Development of a tandem thin-layer chromatography-high-performance liquid chromatography method for the identification and determination of corticosteroids in cosmetic products

A solid-phase extraction clean-up and and a liquid chromatographic method with ultraviolet detection were developed for the analysis of 51 corticosteroids in cosmetic samples in order to screen commercial samples for the presence of undeclared synthetic corticosteroids. A thin-layer chromatographic analysis was carried out on silica gel plates, using different eluants and detection reagents. When such a preliminary chromatographic separation gave some indications about the presence of steroid compounds, the methanol extracts from real samples were applied to a solid-phase extraction C₁₈ cartridge, and the analytes eluted with ethyl ether. The high-performance liquid chromatographic separation was then carried out for the identification and determination of the analytes using a Purospher RP-18 column, an isocratic or a gradient elution with a mixture acetonitrile-water and a photodiode-array detector. The accuracy of the method was determined by spiking experiments on home-made cosmetic samples. The analytical recoveries were satisfactory.     

Mass spectrometry/gas chromatography-mass spectrometry approach for rapid screening/quantitative determination of perchloroethylene in air

A new mass spectrometry/gas chromatography-mass spectrometry (MS/GC-MS) approach has been developed for the screening and quantitative determination of perchloroethylene (PERC) in workplace and outdoor air samples, which could be extended to the screening and analysis of other analytes and samples. This approach may be rapidly modified in order to be used directly as an MS detector for screening purposes or alternatively as a common GC-MS, for confirmation. The screening alternative by MS is approximately 20 times faster than the quantitative-confirmatory determination by GC-MS. Detection limits of both alternatives are sufficiently low to screen and determine PERC in the above-mentioned matrixes. The advantage of this approach over others previously described is that, in the present case, the sample passes through the chromatographic column only when the confirmatory GC-MS is used. For the MS screening method, the chromatographic column is bypassed by using an appropriate selection valve. In this way, the column lifetime is extended and screening time is considerably shortened.     

On-site environmental analysis by membrane extraction with a sorbent interface combined with a portable gas chromatograph system

A novel device, membrane extraction with a sorbent interface (MESI) coupled with a portable gas chromatograph (GC) system, has been developed. The main components of this system include a membrane module, a microtrap, and a control unit for the heater and cooler. The membrane module, as an on-line sample-introduction device for this system, can be manipulated in different configurations, allowing for the selective permeation of analytes across the membrane into the carrier/stripping gas. The analytes are trapped and concentrated onto a microtrap, which serves as an injector for gas chromatography separation. A concentration pulse of the trapped analytes is generated through direct electrical heating of the microtrap. The characteristics of this system have been explored, and its applicability and effectiveness have been demonstrated in field monitoring applications including the analysis of toluene in wastewater, Volatile organic compounds (VOCs) in laboratory air, and chloroform in swimming-pool water. This system is very promising, as it is a simple, fast, and portable tool for on-site process environmental monitoring.     

Determination of atrazine and four organophosphorus pesticides in ground water using solid phase microextraction (SPME) followed by gas chromatography with selected-ion monitoring

A rapid, sensitive, and convenient method is presented for the determination of atrazine and four organophosphorus pesticides (OPP) in small (10 ml) samples of ground water. Samples are initially fortified with ethion (internal standard), then extracted without organic solvent using a 65-microm thickness polydimethylsiloxane/divinylbenzene (PDMS-DVB) solid-phase microextraction (SPME) fiber. The analytes collected are thermally desorbed in a heated gas chromatographic inlet, separated using a fused-silica capillary column, and detected using a mass selective detector in its selected-ion monitoring (SIM) mode. Two independent statistical procedures were used to evaluate the detection limits, which typically range between 2 and 8 microg l(-1) for these analytes. Method performance was also evaluated using "performance evaluation" samples, in which clean authentic ground waters were fortified to known concentrations with at least two of the analytes of interest. Sample-to-sample analysis time is approximately 30 min, making the new method ideal for "quick turn" determinations.     

Configuration and optimization of semiconductor gas sensors as gas chromatographic detectors

A tin oxide, gas-sensitive semiconductor sensor was configured as a gas chromatographic detector and its performance was optimized. Two sensor housings were compared but little difference was found in performance. The flow rate and temperature of the column and the internal heater voltage of the sensor affected both the sensitivity and peak shape. The temperature of the sensor surface was the most critical parameter. Optimal conditions for the gas chromatographic detection of a mixture of alkanes (C₁–C₅) and hydrogen were identified by using the simplex technique. The detection limit for hydrogen was improved by a factor of five to 20 ppb (v/v), illustrating the value of optimization and the excellent sensitivity of the detector. It is concluded that semiconductor gas sensors offer significant advantages as gas chromatographic detectors for the determination of reducing gases.     

Solvent venting interface for capillary gas chromatography and a microwave-induced plasma

A solvent venting system for capillary gas chromatography coupled with a microwave-induced plasma detector was constructed and evaluated. The solvent vent is based on a fluid logic system within the plasma containment tube. During solvent elution, the column effluent is routed to waste and does not pass through the plasma. During analyte elution, the fluid logic system is used to direct the analytes through the plasma for detection. Because the system has no transfer line, problems associated with interface dead volume and analyte degradation reaction due to reactive sites in the transfer line are eliminated. Switching from the vent-on to the vent-off mode is rapid and does not affect plasma stability or flow through the chromatographic column. The baseline shift during switching is negligible. The solvent venting system is simple and easily constructed. Design details are presented and chromatographic results are evaluated.     

Retention indices as identification tool in pyrolysis-capillary gas chromatography

Pyrolysis-capillary gas chromatography (Py-cGC) represents important method to identify the analytes in the mixture after thermal degradation. This combines high effective analyte separation on-line coupled with thermal degradation process that depends on analyte structure. System of retention indices has been used for identification of the analytes after on-line pyrolysis and chromatographic separation. The pyrolysate composition has been studied during thermal degradation of polymethylmethacrylate (PMMA) at different pyrolysis temperatures and chromatographic column conditions. Homologues series of n-alkanes have been used for calculation of pyrolysate Kováts retention indices (I) and compared with mass spectrometric (MS) data of pyrolysate model mixture. To identify PMMA thermal degradation products the high density polyethylene (HDPE) as additive standard producing triplets of the olefin homologous series during co-pyrolysis has been used. These homologous series enable to calculate programmed temperature retention indices (ITPGC) to identify the analytes present in the pyrolysate. Calculated I values were compared with published I values databases to identify analytes yielded at different pyrolysis temperatures.     

Gas chromatographic determination of diquat and paraquat in crops

A sensitive and reproducible gas chromatographic procedure for the determination of diquat and paraquat in potatoes and rapeseed was developed. The volatilization of analytes was carried out via their hydrogenation with sodium borohydride-nickel(II) chloride. After their isolation from the reaction mixture, the derivatives of bipiperidine were separated on a column packed with Apiezon L plus potassium hydroxide. Comparable detection limits (0.005 mg/kg) were achieved with a nitrogen-phosphorus detector and by mass fragmentography, however, the latter method was preferred for analyses of rapeseed extracts owing to its higher selectivity.     

Quantification of N-acetyl- and N-glycolylneuraminic acids by a stable isotope dilution assay using high-performance liquid chromatography-tandem mass spectrometry

The present report describes a method for the quantification of N-acetyl- and N-glycolylneuraminic acids without any derivatization, using their (13)C(3)-isotopologues as internal standards and a C(18) reversed-phase column modified by decylboronic acid which allows for the first time a complete chromatographic separation between the two analytes. The method is based on high-performance liquid chromatographic coupled with electrospray ion-trap mass spectrometry. The limit of quantification of the method is 0.1mg/L (2.0ng on column) for both analytes. The calibration curves are linear for both sialic acids over the range of 0.1-80mg/L (2.0-1600ng on column) with a correlation coefficient greater than 0.997. The proposed method was applied to the quantitative determination of sialic acids released from fetuin as a model of glycoproteins.     

过氧化双环己胺的气相色谱分析

 采用气相色谱法 ,以涂覆OV 10 1固定液的色谱柱测定环己酮、氨与双氧水反应产物中的环己酮和 1 1′ 过氧化双环己胺 (1 1′ PXA) ,并采用内标法进行定量分析。结果表明 :环己酮、1 1′ 过氧化双环己胺测定结果的相对标准偏差均小于 1 5 %,回收率分别为 96 38%～ 10 0 8%和 99 31%～ 10 3 1%。方法简便、灵敏、准确、重现性好 。     

Determination of carboxylic acids in water by gas chromatography using several detectors after flow preconcentration

A novel analytical method is reported that combines continuous solid-phase extraction and gas chromatography for the determination of 22 carboxylic acids in water. The highly polar and hydrophilic analytes were preferentially sorbed on a mixture of LiChrolut EN-Supelclean ENVI-18 (1:1) sorbent column and eluted with methanol; this extraction process did not require derivatisation. The extract was analysed by gas chromatography coupled to a flame ionisation detector as well as a mass spectrometer with electron impact (EI) or positive chemical ionisation modes. The highest sensitivity was achieved when using MS-EI, with good linearity in calibration curves and low detection limits (2-40ngL(-1)) for 50mL of sample. The entire procedure from raw aqueous sample to a ready-to-inject methanol solution of the acids requires less than 15min. Another benefit of this method is the good accuracy (recoveries between 93 and 102%) and precision (relative standard deviation, 3.4-6.2%), which allows the determination of carboxylic acids in environmental water and in real chlorinated and ozonated drinking water.     

Determination of methylcyclopentadienylmanganesetricarbonyl by gas chromatography—atomic absorption spectrometry at ng m-3 levels in air samples

A procedure is given for the determination of methylcyclopentadienylmanganese tricarbonyl (MMT) at ng m^-3 concentrations in air. The method involves trapping of MMT in a small segment of gas chromatographic column and then determination by gas chromatography with an electrothermal atomic absorption detector. The detection limit of the procedure is 0.05 ng m^-3. Air samples from an underground car-park (when MMT was detected) were found to contain between 0.1 and 0.3 ng m^-3 MMT. MMT was not detected in any of the street air samples taken.     

Features of a micro-gas chromatograph equipped with enrichment device and microchip plasma emission detection (muPED) for air monitoring

A field portable gas chromatograph (GC) was constructed allowing the enrichment of organic solutes from air samples on a miniaturized chemical trap and the subsequent gas chromatographic analysis on a resistively heated capillary column. The heart of the system is an integrated chip-based plasma emission detector (muPED). As a non-selective detector, the sensitivity is similar to that of a flame ionization detector (FID). The detector shows good selectivity for phosphorus, sulfur and chlorine-containing compounds with relative selectivities of ca. 5 x 10(5) gP gC(-1), 50 gS gC(-1) and 10(2) gCl gC(-1). The lifetime of the plasma chip under air monitoring conditions exceeded 3000 analyses.     

Determination of clozapine in human serum by capillary gas chromatography

A gas chromatographic method using a fused-silica wide-bore capillary column and a nitrogen-specific detector for the determination of the antipsychotic agent clozapine in human serum is described. This method was found to be suitable for the determination of serum levels down to 1-2 ng/ml. The sensitivity, precision and accuracy of this method are adequate for studies on pharmacokinetics and bioavailability.     

液-液萃取气相色谱法测定地表水中痕量苯酚

建立了液-液萃取气相色谱法测定地表水中痕量苯酚的方法。用盐酸调节水样至pH2左右,以二氯乙烷-乙酸乙酯(体积比为2∶1)混合溶液为萃取剂,以CD-5色谱柱进行分离,氢火焰离子化检测器检测苯酚的含量。苯酚的质量浓度在1.00~20.0μg/L范围内与其色谱峰面积呈良好的线性关系,线性相关系数r=0.999 3,检出限为0.03μg/L。样品加标回收率为93.0%~97.0%,测定结果的相对标准偏差小于2%(n=7)。该方法检出限低,精密度和准确度高,操作简便,适用于地表水中微量苯酚的分析。     

Direct thermal desorption of semivolatile organic compounds from diffusion denuders and gas chromatographic analysis for trace concentration measurement

A novel method for collection and analysis of vapor-phase semivolatile organic compounds (SOCs) in ambient air is presented. The method utilizes thermal desorption of SOCs trapped in diffusion denuders coupled with cryogenic preconcentration on Tenax-TA and analysis by high resolution gas chromatography (GC)-electron-capture detection (ECD). The sampling and analysis methods employ custom-fabricated multicapillary diffusion denuders, a hot gas spike (HGS) apparatus to load known quantities of thermally stable standards into diffusion denuders prior to sample collection, a custom-fabricated oven to thermally desorb SOCs from the diffusion denuder, and a programmable temperature vaporization (PTV) inlet containing a liner packed with Tenax-TA for effective preconcentration of the analytes and water management. High flow rates into the PTV inlet of 750mLmin(-1)during thermal desorption are ca. a factor of ten greater than typically used. To improve resolution and retention time stability, the thermal desorption and PTV inlet programming procedure includes three steps to prevent water from entering the analytic column while effectively transferring the analytes into the GC system. The instrumentation and procedures provide virtually complete and consistent transfer of analytes collected from ambient air into the GC evidenced by recovery of seven replicates of four internal standards of 90.7+/-4.0-120+/-23% (mean+/-95% confidence interval, CI). Retention time based compound identification is facilitated by low retention time variability with an average 95% CI of 0.024min for sixteen replicates of eight standards. Procedure details and performance metrics as well as ambient sampling results are presented.     

Quantitative determination of paraffin oil in blood by capillary gas chromatography

A capillary gas chromatographic method is described for the quantitative determination of liquid paraffin in blood. Paraffin is extracted from blood into n-heptane. After solvent evaporation and dissolution of the residue in 100–200 μl n-heptane one μl is injected into a gas chromatograph fitted with a fused silica capillary column (Permabond® OV-1-CB-0.1, 10 m × 0.32 mm i.d.) and flame ionization detector. Analysis is performed by using an oven program [50°C (3 min)?285°C (5 min), rise 10%min]. The sensitivity (1.5 ng hexadecane) and the reproducibility prove the applicability of the method for the determination of liquid paraffin in blood and for the study of the stability of the liquid paraffin hollow fiber membranes used in an extracorporeal liver support system.     

Rapid gas analyses for the investigation of spontaneous combustion using capillary gas chromatography

A simple and fast but sensitive and precise gas chromatographic method is described for the quantitative determination of O(2), N(2), CO, CO(2), C1 and C2-hydrocarbons for coal research. Gas analyses are necessary to obtain parameters for modelling spontaneous combustion and to predict long term coal behaviour. The method is based on a single PLOT-type capillary column in a single channel gas chromatograph. Using a micro-volume TCD coupled in series with a FID detector containing a capillary methanizer it is possible to determine high and trace level gases simultaneously. Trace quantities of CO and CO(2) can be determined with a single analysis and the detection limits are improved significantly using the capillary methanizer. The detection limit of the described method is approximately ten parts per million CO(2) and one part per million CO. Using the same instrument configuration the O(2)/N(2) ratios (major components), as parameter for coal reactivity, are also determined. The proposed approach is restricted to the determination of gases evolved during coal studies and the application to other gas mixtures is not considered.     

Radio gas chromatography on capillary columns using a multi-column system (column-switching)

Summary A gas chromatographic system with capillary columns (fused silica) for the analysis of radiolabelled compounds is described. The system presented is based on a dual column gas chromatograph equipped with column switching facllity and a variable splitter at the column outlet combined with a dead-volume free adapter for the radioactivity monitor for continous measurement of radioactivity in the column effluent. The first column works as a separation column and the second is roughly shortened and used as a feed to the mass detector. The adjustment of the split ratio is regulated by the inlet pressures for the carrier gas supplying both columns. For mass detection all conventional systems can be used. Detection of radioactivity by a gas proportional counter (system based on a combustion technique). Three flow modes can be adjusted: a) total column effluent to the mass detector or b) to the radioactivity monitor, and c) simultaneous flow (dependent on the chosen split ratio) to mass-and radioactivity detectors. The system was developed for use in clinical chemistry and tested with labelled and unlabelled steroids. The method for peak identification by means of relative retention times and methylene units was possible also for radioactive peaks when a heart cutting technique was used. The radio gas chromatographic system presented allows the development of radiochromatograms with the same peak characteristics as in conventional capillary gas chromatography.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Semiautomatic method for the screening and determination of 23 organochlorine pesticides in horticultural samples by gas chromatography with electron-capture detection.

A rapid, simple, efficient device for the extraction-preconcentration of 23 organochlorine pesticides currently applied to vegetables is proposed. Pesticide residues are extracted from chopped samples by using a mixture of distilled water and light petroleum (1:1, v/v). After phase separation, an aliquot of the organic layer is continuously evaporated to dryness under a N2 stream as it is dropped into a glass tube containing distilled water. The aqueous phase, containing the analytes, is then passed through a miniaturized RP-C18 column for preconcentration, clean-up and subsequent elution with 150 microliters of ethyl acetate. A volume of 1 microliter of the extract containing pesticides is injected into the gas chromatograph, fitted with an electron-capture detector, for their selective determination. Limits of detection vary between 0.04 and 10 ng/ml, with linear ranges from 0.2 to 500 ng/ml; the average relative standard deviation at the low nanogram-per-millilitre level is 5.3%. The potential of the proposed method was realized by applying it to the screening/determination of organochlorine pesticides in horticultural commodities.