Dual Capillary Column Gas Chromatography Research Articles

Method for the determination of organophosphate insecticides in water, sediment and biota

A procedure for the determination of 13 organophosphate insecticides (OPs) in water, sediment and biota at low ppb levels is described. Samples were extracted with dichloromethane or acetone/hexane and cleaned up with micro-column silica gel chromatography. Measurements were made by dual capillary column gas chromatography using both nitrogen-phosphorus (NPD) and electron capture (ECD) detection. Recoveries from fortified water samples ranged from 76% to 102% for all sample types. Practical detection limits ranged between 0.003 and 0.029 μg/l in natural water samples, 0.0004–0.005 μg/g w.w. for sediments, and 0.001–0.005 μg/g w.w for biota using the NPD and ECD method. Losses in sediments were experienced when sulphur was removed. Precision and accuracy were not affected in sediment samples where sulphur was not removed.

Enantioseparation of chiral amino acids as the N(O,S)-ethoxycarbonylated diastereomeric esters by achiral dual-capillary column gas chromatography.

The enantioseparation of 30 racemic amino acids in a single analysis is described for the determination of their absolute configurations. Two-phase extractive ethoxycarbonyl (EOC) reaction with ethyl chloroformate present in the dichloromethane phase was performed to recover amino acids from alkaline aqueous solutions. The resulting N(O,S)-EOC amino acids extracted into an organic solvent after acidification were reacted with a chiral alcohol such as (S)-(+)-3-methylbutan-2-ol, (S)-(+)-butan-2-ol and (S)-(+)-octan-2-ol for gas chromatographic analysis on achiral dual-capillary DB-5 and DB-17 columns of different polarities. Among the chiral reagents examined, (S)-(+)-3-methylbutan-2-ol provided the best diastereomeric structures in resolving all the racemic amino acids into their enantiomeric pairs with high resolution factors (1.2-8.0). Moreover, the temperature-programmed retention index (I) values measured on the two columns were characteristic of each enantiomer. Hence simple I matching with the reference values was useful in cross-checking for chemical identification and also chiral discrimination. When the present method was applied to a fermented dairy product (Yakult), D-alanine, D-aspartic acid, D-glutamic acid and D-proline were positively detected along with their respective L-forms in addition to glycine.

Configurational analysis of chiral acids as O-trifluoroacetylated (−)-menthyl esters by achiral dual-capillary column gas chromatography

The simultaneous enantiomeric separation of 30 racemic acids including 24 hydroxy acids in a single analysis is described for the determination of their absolute configurations. It involves the conversion of each enantiomer into diastereomeric O-trifluoroacetylated (−)-menthyl ester for the direct separation by gas chromatography on achiral dual-capillary columns of different polarities, with subsequent identification and chiral discrimination by retention index ( I) library matching. Among the acids studied, the enantiomers of 27 acids were discriminatively resolved on both non-polar DB-5 and the intermediate-polar DB-17 columns with resolution factors in the range of 0.7–7.7 and separation factors in the range of 1.002–1.021. Enantiomers of 3-hydroxybutyric and α-methoxyphenylacetic acids were partially resolved on DB-5 (resolution factor of 0.9), but not resolved on DB-17, while the baseline resolution for 3-hydroxydecanoic acid and the minimal separation on the peak top (resolution factor less than 0.7) for 2-hydroxyglutaric acid were achieved on DB-17 but not on DB-5. The temperature-programmed I values measured on both columns were characteristic of each enantiomer and thus simple I matching with the reference values was useful in cross-checking for their chemical identification and the chiral discrimination as well. When applied to a clinical urine sample, the present method allowed positive identification of endogenous ( S)-lactic acid and ( S)-2-hydroxybutyric acid along with ( R)-3-hydroxybutyric acid.

Enantiomeric separation and discrimination of 2-hydroxy acids as O-trifluoroacetylated ( S)-(+)-3-methyl-2-butyl esters by achiral dual-capillary column gas chromatography

An efficient method is described for the simultaneous enantiomeric separation of 18 different racemic 2-hydroxy acids for the determination of their absolute configurations. It involves the conversion of each enantiomer into a diastereomeric O-trifluoroacetylated ( S)-(+)-3-methyl-2-butyl ester for the direct separation by achiral dual-capillary column gas chromatography with subsequent identification and determination of its chirality by retention index ( I) library matching. The enantiomers of each acid were well separated with high resolution values ( R≥1.4) on DB-5 and DB-17 columns of different polarity. When temperature-programmed I values of 2-hydroxy acid enantiomers as their diastereomeric derivatives were measured on both columns, the I values were characteristic of each enantiomer. Simple I matching with the reference values was thus useful in cross-checking each acid enantiomer for the identification and chiral discrimination. When applied to urine samples, the present method allowed positive identification of most of the spiked 2-hydroxy acids from normal urine and for endogenous ( S)-lactic acid and ( S)-2-hydroxybutyric acid from a clinical urine specimen.

Gas chromatographic profiling and pattern recognition analysis of urinary organic acids from uterine myoma patients and cervical cancer patients

An efficient organic acid profiling and pattern recognition method is described for the correlation between urinary organic acid profiles and uterine cervical cancer. After methoximation of keto acids in alkalinized urine samples, all free organic acids were recovered by a dual solid-phase extraction procedure, followed by conversion to tert.-butyldimethylsilyl derivatives for the profiling analysis by dual-capillary column gas chromatography (GC) with subsequent screening for acids by retention index ( I) library matching. A total of 50 organic acids were positively identified in urine samples (0.25 ml) from 12 uterine myoma (benign tumor group) and 14 uterine cervical cancer (malignant tumor group) patients studied. When the GC profiles were simplified to their corresponding organic acid I spectra in bar graphical form, characteristic patterns were obtained for each average of benign and malignant tumor groups. Stepwise discriminant analysis performed on the GC data selected 16 acids as the variables discriminating between the two groups. Canonical discriminant analysis applied to these 16 variables correctly classified 26 urine samples into two separate clusters according to tumor types in the canonical plot.

Gas chromatographic amino acid profiling of wine samples for pattern recognition

A rapid gas chromatographic profiling and screening method is described for the determination of free amino acids in wine samples. The amino acids in alkaline aqueous wines were allowed to react with isobutyl chloroformate. The resulting N(O,S)-isobutyloxycarbonyl amino acids were extracted by solid-phase extraction using Chlomosorb P as the adsorbent and diethyl ether as the eluent after acidification, and then converted into stable tert.-butyldimethylsilyl derivatives with subsequent analysis by dual-capillary column gas chromatography and gas chromatography-mass spectrometry. Seventeen free amino acids were identified from the four wine brands studied. When the GC profiles were simplified to the corresponding amino acid retention index spectra in bar graphical form, they presented characteristic patterns for each wine brand. Stepwise discriminant analysis performed on the amino acid profiles provided star symbols characteristic of the wine brands.

Freshwater mussels as biomonitors for organic industrial contaminants and pesticides in the St. Lawrence River

Native mussels ( Elliptio complanata and Lampsilis radiata) were collected from 17 stations in the St. Lawrence River between Lake Ontario and Trois Rivières and from three stations in a major tributary, the Ottawa River, in October, 1985. Mussels were solvent-extracted and analyzed individually by dual capillary column gas chromatography for seven organochlorine pesticides, 11 chlorobenzenes, octachlorostyrene and 63 PCB congeners. Bioconcentration patterns for contaminants in mussel tissues implicated Lake Ontario as the source of Mirex and DDT derivatives to the system and the Grass River as the major source of PCBs. Numbers of PCB congeners in mussels increased from 21–27 in the upper river to 56–59 in the Cornwall/Massena industrial core, mainly due to the appearance of di-, tri- and tetrachlorobiphenyls; an average of 43 congeners persisted as far downstream as Lac Saint-Pierre. Concentrations of most contaminants in mussels from the Ottawa River were 50–75% lower than the lowest values reported for the St. Lawrence River. This study provides information on the origin, bioavailability and persistence of organic contaminants in the St. Lawrence River ecosystem.

Analysis for polychlorinated biphenyls by dual capillary column gas chromatography

AbstractA dual‐column, gas chromatographic, congener‐specific methodology was developed that allows determination of polychlorinated biphenyl (PCB) concentrations in water and sediment samples. The linearity of the detector responses was checked over a range of 1000 at the sub‐ppb range of total PCB in the dual‐column mode, with less than 10−12 g of each congener impinging on the detector. The chromatographic method was checked to ensure that there was minimal interference by the organochlorines with the PCB analysis and vice versa. PCB standards were analyzed, and they yielded values within 10% of the expected amounts. Extracts from sediments were analyzed, and the organochlorine pesticide (OC) values agreed with values obtained using standard methods. The PCB values obtained from the standard and presented methods agreed within a factor of two. Use of the method provides results that are comparable to current methodology, and it requires less time.