used a tandem simplified multilayer silica gel-activated carbon dispersed silica gel column (TS-ML-AC) rather than the conventional two columns. We compared three liquid-liquid extraction (LLE) methods and two pressurized liquid extraction (PLE) methods, when used with this column. For each of these extraction methods, we compared the quantity of lipid obtained when the water washing step was omitted and when it was performed by shaking 30 times by hand or 30 min by a machine. We found that TS-ML-AC was superior to the conventional pair of columns in that only about one third of the solvent and only one quarter of the time was necessary. Of the five extraction methods, the acetone/hexane PLE (AcP) method was superior, since it reduced the amount of organic solvent to half or less of the amount required for the LLE methods. The cleanup step using water was best accomplished by the hand-shaking method. Our results indicate that, for the analysis of dioxin in whole blood samples, the use of AcP together with TS-ML-AC and water washing by hand shaking should be used.     

Maternal body burden of organochlorine pesticides and dioxins.

To investigate the body burden of organochlorine pesticides and dioxins in Japanese women, 125 milk samples were collected from 41 mothers in 1994, 42 in 1995, and 42 in 1996. Of the 125 samples, 82 were from primipara mothers (first delivery) and 43 were from multipara mothers (second or later delivery). By using capillary gas chromatography with electron capture detection, beta-HCH and p,p'-DDE were detected as the major chlorine pesticides in human milk. Average levels of beta-HCH and p,p'-DDE were 475 and 368 ng/g lipid, respectively, in primipara breast milk, 314 and 259 ng/g lipid in multipara breast milk, and 420 and 330 ng/g lipid in total breast milk. Dieldrin, heptachor epoxide, oxychlordane, trans-chlordane, and cis-chlordane were detected at lower average levels of 3, 4, 34, 41, and 5 ng/g lipid, respectively. By using high-resolution gas chromatography with mass spectrometric detection, dioxins were detected in all samples. Average levels of total polychlorinated dibenzo-p-dioxin (PCDD), total polychlorinated dibenzofuran (PCDF), total PCDD + PCDF, total coplanar polychlorinatedbiphenyl (CoPCB), and total dioxin were 10.0, 7.8, 17.7, 9.9, and 27.5 TEQ (toxic equivalent) pg/g lipid, respectively, in primipara breast milk; 7.0, 5.8, 12.8, 7.3, and 20.1 TEQ pg/g lipid in multipara breast milk; and 8.9, 7.1, 16.1, 8.9, and 25.0 TEQ pg/g lipid in total breast milk. In primipara breast milk, significant correlations were found among levels of beta-HCH, p,p'-DDE, total PCDD-TEQ, total PCDF-TEQ, total CoPCB-TEQ, and total TEQ except for less correlation between p,p'-DDE and total PCDF-TEQ. Levels of these analytes also significantly increased depending on mother's age, except for total Co-PCB-TEQ. For the correlation with food habit, the only positive correlation was between total PCDF-TEQs and fish intake.     

Optimisation of programmable temperature vaporizer-based large volume injection for determination of pesticide residues in fruits and vegetables using gas chromatography-mass spectrometry

The applicability of programmable temperature vaporizer (PTV) solvent vent injection to the gas chromatographic (GC) determination of pesticide residues in fruits and vegetables was evaluated with the aim of miniaturizing the current multiresidue method. For that purpose 24 pesticides representing different chemical classes were initially chosen for optimisation of the large volume injection (LVI) parameters. Various parameters related to the optimum injector performance were tested for several types of packed and empty liners using both fast (at-once) and speed-controlled PTV solvent vent injection of standard solutions in ethyl acetate. In the next step, several packed and empty liners were evaluated for their suitability for pesticide multiresidue analysis. Parameters identified as optimal were then applied for PTV solvent vent injection of sample extracts prepared using the miniaturized multiresidue method to assess the long-term stability of the system. The combined use of large volume injection of 10 microl ethyl acetate extract into an empty multi-baffled or a CarboFrit packed liner using PTV injectors and GC-MS analysis enabled the detection and quantification of 124 pesticides in fruit and vegetable samples at the 0.01 mg/kg level using miniaturized reversed-phase solid-phase extraction (RP-SPE) of diluted acetone extract and clean-up on a small anion-exchange SPE column.     

大体积进样技术在气相色谱-质谱法测定 二英类化合物中的应用

利用大体积进样技术(large volume injection,LVI),结合气相色谱-质谱方法对二英的测定效果进行了研究。同时与传统分流/不分流进样技术进行了对比。对进样体积为1,5,10,25,50和100 μL的色谱图进行了分析。研究表明使用大体积进样方式,在不影响色谱分离度的同时,大幅度提高了分析灵敏度。通过对土壤样品的检测,证明该方法可以用于环境样品的实际测定。     

Multiresidue analysis of acidic and polar organic contaminants in water samples by stir-bar sorptive extraction-liquid desorption-gas chromatography-mass spectrometry

The feasibility of stir-bar sorptive extraction (SBSE) followed by liquid desorption in combination with large volume injection (LVI)-in port silylation and gas chromatography-mass spectrometry (GC-MS) for the simultaneous determination of a broad range of 46 acidic and polar organic pollutants in water samples has been evaluated. The target analytes included phenols (nitrophenols, chlorophenols, bromophenols and alkylphenols), acidic herbicides (phenoxy acids and dicamba) and several pharmaceuticals. Experimental variables affecting derivatisation yield and peak shape as a function of different experimental PTV parameters [initial injection time, pressure and temperature and the ratio solvent volume/N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) volume] were first optimised by an experimental design approach. Subsequently, SBSE conditions, such as pH, ionic strength, agitation speed and extraction time were investigated. After optimisation, the method failed only for the extraction of most polar phenols and some pharmaceuticals, being suitable for the determination of 37 (out of 46) pollutants, with detection limits for these analytes ranging between 1 and 800 ng/L and being lower than 25 ng/L in most cases. Finally, the developed method was validated and applied to the determination of target analytes in various aqueous environmental matrices, including ground, river and wastewater. Acceptable accuracy (70-130%) and precision values (<20%) were obtained for most analytes independently of the matrix, with the exception of some alkylphenols, where an isotopically labelled internal standard would be required in order to correct for matrix effects. Among the drawbacks of the method, carryover was identified as the main problem even though the Twisters were cleaned repeatedly.     

Direct determination of recombinant bovine somatotropin in plasma from a treated goat by liquid chromatography/high-resolution mass spectrometry

Recombinant bovine somatotropin (rbST) is used in dairy cattle to enhance milk production. Despite the ban on this hormone in some countries, especially in Europe, there is so far no method available for the direct detection of rbST either in milk or in plasma. An analytical strategy has been developed to analyze rbST in plasma, including a purification procedure based on a precipitation with ammonium sulphate, followed by a solid-phase extraction (SPE)-based clean-up on C4 sorbent and precipitation with cold methanol. The hormone was then digested with trypsin and analyzed by liquid chromatography/high-resolution mass spectrometry (LC/HRMSn) on a linear ion trap coupled with an Orbitrap. The tryptic N-terminal peptide, specific to the difference between the endogenous and recombinant form of the somatotropin, was fragmented and product ions were analyzed at high mass resolution. Applying this approach to goat plasma allowed the direct detection of 10 ng mL(-1) of rbST in fortified samples. It also showed the presence of rbST in plasma collected from a goat treated with the hormone, even 2 days after administration. These results are of a great interest in the field of somatotropin control and undoubtedly constitute a first step in the development of a method for the detection of rbST not only in bovine plasma, but also in other biological matrices such as milk.     

Rapid method for the determination of organochlorine pesticides in milk

This method involved one step solvent extraction of milk with ethyl acetate-acetone-methanol by ultrasonication. The supernatants were further cleaned-up and enriched by solid-phase extraction using octadecyl (C18)-bonded silica cartridges, then assayed by capillary gas-liquid chromatography with electron capture detection. The recoveries of eleven organochlorine pesticides (OCPs) from raw milks were quantitative, ranging from 90-110% at 10 times the limit of detection (LOD). The LOD ranged from 0.5 micrograms/l whole milk for alpha-hexachlorocyclohexane to 2.5 micrograms/l whole milk for 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane. The day-to-day variation of the method was evaluated over 7 days using 3 different pools of spiked cow milks (at the LOD, 5 and 10 times the LOD). The coefficient of variations (C.V.s) were 16 +/- 6, 10 +/- 2 and 9 +/- 3% (mean S.D.), respectively. The method showed no emulsion problems common with conventional non-polar solvent extraction, and the use of solid-phase extraction considerably reduced the sample clean-up process compared with the existing methods. The method also showed that OCPs in milk could be extracted quantitatively without extraction of total fat, and that OCPs spiked into cows milk could be used to construct calibration curves for human milk determinations.     

气相色谱-质谱联用法检测母乳脂肪中反式脂肪酸

建立了母乳中反式脂肪酸(TFAs)的气相色谱-质谱(GC-MS)检测方法,并应用于母乳脂肪中TFAs的检测。母乳用氨水水解,乙醚和石油醚提取脂肪,提取的脂肪加入C21: 0内标,用三氟化硼甲醇溶液在80℃水浴中冷凝回流15 min进行甲酯化,正己烷提取,上清液用GC-MS分析,内标法定量。在低、中、高加标水平上验证方法的准确度与精密度,结果显示该方法可用于母乳中18种TFAs及其同分异构体的检测,其中12种TFAs在母乳脂肪中的方法检出限为4.0~47.1 mg/kg,回收率为80%~113%, RSD为2.9%~14.5%(n=6)。TFAs在部分母乳脂样品中检出,含量为9.54~6.9 mg/kg。该方法定性、定量准确,可有效用于母乳中TFAs的检测,但仍存在脂肪酸本底干扰等问题,可结合银离子固相萃取柱预分离技术进一步完善。     

A Miniaturized Precolumn for On-Line Trace Enrichment and Direct Plasma Injection in Narrow-Bore Liquid Chromatography

Abstract

A precolumn for on-line trace enrichment in narrow-bore liquid chromatography has been designed and some critical parameters like precolumn length, inlet capillary I.D. and flow-rate have been studied. The precolumn allows direct injection of plasma and serum samples without any previous clean-up. Due to the trace enrichment, concentration sensitivity is improved 50-fold when 100 μl samples are applied as compared to standard micro-loop injections of 0.5 μl. The applicability of the system has been demonstrated by the analysis of the anti-cancer drug etoposide (VP-16) in human plasma with comparable or even better results than those obtained with conventional-size systems.