Large Volume On-column Injection Research Articles

Trace level analysis of corky off-flavor compounds: Development of a new analytical method based on solid phase extraction and analysis by multidimensional gas chromatography with mass spectrometric detection

This work describes the development of a trace level (<1ngL−1) analysis of haloanisoles in complex wine matrix. The suggested method involves sample preparation based on solid phase extraction, a clean-up to remove acidic compounds, concentration of the haloanisole fraction and large volume on-column injection into a multidimensional GC–MS system. Mass spectrometric detection in the selected ion mode allowed reliable quantification of 2,4,6-trichloroanisole (TCA) or 2,4,6-tribromoanisole (TBA), via their highly deuterated ([2H5]) isotopologues as internal standards (stable isotope dilution analysis; SIDA), which had prior been synthesized in house. The development of this new method had become necessary, as a one-dimensional HS-SPME–GC-ECD method, routinely applied for analysis of TCA in cork soaks, had to be extended for TeCA and TBA determination, but failed due to co-elutions within wine matrices. The newly developed SPE//MDGC–MS method provided detection limits well below olfactory thresholds of the analytes with 0.05ngL−1 (LOD), 0.19ngL−1 (LOQ) for TCA, 0.06ngL−1 (LOD), 0.21ngL−1 (LOQ) for TeCA, and 0.09ngL−1 (LOD), 0.34ngL−1 (LOQ) for TBA.

Determination of Phenols in Soak Water from Drinking Water Related Products by Gas Chromatography-Mass Spectrometry with Large Volume Injection

A method was developed for the determination of phenols in soak water from drinking water related products by gas chromatography-mass spectrometry (GC-MS) with on-column large volume injection (OCI-LVI) and coupled column separation. The sample was firstly soaked according to related standard method. And then, 0.2 g/L of Na(2)S(2)O(3) was used as reductant to remove excessive chlorine. After spiked 2,4-dibromo-phenol as internal standard, 10 mL of the soak water was adjusted to pH 6. 8, saturated by NaCl and extracted by 1 mL of organic solvent. Approximately 30 mu L. of up-layer extract was used as injecting sample. The advantage of the short coupled polar column in increasing retention capacity of volatile phenols in OCI-GC-MS system was discussed. The LODs were 0.1-1 mu g/L. The recoveries were 76. 7%-112% with 5. 94%-12. 4% of RSD.

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.

State of the art analytical methods for solving taste and odour episodes

This paper summarizes the main types of tastes and odors encountered in drinking waters and describes the best analytical tools available to find the origins of these phenomena. The main complementary extraction-concentration techniques based on stripping and liquid-liquid or liquid-solid principles are discussed. Analysis at pg/L levels using a large volume on-column injection method in GC/MS is described. A sensory-GC/MS device is also presented in detail.

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.

Simultaneous determination of citalopram, fluoxetine, paroxetine and their metabolites in plasma by temperature-programmed packed capillary liquid chromatography with on-column focusing of large injection volumes

A miniaturized temperature-programmed packed capillary liquid chromatographic method with on-column large volume injection and UV detection for the simultaneous determination of the three selective serotonin reuptake inhibitors citalopram, fluoxetine, paroxetine and their metabolites in plasma is presented. An established reversed-phase C 8 solid-phase extraction method was employed, and the separation was carried out on a 3.5-μm Kromasil C 18 0.32×300 mm column with temperature-programming from 35 (3 min) to 100°C (10 min) at 1.3°C/min. The mobile phase consisted of acetonitrile–45 m M ammonium formate (pH 4.00) (25:75, v/v). The non-eluting sample focusing solvent composition acetonitrile–45 m M ammonium formate (pH 4.00) (3:97, v/v) allowed injection of 10 μl or more of the plasma extracts. The method was validated for the concentration range 0.05–5.0 μ M, and the calibration curves were linear with coefficients of correlation >0.993. The limits of quantification for the antidepressants and their metabolites ranged from 0.05 to 0.26 μ M. The within and between assay precision of relative peak height were in the range 2–22 and 2–15% relative standard deviation, respectively. The within and between assay recoveries were in the 61–99 and 54–92% range for the antidepressants, respectively, and between 52–102 and 51–102% for the metabolites.

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.

Determination of chlorophenoxy acid herbicides in water by in situ esterification followed by in-vial liquid–liquid extraction combined with large-volume on-column injection and gas chromatography–mass spectrometry

A new approach for rapidly analysing chlorophenoxy acid herbicides in water is presented. The chlorinated acids are derivatised with dimethyl sulphate in the water sample itself (800 μl) and, next, the methyl esters are extracted with 800 μl of n-hexane. A 200-μl volume of the extract is injected into the GC–MS system. The miniaturisation of both the methylation and extraction steps could be implemented because of the use of large-volume on-column injection and mass spectrometric detection. The optimisation of the methylation reaction for the simultaneous determination of (3,6-dichloro-2-methoxy)benzoic acid, (2-methyl-4-chlorophenoxy)- and (2,4-dichlorophenoxy)acetic acids, (±)-2-(4-chloro-2-methylphenoxy)- and 2-(2,4-dichlorophenoxy)propanoic acids and 4-(4-chloro-2-methylphenoxy)- and 4-(2,4-dichlorophenoxy)butyric acids showed that tetrabutylammonium salts act as catalysts. Addition of sodium hydroxide was required to obtain quantitative reaction yields for 4-(4-chloro-2-methylphenoxy)- and 4-(2,4-dichlorophenoxy)butyric acids. The methylation-cum-extraction procedure takes only 3 min per sample for a batch of seven samples. Linear calibration plots were obtained for the complete procedure and the limits of detection were of 10–60 ng/l with a signal-to-noise ratio ( S/ N) of 6. Relative standard deviations ranged from 8 to 15% ( n=7) for analyte concentrations of 0.5 μg/l in surface water.

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

At-line SPE-GC-MS of micropollutants in water using the PrepStation

An automated at-line SPE-GC-MS system for the determination of micropollutants in aqueous samples, which is based on the PrepStation and uses large-volume on-column injections, has been redesigned. A cartridge made from stainless steel and polychlorotrifluoroethylene and a 2-needle system was constructed which allow the determination of micropollutants at the low ng/L level without interferences from impurities extracted from the septa of the vials or the commercial cartridges. No time-consuming pre-cleaning of the cartridges or septa is required. The SPE sample extract (300 μL) is transferred from the sample preparation module to the autosampler of the GC-MS and 50 or 100 μL are injected. The analytical characteristics of the integrated procedure such as analyte recovery (typically 80-105%) and repeatability (RSDs, 2-9%), were satisfactory. Several micropollutants were detected in (unfiltered) river water at the 0.2-400 ng/L level using full-scan MS acquisition. The system proved to be robust during the analysis of more than 100 tap and river water samples. © Springer-Verlag 1999.

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.

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

Comparison of simplified methods for pesticide residue analysis: Use of large-volume injection in capillary gas chromatography

The combination of manual and automated extraction procedures using low sample volumes (5–50 ml) with large-volume oncolumn injection (LVI) (200 μl) in capillary gas chromatography with flame photometric detection (GC–FPD) has allowed the determination of 16 organophosphorus pesticides in clean water samples at the low ng l −1 level with an important simplification in the sample preparation step. A simple and fast offline liquid–liquid microextraction procedure (2–5 ml water/1 ml methyl tert.-butyl ether) has been applied to spiked groundwater samples (containing 0.5 ng of each pesticide) with good recoveries (over 80%) and precision (better than 10%), giving detection limits between 5 and 100 ng l −1 using 200 μl injections in the GC–FPD system. The application of an inline automated liquid–liquid microextraction–LVI–GC procedure (2 ml water/2 ml methyl tert.-butyl ether: injection of 200 μl in GC–FPD) using the autosampler ASPEC XL led to lower recoveries (>50%) as a result of the low efficiency for mixing organic and aqueous phases, although with very satisfactory coefficients of variation (lower than 7%) and detection limits between 20 and 200 ng l −1. Manual and automated solid-phase extraction procedures using the well known C 18 cartridges and the new Oasis HLB have been applied to groundwater samples (5–50 ml) spiked with 1 ng of each pesticide. Results obtained for both the manual and the automated procedures were satisfactory (recoveries over 80%) and the limits of detection for 50 ml sample volume ranged from 1 to 6 ng l −1.

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

Microextraction procedures combined with large volume injection in capillary gas chromatography for the determination of pesticide residues in environmental aqueous samples

Liquid–liquid microextraction and solid-phase extraction procedures combined with large volume on-column injection (100–150 μl) in capillary gas chromatography with nitrogen phosphorus detector have been applied to the determination of six triazine herbicides (atrazine, simazine, terbutylazine, terbumeton, metribuzin and terbutryn) and two transformation products (deethyl and deisopropyl atrazine) in water samples. A simple and fast off-line liquid–liquid microextraction procedure (5 ml water/1 ml methyl tert butyl ether) was applied to surface water samples spiked at 0.5 μg l −1 level with good recoveries (> 90%) and repeatability (better than 9%) giving detection limits < 0.1 μg l −1. The application of a solid-phase extraction procedure (10–50 ml of water samples passed through 200 mg C 18 cartridges) allowed the quantitative recovery of all pesticides studied with coefficients of variation lower than 11%. Limits of detection for 50 ml sample volume ranged from 10 to 40 ng l −1. Surface water samples have been analyzed using C 18 SPE (10 ml of water sample) combined with large volume injection (150 μl) and the results compared with those obtained with conventional LLE (500 ml of water sample extracted with 2 × 50 ml dichloromethane), showing good match between them.

Determination of triazine herbicides by capillary gas chromatography with large-volume on-column injection

This paper describes a study of the potential of large-volume on-column injection for the determination of triazine herbicides in clean water samples (ground-water). The sensitivity of chromatographic determination has been increased by two orders of magnitude by injection of up to 200 μL of pesticide solutions and nitrogen-phosphorus detection. Analytical characteristics expressed as precision, linear range and limit of detection have been determined, the results indicating adequate analytical performance and the ruggedness of the injection technique. As an application, gas chromatography with large-volume on-column injection and nitrogen-phosphorus detection was combined with off-line liquid-liquid micro-extraction with hexane (1 mL water/1 mL hexane). The procedure was applied to spiked groundwater samples at two concentration levels (1 and 10 μg L−1) with good recoveries (between 81 and 103%, except for deethylatrazine) and repeatability (better than 15% at the 1 μg L−1 level). Limits of detection of the triazine herbicides studied ranged from 0.08 to 0.16 μgL−1.

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.