Solvent Vapor Exit Research Articles

Automated on-line gel permeation chromatography-gas chromatography for the determination of organophosphorus pesticides in olive oil

An on-line combination of gel permeation chromatography and gas chromatography has been designed using either a laboratory-built or a commercially available LC-GC apparatus to determine organophosphorus pesticides in olive oil. Gel permeation chromatography was used for sample pretreatment, viz. to separate the low-molecular-mass pesticides from the higher-molecular-mass fat constituents of the oil. A mixture of n-decane and the azeotropic mixture of ethyl acetate and cyclohexane was found to give an adequate separation between the fat and the organophosphorus pesticides. The pesticide-containing fraction, monitored by a UV detector, was transferred on-line to the gas chromatograph using a loop-type interface. n-Decane (6%, v/v) was added to the eluent in order to widen the application range of the transfer technique towards more volatile pesticides. After solvent evaporation through the solvent vapour exit and subsequent GC separation, the compounds were selectively detected with a thermionic or a flame photometric detector. The set-up allowed the direct analysis of oil samples after dilution in the gel permeation chromatography eluent without further sample clean-up. Detection limits were about 5 and 10 μg/kg with the thermionic and the flame photometric detector, respectively, when using an injection volume of only 30 μl of the 20-fold diluted oil. The total procedure was linear in the 0.01–10 mg/kg range for both detectors. For twenty organophosphorus pesticides, the relative standard deviations were 3–13% at the 20–60 μg/kg level.

Large-volume injection in capillary gas chromatography using a programmed-temperature vaporizing injector in the on-column or solvent-vent injection mode

The use of the programmed-temperature vaporizing (PTV) injector as a versatile interface for large-volume injection in capillary GC is proposed. By using a special on-column insert, in addition to large-volume solvent-vent injection, also large-volume on-column injection can be performed with the PTV injector. For this, a set-up consisting of a retention gap, a retaining precolumn and an early solvent vapour exit is installed between the on-column insert and the analytical column. The performance of this set-up for large-volume injection was evaluated and found to be similar to that of large-volume injection using a conventional on-column injector. The proposed instrument hence allows PTV and on-column large-volume sampling to be performed using only one injector. This greatly reduces instrument costs for large-volume sampling equipment. Guidelines are given for method development for large-volume sampling.

Investigation of on-line reversed-phase liquid chromatography–gas chromatography–mass spectrometry as a tool for the identification of impurities in drug substances

The potential of on-line reversed-phase (RP) LC–GC–MS for the identification of impurities in pharmaceutical products has been investigated. The technical aspects of the system were studied using the potential drug eltoprazine as test compound. After LC separation on a 2 mm id RPLC column, using 5 mmol l–1 methanesulfonic acid in acetonitrile–water (84 + 16 v/v) as eluent, the eltoprazine-containing fraction of 200 µl was introduced on-line into the GC–MS, the mass spectrometer being a magnetic sector instrument. Before this introduction, the methanesulfonic acid was removed on-line from the LC eluent via an anion-exchange membrane. Most of the solvent introduced into the GC–MS was evaporated via a solvent vapour exit installed in front of the capillary GC column. As an application, impurity profiling was performed on the drug substance mebeverine which contained mebeverine amine as test impurity. The addition of acetonitrile was necessary before introduction into the GC; therefore only about 10% v/v of the mebeverine amine LC peak was transferred to the GC–MS. Nevertheless, electron impact and chemical ionization spectra of the impurity could be obtained at a level of 0.1% with respect to the drug.

Online Coupled LC-GC-ITD/MS for the Identification of Alkylated, Oxygenated, and Nitrated Polycyclic Aromatic Compounds in Urban Air Particulate Extracts

A method has been developed to identify oxygenated, nitrated, and alkylated polycyclic aromatic compounds (PAC) adsorbed onto urban air particulates using an on-line coupled chromatographic method and mass spectrometry. High-pressure normal-phase liquid chromatography was coupled to a high-resolution gas chromatograph with an ion trap detector mass spectrometer. The instrument was configured to use an on-column LC-GC interface, enabling partially concurrent solvent evaporation with an early solvent vapor exit. This instrument was used to identify many substituted PAC contained in the extracts obtained from the supercritical fluid extraction of urban air particulates collected roadside by a high volume sampler in Leeds. Compounds identified included alkylated pyrene and chrysene species, nitrated fluoranthene and pyrene species, and many oxygenated quinone and aldehyde PAC.

An on‐line coupled HPLC‐HRGC system for the quantitative characterization of oil fractions in the middle distillate range

AbstractA commercially available HPLC‐HRGC instrument was adapted to enable the full quantitative characterization of oil fractions in the range 150–400°C. The HPLC separates the sample into five fractions: saturates, mono‐aromatics, di‐aromatics, fluorenes + dibenzothiophenes, and tri‐aromatics. These fractions are subsequently quantitatively transferred via an on‐column interface to the HRGC part of the system. This transfer is performed into an empty, wide‐bore precolumn (retention gap), which enables a refocussing effect of the compounds of interest in the tail of the HPLC mobile phase, which acts as a solvent in the GC. A solvent vapor exit in the system enables the vent of the major part of this solvent. The final HRGC separation provides a carbon distribution of the saturates and the mono‐aromatics and enables the identification of a number of compounds in the other three fractions. It is demonstrated that the described method is quantitative for the hydrocarbons, but also for sulphur‐containing compounds in only those samples that have a low sulphur content. © 1995 John Wiley & Sons, Inc.

Large‐volume on‐column injections for gas chromatography

AbstractLarge‐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.

Continuous liquid‐liquid extraction combined on‐line with capillary gas chromatography‐atomic emission detection for environmental analysis

AbstractThe on‐line coupling of a liquid‐liquid extraction system with capillary gas chromatography using atomic emission detection (GC‐AED) has been studied. The required large volumes of about 100 μl of an iso‐octane solution can be introduced into the GC‐AED system by using the AED solvent vent and a solvent vapor exit in front of the capillary analytical column. Test solutions containing several pesticides were detected using the carbon, chlorine, nitrogen and sulfur channels. Analyte detectability (in concentration units) was improved significantly and low concentractions of the test compounds could be determined (1–5 ng/ml). Aqueous samples were on‐line extracted and analyzed. The precision of the large‐volume injection itself as well as the total extraction‐GC‐AED system was satisfactory (RSD of ca. 2 and 4%, respectively). As a real‐life application, several ground water samples were screened.

Identification of polycyclic aromatic compounds in urban air particulate extracts by on-line coupled LC–GC–ITD–MS

A method has been developed to identify and quantify parent, oxygenated, nitrated and alkylated polycyclic aromatic compounds (PAC) adsorbed onto urban air particulates by using supercritical fluid extraction and online multidimensional chromatographic methods coupled to mass spectrometry. High pressure, normal phase, liquid chromatography has been coupled to a high resolution gas chromatograph and an ion trap detector mass spectrometer. The instrument was configured to use an on-column LC–GC interface, enabling partially concurrent solvent evaporation with an early solvent vapour exit. This instrument was used to identify substituted polycyclic aromatic compounds contained in the extracts obtained from the supercritical fluid extraction of urban air particulates collected at the roadside in Leeds by a high volume sampler. Compounds identified included alkylated pyrene and chrysene species, nitrated fluoranthene and pyrene species and many oxygen containing PAC.

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

AbstractA 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.

Analysis of tocopherols in margarine by on‐line HPLC–HRGC coupling

AbstractTocopherol analysis in margarine is usually carried out by HPLC after saponification of the sample and extraction of the vitamin compounds; these steps consume both time and solvents. In this paper we propose an on‐line HPLC–HRGC coupling method, which allows us to simplify the preparation of the analytical sample. The sample of margarine is solubilized in hexane in an ultrasonic bath in the dark; the filtered solution is then injected into the liquid chromatograph using a normal phase microbore column eluted with hexane–isopropanol 99.8:0.2. The α‐tocopherol, which is eluted with some wax esters, is transferred on‐line to the gas chromatograph, using a loop‐type interface with the concurrent eluent evaporation and solvent vapor exit, thus it is separated from interfering compounds and determined using an Alltech RSL 300 column (22 m × 0.25 μm i.d., 0.2 μm film thickness). The β, γ, and δ–tocopherols are determined in the same LC run, using fluorimetric detection. The analysis was carried out in 50 min.

Fully automated water analyzer based on on‐line solid phase extraction‐gas chromatography

AbstractAn automated procedure for the analysis of aqueous samples by membrane disk extraction coupled on‐line to capillary gas chromatography (GC) is presented. Organophosphorus pesticides are preconcentrated from aqueous samples on three 0.5 mm thick, 4.0 mm diameter XAD‐2 membrane extraction disks which are mounted in a polymer holder for use in a PROSPEKT sample processor. The layers are dried by a stream of nitrogen (30 min at ambient temperature). Desorption of the analytes is carried out with ethyl acetate which is directly introduced into a retention gap under partially concurrent solvent evaporation conditions, using an early solvent vapor exit. The method is a fully software‐controlled automated system, and includes sample preparation, sample transfer and GC analysis. The final analysis is carried out by GC with nitrogen‐phosphorus (NPD) or mass‐selective detection. The technique is applied to the determination of a series of organophosphorus pesticides in tap water and water from European rivers. With a sample volume of only 2.5 mL, the detection limits achieved with the NPD were 20–50 ng L−1 in tap water and 20–100 ng L−1 in river water.

Selective and sensitive detection of organic contaminants in water samples by on‐line trace enrichment–gas chromatography–mass spectrometry

AbstractLiquid chromatographic (LC) type trace enrichment is coupled online with capillary gas chromatography (GC) with mass spectrometric (MS) detection for the analysis of aqueous samples. A volume of 1–10 ml of an aqueous sample is preconcentrated on a trace‐enrichment column packed with a polymeric stationary phase. After cleanup with HPLC‐grade water the precolumn is dried with nitrogen and subsequently desorbed with ethyl acetate. A fraction of 60 μl is introduced on‐line into a diphenyltetramethyldisilazane‐deactivated retention gap under partially concurrent solvent evaporation conditions and using an early solvent vapor exit. The analytes are separated and detected by means of GC–MS. The potential of the LC–GC–MS system for monitoring organic pollutants in river and drinking water is studied. Target analysis is carried out with atrazine and simazine as model compounds; the detection limits achieved under full‐scan and multiple ion detection conditions are 30 pg and 5 pg, respectively. Identification of unknown compounds (non‐target analysis), is demonstrated using a river water sample spiked with 168 pollutants varying in polarity and volatility.

Determination of organophosphorus pesticides in aqueous samples by on-line membrane disk extraction and capillary gas chromatography

A fast and simple procedure for the analysis of aqueous samples by on-line membrane disk extraction and capillary gas chromatography (GC) is presented. As an example, organophosphorus pesticides are preconcentrated from aqueous samples on three 0.5 mm thick, 4.2 mm diameter extraction disks. The layers are dried by a stream of nitrogen (10–15 min; ambient temperature). Desorption of the analytes is carried out with ethyl acetate which is directly introduced into a retention gap under partially concurrent solvent evaporation conditions, using an early solvent vapour exit. The final analysis is carried out by GC with thermionic detection. The technique is applied to the determination of a series of organophosphorus pesticides in tap water and water from two European rivers. With a sample volume of only 2.5 ml, detection limits of 10–30 ppt are achieved in tap water and of 50–100 ppt in river water.

Clean‐up of some organochlorine and pyrethroid insecticides by automated solid‐phase extraction cartridges coupled to capillary GC‐ECD

AbstractThe ASPEC (Automatic Sample Preparation with Extraction Columns) system has been coupled on‐line to capillary GC‐ECD by means of a loop‐type interface equipped with a solvent vapour exit. Both ASPEC and GC conditions have been optimized leading to an effective clean‐up of the extracts analyzed.By means of solid‐phase extraction cartridges filled with silica, it has been possible to analyze concentrated surface water extracts for a group of 18 electron‐capturing compounds present in the water at ppt levels. ASPEC‐GC has also been applied to the determination of synthetic pyrethroids at ppt levels in surface water.The complete analytical procedure is greatly facilitated by automation and miniaturization. Miniaturization results in a considerable decrease in the sample volume required. The potential of the method for the analysis of other pesticides is estimated.

On-line coupling of liquid chromatography, capillary gas chromatography and mass spectrometry for the determination and identification of polycyclic aromatic hydrocarbons in vegetable oils

An on-line combination of liquid chromatography, gas chromatography and mass spectrometry has been realized by coupling a quadrupole mass spectrometer to an LC-GC apparatus. Liquid chromatography was used for sample pretreatment of oil samples of different origin. The appropriate LC fraction, containing polycyclic aromatic hydrocarbons, was transferred to the gas chromatograph using a loop-type interface. After solvent evaporation through the solvent vapour exit and subsequent GC separation, the compounds were introduced into the mass spectrometer for detection and identification. The GC column was connected to a short piece of deactivated fused silica that protruded into the ion source. The total analytical set-up allowed the direct analysis of oil samples after dilution in n-pentane without any sample clean-up. Detection limits are about 40 pg in the full scan mode and about 1 pg with selective ion monitoring, i.e. 20 ppb and 0.5 ppb respectively.

Coupled LC‐GC: Evaporation rates for partially concurrent eluent evaporation using an early solvent vapor exit

AbstractPartially concurrent eluent evaporation presupposes an eluent evaporation rate in the GC pre‐column that approaches the LC flow rate. Discharging the vapors through the whole GC column, evaporation rates reach 10–30 μl/min, i.e. are suitable just for LC flow rates typical for packed capillary LC columns. With an early vapor exit, evaporation rates are increased to 100–200 μl/min (under extreme conditions to some 800 μl/min), thus fitting the LC flow rates of 2 mm i.d. columns.Evaporation rates were measured for a standard set of pre‐columns and conditions. The dependence of the evaporation rate on temperature, inlet pressure, carrier gas, and internal diameter of the retaining pre‐column are discussed in order to allow the design of a GC system producing a desired evaporation rate.

Early solvent vapor exit in GC for coupled LC‐GC involving concurrent eluent evaporation

AbstractUse of early solvent vapor exits for concurrent eluent evaporation with the loop‐type interface has two purposes: protection of the GC detectors from large amounts of solvent vapors and more efficient discharge of the vapors to accelerate eluent evaporation and help avoiding broad solvent peaks. Use of a retaining pre‐column after the uncoated pre‐column can rule out losses of solute materials that form sharp peaks.

Analysis of dicamba in tobacco by on-line coupled liquid chromatography—gas chromatography

A new analysis procedure for determining dicamba in dried tobacco is presented. The method consists of a simple sample extraction followed by esterification and a final analysis using on-line coupled liquid chromatography-gas chromatography ( LC—GC). Clean-up and preseparation of a sample is by LC and the fraction of interest is analysed using GC with electron-capture detection. The conditions during sample transfer produce concurrent solvent evaporation and vapours are vented out through a solvent vapour exit placed after the separation column. The detection limit is low and the method is simple and sensitive.