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  • 1
    Electronic Resource
    Electronic Resource
    Microcolumn liquid chromatography with thermionic detection of the enantiomers of O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX) (1994)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 95-97 
    Details
    ISSN: 0935-6304
    Keywords: Chemical warfare agents ; Microcolumn liquid chromatography ; Enantiomeric separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved interface for the on-line coupling of microcolumn liquid chromatography (micro-LC) with thermionic detection (TID) is described. Modifications have been made to enable separate adjustment of the eluent introduction and the detector flame temperature in order to improve the sensitivity and ease of use of the system.The micro-LC-TID was used for the chiral separation of the nerve agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX). Baseline separation for the enantiomers of VX was obtained on Chiralcel OD using 1% isopropanol in hexane as the eluent. The detection limit of VX using 60 nl injections is ca. 5 μg/ml (ppm range). However, when using large-volume injections (10 μl) the detection limit is ca. 25 ng/ml (ppb range).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240170210
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  • 2
    Electronic Resource
    Electronic Resource
    Ethyl acetate for the desorption of a liquid chromatographic precolumn on-line into a gas chromatograph (1990)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 157-161 
    Details
    ISSN: 0935-6304
    Keywords: Coupled LC-GC ; Partially concurrent solvent evaporation ; Trace enrichment ; Surface water ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The feasibility of using ethyl acetate for the desorption of trace pollutants from a liquid chromatographic precolumn on-line into a diphenyltetramethyldisilazane-deactivated retention gap and, subsequently analysis by means of capillary gas chromatography has been demonstrated. First 5% of methanol are added to the water sample to prevent sorption of analytes onto parts of the preconcentration system. About 1 ml of this aqueous sample is injected onto a precolumn containing a polymeric stationary phase, using water-methanol (95:5, v/v) for transport and clean-up. The precolumn is desorbed with ethyl acetate and a fraction of 75 μl is injected on-line into the retention gap; separation is then achieved on a capillary CP Sil 19 column. No breakthrough of the test compounds was observed in the preconcentration step. The recovery was quantitative and the response obtained with flame ionization detection was linear in the range 0.1-100 ng/ml. The effect of varying the sorption flow rate on the recovery was studied. The system was applied to the analysis of river water.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240130303
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  • 3
    Electronic Resource
    Electronic Resource
    Microcolumn liquid chromatography of the enantiomers of organophosphorus pesticides with thermionic and ultraviolet detection (1991)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 14 (1991), S. 460-464 
    Details
    ISSN: 0935-6304
    Keywords: Micropacked liquid chromatography ; Enantiomer separation ; HPLC-TID ; Organophosphorus pesticides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Microcolumn liquid chromatography (micro-LC) of some chiral organophosphorus pesticides has been studied using Chiralcel OD columns and simultaneous ultraviolet (UV) and phosphorus selective detection, the latter by means of a micro-UV cell coupled on-line to a thermionic detector (TID). Micro-LC showed a ca. 5-fold improved separation impedance, a ca. 1.8-fold increased column permeability, and greater inertness compared with conventional LC.By using the TID, organophosphorus pesticides could be satisfactorily determined at trace levels, the detection limit being 4 pg/s of phosphorus. The response of the micro-LC-TID system is linear in the range of 0.05-20 ng (r = 0.9994).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240140708
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  • 4
    Electronic Resource
    Electronic Resource
    On-line solid phase extraction - thermal desorption for introduction of large volumes of aqueous samples into a gas chromatograph (1991)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 14 (1991), S. 455-459 
    Details
    ISSN: 0935-6304
    Keywords: LC-GC ; Aqueous samples ; Solid phase extraction ; Thermal desorption ; PTV ; Tenax GC© ; Reversed phase adsorbent ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new approach to the introduction of large aqueous samples into a gas chromatograph, solid phase extraction - thermal desorption, is presented. Carrier gas pushes the sample through a packed liner mounted in a programmed temperature vaporizer; analytes retained by the packing material are thermally desorbed after drying of the adsorbent. The sorption properties and thermal stability of some packing materials have been studied off-line. Tenax GC®, and octyl-modified silica silylated with diphenyltetramethyldisilazane to improve its thermal stability, appeared to be suitable materials.The drying period and the desorption temperature are critical for satisfactory performance of the method. When Tenax GC® is used as packing material, thermal desorption at 250°C for 15 min gives quantitative recovery for methyl esters up to hexacosanoic acid methyl ester. With the silylated octyl-modified silica, the application range is limited to the methyl esters of decanoic to octadecanoic acids.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240140707
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  • 5
    Electronic Resource
    Electronic Resource
    Packed capillary supercritical fluid chromatography of organophorus pesticides: Selective detection and applications (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 6 (1994), S. 55-62 
    Details
    ISSN: 1040-7685
    Keywords: supercritical fluid chromatography ; packed capillary columns ; thermionic detection ; organophosphorus pesticides ; vegetable extracts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Packed capillary supercritical fluid chromatography coupled with thermionic detection was used for the selective determination of nineteen organophosphorus pesticides in vegetable extracts. The chromatographic behavior of some pesticides was studied using seven different stationary phases. Addition of an organic modifier to carbon dioxide was needed to improve peak shape and reduce retention. Quantitation of organophosphorus pesticides in vegetable extracts showed good linearity. Extraction was performed in a one-step extraction procedure using a water-miscible solvent (acetone) and an organic solvent with limited water capacity (dichloromethane). Under these conditions a wide range of both polar and apolar pesticides can be recovered from vegetable extracts down to the 3-25 μg kg-1 level. The recoveries found ranged from 35 to 95% depending on the polarity of the pesticides.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220060111
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  • 6
    Electronic Resource
    Electronic Resource
    Large-volume on-column injections for gas chromatography (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 7 (1995), S. 383-394 
    Details
    ISSN: 1040-7685
    Keywords: large-volume injection ; gas chromatography ; on-column injector ; environmental analysis ; organophosphorus pesticides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Large-volume injection is an attractive means to improve detection limits when analyzing dilute sample extracts. There is now no need to achieve enrichment by means of solvent evaporation, which makes the total analytical procedure less reliable and less robust due to loss of volatile compounds. In this study on-column injection was applied for large-volume injection using an on-column injector in combination with a deactivated uncoated fused silica capillary (retention gap) and an early solvent vapor exit. Two strategies are described. The first one relies on the programmable speed of an infusion pump, which is adapted such that it lies just above the evaporation rate of the extraction solvent used. With the second procedure, which can be used for a commercially available autosampler, the evaporation speed is adjusted to the fixed speed of injection by varying the temperature during injection. During optimization the additional solvent evaporation time was determined. The optimum conditions for an injection volume of 100 μL of either n-hexane or ethyl acetate are reported. Large-volume injection was used for simplified and miniaturized solid-phase extraction procedures. The procedures were used to determine various organic micropollutants, such as organophosphorus pesticides and triazine herbicides, in tap and surface water extracts, using a flame photometric, and a mass spectrometric detector. For both methods good recovery for most of the analytes (70-87%), linear calibration curves (0.01-5 μg/L range), and relative standard deviations of less than 10% were obtained. Detection limits typically were in the range of 1-10 ng/L for GC-FPD and 10-150 ng/L for GC-MS. When working in the time-scheduled multiple ion detection mode detection limits in GC-MS were one order of magnitude lower. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220070411
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  • 7
    Electronic Resource
    Electronic Resource
    Verification of nonproduction of chemical warfare agents: I. Determination of organophosphorus compounds by microcolumn liquid chromatography with flame photometric or thermionic detection (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 4 (1992), S. 465-475 
    Details
    ISSN: 1040-7685
    Keywords: micro-LC ; flame photometric detection ; thermionic detection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Microcolumn liquid chromatography (micro-LC) with on-line flame photometric (FPD) or thermionic detection (TID) has been used for the determination of a series of organophosphoric and organophosphonic acids isolated from various sample matrices. Silica-based ion-exchange materials and polymer packings have been used as stationary phases. In order to improve the sensitivity (expressed in concentration units) of the technique, trace enrichment via a miniaturized precolumn (4 mm × 1 mm i.d.) and direct large-volume injections (1-10 μL) of aqueous samples have been studied. As an application, the verification of nonproduction of chemical warfare agents and their alleged use have been investigated by analyzing their hydrolysis products in spiked surface water and soil samples. The application of both the precolumn technique and large-volume injections permit the detection of organophosphorus acids in water and soil at the low ppm level.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220040602
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  • 8
    Electronic Resource
    Electronic Resource
    Reversed-phase liquid chromatography coupled on-line with capillary gas chromatography II. Use of a solvent vapor exit to increase introduction volumes and introduction rates into the gas chromatograph (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 6 (1994), S. 207-215 
    Details
    ISSN: 1040-7685
    Keywords: capillary GC ; reversed-phase LC ; on-line coupling ; solvent vapor exit ; pressure-balanced carrier gas system ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A large-volume introduction system for capillary gas chromatography (GC) is described which can be coupled on-line with reversed-phase liquid chromatography (LC) using 2 mm i.d. LC columns. An on-column interface with a special retention gap, coated with a very thin film (0.02 μm) of Carbowax was used. Insertion of a solvent vapor exit before the analytical gas chromatography column allowed the solvent evaporation rate for an azeotropic acetonitrile/water mixture (84:16, v/v) to increase from 20 to 175 μL min-1 at 91°C and 150 kPa inlet pressure. A volume of 200 μL of this mixture containing phenanthrene and the potential basic drug eltoprazine, could be injected into the retention gap at introduction rates up to 200 μL min-1, under partially concurrent solvent evaporation conditions. Repeatability (CV = 2.4%) and linearity (at least 10-1000 ng mL-1) were satisfactory. The Carbowax-coated retention gap has a relatively large retention power for the polar solute. This means that the solvent can be completely evaporated through the vapor exit without loss of analyte. With apolar solutes, losses will occur if evaporation is unduly prolonged. In order to allow the use of a nitrogen-phosphorus detector, a special pressure-balanced carrier gas circuit was designed and tested for total solvent-free performance of the detector. With this set-up, 150 μL injections of eltoprazine in the acetonitrile/water azeotrope were made at an introduction rate of 200 μL min-1. No traces of acetonitrile were detected, while analyte detectability was 20-fold higher than with the FID.Finally, the practicability of reversed-phase LC-GC was demonstrated by on-line heart-cutting of the phenanthrene-containing fraction from a 2 mm i.d. LC column using acetonitrile/water (84:16, v/v) as eluent, and analyzing it by capillary GC-FID.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220060303
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  • 9
    Electronic Resource
    Electronic Resource
    Verification of nonproduction of chemical warfare agents: II. Large volume injections in microcolumn liquid chromatography using flame photometric detection (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 4 (1992), S. 477-483 
    Details
    ISSN: 1040-7685
    Keywords: micro-LC ; large-volume injections ; flame photometric detection ; organo-phosphates ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sensitivity and separation performance of microcolumn liquid chromatography coupled with a flame photometric detector were considerably improved by the direct injection of large sample volumes (approximately 10 μL) and by peak compression. Extremely narrow peaks can be obtained by adding displacers such as hydrochloric acid (ion-exchange mode) or n-butanol (reversed-phase mode) to the sample.The system was used for the determination of ethyl methylphosphonic acid, isopropyl methylphosphonic acid, and pinacolyl methylphosphonic acid which are the hydrolysis products of the super-lethal nerve agents VX, sarin, and soman, respectively, and of the final degradation product, methylphosphonic acid. The detection limits for the alkyl methylphosphonic acids and sarin in water were 1-20 ppb.Two examples were used to demonstrate the practicality of the present procedure. Sarin and the much more polar isopropyl methylphosphonic acid were simultaneously determined in a spiked surface water sample used for verification studies. Low-ppb levels of phosphorous acid were identified in mustard gas.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220040603
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  • 10
    Electronic Resource
    Electronic Resource
    Variable splitter for regulation of the solvent evaporation rate in the coupling of liquid chromatography with gas chromatography (1990)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 405-409 
    Details
    ISSN: 0935-6304
    Keywords: Coupled LC-GC ; Retention gap ; Variable splitter ; Partially concurrent solvent evaporation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A system is described which accelerates the solvent evaporation rate in the retention gap. The evaporation is due to a saturation effect of the carrier gas stream, and a considerable increase in evaporation rate is obtained by inserting a split outlet between the retention gap and the capillary separation column in the gas chromatograph. By varying the backpressure of the spliter device, the flow rate through the retention gap can be adjusted and so too the evaporation rate. The evaporation process was monitored by inserting a dectecter in the split outlet line. The technique was applied to the on-line LC trace enrichment/GC analysis of water containing a mixture of polycyclic aromatic hydrocarbons.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240130604
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