Concurrent Eluent Evaporation Research Articles

Programmed temperature vaporizing injector to filter off disturbing high boiling and involatile material for on-line high performance liquid chromatography gas chromatography with on-column transfer

Insertion of a programmed temperature vaporizing (PTV) injector under conditions of concurrent solvent recondensation (CSR) into the on-line HPLC–GC interface for on-column transfer (such as the retention gap technique with partially concurrent eluent evaporation) enables filtering off high boiling or involatile sample constituents by a desorption temperature adjusted to the required cut-off. Details of this technique were investigated and optimized. Memory effects, observed when transferred liquid was sucked backwards between the transfer line and the wall of the injector liner, can be kept low by a small purge flow rate through the transfer line at the end of the transfer and the release of the liquid through a narrow bore capillary kept away from the liner wall. The column entrance should be within the well heated zone of the injector to prevent losses of solute material retained on the liner wall during the splitless period. The desorption temperature must be maintained until an elevated oven temperature is reached to prevent peak broadening resulting of a cool inlet section in the bottom part of the injector.

Wax ester fraction of edible oils: Analysis by on‐line LC‐GC‐MS and GC×GC‐FID

AbstractThe wax ester fraction of various plant oils was isolated by normal‐phase HPLC (NPLC) on‐line coupled to GC via the on‐column interface and applying concurrent eluent evaporation. The esters were analyzed by on‐line NPLC‐GC‐MS and by comprehensive two‐dimensional GC with flame ionization detection (GC×GC‐FID) off‐line combined with NPLC‐GC. GC×GC‐FID enables to group the various classes of wax esters, in particular the phytol esters, geranylgeraniol esters and the straight‐chain esters of palmitic acids and the unsaturated C18 acids. Optimization of the GC×GC columns and the conditions must take into account the limited thermostability of the diterpene esters. Chromatograms are shown for a range of oils, with particular focus on the various classes of wax esters in olive oil and the geranylgeraniol esters 22:0 and 24:0 in a variety of oils.

Characterisation of organic compounds in aerosol particles from a Finnish forest by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry.

During the European Union project Quantification of Aerosol Nucleation in the European Boundary Layer (QUEST), which began in spring 2003, atmospheric aerosol particles were collected in a Finnish Scots pine forest using a high-volume sampler. The organic compounds in the filter samples were then analysed by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry (SFE-LC-GC-MS). The sample was first extracted by SFE. During LC the extracts were fractionated into three fractions according to polarity. The final separation was carried out by GC-MS. A fraction volume as high as 840 microL was transferred to the GC, using the partial concurrent eluent evaporation technique. The same instrumentation, with an in-situ SFE derivatisation method, was used to analyse organic acids. Major compounds such as n-alkanes and PAH were analysed quantitatively. Their concentrations were lower than those usually observed in urban areas or in other forest areas in Europe. The wind direction was one of the most important factors affecting changes in the daily concentrations of these compounds. Scots pine needles were analysed with the same system to obtain reference data for identification of biogenic compounds in aerosol particles. Other organic compounds found in this study included hopanes, steranes, n-alkanals, n-alkan-2-ones, oxy-PAH, and alkyl-PAH; some biogenic products, including oxidation products of monoterpenes, were also identified.

On‐line solvent evaporator for coupled normal phase‐reversed phase high‐performance liquid chromatography systems: Heavy polycyclic aromatic hydrocarbons analysis

AbstractAn on‐line system for coupling a normal phase liquid chromatography (LC) column to a reversed‐phase LC column is described. The interface consists of an on‐line solvent evaporator working on the principles of concurrent eluent evaporation and vapor overflow, and two additional 10 port valves. Optimization of the on‐line procedure as well as recoveries, repeatability and linearity characteristics were tested in a simplified system simulating determination of heavy polycyclic aromatic hydrocarbons in edible oils. An application on a real extra virgin olive oil sample is also reported. © 2001 John Wiley & Sons, Inc. J Micro Sep 13: 13–18, 2001

Determination of solvent recondensation or evaporation in the GC‐precolumn by measurement of temperature changes on the column wall

AbstractTemperature measurements on the column outer well were used for detecting recondensation or evaporation of solvent inside the precolumn during injection or on‐line transfer of large solvent volumes. This facilitates the choice of the most critical parameter of these techniques, i.e. oven temperature. When using the vaporizer/precolumn solvent split/gas discharge system, the dew point of the solvent is determined, either to just prevent solvent recondensation or to limit it to the capacity of the precolumn to retain liquid. In concurrent eluent evaporation through the loop type LC‐GC interface, temperature measurement enables the determination of whether or not the flooded zone exceeds a given limit. Fanally, when solvent trapping is used (on‐column injector/partially concurrent solvent evaporation evaporation or vaporizer/partial recondensation), temperature measurement near the front end of the flooded zone is used as a signal for accurate closure of the vapor exit shortly before the end of solvent evaporation.

Determination of acylglycerols in vegetable oil methyl esters by on‐line normal phase LC‐GC

AbstractAn on‐line LC‐GC method for the analysis of mono‐, di‐, and triacylglycerols in vegetable oil methyl esters has been developed. The concentrations of these components have turned out to be key parameters for the quality of diesel fuel substitutes. Separation of all classes of acylglycerols from the fatty acid methyl ester matrix is achieved by LC after acetylation of the hydroxyl groups. The acylglycerol fraction is transferred on‐line to GC, using the loop‐type interface and concurrent eluent evaporation. Quantification of mono‐, di‐, and triacylglycerols is performed by combining external calibration with internal standardization. Both recovery of the procedure and reproducibility of the quantitative results are evaluated.

Liquid chromatographic sample cleanup coupled on-line with gas chromatography in the analysis of beta-blockers in human serum and urine.

An on-line coupled reversed-phase liquid chromatographic-gas chromatographic (LC-GC) method with minimal manual sample preparation is developed for the analysis of metoprolol, oxprenolol, propranolol, timolol, and codeine (as an internal standard) in human serum and urine. The method is based on a loop-type interface and concurrent eluent evaporation technique. On-line liquid-liquid extraction (LLE) is used to extract the analytes from aqueous eluent to organic solvent before injection onto the GC, and the two phases are separated with a sandwich-type phase separator. The LC is used for cleanup, and the GC is used for the final separation and detection of the analytes. Total analysis time is less than 45 min, which is much less than those of traditional analysis methods. Recoveries in LC cleanup and on-line LLE are excellent. A marked increase in the recoveries with on-line LLE is obtained by heating the aqueous eluent and the extraction coil. Linearity and repeatability of the method are good for both serum and urine, and the limits of quantitation for the analytes are 18-44 ng/mL.

Determination of morphine and its analogues in urine by on-line coupled reversed-phase liquid chromatography-gas chromatography with on-line derivatization

An on-line coupled reversed-phase liquid chromatography-gas chromatography (RPLC-GC) method requiring minimal manual sample preparation was developed for the determination of morphine, codeine, heroin, dihydrocodeine and ethylmorphine in urine. A loop-type interface and concurrent eluent evaporation technique were used in the coupling, and the aqueous phase was changed to organic solvent by continuous liquid-liquid extraction before transfer to the GC. The two phases were separated with a sandwich-type phase separator. The analytes were also derivatized on-line before GC separation. The LC was used for clean-up, and the GC for the final separation and detection of the analytes. Total analysis time was less than 60 min, which is much shorter than with traditional analysis methods. A marked increase in the recoveries in liquid-liquid extraction (LLE) was obtained by heating the aqueous eluent and the extraction coil. Linearity and repeatability of the method were good and the limits of quantification for the analytes were between 61 and 92 ng/ml.

Screening of four beta‐blockers and codeine in urine by on‐line coupled RPLC‐GC with on‐line derivatization

AbstractOn‐line coupled reversed phase liquid chromatography‐capillary gas chromatography (RPLC‐GC) was used in the separation of four derivatized beta‐blockers and codeine in urine. Sample clean‐up was accomplished in the LC part and compounds were separated in the GC part. After the LC column the aqueous phase was switched to organic solvent by on‐line liquid‐liquid extraction and the two phases were separated in a sandwich‐type phase separator. The organic extract was then transferred to a loop‐type LC‐GC interface. Beta‐blockers were derivatized on‐line in the interface before GC analysis. Concurrent eluent evaporation was used during the introduction of the sample fraction, and excess of solvent vapors was removed via an early vapor exit. The sample pretreatment was minimal; the only manual pretreatment step was the filtration of the urine sample.

On‐line HPLC‐HRGC coupling and simultaneous transfer of two different LC fractions: Determination of aliphatic alcohols and sterols in olive oil

AbstractA modified loop‐type interface is decribed which uses two 6‐way valves and concurrent eluent evaporation to perform an on‐line transfer and simultaneous gas chromatographic analysis of two different fractions pre‐separated by liquid chromatography. The interface is used to simultaneously analyze aliphatic alcohols and sterols present in olive oil. LC pre‐separation is carried out using a normal phase column (20 cm × 0.21 cm i.d.) and hexane‐isopropanol (99:1) as a mobile phase at a flow of 0.2 ml/min; for the GC analysis a 5 % phenyl, 95 % dimethyl siloxane (25 m × 0.32 mm i.d., 0.4 μm film thickness) column is used.

On‐line LC‐GC transfer via a hot vaporizing chamber and vapor discharge by overflow; increased sensitivity for the determination of mineral oil in foods

AbstractThe modified LC‐GC transfer technique with concurrent eluent evaporation reduces losses of volatile components. The LC fraction is transferred by the LC pump. Evaporation occurs in a heated capillary into which a piece of wire is introduced. Vapors are discharged by overflow. This enables the reduction of the oven temperature to the minimum that prevents recondensation and to obtain more efficient phase soaking for the retention of volatile solutes. The technique was applied to improve sensitivity of the analysis of mineral oil in foods. © 1995 John Wiley & Sons, Inc.

On-line liquid chromatography—gas chromatography for the analysis of free and esterified sterols in vegetable oil methyl esters used as diesel fuel substitutes

An on-line LC—GC method for the analysis of free and esterified sterols in vegetable oil methyl esters has been set up. Qualitative and quantitative information about this important group of minor components is provided without saponification and off-line pre-separation. Prior to analysis the free sterols are silylated with N-methyl-N-trimethylsilyltrifluoroacetamide; betulinol is used as an internal standard. Using concurrent eluent evaporation with the loop-type interface for eluent transfer, transfer temperature and transfer efficiency are carefully optimized. The concentration of the free sterols as well as their qualitative and quantitative composition and the concentration of the sterol esters are determined in five different types of vegetable oil methyl esters. The recovery of the LC—GC procedure and the reproducibility of the quantitative results are evaluated.

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.

Food contamination by hydrocarbons from packaging materials determined by coupled LC-GC

Paraffins from raw extracts of foods and packing materials were isolated by LC and directly transferred to GC, applying concurrent eluent evaporation and a loop-type interface. Paraffins from various packing materials have been characterized: sisal bags, cardboard boxes, plastic films, wax-coated paper and cardboard as well as paraffin coatings. Important food contamination was found for sisal bags, cardboard boxes, and wax-coated paper/cardboard. Contamination by paraffin coatings on cheese was surprisingly small.

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.

Partially concurrent eluent evaporation with an early vapor exit; detection of food irradiation through coupled LC‐GC analysis of the fat

AbstractThis paper reports two subjects. It describes LC‐GC transfer by partially concurrent eluent evaporation at a greatly accelerated rate, as required for optimal compatibility with 2–3 mm i.d. LC columns and LC flow rates up to some 500 μl/min. Evaporation rates around 200 μl/min were obtained using a 0.53 mm. i.d. uncoated pre‐column and an early vapor exit. A stationary‐phasecoated “retaining” pre‐column was used for preventing escape of volatile solutes through the vapor exit.The technique was used for the detection of food irradiation by analyzing selected radiolysis products of triglycerides, namely alkanes/alkanes and aldehydes. Extracted fat of chicken, hazel‐nuts, and soup mixes was injected in LO and the relevant fractions were transferred on‐line to GC. For chicken and nuts, detection of irradiation was possible down to doses below 0.5 kGy. Detection limits were higher for soup mixes due to interfering peaks.

Concurrent eluent evaporation with co-solvent trapping for on-line reversed-phase liquid chromatography gas chromatography : Optimization of conditions

The pressure drop over a restriction built into the carrier gas supply line allows monitoring of the carrier gas flow-rate during transfer of a liquid chromatographic eluent into a gas chromatograph. A high inlet pressure indicates blockage of the gas flow by the plug of sample liquid; a layer of evaporating solvent still reduces the flow-rate owing to its vapour pressure, causing the inlet pressure to remain above that prior to transfer. The decrease in the inlet pressure at the end of the transfer provides the signal for closing the vapour exit, but also gives information for the optimization of the co-solvent concentration in the sample and of the column temperature during transfer. The co-solvent peak within the highly attenuated solvent peak indicates the amount of co-solvent left in the precolumn after the main solvent has been fully evaporated, helping to find the optimum co-solvent concentration in the sample.

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.

Simple high-performance liquid chromatographic methods for resolving complex mixtures

~1) had to be transferred. HPLC-GC transfer was automated, allowing the instrument to be situated in a production plant and run by non-laboratory personnel . Maris et a1.16 determined PCBs in sediment samples using HPLC for sample clean-up. Excellent agreement of the HPLC-GC results with GC results obtained with conventional sample pre-treatment was found. Volumes of 1804 were transferred into a 5-m uncoated pre-column using the retention-gap technique with efficient partially concurrent eluent evaporation (on-column interface). Results of another study17, viz. on the determination of organochlorine pesticides in surface water are shown in Fig. 3. Towards automated analysis Automation in the sense of applying autosamplers has become common practice. However, in view of the tremendous work involved in sample preparation, this represents automation of only a small portion thereof. More recently, robotics were introduced for automating simple manual routine work. However, robotics only allow automation of classical, inefficient techniques. We need higher separation power for removing by-products, to achieve more efficient sample preparation in fewer steps, and, ideally, these steps should be integrated on-line into the final analysis. Column switching techniques in HPLC are one approach towards this end. From this point of view, automated coupled HPLC-GC should become a must for all laboratories that must analyze large numbers of complex samples efficient1Y.

Coupled reversed-phase liquid chromatography—capillary gas chromatography for the determination of atrazine in water

A fully automatable method for determining atrazine in water is described, based on enrichment of the atrazine from 10 ml of water on a small ODS liquid chromatographic column, desorption with methanol-water (60:40) + 5% 1-propanol and transfer to a gas chromatograph by concurrent eluent evaporation using a loop-type interface. The total analysis time is 35 min with a detection limit of ca. 3–5 ppt. Concurrent eluent evaporation of aqueous eluent mixtures suffers from a large temperature difference between transfer and elution of the first sharp peaks. On transfer at 112°C, the atrazine peaks were perfectly shaped only when eluted at about 250°C.