Two-dimensional Capillary Gas Research Articles

Flavour Components of Whiskey. II Ageing Changes in the High-Volatility Fraction

The volatile compounds isolated from whiskey by fractional vacuum distillation were identified by two-dimensional capillary gas chromatography/mass spectrometry. Changing levels with ageing were quantified for the most abundant compounds by direct split injection of whiskeys on a gas chromatograph equipped with a flame ionisation detector. The ageing decreases in volatile sulfides were similarly determined using a sulfur chemiluminescence detector. Large volume headspace injection sufficiently reproduced the distillation enrichment to allow direct twodimensional determination of similar ageing changes for other trace compounds. Seven compounds at μg/L and low mg/L levels were monitored and quantified.

Considerations on the determination of the limit of detection and the limit of quantification in one-dimensional and comprehensive two-dimensional gas chromatography

Methods based on the blank signal as proposed by IUPAC procedure and on the signal to noise ratio (S/N) as listed in the ISO-11843-1 norm for determination of the limit of detection (LOD) and quantitation (LOQ) in one-dimensional capillary gas chromatography (1D-GC) and comprehensive two-dimensional capillary gas chromatography (CG×GC) are described in detail and compared for both techniques. Flame ionization detection was applied and variables were the data acquisition frequency and, for CG×GC, also the modulation time. It has been stated that LOD and LOQ estimated according to IUPAC might be successfully used for 1D-GC–FID method. Moreover, LOD and LOQ decrease with decrease of data acquisition frequency (DAF). For GC×GC–FID, estimation of LOD by IUPAC gave poor reproducibility of results while for LOQ reproducibility was acceptable (within ±10% rel.). The LOD and LOQ determined by the S/N concept both for 1D-GC–FID and GC×GC–FID methods are ca. three times higher than those values estimated by the standard deviation of the blank. Since the distribution pattern of modulated peaks for any analyte separated by GC×GC is random and cannot be predicted, LOQ and LOD may vary within 30% for 3s modulation time. Concerning sensitivity, 1D-GC–FID at 2Hz and of GC×GC–FID at 50Hz shows a ca. 5 times enhancement of sensitivity in the modulated signal output.

Multiresidue Method for Pesticides and Persistent Organic Pollutants (POPs) in Milk and Cream Using Comprehensive Two-Dimensional Capillary Gas Chromatography−Time-of-Flight Mass Spectrometry

A method for the analysis of pesticides and their metabolites including most of the persistent organic pollutants (POPs) in milk and cream is described. The method was single-laboratory validated through milk fortification in quadruplicate with 34 pesticides, isomers, and metabolites including 12 of the insecticide POPs and their metabolites. Whole cow's milk was fortified at 0.2, 0.4, 1, 2, 10, or 50 microg/kg wet weight and extracted with acetone/cyclohexane/ethyl acetate (2:1:1) with the addition of Mg(2)SO(4) and NaCl. Fat recovered in the extract accurately reflected the fat content of the milk or cream. All test portions were purified on a gel permeation chromatograph (GPC) followed by solid phase extraction (SPE) cleanup on a mixed bed graphitized carbon black (GCB) and primary/secondary amine silica gel (PSA) column before determination using a comprehensive two-dimensional gas chromatograph interfaced to a time-of-flight mass spectrometer. Average recoveries were 77, 72, 73, 66, 77, and 84% for 0.2, 0.4, 1, 2, 10, and 50 microg/kg wet weight whole milk, respectively. The average relative standard deviations for 0.2, 0.4, 1, 2, 10, and 50 microg/kg were 10, 8, 7, 7, 3, and 3%, respectively. The limits of quantification (LOQs) for all pesticides were 0.2 or 0.4 microg/kg wet weight. An archived cream sample collected in 1982 on Oahu, Hawaii, was found to contain only hepatachlor epoxide (HE) and DDE-p,p' at 380 +/- 24 and 69 +/- 17 microg/kg fat, significantly elevated over the current action level of 50 microg/kg fat for HE.

Direct stereoselective assay of fluoxetine and norfluoxetine enantiomers in human plasma or serum by two-dimensional gas–liquid chromatography with nitrogen–phosphorus selective detection

A method was developed and validated for the direct enantioselective assay of fluoxetine and norfluoxetine in human plasma or serum by two-dimensional capillary gas–liquid chromatography (GC). A Rtx-1 fused-silica capillary (15 m×0.25 mm I.D., 1.0 μm film thickness) and a hydrodex-β-6-TBDM fused-silica capillary (25 m×0.25 mm I.D., 0.25 μm film thickness) were used. A three-step liquid–liquid extraction was used for sample preparation with fluvoxamine and nisoxetine as internal standards. The method provided linear calibration between about 5 and 250 ng/ml for ( R)- and ( S)-fluoxetine as well as 15 and 250 ng/ml for ( R)- and ( S)-norfluoxetine. The limits of detection were about 1.5 and 6 ng/ml, respectively. Intra-day precision (coefficient of variation) was estimated as being between 5.4 and 12.7% at plasma levels of 25, 100 and 200 ng/ml for the four enantiomers. Inter-day precision was between 5.3 and 9.1% at 100 ng/ml. The enantioselective separation of some racemic psychopharmaceuticals was tested with various cyclodextrin GC-capillaries. Advantages and disadvantages of direct enantioselective GC are discussed for the assay of racemic psychopharmaceuticals. Samples from a patient who was treated with racemic fluoxetine were measured. In agreement with literature, plasma levels of the ( R)-enantiomers of fluoxetine and norfluoxetine were considerably decreased in comparison to the ( S)-enantiomers.

Direkte Analyse von Dimethylnaphthalinen in Erdölen mittels zweidimensionaler Kapillar-Gas-Chromatographie

Quantitation of dimethylnaphthalenes in crude oils by means of two-dimensional capillary gas chromatography.) Occurrence and behaviour of aromatic hydrocarbons in crude oils and bitumina are thoroughly investigated in organic geochemistry. For instance, concentration ratios derived from alkylnaphthalene and alkylphenanthrene isomer distribution are applied for the assessment of the geological and thermal history of sedimentary organic matter. The present contribution focusses on the separation and quantitation of 1,4-, 2,3- and 1,5-dimethylnaphthalenes in crude oils by two-dimensional capillary gas chromatography. Usually, the separation of these isomers cannot be achieved without difficulties on a single stationary phase. The geochemical interest arises from the application of the 2,3- to 1,4-dimethylnaphthalene concentration ratio as a“maturity parameter”. Another advantage of the method is, in addition to the speed of the analysis, the possibility to analyse original. untreated crude oil samples, i.e., with no further preseparation.

Two-dimensional capillary gas chromatography with three selective detectors as a valuable tool in residue analysis ? state-of-the art

A method for pesticide residue analysis applying the technique of two-dimensional gas chromatography with effluent splitting to three selective detectors in parallel is described. Screening and confirmation procedures are combined in one single instrument. The column combination used allows the separation and identification of more than three hundred pesticides on the basis of the resulting retention times and detector signals. Critical pairs of pesticides are distinguished by using the response ratio of the selective detectors characteristic for each substance. An example is given to demonstrate the merits of the described GC-system using the multimethod S19 of the DFG Pesticide Commission for clean-up.

Aromatic Volatile Composition of Celery and Celeriac Cultivars

A two-dimensional capillary gas chromatographic method was developed to separate and quantify aromatic volatiles of celery in one analysis. The isolation, identification, and quantification of the volatile compounds of four cultivars of blanching celery (Apium graveolens L. var. dulce) and six cultivars of celeriac (Apium graveolens L. var. rapaceum) are described. The qualitative composition of Likens-Nickerson extracts of both cultivars is similar. The concentration of terpenes and phthalides, the key volatile components, found in various cultivars of both celery and celeriac varied over a wide range.

Determination of the new aromatic retinoic acid Ro 13-7410 in plasma by two-dimensional gas chromatography negative ion chemical ionization mass spectrometry with selected-ion monitoring

A highly sensitive and specific method for the determination of the aromatic retinoic acid Ro 13-7410 in plasma at the picogram per millilitre level is described. The method involves extraction of plasma using Extrelut-1 columns, purification of the extract with Bond Elut-NH2 cartridges, derivatization with pentafluorobenzyl bromide, and subsequent analysis by two-dimensional capillary gas chromatography using the zone-cutting technique, stable isotope dilution and selective negative ion monitoring chemical ionization mass spectrometry. A tetradeuterated analogue is used as internal standard. Quantification is possible down to 25 pg/ml using 1 ml of plasma. The coefficients of variation of the method as calculated from quality control samples are 8.5 and 4.2% at the 100 and 400 pg/ml levels. The method has been applied to the analysis of plasma of volunteers following an oral dose of 40 micrograms Ro 13-7410 and plasma of dogs following an intravenous and oral dose of 25 and 50 micrograms, respectively.

Direct analysis of alkylnaphthalenes in crude oils by two-dimensional capillary gas chromatography

Diaromatics are geochemically significant constituents of crude oils. Their determination is usually achieved by elaborate prefractionation methods, such as medium pressure liquid chromatography and HPLC, prior to capillary gas chromatography. The present contribution describes the quantitative analysis of methylnaphthalenes, ethylnaphthalenes, and dimethylnaphthalenes in selected crude oils by two-dimensional capillary GC. Since the method does not comprise any work-up procedure the determination of geochemical parameters (alkylnaphthalene concentration ratios) is performed on the original, untreated crude oil samples. Accordingly, the analytical results reflect the original composition. The influence by evaporational losses in the laboratory is minimized.