Solvent Vapor Exit Research Articles

Research Progress of Analysis of Mineral Oil Hydrocarbons using On-line High Performance Liquid Chromatography Coupled with Gas Chromatography

Abstract In the past decades, the application of on-line high performance liquid chromatography coupled with gas chromatography (HPLC-GC) has been rapidly developed for the quantitative analysis of mineral oil hydrocarbons (MOH). MOH are derived from petroleum and synthetic fuels, and cover a large range of boiling points, mainly consisting of mineral oil saturated hydrocarbons (MOSH) and aromatic hydrocarbons (MOAH). MOH can migrate into food and environment through a variety of pathways, consequently impose an adverse impact on human health. However, the analysis of MOH is challenging due to the limited selectivity and sensitivity of hydrogen flame ionization detector (FID). On-line HPLC-GC combines the high separation efficiency of HPLC with the equal-carbon-response detection of GC-FID, which solves the problems associated with selectivity and sensitivity of MOH analysis. The innovation of the retention gap, Y-piece interface, and solvent vapor exit (SVE) with which the HPLC-GC is equipped enables large-volume injection into GC-FID. By allowing the elution fractions from HPLC to be completely transferred into the GC, the analytical sensitivity of the MOH is enhanced by more than two orders of magnitude, and the contaminants introduced are minimized during the analytical procedure, ensuring the reproducibility and accuracy of the MOH analysis. In this paper, the research history of the interfaces used in on-line HPLC-GC and the matching conditions between HPLC and GC were described in detail, and the sample preparation methods for the removal of interferences and the enrichment of MOH based on HPLC-GC were reviewed. In addition, the limitations of HPLC-GC were summarized, and the future applications of this technology and the trends in the development of MOH analysis were prospected.

On-line coupling of solid-phase extraction to gas chromatography–mass spectrometry to determine musk fragrances in wastewater

An on-line coupling solid-phase extraction (SPE) has been developed for the first time to preconcentrate trace amounts of 17 musk fragrances extensively used in personal care products (6 polycyclic musks, 3 nitro musks, 7 macrocyclic musks and 1 polycyclic musk degradation product) from wastewater samples, prior to analysis by gas chromatography and mass spectrometry through an on-column interface. A 10mm×2mm I.D. precolumn packed with Oasis HLB (60μm) or C18 (60μm) was compared for the optimization of the solid-phase extraction process. The parameters affecting the transfer of the analytes from the precolumn to the GC system (e.g. flow-rate, temperature and solvent vapor exit time) as well as SPE parameters (e.g. sample flow, sample volume, elution solvent, etc.) were optimized. An organic modifier such as methanol was added to the sample before the extraction process to avoid adsorption problems. The use of the MS detector under selected ion monitoring acquisition enabled the analytes to be quantified at low ngL−1 levels, preconcentrating only 10mL of sample, and the limits of detection were between 1 and 30ngL−1. The method was applied for the determination of musk fragrances in wastewater samples from three urban wastewater treatment plants (WWTPs). The analysis of influent urban wastewater revealed that galaxolide, tonalide and ambrettolide were the most abundant musk compounds with concentrations ranging between 18ngL−1 and 45,091ngL−1, 852ngL−1 and 49,904ngL−1 and 507ngL−1 and 21,528ngL−1 respectively. The remaining musks were present at lower concentrations and two of the macrocyclic musk studied (musk MC4 and civetone) were not detected. The analysis of effluent wastewater showed a decrease in the concentrations of all of the compounds present in influent samples, with the decrease being more significantly in the case of polycyclic and nitro musks than for macrocyclic musks. Only HHCB-lactone remained constant or increased its concentration.

Applications of large-volume injection for environmental analysis

Large-volume injection (LVI) in capillary gas chromatography (CGC) was developed for determining the trace components in environmental samples and for reducing (or even eliminating) the need for cleanup step, also for on-line connection of liquid chromatography (LC) with CGC. The key features of the LVI include sample retained by a large capacity volume liner or a retention gap, and solvent vapor eliminated by solvent vapor exit. There are many kinds of LVI techniques for different analyses, capillary columns and purposes. This review summarizes the recent developments of LVI for environmental analysis, include on column injection (OCI), programmed temperature vaporizer (PTV), AT-column, direct sample introduction/difficult matrix injection, concurrent solvent recondensation large volume splitless injection, and also through oven transfer adsorption desorption interface for on-line connection of LC with CGC.

A study of large-volume on-column injection GC–ECD for the ultratrace analysis of organochlorine pesticides in water

In this work, a large-volume on-column injection method for the analysis of 21 organochlorine pesticides, including HCH isomers, DDT derivatives and cyclodiene derivatives, was optimized. The solvent selected to carry out the study was ethyl acetate and the injection volume was 100 μl. Some factors were introduced in a Plackett–Burman design to determine their influence in the vaporization efficiency. The significant factors were then studied by a univariate procedure and sorted according to their importance on the response. The effect of the injection conditions on the peak resolution was also noted. The conditions selected according to sensitivity and resolution were: initial oven temperature 75 °C, injection speed 20 μl s −1, solvent vapor exit (SVE) valve closure time 60 s, initial pressure 100 kPa and isothermal oven time 1 min. Analytical characteristics expressed in terms of precision, linear range, and limit of detection have been determined and compared with those obtained by splitless injection. The degradation of endrin and p,p′-DDT thermolabile pesticides was evaluated for both injection techniques. Finally the developed method was successfully applied to the ultratrace analysis of pesticides in natural waters. With this purpose a micro liquid–liquid extraction method using 2 ml of ethyl acetate to extract 10 ml of water sample was proposed. Recoveries between 69 and 107% were obtained with a very good precision (0.2–1.3%) for the studied pesticides, except for p,p′-DDD. Detection limits between 0.3 and 25 ng l −1, which fulfill the limits established by the new water directive 2008/105/EC, were achieved. The MLLE method was compared with the SPE method by the analysis of some water samples using both procedures, and good concordance was obtained.

Large Volume Cold On-Column Injection for Gas Chromatography−Negative Chemical Ionization−Mass Spectrometry Analysis of Selected Pesticides in Air Samples

A new gas chromatographic method is described for the analysis of fungicides captan, captafol, and folpet from organic extracts of air samples using large volume injection (LVI) via a cold on-column (COC) inlet coupled with gas chromatography-negative chemical ionization-mass spectrometry (GC-NCI-MS). Although standard split/splitless injection due to high injection port temperatures (>225 degrees C) have been shown to degrade these thermally labile fungicides, COC injection minimizes degradation. Insecticides such as chlorpyrifos and diazinon were also examined to show added selectivity. By using a solvent vapor exit with the COC inlet, injection volumes of 10-100 microL can be made to lower detection levels. GC-NCI-MS was compared to GC-electron impact ionization-mass spectrometry for each pesticide using LVI-COC injections and was found to be 2-80 times more sensitive, depending on the pesticide. Method detection limit (MDL) values with 100 microL injections were 2.5 microg L-1 for captan, folpet, and diazinon, 5.0 microg L-1 captafol, and 1.0 microg L-1 for chlorpyrifos, with the normal working range examined for sample analysis from MDL to 100 microg L-1. Detection of all pesticides except captafol, used only in the United States but not Canada, was demonstrated from air samples taken from Abbotsford, British Columbia, Canada.

Large volume injection GC‐MS in electron capture negative ion mode utilizing isotopic dilution for the determination of polybrominated diphenyl ethers in air

AbstractA large volume injection GC‐MS method for the determination of polybrominated diphenyl ethers (PBDEs) is presented. A loop‐type injection system with an early solvent vapor exit has been constructed and evaluated. With this system sample volumes up to 500 μL could be injected with high reproducibility and low carry‐over. The peak distortion problem associated with this kind of injection system is discussed in detail and solutions are suggested. We also introduce 13C‐labeled BDE‐209 as internal surrogate standard for the determination of high molecular weight PBDEs in low‐resolution mass spectrometry electron capture negative ionization mode. The complete method has been applied to air samples from an electronic waste dismantling facility, collected with personal exposure measurement equipment. Nine BDE congeners have been identified and quantified.

Enhanced Detection of Nitroaromatic Explosive Vapors Combining Solid-Phase Extraction-Air Sampling, Supercritical Fluid Extraction, and Large-Volume Injection-GC

A complete method for sampling and analyzing of energetic compounds in the atmosphere is described. The method consists of the hyphenation of several techniques: active air sampling using a solid-phase extraction cartridge to collect the analytes, extraction of the sorbed analytes by toluene/methyl tert-butyl ether modified supercritical fluid extraction (SFE), and analysis of the extract by large-volume injection GC-nitrogen/phosphorus detection. The GC system is equipped with a loop-type injection interface with an early solvent vapor exit, a utilizing concurrent solvent evaporation technique. Chemometric approaches, based on a Plackett-Burman screening design and a central composite design for response surface modeling, were used to determine the optimum SFE conditions. The relative standard deviations of the optimized method were determined to be 4.3 to 7.7%, giving raise to method detection limits ranging from 0.06 to 0.36 ng in the sampling cartridge, equivalent to 6.2-36.4 pg/L in the atmosphere, standard sampling volume 10 L. The analytical method was applied to characterize headspace composition above military grade trinitrotoluene (TNT). Results confirm that 2,4-dinitrotoluene (DNT) and 1,3-dinitrobenzene (DNB) constitute the largest vapor flux, but TNT, 2,6-DNT, and trinitrobenzene TNB were also consistently detected in all the samples.

Automated rotary valve injection for polybrominated diphenyl ethers in gas chromatography

AbstractA simple, automated rotary valve injector for gas chromatography was constructed and evaluated for injection of polybrominated diphenyl ethers with molecular weights ranging from 485 to 949 Dalton. These congeners, particularly those with nine and ten bromine substituents, constitute a severe problem when a split/splitless vaporizing injector is used for gas chromatographic determination of polybrominated diphenyl ethers. Volumes up to 50 μL were injected without the need for a solvent vapor exit. Discrimination of the high molecular weight brominated diphenyl ether congeners with seven to ten bromine substituents is strongly reduced. The injector exhibits both high reproducibility and low carry‐over effects. Average relative standard deviation of the absolute peak area was less than 3.5% and for the carryover it was less than 0.4%. An important observation is that the electron capture detector response factors remained constant independent of injection volume, allowing large volume injection to decrease sample concentration detection limits, which is an important feature regarding determination of high molecular weight polybrominated diphenyl ethers. A further advantage is that the rotary valve large volume injector facilitates on‐line coupling of various clean‐up systems to the gas chromatograph.

Role of the retaining precolumn in large-volume on-column injections of volatiles to gas chromatography

In the present study the retaining precolumn, which is commonly used in a set-up for large-volume on-column injections, or when solid-phase extraction (SPE) or liquid chromatography is coupled to gas chromatography (GC), was removed after varying its length from the standard length of 3 m down to zero. A dramatic increase of the evaporation rate of the injected organic solvent was obtained from a typical value of 100 μl/min up to 300 μl/min. The increased evaporation rate allowed (i) injection of a larger volume in the same retention gap, (ii) faster injection/transfer of the organic solvent and (iii) reduction of the transfer temperature. As volatile compounds under partially concurrent solvent evaporation conditions are easily lost once the organic solvent has been removed via a solvent-vapour exit (SVE), the parameters for large-volume injection, i.e. the evaporation rate and injection speed, were optimised using accurate measurements of the real flow-rate of the carrier gas into the GC system. All these options have been evaluated over the last 4 years. In order to demonstrate that omitting the retaining precolumn had no effect on the application range of the on-column interface, analytes as volatile as benzene were injected into GC–MS using 50–200 μl of n-pentane solutions. Contaminants were extracted from river water and wastewater into n-pentane using in-vial liquid–liquid extraction. The detection limits for benzene, toluene, ethylbenzene and m-xylene were ∼10 ng/l. To obtain optimum results the SVE had to be closed 1 s before the end of evaporation. Several brands of n-pentane were analysed to check for the presence of benzene. Most of them contained interfering compounds and benzene at the low μg/l level and therefore had to be cleaned by means of column chromatography. As another example C 8–C 17 alkylphenones were extracted from wastewater with n-hexane. Detection limits were 10–40 ng/l.

Investigations on analyte losses in systems suited for large-volume on-column injections

Use of a large-volume injection system with a solvent vapour exit (SVE) requires optimisation. An appropriate strategy is to determine the evaporation rate by increasing the injection time at a fixed injection speed, injection temperature and head pressure. When measuring the flow rate in the carrier gas supply line to the on-column injector, optimisation can be very rapid: some five injections of pure solvent will be sufficient.

Standard on-column injection: A fast and simple method for large volume injection in medium-resolution gas chromatography

In gas chromatography (GC) large volume injection of samples containing very high molecular weight analytes presents unique problems. Standard programmed-temperature vaporizing or on-column large volume injection systems cannot be used, mainly due to instrumental difficulties. A new, simple solution to this problem is presented. If short, wide-bore columns are used at carrier gas velocities above optimum, the cloud of vapor formed upon evaporation of the solvent can be rapidly discharged from the system by the column flow alone. Hence, in medium-resolution GC, large sample volumes (e.g., 50 μL) can be injected using a standard on-column injector. Neither a retention gap nor a solvent vapor exit is needed. The absence of column connectors makes this setup extremely rugged. The optimization of the direct on-column large volume injection is described. The applicability of the new technique for the injection of large volumes of triacylglycerides and heavy mineral oil fractions is shown. It is demonstrated that the new technique is relatively insensitive toward solvent composition. This makes the new method eminently suited for combination with gradient liquid chromatography preseparations. © 2000 John Wiley & Sons, Inc. J Micro Sep 12: 523–529, 2000

Optimization of large-volume on-column injection conditions in gas chromatography by monitoring the actual carrier gas flow

The change of the evaporation rate of the solvent during injection and evaporation is the most critical aspect during optimization of large-volume on-column injection conditions in gas chromatography. The change is caused by the pressure drop along the retention gap when using an early solvent vapour exit (SVE) and can be described by a mathematical model. Four procedures for the optimization of the injection conditions were compared. It was found that different procedures often yield different evaporation rates, which may also depend on the injection speeds used during optimization. For optimization of a new set-up, i.e. if little is known about the optimal injection conditions, the evaporation rate should be determined by increasing the injection time at a fixed injection speed, injection temperature and head pressure; subsequently, an appropriate injection speed can be calculated. If a mere re-optimization is required as e.g. after the exchange of the retention gap, adjusting the evaporation rate to the injection speed by varying the injection temperature at a constant injection speed is the preferred procedure. With both methods, optimization can be achieved by means of 2–5 injections of pure solvent and monitoring the helium carrier gas flow. That is, optimization of the injection conditions takes less than 1 h. When using this strategy, analytes as volatile as monochlorobenzene can be determined in aqueous samples by in-vial liquid–liquid extraction–gas chromatography–mass spectrometry. Closing the SVE at the very end of solvent evaporation results in a considerable increase of the capacity of the retention gap compared to closing the SVE before all solvent is evaporated.

Capacity of Uncoated 0.53 mm i.d. Pre-Columns for Retaining Sample Liquid in the Presence of a Solvent Vapor Exit

Capacity of Uncoated 0.53 mm i.d. Pre-Columns for Retaining Sample Liquid in the Presence of a Solvent Vapor Exit

Automated On-Line GPC-GC-FPD Involving Co-Solvent Trapping and the On-Column Interface for the Determination of Organophosphorus Pesticides in Olive Oils

The robustness of an automated on-line GPC-GC-FPD method for the determination of Organophosphorus (OP) Pesticides in olive oil has been significantly improved, now allowing a routine operation. The original GPC-GC transfer technique employed a loop type interface with an early vapor exit and co-solvent trapping. Shooting, caused by boiling delay and malfunctioning of the solvent vapor exit during the transfer of the 3 mL solvent fraction to the retention gap, resulted in insufficient focusing of the OP-pesticides. In this interfacing concept, the GPC fraction is introduced directly into the carrier gas stream during a certain time interval using the Dualchrom pressure- and flow regulation, resulting in a very stable transfer. The interface now basically corresponds to an on-column interface with flow regulation. Via a Pyrex glass door behind the GC-oven door it can be seen that the liquid flow is broken up into alternating gas-liquid segments by the carrier gas flow during transfer. This avoids shooting in the retention gap and broadens the temperature range for successful transfer. By using a smaller sized GPC column the solvent fraction transferred was reduced to 1.3 mL. Methyl acetate/cyclopentane and the co-solvent n-nonane were selected for their lower boiling points. The modified method is very robust and has been applied to the analysis of 28 different OP-pesticides in olive oil with an overall detection limit of 0.002 mg/kg. Routinely 24 h of unattended operation is possible with a cycle time of 75 min.

Automated On-Line GPC-GC-FPD Involving Co-Solvent Trapping and the On-Column Interface for the Determination of Organophosphorus Pesticides in Olive Oils

The robustness of an automated on-line GPC-GC-FPD method for the determination of Organophosphorus (OP) Pesticides in olive oil has been significantly improved, now allowing a routine operation. The original GPC-GC transfer technique employed a loop type interface with an early vapor exit and co-solvent trapping. Shooting, caused by boiling delay and malfunctioning of the solvent vapor exit during the transfer of the 3 mL solvent fraction to the retention gap, resulted in insufficient focusing of the OP-pesticides. In this interfacing concept, the GPC fraction is introduced directly into the carrier gas stream during a certain time interval using the Dualchrom pressure- and flow regulation, resulting in a very stable transfer. The interface now basically corresponds to an on-column interface with flow regulation. Via a Pyrex glass door behind the GC-oven door it can be seen that the liquid flow is broken up into alternating gas-liquid segments by the carrier gas flow during transfer. This avoids shooting in the retention gap and broadens the temperature range for successful transfer. By using a smaller sized GPC column the solvent fraction transferred was reduced to 1.3 mL. Methyl acetate/cyclopentane and the co-solvent n-nonane were selected for their lower boiling points. The modified method is very robust and has been applied to the analysis of 28 different OP-pesticides in olive oil with an overall detection limit of 0.002 mg/kg. Routinely 24 h of unattended operation is possible with a cycle time of 75 min.

On-line coupling of solid-phase extraction to gas chromatography with mass spectrometric detection to determine pesticides in water

A group of pesticides with different chemical structures was determined in water by on-line coupling of solid-phase extraction to gas chromatography with mass spectrometric detection through an on-column interface. A 10 mm×2 mm I.D. precolumn packed with PLRP-S was selected for the solid-phase extraction process. The parameters affecting the transfer of the analytes from the precolumn to the GC system (e.g. flow-rate, temperature and solvent vapor exit time) were optimized. An organic modifier was added to the sample before the extraction process to avoid adsorption problems. The use of the MS detector under selected ion monitoring acquisition enabled the analytes to be quantified at sub microgram-per-litre levels preconcentrating only 10 ml of sample, and the limits of detection ( S/ N=3) were between 2 and 20 ng l −1. The method was applied to the determination of the pesticides in tap and river water, and molinate was determined in Ebro river water.

Monitoring the actual carrier gas flow during large-volume on-column injections in gas chromatography as a means to automate closure of the solvent vapour exit

Monitoring of the helium flow into a gas chromatograph (GC) by means of an electronic flow meter has been used to optimize and control large-volume on-column injections. The nature of the observed carrier gas flow-rate profiles is discussed in some detail. A rather strong dependence of the evaporation rate on the injection speed was found for injections into a 0.32 mm I.D. retention gap, which can be attributed to the pressure drop along the retention gap when using a solvent vapour exit (SVE). The variation of the evaporation rate with the injection speed was found to be less critical for a 0.53 mm I.D. retention gap. The carrier gas flow-rate profile during the actual injection was used to effect the automated closure of the SVE precisely at the end of the evaporation process. Retention gaps of 0.53 mm I.D. were preferred over 0.32 mm I.D. retention gaps, as 0.53 mm I.D. retention gaps allowed a clearer detection of the end of the evaporation process. Compared with the conventional procedure which involves closure of the SVE at a predetermined time, the present approach is more robust and hardly any optimization is required; it did not cause losses of volatile analytes. The procedure considerably simplifies the use of large-volume on-column injections. Large-volume injections of alkanes were used to study the potential of the large-volume injection–GC system.

In-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of anilines in tap, surface, and wastewater

In this study miniaturized liquid–liquid extraction carried out in an autosampler vial was used to determine a series of anilines in tap, surface, and industrial wastewater. The analytes were extracted from the aqueous phase into n-hexane and 100 μl of the extract, i.e., 10–20%, was injected into the gas chromatography (GC) system using an on-column injector in combination with a deactivated uncoated fused silica capillary (retention gap) and an early solvent vapor exit. A mass spectrometer was used for detection and identification. The parameters for large-volume injection, i.e., the evaporation rate, speed of injection, and injection temperature, were optimized using accurate measurement of the actual flow rate of the carrier gas into the GC system. This measurement was used as input for a solvent vapor-exit controller, which was equipped with a microprocessor for determination of the endpoint of the evaporation process. The optimum conditions for an injection volume of 100 μL of n-hexane are reported. Extraction with a water-to-n-hexane-ratio (1:1, v/v) gave quantitative recoveries except for aniline (46%). The addition of sodium chloride improved the extraction yield for aniline about 10%. Linear calibration curves were obtained in the 0.01–1-μg/L concentration range, relative standard deviations were less than 10%, and detection limits typically were 4–20 ng/L for GC–mass spectrometry in the multiple-ion-detection mode. The total procedure allowed the analysis of unfiltered water samples; that is, no sample treatment was necessary. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 581–588, 1998

In‐vial liquid–liquid extraction with subsequent large‐volume on‐column injection into GC–MS for the determination of anilines in tap, surface, and wastewater

In this study miniaturized liquid–liquid extraction carried out in an autosampler vial was used to determine a series of anilines in tap, surface, and industrial wastewater. The analytes were extracted from the aqueous phase into n-hexane and 100 μl of the extract, i.e., 10–20%, was injected into the gas chromatography (GC) system using an on-column injector in combination with a deactivated uncoated fused silica capillary (retention gap) and an early solvent vapor exit. A mass spectrometer was used for detection and identification. The parameters for large-volume injection, i.e., the evaporation rate, speed of injection, and injection temperature, were optimized using accurate measurement of the actual flow rate of the carrier gas into the GC system. This measurement was used as input for a solvent vapor-exit controller, which was equipped with a microprocessor for determination of the endpoint of the evaporation process. The optimum conditions for an injection volume of 100 μL of n-hexane are reported. Extraction with a water-to-n-hexane-ratio (1:1, v/v) gave quantitative recoveries except for aniline (46%). The addition of sodium chloride improved the extraction yield for aniline about 10%. Linear calibration curves were obtained in the 0.01–1-μg/L concentration range, relative standard deviations were less than 10%, and detection limits typically were 4–20 ng/L for GC–mass spectrometry in the multiple-ion-detection mode. The total procedure allowed the analysis of unfiltered water samples; that is, no sample treatment was necessary. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 581–588, 1998

Microwave-induced Plasma Atomic Emission Spectrometer Used as the Detector for On-line Coupled High-performance Liquid Chromatography–Gas Chromatography

Atmospheric helium microwave-induced plasma atomic emission spectrometry (MIP-AES) was used successfully as a mode of detection for on-line coupled LC–GC. A loop-type interface was used for the on-line coupling. An early solvent vapor exit was used between the retention gap and the separation capillary column to accelerate solvent evaporation. The interface between MIP-AES and GC was achieved using a TM 010 cavity operated at atmospheric pressure. On-line coupled LC–GC provided a high efficiency separation for analytes in a complex sample matrix using LC as an on-line clean-up and enrichment approach. MIP-AES offered simultaneous multi-element detection ability which provided valuable information for the correct identification of compounds.