Injection Gas Chromatography Research Articles

Flow injection gas chromatography with sulfur chemiluminescence detection for the analysis of total sulfur in complex hydrocarbon matrixes.

A fast and reliable analytical technique for the determination of total sulfur levels in complex hydrocarbon matrices is introduced. The method employed flow injection technique using a gas chromatograph as a sample introduction device and a gas phase dual-plasma sulfur chemiluminescence detector for sulfur quantification. Using the technique described, total sulfur measurement in challenging hydrocarbon matrices can be achieved in less than 10s with sample-to-sample time <2min. The high degree of selectivity and sensitivity toward sulfur compounds of the detector offers the ability to measure low sulfur levels with a detection limit in the range of 20ppb w/w S. The equimolar response characteristic of the detector allows the quantitation of unknown sulfur compounds and simplifies the calibration process. Response is linear over a concentration range of five orders of magnitude, with a high degree of repeatability. The detector's lack of response to hydrocarbons enables direct analysis without the need for time-consuming sample preparation and chromatographic separation processes. This flow injection-based sulfur chemiluminescence detection technique is ideal for fast analysis or trace sulfur analysis.

Coiled wire filament sample introduction for gas chromatography–mass spectrometry

A simple device based on a tiny, coiled wire filament (CWF), similar in operation to solid phase microextraction (SPME), was reported almost a decade ago for sampling, concentrating, and minimizing contamination for Injection of liquid samples in gas chromatography (GC). However, the pliability of the platinum wire from which the CWF was fabricated was a hindrance when using this technique. In this work, we utilized a much stiffer stainless steel wire to form the CWF, and explored a number of ways to use it for sampling and sample introduction in GC and GC–MS. The coil radius and number of turns in the CWF (i.e., length of the coil) determined the sampling volume. The CWF was attached to a retractable plunger (part of a hand-held syringe-type holder) such that it could be retracted inside a 19G needle for insertion into a standard GC injection port. Sampling was easily performed by either dipping the CWF in a liquid sample (i.e., sample dissolved in a solvent), which was drawn up into the wire coil by capillary action, or by applying a specific volume of liquid sample onto the CWF using a micro-syringe. Analytes trapped in/on the CWF could be introduced into the GC injection port before or after solvent evaporation. For semi-volatile compounds, the sample solvent was evaporated before injection, while for volatile compounds, some or all of the sample solvent was retained in the coil during injection. Repeatable volumes from 0.05 to 0.7μL were sampled using CWFs with 5–70 turns, respectively, when sampling by dipping. Advantages of using a CWF compared to a conventional syringe include: (1) the chromatographic system is protected from contamination caused by accumulation of sample residues, (2) high quantitative repeatability is obtained for small volume injections (0.05–0.2μL), (3) large sample injections can be performed for trace analysis by evaporating the solvent before injection, and (4) carryover and discrimination of semi-volatile compounds are minimized. These advantages enable easy and rapid (10min total analysis time) trace (0.1–5ppb) detection of a variety of different types of compounds, including polycyclic aromatic hydrocarbons, biphenyl congeners, organochlorine pesticides, pyrethroid pesticides, phthalate esters, and n-alkanes from C10 to C40 in water and waste water.

Concurrent Lactic and Volatile Fatty Acid Analysis of Microbial Fermentation Samples by Gas Chromatography with Heat Pre-treatment.

Organic acid analysis of fermentation samples can be readily achieved by gas chromatography (GC), which detects volatile organic acids. However, lactic acid, a key fermentation acid is non-volatile and can hence not be quantified by regular GC analysis. However the addition of periodic acid to organic acid samples has been shown to enable lactic acid analysis by GC, as periodic acid oxidizes lactic acid to the volatile acetaldehyde. Direct GC injection of lactic acid standards and periodic acid generated inconsistent and irreproducible peaks, possibly due to incomplete lactic acid oxidation to acetaldehyde. The described method is developed to improve lactic acid analysis by GC by using a heat treated derivatization pre-treatment, such that it becomes independent of the retention time and temperature selection of the GC injector. Samples containing lactic acid were amended by periodic acid and heated in a sealed test tube at 100°C for at least 45 min before injecting it to the GC. Reproducible and consistent peaks of acetaldehyde were obtained. Simultaneous determination of lactic acid, acetone, ethanol, butanol, volatile fatty acids could also be accomplished by applying this GC method, enabling precise and convenient organic acid analysis of biological samples such as anaerobic digestion and fermentation processes.

Application of Programmed Temperature Vaporization Large Volume Injection Gas Chromatography (PTV-LVI-GC) to the Analysis of Polycyclic Aromatic Hydrocarbons (PAHs) in Soils

A sensitive, selective and robust method was developed to quantify low levels of polycyclic aromatic hydrocarbons (PAHs) in soils by means of Programmed Temperature Vaporization - Large Volume Injection (PTV-LVI) coupled to gas chromatography with flame ionization detection. Optimal vent pressure and flux at the PTV inlet of the GC system were determined by comparison of peak areas obtained from injection of a standard PAHs mixture at different conditions. Assessment of method performance was carried out with home-made standards prepared by spiking three non-PAH contaminated soils that contained 1.8%, 4.6% and 25% natural organic matter (NOM), with mixtures of six different PAHs at low concentration levels. Detection limits between 9 and 12 ng g-1 and variation coefficients below 11% were determined from analysis of spiked samples of the soil with lowest NOM content. PAHs recoveries typically ranged from 61% to 96% for the three studied soils.

Determination of genotoxic epoxide at trace level in drug substance by direct injection GC/MS

A novel direct injection gas chromatography method coupled with selective ion monitoring mass spectrometry (GC/SIM-MS) was developed for quantitation of trace levels of high boiling point (HBP) epoxide genotoxic impurity (GTI) in drug substance. The injector temperature was optimized with the aims to minimize matrix effects and enhance SIM signal response. The final injector temperature 160°C was selected after balancing between these two factors. The column screening was conducted as well and MN OPTIMA delta-3 silica capillary column was selected since it showed good peak symmetry without column bleeding. The good linearity was established for the concentration in the range from 0.0045μg/mL to 0.5μg/mL with a R2=0.9999. The limit of detection (LOD) and the limit of quantitation (LOQ) were 0.0014μg/mL and 0.0045μg/mL, respectively. The recovery which ranged from 95.0% to 112.5% could meet the ICH acceptance criteria. The validation results demonstrated the good linearity, precision and accuracy of the method which can be further adopted as an adequate quality control tool for quantitation of epoxide impurity at trace levels in drug substance and drug product.

A novel needle trap device with nanoporous silica aerogel packed for sampling and analysis of volatile aldehyde compounds in air

In this study a needle trap device (NTD) packed with nanoporous silica aerogel (NPSA) was developed as a rapid determination technique for formaldehyde and acrolein in air. The performance of NTD-NPSA, which was characterized using several analytical figures of merit including linearity, repeatability, recovery, limit of detection (LOD), and limit of quantification (LOQ), was then compared to NIOSH 2541 method. The LOD and LOQ of NTD-NPSA for the two compounds were 0.01–0.02μgL−1 and 0.033–0.068μgL−1, respectively. The intra and inter-day relative standard deviation of method were 3.6–6.9% and 5.1–9.4%, respectively. The result of this comparative study showed that NTD-NPSA had a better performance than the NIOSH 2541 method. Unlike the NIOSH 2541method, the NTD-NPSA is a solvent-free technique, in which the desorption of the analyte is directly performed thermally inside the gas chromatograph injection port. The fact that NTD-NPSA does not require a solvent and, also, the reusability of the technique can reduce the total sampling costs for the procedure compared with costs for solvent-based sampling and extraction methods. Thus, this technique is a reliable and effective method for the determination of aldehyde in both indoor and outdoor environments.

Fast Method for the Determination of Residual Solvents in Radiopharmaceutical Products

The aim of this work was the development and validation of a fast analytical method to determine the residual solvents content in radiopharmaceuticals such as: 18F-Fluorodeoxyglucose (18F-FDG), 18F-Fluoroestradiol (18F-FES), 18F-Fluorothymidine (18F-FLT),18F-Fluoromisonidazole (18F-FMISO). Radiopharmaceuticals are radioactive preparations for medical purposes used in nuclear medicine as tracers in diagnostic imaging and treatment of certain diseases. Positron Emission Tomography (PET) is a medical imaging technique that consists in introducing into the body of a small amount of a biologically active chemical compound labelled with a short lived positron-emitting radioisotope (18F, 11C, 68Ga). Residual solvents are critical impurities in radiopharmaceuticals that can affect labelling, stability and physicochemical properties of drugs. Therefore, the determination of these solvents is essential for quality control of radiopharmaceuticals. Validation of the control method for residual solvents by gas chromatography is referred by the European Pharmacopoeia using a special injection technique (head space). The parameters of the method, which comply with International Conference on Harmonization guidelines, are: accuracy, precision, linearity, limit of detection, limit of quantification and robustness. The proposed method (direct gas chromatography injection) proved to be linear, precise, accurate and robust. Good linearity was achieved for all the solvents and correlation coefficients (R2) for each residual solvent were found more than 0.99.

Optimized Method to Analyze Rose Plant Volatile Organic Compounds by HS-SPME-GC-FID/MSD

A method involving Headspace solid-phase microextraction (HS-SPME) fiber combined with gas chromatography (GC) coupled with flame ionization detection (FID) and gas chromatography with mass spectrometry (GC-MS) was developed and optimized to investigate volatile organic compounds (VOCs) from different tissues (flowers, leaves, stems, rhizosphere and whole plants) of Floribunda and Hybrid Tea roses (intact and cut). Three-phase fiber 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) was used. Two types of chambers (Tedlar bag and glass jar) were evaluated for collection of VOCs and glass jar was selected. Absorbed compounds on the fiber were completely desorbed in the GC injector port at three desorption times (5, 10 and 15 min), and 5 min at 250?C was used. The maximum extraction efficiency for flowers tissues (equilibrium absorption) was achieved 2 h after fiber exposure in the headspace for intact and cut Floribunda and Hybrid Tea flowers. Under the optimized HS-SPME and GC-FID/MS conditions, 1h extraction time was chosen for intact and cut Floribunda and Hybrid Tea leaves and stems. The results demonstrated that 5 cm depth was selected for root and soil part (rhizosphere) for both rose cultivars, and 6 h and 12 h extraction time of VOCs from rhizosphere was achieved for Floribunda and Hybrid Tea, respectively. One hour was chosen for VOCs released from whole rose plants for both cultivars. In this study, the VOC profiles of two rose cultivars were characterized by the optimized HS-SPME-GC method. The different tissues of rose plants gave wide range of the VOCs; also the chromatograms of different cultivars were quite different and the specific VOC pattern of rose types depends on the species. Results from this study demonstrate the feasibility of this method for identifying VOCs from two rose cultivars and the potential use of this method for physiological studies on rose plants or on other floriculture plants.

Prototype of an Interface for Hyphenating Distillation with Gas Chromatography and Mass Spectrometry.

Chemical analysis of complex matrices-containing hundreds of compounds-is challenging. Two-dimensional separation techniques provide an efficient way to reduce complexity of mixtures analyzed by mass spectrometry (MS). For example, gasoline is a mixture of numerous compounds, which can be fractionated by distillation techniques. However, coupling conventional distillation with other separations as well as MS is not straightforward. We have established an automatic system for online coupling of simple microscale distillation with gas chromatography (GC) and electron ionization MS. The developed system incorporates an interface between the distillation condenser and the injector of a fused silica capillary GC column. Development of this multidimensional separation (distillation-GC-MS) was preceded by a series of preliminary off-line experiments. In the developed technique, the components with different boiling points are fractionated and instantly analyzed by GC-MS. The obtained data sets illustrate dynamics of the distillation process. An important advantage of the distillation-GC-MS technique is that raw samples can directly be analyzed without removal of the non-volatile matrix residues that could contaminate the GC injection port and the column. Distilling the samples immediately before the injection to the GC column may reduce possible matrix effects-especially in the early phase of separation, when molecules with different volatilities co-migrate. It can also reduce losses of highly volatile components (during fraction collection and transfer). The two separation steps are partly orthogonal, what can slightly increase selectivity of the entire analysis.

A gas chromatography/mass spectrometry study of the conversion of alicyclic alcohols on membrane-type catalysts using a pulse microreactor implanted into a gas chromatograph injector

A pulse microreactor implanted directly into a gas chromatograph injector combined with a mass spectrometer has been proposed for monitoring the activity of heterogeneous catalysts. The microreactor was made of a standard commercial liner for a particular gas chromatograph and contained a catalytic bed. A heated injector oven was used simultaneously for heating the catalytic region, rapid evaporation of the substrate, and pulsed introduction of reaction products into a chromatographic column. The temperature of the oven could be varied in the range 200–300°C. The method ensures the detailed description of the qualitative composition of the reaction products. The potential of the proposed microreaction system was demonstrated in the study of membrane-type catalysts (nanodiamonds modified by Pt–Ru and Pt–Ni and also catalytic phosphate systems with NASICON structure) in reactions of cyclohexanol, cyclopentanol, and cyclobutanol. The studied heterogeneous catalysts can be divided in two groups. One group (based on nanodiamonds) promotes dehydrogenation reactions. The NASICON catalytic group catalyzes dehydration reactions with the formation of cycloalkenes and dicycloalkyl ethers.

Environmentally friendly solid-phase microextraction coupled with gas chromatography and mass spectrometry for the determination of biogenic amines in fish samples.

In this work, a facile and environmentally friendly solid-phase microextraction assay based on on-fiber derivatization coupled with gas chromatography and mass spectrometry was developed for determining four nonvolatile index biogenic amines (putrescine, cadaverine, histamine, and tyramine) in fish samples. In the assay, the fiber was firstly dipped into a solution with isobutyl chloroformate as derivatization reagent and isooctane as extraction solvent. Thus, a thin organic liquid membrane coating was developed. Then the modified fiber was immersed into sample solution to extract four important bioamines. Afterwards, the fiber was directly inserted into gas chromatography injection port for thermal desorption. 1,7-Diaminoheptane was employed as internal standard reagent for quantification of the targets. The limits of detection of the method were 2.98-45.3 μg/kg. The proposed method was successfully applied to the detection of bioamines in several fish samples with recoveries ranging 78.9-110%. The organic reagent used for extraction was as few as microliter that can greatly reduce the harm to manipulator and environment. Moreover, the extraction procedures were very simple without concentration and elution procedures, which can greatly simplify the pretreatment process. The assay can be extended to the in situ screening of other pollutant in food safety by changing the derivatization reagent.

Determination of Trace Levels of Irgarol in Estuarine Water Matrices by Bar Adsorptive Microextraction.

Bar adsorptive microextraction (BAµE), using selective sorbent phases, followed by liquid desorption in combination with large volume injection-gas chromatography coupled to mass spectrometry (BAµE-LD/LVI-GC-MS), is proposed for the determination of trace levels of irgarol in estuarine water matrices. While we compared several polymers and activated carbons, one of the latter coatings showed much higher selectivity through BAµE. Assays performed on 25 mL of ultra-pure water sample fortified at 0.6 µg/L levels of irgarol yielded recoveries of 74.5 ± 8.6%, under optimized experimental conditions. The proposed analytical procedure showed convenient detection limits (16.0 ng/L) and good linear dynamic range (0.2-16.0 µg/L), with determination coefficients of 0.9982. Good precision was also achieved with RSD lower than 12.0%. The application of the present analytical approach on estuarine water samples by using the standard addition methodology revealed good sensitivity and linearity. The proposed methodology, using nanostructured sorbents and operating under the floating sampling technology, proved to be a suitable analytical alternative to monitor irgarol in estuarine water matrices. Moreover, it is easy to implement, reliable, sensitive, require low sample volume and have the possibility to choose the most selective sorbent coating according to the target compound involved.

Solid-phase microextraction may catalize hydrogenation when using hydrogen as carrier in gas chromatography

When hydrogen is used as carrier gas, carbon-carbon double bonds may be hydrogenated in the hot gas chromatograph (GC) injector if introduced by solid-phase microextraction (SPME). SPME fibers coated with polydimethylsiloxane (PDMS)/carboxen/divinylbenzene (DVB), PDMS/carboxen, polyacrylate, PDMS/DVB and PDMS on fused silica, stableflex or metal alloy core have been tested with fatty acid methyl esters (FAMEs) from olive oil. Using coatings containing DVB, hydrogenation took place with high conversion rates (82.0–92.9%) independently of the core material. With all fibers having a metal core, hydrogenation was observed to a certain extent (27.4–85.3%). PDMS, PDMS/carboxen and polyacrylate coated fibers with a fused silica or stableflex core resulted in negligible hydrogenation (0.2–2.5%). The occurrence of hydrogenation was confirmed also with other substances containing carbon-carbon double bonds (n-alkenes, alkenoic acids, mono- and polyunsaturated fatty acid methyl and ethyl esters).

Extraction of Citrus paradisi Volatile Components by Headspace Single-Drop Microextraction and Statistical Modeling.

In present study, headspace single-drop microextraction (HS-SDME) was applied for the extraction and preconcentration of the volatile components of the plant sample into a microdrop surface. The extraction occurred by suspending a microliter drop of the solvent from the tip of a microsyringe to the headspace of a ripe fruit sample (grapefruit Citrus paradisi) in a sealed vial for a preset extraction time. Then the microdrop was retracted back into the microsyringe and injected directly into a gas chromatography injection port. The chemical composition of the SDME extracts was confirmed according to their mass spectra, and quantitative analysis was performed by gas chromatography-flame ionization detector (GC-FID). Response surface methodology along with Box-Behnken design was applied to optimize the extraction condition of four components, d-limonene, β-myrcene, α-pinene and β-pinene, from the peel of grapefruit. Parameters considered for SDME include the kind of the extracting solvent, size of drop, extraction temperature and extraction time. The optimized condition was microdrop volume of 1 µL, extraction time of 2 min and sample temperature of 50°C.

Influence of the drying step within disk-based solid-phase extraction both on the recovery and the limit of quantification of organochlorine pesticides in surface waters including suspended particulate matter

In this study, 21 organochlorine pesticides (OCPs) were determined based on sample preparation using solid-phase extraction disks (SPE disks) coupled with programmable temperature vaporizer (PTV)—large-volume injection gas–chromatography mass spectrometry (LVI-GC–MS). The work includes a comprehensive testing scheme on the suitability of the method for routine analysis of surface and drinking water including suspended particulate matter (SPM) with regard to requirements derived from the European Water Framework Directive (WFD, Directive 2000/60/EC). SPM is an important reservoir for OCPs, which contributes to the transport of these compounds in the aquatic environment. To achieve the detection limits required by the WFD, a high pre-concentration factor during sample preparation is necessary, which was achieved by disk SPE in this study. The performance of disk SPE is strongly influenced by the drying step, which could be significantly improved by effective elimination of the residual water by combination of a high vacuum pump and a low humidity atmosphere. Detection limits of the WFD in the ng/L range were achieved by large volume injection of 100μL sample extract. The recoveries ranged from 82% to 117% with an RSD smaller than 13%. The applicability of this method to natural samples was tested for instrumental qualification and system suitability evaluation. Successful participation in an interlaboratory comparison proved the suitability of the method for routine analysis.

Determination of synthetic phenolic antioxidants in edible oils using microvial insert large volume injection gas-chromatography

Three synthetic phenolic antioxidants, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ), were determined in different edible vegetable oil samples. The analyses were carried out by gas chromatography–mass spectrometry (GC–MS) using microvial insert large volume injection (LVI). Several parameters affecting this sample introduction step, such as temperatures, times and gas flows, were optimised. Quantification was carried out by the matrix-matched calibration method using carvacrol as internal standard, providing quantification limits between 0.08 and 0.10ngg–1, depending on the compound. The three phenolic compounds were detected in several of the samples, BHT being the most frequently found. Recovery assays for oil samples spiked at two concentration levels, 2.5 and 10ngg–1, provided recoveries in the 86–115% range.

Evolved gas composition monitoring by repetitive injection gas chromatography

Performance characteristics and applications of a small volume gas chromatograph oven are described. Heating and cooling properties of the apparatus are evaluated and examples are given illustrating the advantages of greatly reducing the air bath volume surrounding fused silica columns. Fast heating and cooling of the oven permit it to be employed for repetitive injection analyses. By using fast gas chromatography separations to achieve short assay cycle times, the apparatus can be employed for on-line species-specific gas stream composition monitoring when volatile species concentrations vary on time scales of a few minutes or longer. This capability facilitates repeated sampling and fast gas chromatographic separations of volatile product mixtures produced during thermal analyses. Applications of repetitive injection gas chromatography–mass spectrometry evolved gas analyses to monitoring purge gas effluent streams containing volatile acid catalyzed polymer cracking products are described. The influence of thermal analysis and chromatographic experimental parameters on effluent sampling frequency are delineated.

Analysis of polycyclic aromatic hydrocarbons in aqueous samples by large volume injection gas chromatography–mass spectrometry using the through oven transfer adsorption desorption interface

A new procedure for the determination of 17 polycyclic aromatic hydrocarbons (PAHs) in aqueous samples by large volume injection–gas chromatography–mass spectrometry (LVI–GC–MS) using the Through Oven Transfer Adsorption Desorption (TOTAD) interface with nitrogen for solvent elimination is developed and validated. Up to 75mL of aqueous samples were injected to be sure that good solvent elimination were achieved, although 500µL were sufficient to achieve the required sensitivity.The performance of the developed method can be considered good: the relative standard deviation (RSD), (n=3) was lower than 13.8% for all the target analytes, the concentration of each PAH being 0.25μgL−1, the limit of detection and limit of quantitation ranged from 21.5 to 211.0 ng L−1 and from 71.7 to 703.3ngL−1 respectively, and the correlation coefficients (R2) were all higher than 0.9764 in the 1–16μgL−1 range.

Application of Bar Adsorptive Microextraction-Large-Volume Injection-Gas Chromatography-Mass Spectrometric Method for the Determination of Trace Levels of Agrochemicals in Real Matrices

Bar adsorptive microextraction followed by liquid desorption in combination with large volume injection gas chromatography coupled to mass spectrometry, under selected ion monitoring mode acquisition (BAµE-LD/LVI-GC-MS(SIM)), was applied for the determination of trace levels of different classes of agrochemicals (using alachlor, diniconazole, fenpropathrin, as well as cis and trans-permethrin as model compounds) in environmental water and wine matrices. Assays performed on 25 mL of ultra-pure water samples spiked at the 2.0 µg L-1 level, yielded recoveries ranging from 55.2 to 105.6%, under optimized experimental conditions. The analytical performance showed convenient detection limits (8.0 to 32.0 ng L-1) and good linear dynamic ranges (0.03 to 4.00 µg L-1), with remarkable determination coefficients (r2 > 0.9982). Excellent repeatability, based in relative standard deviation (RSD) was also achieved through intraday (RSD < 7.5%) and interday (RSD < 7.0%) assays. Studies performed on surface and ground water, as well as wine samples, using the standard addition method, revealed good sensitivity at the trace level.

Practical method for the confirmation of authentic flours of different types of cereals and pseudocereals

Gas chromatography with mass spectrometry was used to perform a qualitative analysis of the liposoluble flour extract of different types of cereals (bread wheat and spelt) and pseudocereals (amaranth and buckwheat). In addition to major fatty acids, the liposoluble extract also contained minor fatty acids with more than 20 carbon atoms, higher hydrocarbons and phytosterols. TMSH (trimethylsulfonium hydroxide, 0.2mol/l in methanol) was used as a trans-esterification reagent. In a trans-esterification reaction, triglycerides esterified from acilglycerols to methyl-esters. SIM (selected ion monitoring) was applied to isolate fatty acid methyl esters on TIC (total ion current) chromatograms, using the 74Da fragment ion, which originated from McLafferty rearrangement, and is typical for methyl-esters. GC–MS system was used for the trans-esterification of triglycerides to fatty acid methyl esters in the gas chromatographic injector. This eliminated laboratory preparation for fatty acid methyl esters.Cluster analysis was applied to compare the liposoluble flour extract from different types of cereals and pseudocereals. Statistical data showed the liposoluble extract analysis enabled determination of flour origin and, because the results were unambiguous, this approach could be used for quality control.