Kinetic calibration for automated hollow fiber-protected liquid-phase microextraction

Recently, a kinetic calibration method was developed for the quantification of microextraction. In this study, we proved that the sample volume and sampling time do not affect the feasibility of the calibration method, theoretically. The new theoretical considerations of the kinetic calibration method were validated through the investigation of the kinetics of the absorption and desorption processes of hollow fiber-protected liquid-phase microextractrion (HF-LPME). The kinetic calibration method for HF-LPME was successfully used to correct the matrix effects in the carbaryl analysis of a red wine sample. This research extends the kinetic calibration approach to fast sampling and some in-vial analyses, whereby the sample volume is not much larger than the product of the distribution coefficient and the volume of the extraction phase. HF-LPME technique was successfully automated with a CTC CombiPal autosampler, and a new device was designed for the automation of HF-LPME in this study. All steps of the HF-LPME technique, including the filling of the extraction solvent, sample transfer and agitation, withdrawing the solvent to a syringe, and introducing the extraction phase into the injector, were automated by a CTC autosampler. The fully automated HF-LPME technique is more convenient and more accurate. The good reproducibility of the fully automated HF-LPME technique eliminates the need for an internal standard to improve the analytical precision. The automated HF-LPME technique can be also used to obtain the distribution coefficient between the sample matrix and the extraction phase. The distribution coefficients of carbaryl and (13)C-carbaryl between 1-octanol and red wine, at 25 degrees C, were obtained with this technique.     

Solid-phase microextraction coupled to gas chromatography/mass spectrometry for determining polycyclic aromatic hydrocarbon-micelle partition coefficients

Solid-phase microextraction (SPME) coupled to gas chromatography with MS detection has been employed to study the partition coefficients of PAHs to ionic and nonionic micelles. The results obtained in this work for seven PAHs, using 85-microm polyacrylate- and 100-microm poly(dimethylsiloxane)-coated fibers and anionic (sodium dodecyl sulfate), cationic (cetyltrimethylammonium bromide), and nonionic (polyoxyethylene-10-lauryl ether) surfactants, indicate that SPME is a viable method for estimating the partition coefficients of PAHs to micelle. The procedure could also be potentially extended to the measurement of partition coefficients between a wide variety of semi- or nonvolatile compounds and micellar media.     

Fully automated dynamic in-syringe liquid-phase microextraction and on-column derivatization of carbamate pesticides with gas chromatography/mass spectrometric analysis

A new fully automated dynamic in-syringe liquid-phase microextraction (LPME) and on-column derivatization approach, with gas chromatography/mass spectrometric (GC/MS) analysis, was developed to determine carbamate pesticides from water samples. With the use of a CTC CombiPal autosampler and its associated Cycle Composer software, a sample preparation-GC/MS method was enabled that allowed sample extraction, extract injection, and analyte derivatization to be carried out completely automatically. Optimization of extraction parameters was carried out by orthogonal array design which required a minimum of 16 experiments; the entire set of experiments was performed completely automatically and consecutively without any human intervention. Low limits of detection ranging from 0.05 to 0.1 μg/L were achieved for the carbamates. Effective enrichment of the analytes at a low concentration of 0.01 mg/L was also achieved (enrichment factors of between 57 and 138). The precision of the optimized method was satisfactory, with relative standard deviations of <6.0% (n = 6). High relative recoveries of between 81 and 125% were obtained when the method was applied to the analysis of real water samples, indicating that the sample matrix had little effect on the developed method. This automated dynamic in-syringe LPME approach demonstrated the feasibility of a complete analytical system comprising sample preparation and GC/MS that might be operated onsite, fully automatically without human intervention.     

Liquid-phase microextraction combined with hollow fiber as a sample preparation technique prior to gas chromatography/mass spectrometry

Two modes of liquid-phase microextraction (LPME) combined with hollow fiber (HF) were developed for gas chromatography/mass spectrometry (GC/MS). Both methodologies, that is, static LPME with HF and dynamic LPME with HF, involved the use of a small volume of organic solvent impregnated in the hollow fiber, which was held by the needle of a conventional GC syringe. In static LPME/HF, the hollow fiber impregnated with solvent was immersed in the aqueous sample, and the extraction processed under stirring; in dynamic LPME/HF, the solvent was repeatedly withdrawn into and discharged from the hollow fiber by a syringe pump. This is believed to be the first reported instance of a semiautomated liquid microextraction procedure. The performance of the two techniques was demonstrated in the analysis of two PAH compounds in an aqueous sample. Static LPME/HF provided approximately 35-fold enrichment in 10 min and good reproducibility (approximately 4%). Dynamic LPME/HF could provide higher enrichment (approximately 75-fold) in 10 min and even better reproducibility (approximately 3%). Both methods allow the direct transfer of extracted analytes to a GC/MS system for analysis.     

Quantitative determination of sulfonated aliphatic and aromatic surfactants in sewage sludge by ion-pair/supercritical fluid extraction and derivatization gas chromatography/mass spectrometry.

Secondary alkanesulfonate (SAS) and linear alkylbenzene-sulfonate (LAS) surfactants were quantitatively (> 90%) extracted from sewage sludges as their tetrabutylammonium ion pairs using 400 atm of supercritical CO2 for 5 min of static extraction followed by 10 min of dynamic extraction at 80 degrees C. Ion pairs of SAS and LAS quantitatively formed butyl esters in the injection port of the gas chromatograph and were determined by gas chromatography/mass spectrometry without class fractionation of the sewage sludge extracts. Concentrations of SAS and LAS in sludges from five different sewage treatment plants ranged from 0.27 to 0.80 g/kg of dry sewage sluge and from 3.83 to 7.51 g/kg, respectively. Good reproducibility was achieved with RSDs of typically 5% for replicate extractions and analyses. Homologue and isomer distributions of SAS in sewage sludge indicated an enrichment of the more hydrophobic components in sewage sludge during sewage treatment.     

A solid-phase microextraction device for the analysis of electrochemical reaction products by gas chromatography/mass spectrometry

Presented is a solid-phase microextraction syringe-electrode assembly that may be used to identify electrode reaction products. After an electrochemical experiment, the electrode within this syringe-electrode assembly can be introduced into the injection port of a gas chromatograph. Electrochemical reaction products can be analyzed, provided they adhere to the electrode surface and are amenable to gas chromatographic/mass spectrometric analysis. We highlight the potential usefulness of this device using well-known electrochemical reaction of quinones.     

Simultaneous measurement of urinary bisphenol A and alkylphenols by automated solid-phase extractive derivatization gas chromatography/mass spectrometry

Bisphenol A (BPA) and alkylphenols (APs) are widely used industrial chemicals. BPA is used to manufacture polycarbonate plastic and epoxy resins; APs are used to make alkylphenol ethoxylates, common nonionic surfactants. BPA and APs can leach into the environment during industrial production and after degradation of the polycarbonate plastics and nonionic surfactants. Environmental exposure to these phenolic compounds has been associated with adverse reproductive and developmental effects in wildlife. We developed a sensitive and robust method for measuring BPA and six APs; 3-tert-butylphenol, 4-tert-butylphenol, 4-n-octylphenol, 4-tert-octylphenol, 4-n-nonylphenol, and technical-grade nonylphenol in urine. The method is based on the use of automated solid-phase extraction (SPE) coupled to isotope dilution-gas chromatography/mass spectrometry (GC/MS). During the automated SPE process, the phenols are both extracted from the urine matrix and derivatized, using pentafluorobenzyl bromide, on commercially available styrene-divinylbenzene copolymer-based SPE cartridges. After elution from the SPE column, the derivatized phenols in the SPE eluate are analyzed by GC/MS. The method, validated on spiked pooled urine samples and on urine samples from exposed persons, has limits of detection of approximately 0.1 ng in 1 mL of urine.     

Exact mass measurements for confirmation of pesticides and herbicides determined by liquid chromatography/time-of-flight mass spectrometry

The accuracy and precision of exact mass measurements are determined using positive ions formed in the electrospray of 10 nonvolatile or thermally unstable carbamate, urea, and thiourea pesticides and herbicides. Environmentally significant approximately 7-ng quantities of the analytes were separated with microbore liquid chromatography, and the exact mass measurements were made in real time with a benchtop time-of-flight mass spectrometer. The positive ion electrospray mass spectra of the analytes generally consist of one or a few ions which are usually adducts of the molecule with a proton, a sodium ion, or an ammonium ion. Fragment ions and the rich mass spectra typical of electron ionization (EI) are generally not produced in the soft electrospray ionization process. Confirmation of the identity of a nonvolatile pesticide or herbicide depends largely on the masses of the few ions formed and the retention time, which can vary with chromatography conditions. Identifications of these analytes in environmental or other samples are less certain than identifications of volatile pesticides determinated by gas chromatography and EI mass spectrometry. The benchtop time-of-flight mass spectrometer was equipped with an electrostatic mirror, and resolving powers of 3500-5000 were routinely obtained and used for these exact mass measurements. This type of mass spectrometer is significantly less costly and complex than other types of mass spectrometers with exact mass measurement capabilities. The mean errors from three replicate exact mass measurements of the 10 test analytes were in the range of 0-5.4 parts-per-million. Potential interferences from substances with similar exact masses were evaluated.     

Analysis of cigarette smoke condensates by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry I acidic fraction

Cigarette smoke condensate is a complex chemical matrix, and analysis of its components is very difficult because of the limitation of the peak capacity and sensitivity of conventional chromatography and the extensive and laborious sample preparation that is frequently required. In this study, the acidic fraction of mainstream cigarette smoke condensate has been investigated by using comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GCxGC/TOFMS). Different column systems were tested and compared under proper GCxGC/TOFMS conditions. Auto data processing by TOFMS software combined with manual identification was used to assign the components. Over 1000 compounds, with S/N > or = 100, including 139 organic acids and over 150 phenols were tentatively identified by the developed method.     

Applications of Hadamard transform to gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry

Successful application of the Hadamard transform (HT) technique to gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) is described. Novel sample injection devices were developed to achieve multiple sample injections in both GC and LC instruments. Air pressure was controlled by an electromagnetic valve in GC, while a syringe pump and Tee connector were employed for the injection device in LC. Two well-known, abused drugs, 3,4-methylenedioxy-N-methylamphetamine (MDMA) and N, N-dimethyltryptamine (DMT), were employed as model samples. Both of the injection devices permitted precise successive injections, resulting in clearly modulated chromatograms encoded by Hadamard matrices. After inverse Hadamard transformation of the encoded chromatogram, the signal-to-noise (S/N) ratios of the signals were substantially improved compared with those expected from theoretical values. The S/N ratios were enhanced approximately 10-fold in HT-GC/MS and 6.8 in HT-LC/MS, using the matrices of 1023 and 511, respectively. The HT-GC/MS was successfully applied to the determination of MDMA in the urine sample of a suspect.     

Enzyme-linked immunosorbent assay compared with gas chromatography/mass spectrometry for the determination of triazine herbicides in water

An enzyme-linked immunosorbent assay (ELISA) was compared to a gas chromatography/mass spectrometry (GC/MS) procedure for the analysis of triazine herbicides and their metabolites in surface water and groundwater. Apparent recoveries from natural water and spiked water by both methods were comparable at 0.2-2 micrograms/L. Solid-phase extraction (SPE) was examined also, and recoveries were determined for a suite of triazine herbicides. A significant correlation was obtained between the ELISA and GC/MS method for natural water samples that were extracted by SPE. Because ELISA was developed with an atrazine-like compound as the hapten with conjugation at the 2-position, it was selective for triazines that contained both ethyl and isopropyl side chains. Concentrations for 50% inhibition (IC50) were as follows: atrazine, 0.4 microgram/L; ametryne, 0.45 microgram/L; prometryn and propazine, 0.5 microgram/L; prometon, 0.7 microgram/L; simazine and terbutryn, 2.5 micrograms/L; hydroxyatrazine, 28 micrograms/L; deethylatrazine and deisopropylatrazine, 30 micrograms/L; cyanazine, 40 micrograms/L; didealkylatrazine had no response. The combination of screening analysis by ELISA, which requires no sample preparation and works on 160 microL of sample, and confirmation by GC/MS was designed for rapid, inexpensive analysis of triazine herbicides in water.     

Microbial metabolomics with gas chromatography/mass spectrometry

An analytical method was set up suitable for the analysis of microbial metabolomes, consisting of an oximation and silylation derivatization reaction and subsequent analysis by gas chromatography coupled to mass spectrometry. Microbial matrixes contain many compounds that potentially interfere with either the derivatization procedure or analysis, such as high concentrations of salts, complex media or buffer components, or extremely high substrate and product concentrations. The developed method was extensively validated using different microorganisms, i.e., Bacillus subtilis, Propionibacterium freudenreichii, and Escherichia coli. Many metabolite classes could be analyzed with the method: alcohols, aldehydes, amino acids, amines, fatty acids, (phospho-) organic acids, sugars, sugar acids, (acyl-) sugar amines, sugar phosphate, purines, pyrimidines, and aromatic compounds. The derivatization reaction proved to be efficient (>50% transferred to derivatized form) and repeatable (relative standard deviations <10%). Linearity for most metabolites was satisfactory with regression coefficients better than 0.996. Quantification limits were 40-500 pg on-column or 0.1-0.7 mmol/g of microbial cells (dry weight). Generally, intrabatch precision (repeatability) and interbatch precision (reproducibility) for the analysis of metabolites in cell extracts was better than 10 and 15%, respectively. Notwithstanding the nontargeted character of the method and complex microbial matrix, analytical performance for most metabolites fit the requirements for target analysis in bioanalysis. The suitability of the method was demonstrated by analysis of E. coli samples harvested at different growth phases.     

A thermogravimetry-capillary gas chromatography/mass spectrometry interface

An interface and gas chromatograph oven are described that couple a thermogravimetric analyzer with a mass spectrometer and permit multiple capillary gas chromatographic separations of volatile thermal decomposition products generated during a single thermogravimetric analysis. Examples of the use of this apparatus for identifying the volatile products generated during poly(vinyl butyral) thermal decomposition in the presence of γ-alumina and catalytic cracking of poly(styrene) and poly(ethylene) are described. TG-GC/MS analyses employing isothermal, temperature programmed, and subambient temperature ramp gas chromatography separations are described. The apparatus permits repetitive temperature-programmed capillary gas chromatographic analyses of thermogravimetric effluent containing more than 25 constituents in 3-min intervals.     

Determination of nicotine and other minor alkaloids in international cigarettes by solid-phase microextraction and gas chromatography/mass spectrometry

Nicotine, nornicotine, anabasine, and anatabine are the most abundant alkaloids in tobacco. Along with the addictiveness of nicotine, other properties, including their occurrence in tobacco at relatively high concentrations, and as the primary precursors for the highly carcinogenic tobacco-specific nitrosoamines, make these chemicals important from a public health standpoint Therefore, developing a fast and accurate quantitative method to screen large numbers of cigarette samples for these alkaloids was important. This report describes the first use of headspace analysis using solid-phase microextraction combined with gas chromatography/mass spectrometry for the unambiguous detection of tobacco alkaloids. Detection and confirmation of each analyte isestablished by both chromatographic retention times and the ratio of reconstructed ion chromatogram peak areas from characteristic quantitation ion and confirmation ion. Twenty-eight cigarette brands from 14 countries were analyzed. Surprisingly, the minor alkaloids' response factors varied considerably among different styles of cigarettes. Accurate quantification was achieved using a three-point standard addition protocol. The standard addition approach was essential to obtain accurate measurements by minimizing matrix effects that would otherwise have contributed to quantitation bias. Significant differences in the alkaloid profiles were measured in the different cigarette brands. These results strongly suggest that such differences reflect variations associated with blend compositions, tobacco quality, and manufacturing practices.     

Headspace analysis of engine oil by gas chromatography/mass spectrometry

This study establishes the rationale necessary for determining the time to change engine oil. This is based on identifying gaseous components in new and used automobile lubricants. Key compounds, so-called "signature", are separated and identified qualitatively by coupled gas chromatography/mass spectrometry. Volatile antioxidants at zero miles and fuel contaminants at low mileage are observed in the headspace of engine oil. Several oxidative degradation components have been positively identified in the used oil, which include the following: acetaldehyde, acetone, butanal, 2-propanol, acetic acid, 2-hexanol, benzoic acid, benzaldehyde, and 1-pentanol. This study strongly suggests that the status of lubricating oil can be determined by the analysis of the gas phase above the oil. Most importantly, it opens the possibility of performing conditional maintenance of the combustion engine based on information obtained from gas sensors.     

Analysis of hydrazine in drinking water by isotope dilution gas chromatography/tandem mass spectrometry with derivatization and liquid-liquid extraction

A new isotope dilution gas chromatography/chemical ionization/tandem mass spectrometric method was developed for the analysis of carcinogenic hydrazine in drinking water. The sample preparation was performed by using the optimized derivatization and multiple liquid-liquid extraction techniques. Using the direct aqueous-phase derivatization with acetone, hydrazine and isotopically labeled hydrazine-(15)N2 used as the surrogate standard formed acetone azine and acetone azine-(15)N2, respectively. These derivatives were then extracted with dichloromethane. Prior to analysis using methanol as the chemical ionization reagent gas, the extract was dried with anhydrous sodium sulfate, concentrated through evaporation, and then fortified with isotopically labeled N-nitrosodimethylamine-d6 used as the internal standard to quantify the extracted acetone azine-(15)N2. The extracted acetone azine was quantified against the extracted acetone azine-(15)N2. The isotope dilution standard calibration curve resulted in a linear regression correlation coefficient (R) of 0.999. The obtained method detection limit was 0.70 ng/L for hydrazine in reagent water samples, fortified at a concentration of 1.0 ng/L. For reagent water samples fortified at a concentration of 20.0 ng/L, the mean recoveries were 102% with a relative standard deviation of 13.7% for hydrazine and 106% with a relative standard deviation of 12.5% for hydrazine-(15)N2. Hydrazine at 0.5-2.6 ng/L was detected in 7 out of 13 chloraminated drinking water samples but was not detected in the rest of the chloraminated drinking water samples and the studied chlorinated drinking water sample.     

新型液-液微萃取--气相色谱法测定海水中的有机氯农药

本文采用了一种新型的液---液两相微萃取技术作为海水样品前处理方法,对海水中的八种有机氯农药(α-BHC,β-BHC,γ-BHC,δ-BHC,p,p,-DDE,o,p,-DDT,p,p,-DDD,p,p,-DDT)进行萃取、富集和分离,采用配微池电子捕获检测器气相色谱法分析测定。对影响萃取效率的因素进行了优化。结果表明,在优化条件下,六六六、滴滴涕在1.0-100.0μg/L范围内有良好的线性关系,R≥0.9963,检测限为0.004~0.016μg/L。