Miniature radio-frequency mobility analyzer as a gas chromatographic detector for oxygen-containing volatile organic compounds, pheromones and other insect attractants

A high electric field, radio-frequency ion mobility spectrometry (RF-IMS) analyzer was used as a small detector in gas chromatographic separations of mixtures of volatile organic compounds including alcohols, aldehydes, esters, ethers, pheromones, and other chemical attractants for insects. The detector was equipped with a 2 mCi 63Ni ion source and the drift region for ion characterization was 5 mm wide, 15 mm long and 0.5 mm high. The rate of scanning for the compensation voltages was 60 V s(-1) and permitted four to six scans to be obtained across a capillary chromatographic elution profile for each component. The RF-IMS scans were characteristic of a compound and provided a second dimension of chemical identity to chromatographic retention adding specificity in instances of co-elution. Limits of detection were 1.6-55 x 10(-11) g with an average detection limit for all chemicals of 9.4 x 10(-11) g. Response to mass was linear from 2-50 x 10(-10) g with an average sensitivity of 4 pA ng(-1). Separations of pheromones and chemical attractants for insects illustrated the distinct patterns obtained from gas chromatography with RF-IMS scans in real time and suggest an analytical utility of the RF-IMS as a small, advanced detector for on-site gas chromatographs.     

Quantification of amitriptyline, nortriptyline, and 10-hydroxy metabolite isomers in plasma by capillary gas chromatography with nitrogen-sensitive detection

A selective, sensitive method for the determination of amitriptyline and its metabolites is described. This method involves liquid-liquid extraction and capillary gas chromatography with nitrogen-sensitive detection. The detection limits of amitriptyline, nortriptyline, 10-hydroxy(E)amitriptyline, 10-hydroxy(E)nortriptyline, and 10-hydroxy(Z)nortriptyline were slightly less than 0.5 ng/ml in 1.0-ml plasma samples. The coefficients of variation for within-run and between-run analyses of samples containing 100 ng/ml were less than 12% and 9%, respectively. The method offers rapid analysis of individual isomers, increased sensitivity over high-performance liquid chromatographic methodology and the conveniences of the gas chromatographic technique.     

Detection of lysergic acid diethylamide, delta-9-tetrahydrocannabinol and related compounds by plasma chromatography.

Plasma chromatography as a method for ultratrace qualitative and quantitative detection of organic compounds is especially well suited for detection of gas chromatographic effluents. The optimum range of sample quantity is 10-6 to 10-12 g for detection and identification of a compound by use of its characteristic positive and negative mobility spectra. The type of reference mobility spectra produced by alkanes, aromatics, esters, halogenated compounds, nitrogenated compounds and organic acids have been previously reported. This study presents the reference mobility spectra produced for lysergic acid diethylamide (LSD), delta-9-tetrahydrocannabinol (delta-9-THC), digitoxigenin and several biochemical compounds of research significance. LSD and delat-9-THC in a mixture can be detected and identified by plasma chromatography positive mobility spectra in quantities of 10-7 g or less. All the compounds investigated in this study display strong MH-+ ions along with other ions primarily of the type (M)NO-+, (M)2H-+. None of these compounds exhibits negative mobility spectra.     

Temperature dependence of the mass accommodation coefficients of 2-nitrophenol, 2-methylphenol, 3-methylphenol, and 4-methylphenol on aqueous surfaces

The uptake of 2-nitrophenol, 2-methylphenol, 3-methylphenol, and 4-methylphenol on aqueous surfaces was investigated between 278 and 303 K, using the wetted-wall flow tube technique coupled with UV absorption spectroscopic detection. The uptake coefficients gamma were found to be independent of the aqueous phase composition and of the gas-liquid contact times. In addition, the uptake coefficients and the derived mass accommodation coefficients alpha show a negative temperature dependence in the temperature range studied. The mass accommodation coefficients decrease from 5.2 x 10(-3) to 8.3 x 10(-4), from 5.0 x 10(-3) to 3.1 x 10(-4), from 6.7 x 10(-3) to 7.3 x 10(-4), and from 1.2 x 10(-2) to 5.9 x 10(-4) for 2-nitrophenol, 2-methylphenol, 3-methylphenol, and 4-methylphenol, respectively. These results are used to discuss the incorporation of these species into the liquid using the nucleation theory. These data combined with the Henry's law constants were used to estimate the partitioning of the phenolic compounds between gaseous and aqueous phases and the corresponding atmospheric lifetimes under clear sky (tau(gas)) and cloudy conditions (tau(multiphase)) have then been derived.     

Determination of simazine, terbuthylazine, and their dealkylated chlorotriazine metabolites in soil using sonication microextraction and gas chromatography

A rapid analytical method is proposed for the determination of simazine, terbuthylazine, and their chloro dealkylated metabolites (simazine-desethyl, simazine-bisdesethyl, and terbuthylazine-desethyl) in soil. A sonication micromethod is presented for the extraction of -triazine herbicides and their metabolites. Final determination is by gas chromatography (GC) with nitrogen-phosphorus detection. The identity of all compounds was confirmed by GC with mass selective detection in the selected-ion monitoring mode. All chromatograms were very clean, without interfering peaks, and no cleanup was needed. The limits of detection were 1 pg for simazine-bisdesethyl; 5 pg for simazine, terbuthylazine, and terbuthylazine-desethyl; and 10 pg for simazine-desethyl. The limits of quantitation were 1, 5, and 10 ppb, respectively. Mean recoveries from fortified soils ranged from 76% for simazine-bisdesethyl to 102% for simazine-desethyl, with relative standard deviations of 3-6%.     

Determination of acetone, 2-butanone, diethyl ketone and BTX using HSCC-UV-IMS

A combination of a custom-designed ion mobility spectrometer (IMS) with a UV ionization source and a high speed capillary column (HSCC) has been developed as an analytical device for the sensitive detection of volatile organic compounds (VOCs), e.g. 2-propanone (acetone), 2-butanone and 3-pentanone (diethyl ketone) in the gas phase. A fast separation of the three selected substances and benzene, toluene and m-xylene (BTX) - all of which occur in human breath - has been achieved within less than four minutes at a carrier gas flow rate of 4.5 mL x min(-1). Multi-dimensional correlations presented support the interpretation of the acquired spectra of mixtures. Method detection limits were 2.7 microg x L(-1) for acetone and 2-butanone and 3.0 microg x L(-1) for diethyl ketone in nitrogen, respectively. The assay linear dynamic range is 4-320 microg x L(-1).     

Flame photometric detection inside of a capillary gas chromatography column

A novel micro-flame photometric detector (FPD) employing a miniature counter-current flame is described. The micro-FPD flame, encompassing a volume of about 30 nL, is operated inside the end of a capillary gas chromatography column (i.e. on-column) or inside of a quartz capillary after the column (i.e. post-column). Either air or oxygen can support a hydrogen flame in the device, although oxygen is far preferable. The detector can be operated for several hours without any observed degradation in performance or flame stability. The optimal gas flows established for the detection of sulfur and phosphorus are in the range of 4 mL min(-1) of oxygen and 9 to 13 mL min(-1) of hydrogen. The fuel-rich micro-FPD flame generates chemiluminescent blue S2* emission for sulfur and green HPO* emission for phosphorus, similar to a conventional FPD. Sulfur response in the micro-FPD is quadratic over nearly 3 orders of magnitude while that of phosphorus is linear over nearly 5 orders of magnitude. The micro-FPD detection limit for sulfur is 1 x 10(-9) g S s(-1), and that of phosphorus is 2 x 10(-10) g P s(-1). The properties established for the initial prototype of the micro-FPD make this counter-current flame method potentially suitable for integration with on-chip gas chromatography or other micro-analytical devices where flame-based detection methods are desirable.     

Multiresidue method for the simultaneous determination of four groups of pesticides in ground and drinking waters,using solid-phase microextraction-gas chromatography with electron-capture and thermionic specific detection

A common sample preparation procedure capable of efficiently concentrating various groups of pesticides, taking advantage of universal detectors like the mass spectrometer or combined techniques of group selective detectors like gas chromatography-electron capture detection (ECD)/thermionic specific detection (TSD), is desirable in environmental analysis. Six solid-phase microextraction fibres available for analysis of semi-volatiles (7, 30 and 100 microm poly(dimethylsiloxane) (PDMS), 85 microm polyacrylate, 60 microm PDMS-divinylbenzene (PDMS-DVB) and 65 microm Carbowax-DVB) were evaluated and the 60 microm PDMS-DVB was selected for the simultaneous extraction of 34 compounds, included in the organochlorine (OCPs), organophosphorous (OPPs), pyrethroid and triazine pesticide groups. All parameters affecting the extraction efficiency from water samples, namely fibre coating, sample agitation, pH and ionic strength, extraction temperature and time, were optimised. The analytical procedure involves solid-phase microextraction extraction, gas chromatographic separation and subsequent ECD and TSD via a post-column splitter adjusted to a split ratio of 1:10, respectively. Detection limits in the range of 1-10 ng l(-1) for OCPs, 1-30 ng l(-1) for OPPs, 20-30 ng l(-1) for pyrethroids and 8-50 ng l(-1) for triazines are easily attainable with the optimised procedure. The method validated for ground and drinking waters has low cost of implementation and operation although it requires careful maintenance.     

Semiochemicals of the Scarabaeinae VIII. Identification of active constituents of the abdominal sex-attracting secretion of the male dung beetle, Kheper bonellii, using gas chromatography with flame ionization and electroantennographic detection in parallel

Using gas chromatography with flame ionization detection and electroantennographic detection in parallel (GC-FID/EAD), the active constituents of the sex attractant of male dung beetles of Kheper bonellii were located in the gas chromatogram of an extract of the secretion. These constituents were identified as propanoic acid, butanoic acid, indole, 3-methylindole (skatole) and methyl cis-cascarillate (methyl cis-2-2'-hexylcyclopropylacetate) by, inter alia, GC-MS, (1)H and (13)C NMR analysis, and synthesis. These compounds elicited EAD responses in male as well as female antennae. Racemic methyl cis-cascarillate was synthesized for comparison with the natural methyl ester. Enantioselective GC-FID/EAD using a capillary column coated with OV-1701-OH containing 10% heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin showed that the natural compound co-eluted with the first-eluting enantiomer of the racemic methyl cis-cascarillate, which was the only enantiomer that elicited EAD responses in the antennae of male and female K. bonellii. The absolute configuration of this enantiomer was established by a stereoselective synthesis, which gave methyl (R,R)-cascarillate [methyl (1'R,2'R)-2-2'-hexylcyclopropylacetate] in an enantiomeric excess of 69%.     

Electron attachment to MoF6, ReF6, and WF6; reaction of MoF6(-) with ReF6 and reaction of Ar+ with MoF6

Rate constants were measured for electron attachment to MoF(6), ReF(6), and WF(6) in 133 Pa of helium gas using a flowing-afterglow Langmuir-probe apparatus. The experiment is a thorny one because the molecules tend to form oxide impurities on feedline surfaces and because of thermal decomposition of MoF(6) on surfaces as the gas temperature is increased. The electron attachment rate constant for MoF(6) is (2.3+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only MoF(6) (-) is formed in the temperature range of 297-385 K. The rate constant increases with temperature up to the point where decomposition becomes apparent. Electron attachment to ReF(6) occurs with a rate constant of (2.4+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only ReF(6) (-) is produced. MoF(6) (-) reacts with ReF(6) to form ReF(6) (-) on essentially every collision, showing definitively that the electron affinity of ReF(6) is greater than that of MoF(6). A rate constant of (5.0+/-1.3)x10(-10) cm(3) s(-1) was measured for this ion-molecule reaction at 304 K. The reverse reaction is not observed. The reaction of Ar(+) with MoF(6) was found to produce MoF(5) (+)+F, with a rate constant of (1.8+/-0.5)x10(-9) cm(3) s(-1). WF(6) attaches electrons so slowly at room temperature that the attachment rate was below detection level (< or =10(-12) cm(3) s(-1)). By 552 K, the attachment rate constant reaches a value of (2+/-1)x10(-10) cm(3) s(-1).     

Simultaneous analysis of flunixin, naproxen, ethacrynic acid, indomethacin, phenylbutazone, mefenamic acid and thiosalicylic acid in plasma and urine by high-performance liquid chromatography and gas chromatography-mass spectrometry.

Simple and reproducible high-performance liquid chromatographic (HPLC) and gas chromatographic-mass spectrometric (GC-MS) methods have been developed for the simultaneous analysis of several acidic drugs in horse plasma and urine. Although the capillary GC-MS column provided better separation of the drugs than the reversed-phase C8 (3 microns, 75 mm) HPLC column, the total analysis time with HPLC was shorter than the total analysis time with GC-MS. The HPLC system equipped with a diode-array detector provided simultaneous screening (limit of detection 100-500 ng/ml) and confirmation (limit 1.0 micrograms/ml) of the drugs. The HPLC system equipped with fixed-wavelength ultraviolet and fluorescence detectors provided a relatively sensitive screening [limit of detection 50-150 ng/ml for ultraviolet and 10 ng/ml for fluorescence (naproxen only) detectors] of the drugs. However, the positive samples had to be confirmed by using either the diode-array detector or the GC-MS system. The GC-MS system provided simultaneous screening and confirmation of the drugs at very low concentrations (20-50 ng/ml).     

Continuous solid-phase extraction and gas chromatographic determination of organophosphorus pesticides in natural and drinking waters

A simple, rapid continuous-flow solid-phase extraction method with gas chromatographic detection for the determination of organophosphorus pesticides is proposed. The continuous system consists of an adsorbent column where pesticides are preconcentrated and subsequently eluted with ethyl acetate. Various sorbent materials were assayed of which RP-C18 was found to provide the best results, with a sorption efficiency close to 100%. A comparative study of the determination of pesticides in aqueous samples was conducted using gas chromatography with nitrogen-phosphorus (NPD) and flame ionization (FID) detection. The detection limits of the method for 10 ml of sample were between 50-130 ng/l and 4.5-1 1.7 microg/l with NPD and FID detection, respectively. The method was used to determine organophosphorus pesticides in river, pond, well and tap waters, all with good precision (2.9-4.3%) and recoveries ranging from 93.8 to 104.5%.     

Routine method for the simultaneous quantification of 17alpha-hydroxyprogesterone, testosterone, dehydroepiandrosterone, androstenedione, cortisol, and pregnenolone in human serum of neonates using gas chromatography-mass spectrometry

Steroid determination by immunoassays results in significant interferences and inaccurate results. This study describes the development and validation of a new gas chromatographic-mass spectrometric method for the simultaneous quantification of 17alpha-hydroxyprogesterone (17alphaOHP), testosterone (T), dehydroepiandrosterone (DHEA), androstenedione (Delta4-A), cortisol (F) and pregnenolone (Preg) in serum of neonates. Steroids were extracted and purified from 0.5 mL serum using diethyl ether and Extrelut mini NT1 column. The extracts were derivatized with N-methyl-N-trimethylsilyl-trifluoroacetamide (MSTFA)/trimethylsilyl iodide (TMSI)/dithioerythritol (DTE) and the resulting trimethylsilyl derivatives were quantified by gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS). The detection limit for all steroids was lower than 0.1 ng/mL. The limit of quantification was 0.1 ng/mL for all steroids except cortisol which was at 0.25 ng/mL. d3-Testosterone and methyltestosterone served as internal standards. Precision for all compounds at the concentrations of 0.5, 1, 5 and 10 ng/mL (n = 10) in fortified steroid-free serum samples ranged from 0.8% to 16.6%. Accuracy was calculated at the concentrations of 0.5, 1, 5 and 10 ng/mL and ranged from -9.2% to 10.6% (n = 10). Linear calibration equations were obtained for all five steroids (0.125-31.25 ng/mL) and for cortisol (0.125-200 ng/mL). Relative recoveries at concentrations 1.0 and 12.5 ng/mL ranged from 70.5% to 97.5%. Absolute recoveries at the same concentrations ranged from 73.2% to 96.6%. Reference intervals were estimated for infants aged from 9 to 40 days. The proposed steroid profile is suitable for routine analysis and provides meaningful data for samples within normal range as well as those with elevated levels.     

Gas chromatographic determination of benzene, toluene, ethylbenzene and xylenes using flame ionization detector in water samples with direct aqueous injection up to 250 microl

A simple method of solventless extraction of volatile organic compounds (benzene, toluene, ethylbenzene and xylenes) from aqueous samples was developed. This method allows direct injection of large volume of water sample into a gas chromatograph using the sorption capacity of the sorbent Chromosorb P NAW applied directly in the injection port of gas chromatograph. The system prevent water penetration into a column, keep it adsorbed on its surface until the analytes are stripped into a column, and the residual water is purging using split flow. The limit of detection ranging from 0.6 for benzene to 1.1 microg l(-1) for o-xylene and limit of quantification ranging 2.0-3.6 microg l(-1) are lower that those reached by gas chromatography with flame ionization detection and direct aqueous injection before.     

A simple method for the trace determination of methanol, ethanol, acetone and pentane in human breath and in the ambient air by preconcentration on solid sorbents followed by gas chromatography

A simple technique has been developed for preconcentration of gaseous trace organic compounds on solid sorbents, followed by gas chromatography. The sorbent is packed in a cartridge from a syringe needle placed in the gas chromatographic injector and the analytes previously adsorbed are thermally desorbed at the injector temperature and then directly swept by the carrier gas into the column. The system has been tested for a charcoal-based adsorbent and silica gel, with pentane, methanol, ethanol and acetone as the model analytes. The procedure is rapid, the detection limits vary from a few nmol l(-1) to values below 0.1 nmol l(-1) (i.e., a few ppb), the linear dynamic range amounts to at least five concentration decades and a typical relative standard deviation is 10% at the nmol l(-1) concentrations. It has been shown that the method is readily applicable to determination of instantaneous concentrations of the analytes in natural and industrial atmosphere and to their monitoring in human breath which is important for medical and hygienic practice. In general, the procedure is applicable to low-molecular volatile organic compounds.     

Investigation of a flat sheet membrane desolvator for aqueous solvent removal with inductively coupled plasma atomic emission spectrometry

Results obtained from a preliminary investigation of the performance of a flat sheet membrane desolvator (FSMD) utilizing dual hydrophobic polypropylene membranes with an average pore size of 0.05 mum and a 50 +/- 5 mum thickness are reported. The membranes have a desolvation area of 241 cm(2). The volume-to-surface area ratio is 0.3 cm. Using the FSMD with an ultrasonic nebulizer (USN), aqueous solvent desolvation efficiencies of greater than 99.9% were obtained at all nebulizer gas flow rates investigated (0.8, 1.2, and 1.8 l min(-1)). This efficient desolvation occurred when the countercurrent gas flow rate was equal to or slightly greater than the applied nebulizer gas flow rate. Under these conditions preconcentration factors of 18, 44, and 590 were observed with flows of 0.8, 1.2 and 1.8 l min(-1), respectively. Operating with countercurrent gas flow rates much higher than the nebulizer gas flow rates leads to a significant reduction in analyte flux, thus increasing detection limits. Depending on the nebulizer and countercurrent gas flow rate conditions, the FSMD contributed between 10-40% to the overall analyte loss in the system. The lowest detection limit observed for aqueous copper with the USN-FSMD system is 0.4 ppb at nebulizer and countercurrent gas flow rates of 1.2 and 1.4 l min(-1), respectively. At this nebulizer gas flow rate, replacing the FSMD in the system with a commercial tubular membrane desolvator, MDX100, gave a lowest Cu detection limit of 0.2 ppb at a countercurrent gas flow rate of 1.2 l min(-1). These detection limits represents improvements over the 0.7 and 8 ppb obtained with USN and pneumatic nebulization, respectively.     

S_2OF_(10)气体标准样品制备方法和测定方法研究

提出了一系列的安全、方便、可靠、在线和可连续操作的热解吸／色谱分析柱制备Ｓ２ＯＦ１０纯品、指数稀释法配制Ｓ２ＯＦ１０标准样品、应用定量校正系数测定样品中痕量Ｓ２ＯＦ１０的方法和技术。分别采用气相色谱、红外光谱、气相色谱／质谱等方法对色谱制备的Ｓ２ＯＦ１０纯品进行了纯度分析和测定。配制Ｓ２ＯＦ１０标准气体的体积分数范围为８．０×１０－７～２．６×１０－４。气相色谱测定Ｓ２ＯＦ１０的定量校正系数为０．１９７,测定方法的相对误差范围为１．８％～２０％。     

The surface-enhanced Raman spectra of aflatoxins: spectral analysis, density functional theory calculation, detection and differentiation

High-quality surface-enhanced Raman scattering (SERS) spectra of aflatoxin (AF) B(1), B(2), G(1) and G(2) have been acquired using silver nanorod (AgNR) array substrates fabricated by oblique angle deposition method. Significant vibrational peaks are identified on the argon plasma-cleaned substrates, and those peaks agree very well with the Raman spectra calculated by density function theory (DFT). The concentration-dependent SERS detection is also explored. The relationship between the concentration (C) of different AFs and the SERS intensity (I) of the Raman peak at Δν = 1592 cm(-1) is found to follow the general relationship I = AC(α), with α ranging from 0.32 to 0.46 for the four AFs. The limits of detection (LODs) reach 5 × 10(-5) mol L(-1) for AFB(1), 1 × 10(-4) mol L(-1) for AFB(2), and 5 × 10(-6) mol L(-1) for both AFG(1) and AFG(2) in bulk solution, or 6.17 × 10(-16) mol/1.93 × 10(-4) ng of AFB(1), 1.23 × 10(-15) mol/3.88 × 10(-4) ng for AFB(2), 6.17 × 10(-17) mol/2.03 × 10(-5) ng for AFG(1), and 6.17 × 10(-17) mol/2.04 × 10(-5) ng for AFG(2) per laser spot. Principal component analysis (PCA) is used to successfully differentiate these four different kinds of AFs at different concentrations up to their detection limits. The LODs obtained from PCA agree with the LODs obtained by using peak fitting method. With such a low detection limit and outstanding differentiation ability, we prove the possibility of utilizing the SERS detection system as a platform for highly sensitive mycotoxin detection.     

Determination of tributyrin and its metabolite butyrate in Wistar rat plasma samples by gas chromatography/mass spectrometry

A gas chromatographic (GC) method with mass spectrometric (MS) detection was developed for the determination of tributyrin and its metabolite butyrate in rat plasma. Following precipitation of plasma protein with acetonitrile, the analytes in the samples were separated on a DB-5ms capillary column with helium as carrier gas. Phenylmethylsulfonyl fluoride (PMSF), an inhibitor for serine proteases, papain and acetylcholinesterase, was found to be essential to inhibit the activity of enzyme(s) responsible for the hydrolysis of tributyrin in both rat and human blood samples. The enzyme inhibitor in 5 mM (final concentration) was added immediately into the blood samples after collection to prevent the hydrolysis. The linear concentration ranges for tributyrin and butyrate were 0.1-2.0 and 1-20 microM, respectively. The coefficients of variation for intra-day and inter-day assays for tributyrin were all <10%, and those for butyrate were also <10%, except for the lowest concentration (1 microM), which was less than 20%. The accuracy of all concentration determinations ranged from 96.0-110.0%. The limit of quantification (LOQ) was 0.1 microM for tributyrin and 1.0 microM for butyrate. This method could detect tributyrin and butyrate simultaneously, and represents an improvement in sensitivity for the detection of tributyrin compared with the previous gas chromatography-flame ionization detection (GC-FID) method.     

利用Cr_2O_3-LaCoO_3-Pt纳米材料催化发光测定大气中的氨分子

研究了氨分子在Cr_2O_3纳米粒子（粒径50 ～ 80 nm）表面的化学发光行为， 发现这种纳米材料对氨分子具有较强的选择性。进一步的研究表明，在掺杂了 LaCoO_3纳米粒子（粒径20 nm）和Pt纳米粒子（粒径≤10 nm）后，化学发光强度 增强了近25倍。在最佳反应条件下，化学发光强度与氨分子的浓度在15.0 * 10~(- 6) ～ 750 * 10~(-6)内呈良好的线性关系（r = 0.995），检出限为4.0 * 10~(- 6)。