Gas Chromatographic Method For Analysis Research Articles

Polycondensation and disproportionation of an oligosiloxanol in the presence of a superbase

Kinetics of reactions of model oligosiloxanols, 1,1,3,3,3-pentamethyldisiloxane-1-ol (MDH) and 1,1,3,3,5,5,5-heptamethyltrisiloxane-1-ol (MD 2H), which occur in the presence of phosphazenium superbase, hexapyrrolidine-diphosphazenium hydroxide, in an acid–base inert solvent, toluene, was studied using sampling and gas chromatographic analysis method. In addition, kinetics of reactions of MDH and MD 2H with trimethylsilanol (MH) was studied. In the MDH and MD 2H systems the oligosiloxanol condensation competes with the oligosiloxanol disproportionation, the latter being the dominating process. The disproportionation products, i.e. MD n+1 H and MD n−1 H, n=1, 2, … undergo analogous consecutive disproportionation and condensation reactions. The kinetic law was derived and rate parameters determined from initial rates and by computer simulation to the best agreement with experimental data. Both competing reactions, the disproportionation and the condensation, conform to the same general kinetic law being first internal order in substrate and first order in catalyst. Activation parameters of these reactions were determined. The results were interpreted in terms of a bimolecular mechanism in which nucleophilic attack of the silanolate anion directed to silicon of the silanol group causes the cleavage of one of its geminal bonds to oxygen, either the one to hydroxyl leading to condensation or the one to siloxane which leads to disproportionation. The latter is faster as the silanolate is a better leaving group compared with OH −. Moreover, in the pentacoordinate silicon transition state (or intermediate) the siloxane substituent preferentially enters the apical position, thus driving the OH substituent into the unreactive equatorial position.

Development and validation of a gas chromatographic method for analysis of fosfomycin in chicken muscle samples

A gas chromatographic method for the determination of residues of Fosfomycin in chicken muscle samples has been developed. Muscle samples were homogenised with TRIS buffer, containing phenylphosphonic acid (as internal standard) and Fosfomycin using a tissue homogenizer. Afterwards, the samples were ultrafiltered and the ultrafiltrate was evaporated to dryness. A silylation reagent for derivatization was used in order to reconstitute the residue. The linear concentration range of application was 10–150 μgg−1, with a detection and quantitation limit of 3.11 and 10 μgg−1, respectively. The method was efficient with a mean recovery of 87.83% from spiked muscle. The results obtained show that gas chromatography is a useful method for the determination of Fosfomycin residues in chicken muscle samples.

Method validation for strobilurin fungicides in cereals and fruit

Strobilurins are a new class of fungicides that are active against a broad spectrum of fungi. In the present work a GC method for analysis of strobilurin fungicides was validated. The method was based on extraction with ethyl acetate/cyclohexane, clean-up by gel permeation chromatography (GPC) and determination of the content by gas chromatography (GC) with electron capture (EC-), nitrogen/phosphorous (NP-), and mass spectrometric (MS-) detection. Three strobilurins, azoxystrobin, kresoxim-methyl and trifloxystrobin were validated on three matrices, wheat, apple and grapes. The validation was based on recovery tests at three or four spiking levels, determined as double determinations and repeated three times (n = 6). The mean recoveries for the three detectors were in the range of 70-114%, and the LODs were between 0.004mg/kg and 0.014mg/kg, for all three strobilurins. The values for repeatability and reproducibility were within the limits for repeatability and reproducibility given by the Horwitz equation. Validation was not accepted for azoxystrobin in grapes on all three detectors and for azoxystrobin in apple for the MS-detector. A comparison of matrix-matched standards versus standards in solvent showed varying differences

Gas chromatographic determination of coumaphos and tau-fluvalinate residues in royal jelly produced under commercial conditions

SUMMARYA gas chromatographic analytical method was developed and used to determine coumaphos (Perizin) and tau-fluvalinate (Apistan) residues in royal jelly. The method involves sample dilution with a mixture of isopropyl alcohol/acetonitrile, centrifugation for phase separation, extraction with methylene chloride and analysis by gas chromatography-mass spectrometry. Recoveries ranged from 82–93% with coefficients of variation of 3–15% at the 95% confidence limit level. The quantification limit obtained was 5 ng/g for both coumaphos and tau-fluvalinate. The pesticides were applied inside the hives either as a spray (coumaphos) or as plywood inserts (tau-fluvalinate) to control varroa. It was found that when coumaphos was sprayed, the time interval between the last application and royal jelly collection (pre-harvest interval) should to be at least 42 days. No residues were detected when plywood inserts impregnated with tau-fluvalinate were used.

Distinctness of spore and vegetative cellular fatty acid profiles of some aerobic endospore-forming bacilli

A gas chromatographic analysis method was employed to determine the cellular fatty acid (CFA) profiles of spores and vegetative cells of some aerobic endospore-forming bacilli. The harvests of experimental strains were processed to obtain pure spores and acquire whole cell fatty acid methyl esters for the subsequent gas chromatographic analysis, and the corresponding vegetative cells were set as control. Evaluation of reproducibility of spore CFA components revealed that, provided under standardized experimental procedure, spore CFA composition was stable enough for research purposes. Fatty acids recovered in spores in greater quantities were saturated branched-chain acids containing 15 and 17 carbon atoms, similar to the vegetative cells. Commonly, the proportions of saturated branched-chain acids in spores were greater than in vegetative cells. The dendrograms obtained by cluster analysis provided some meaningful taxonomic information of the experimental strains. The fatty acids analysis of spores seems to be a promising supplementary tool for the chemotaxonomic research of aerobic endospore-forming bacilli.

Improved method for gas chromatographic analysis of genistein and daidzein from soybean (Glycine max) seeds.

Improved method for gas chromatographic analysis of genistein and daidzein from soybean (Glycine max) seeds.

Gas Chromatographic Analysis of Fosfomycin in Plasma for Pharmacokinetic Analysis

An efficient method for gas chromatographic analysis of fosfomycin in plasma was developed for preliminary investigations of the bioavailability in poultry of 3 commercial complexes of fosfomycin: a levorotatory Ca(-) salt, a racemic Ca(+/-) salt, and a tromethamine (THAM) salt. The method was used to determine whether the less expensive racemic mixture would provide equivalent levels of fosfomycin in blood as the pure Ca(-) form and the THAM salt. The THAM salt, a more expensive product to market, was thought to have the greatest bioavailability. The assay is selective, sensitive, and applicable to pharmacokinetic analysis.

In vivo evaluation of a new method for chemical analysis of volatile components in the respiratory gas of mechanically ventilated patients*

Using the volatile anaesthetic isoflurane as a marker substance a gas chromatographic method for analysis of exhaled gas in mechanically ventilated patients was evaluated. Twelve patients with and 10 patients without preceding isoflurane exposure and seven blank respiratory circuits were investigated. Respiratory gas was sampled at four different sites in the respiratory tubing system. Analysis of volatile components was based upon adsorption onto activated charcoal, desorption by means of microwave energy, gas chromatographic separation and flame ionisation or mass spectrometric detection. Isoflurane concentrations in the blank respiratory circuits, in the control group, and in the inspiratory limb of patients with preceding isoflurane inhalation were at the limit of detection (<10(-12) mol/l). In the isoflurane group, isoflurane concentrations in the inspiratory and expiratory limb differed considerably. Using the method described, substances at very low concentrations could be identified as originating in the patient or as coming from the gas delivery system.

Comparison of gas chromatographic methods for analysis of butyric acid in milk fat and fats containing milk fat

The analysis of butyric acid (C4) is of importance for the determination of the proportion of milk fat in mixed fats. Three gas chromatographic methods were compared with regard to their precision for the measurement of C4, i.e. analysis of butyric acid methyl ester after trans-esterification of fat by sodium methylate (method A) or trimethyl sulphonium hydroxide (method B), as well as analysis of free butyric acid (method C), using an internal standard with each method. The examination of 30 milk fats which varied greatly in terms of their C4 content, using methods A, B and C, resulted in mean values of C4 of 3.42 g/100 g fat, 3.71 g/100 g fat and 3.06 g/100 g fat, respectively. The value determined using method B seemed too high, and this may have been due to the presence of co-eluting artefacts, whereas the value determined using method C was clearly too low, and can probably be attributed to losses during sample preparation. The standard deviation (SD) of 0.015 obtained from repeated analyses using method A was quite good. Results obtained using methods B and C had SDs of 0.029 and 0.074, respectively. Different levels of free fatty acids did not affect the results obtained using method A. When method A was checked by analysis of the reference fat, CRM 164, the C4 level determined was found to deviate from the certified C4 content of 3.49 (± 0.06) g/100 g fat by only 0.05 g C4/fat 100 g. Thus method A proved the most suitable for the determination of the proportion of milk fat in mixed fats by analysis of butyric acid.

New clean-up method for gas chromatographic analysis of pyrethroid residues

A fast and efficient method has been developed for clean-up of fenpropathrin and fluvalinate for gas chromatographic determination of their residues in crops, grain and soil. Charcoal (Darco-G-60) was used as adsorbent and the pyrethroids recovered by washing the adsorbent with hexane-acetone (9∶1). The method provides a clear filtrate with no interfering peaks in the chromatogram. Recoveries ranged 91.00–100%.

Highly accurate gas chromatographic analysis of reference gases for use in vehicle emission measurements

A highly accurate gas chromatographic analytical method has been developed for the determination of the composition of gas mixtures. It was tested using a reference gas as an example consisting of 3.5% of CO, 14% of CO2, 0.2% of propane and residual N2 intended for the use in vehicle emission measurements. The method is based on comparison measurements with samples of a calibration gas, whose composition is iteratively adapted to that of the sample investigated using a gravimetric gas mixing method. For the gas chromatographic measurement, a molecular sieve column and a polymer column are used in parallel and in isothermal operation. All gas components can be determined by a single gas chromatographic measurement, and the relative uncertainty of measurement achievable is ?0.4%.

Development and Validation of an Analytical Method for Naled and Dichlorvos in Air

A new gas chromatographic method for analysis of the thio organophosphate pesticide naled and its transformation product dichlorvos (DDVP) was developed and validated. Naled and DDVP in air were trapped on XAD-4 resin. The pesticides were recovered from the resin with ethyl acetate. Ethyl acetate extract was analyzed for naled and DDVP by using a gas chromatograph equipped with a DB-5 Megabore capillary column and a nitrogen−phosphorus detector. The limits of quantitation for naled and DDVP were 0.05 and 0.10 μg/sample, respectively. Naled and DDVP trapped on the resin were stable over 21 days at −20 °C. Trapping efficiencies of naled and DDVP in the air samples were 74.5 ± 3.5% and 49.7 ± 3.3%, respectively. The newly developed method showed excellent results for the air samples collected at the application sites. Maximum observed concentrations of naled and DDVP at the application sites were 6.30 and 0.99 μg/m3, respectively. Keywords: Air sample; naled; dichlorvos; gas chromatography

Systematic approach to the profiling analysis of illicit amphetamine

The use of automated workstations for the study of the origin of illicit produced amphetamine was examined by comparing the precision of peak identification methods of gas chromatographically determined impurities of confiscated amphetamine powders. The identification parameters used were absolute and relative retention times and retention indices. The retention index monitoring proved to be the most precise identification method when intralaboratory repeatability was examined. Preprocessing of gas chromatographic data is needed when automating pattern recognition for rapid screening of the impurities of amphetamine powder. Normalisation of peak areas of the impurity components was studied; scaled data were calculated by dividing peak areas of the chromatogram by the peak area of a selected impurity component of the same chromatogram. The precision of the gas chromatographic method of analysis in a large impurity concentration range was determined by comparing both the normalisation and the quantitation method of analysis with each other. Normalisation was a more precise way to preprocess data than quantitation on the basis of relative standard deviation values for the comparison. In order to get chromatographic data quickly for pattern recognition it is appropriate to prepare amphetamine powders with the same moisture content before making the analysis. The method of drying powders was studied by comparing gas chromatographically produced results of analyses of powders dried at an ambient temperature to those dried using infra-red radiation. The infra-red drying method proved to be suitable for the rapid preparation and analysis of amphetamine powders.

Interference of Transformer oil Matrices to the Internal Standards on PCB Quantification

Abstract Polychlorinated biphenyls (PCBs) are toxic, perssstent, global environmental contaminants which were formulated as complex mixtures of congeners. Many methods have been developed in the past to analyze PCB in transformer oil samples for regulatory purposes. The most important consideration in the cleanup procedure is the ability to remove the oil from the sample matrix, since trace amount of oil will interfere with the subsequent GC-MS analysis. Electron capture detection (ECD) has been the most common method for gas chromatographic analysis of PCBs because of its high sensitivity toward halogenated compounds. ECD can also respond to some non-PCB compound resulting in biased concentrations of PCB. In this work, a two-stage cleanup method, using DMSO liquid/liquid extraction and HPLC column chromatography. has been applied to two types of transformer oil. Five internal standards have been selected to show their performance in the presence of different oil matrices. The comparison of the PCB quanti...

N,N-dimethylbenzylamine: occupational exposure, analysis and biological monitoring.

Dimethylbenzylamine (DMBA) is used in the production of epoxy resins. The aims of this study were to assess occupational exposure to DMBA and evaluate the usefulness of monitoring the urinary excretion of DMBA and DMBA metabolites as indicators of exposure to DMBA. A sensitive gas chromatographic method for analysis of DMBA in air and in urine has been developed. The detection limit for DMBA in air for a 60-l air sample collected in 10 ml absorption solution was 2 micrograms/m3 and in charcoal tubes, 0.3 micrograms/m3. The detection limit for DMBA in urine was 0.02 mg/l. Ten male workers manufacturing epoxy resin were monitored during a full shift in the working environment and urine samples were collected at the end of exposure. The mean exposure and the highest DMBA concentration observed in air were 18 micrograms/m3 (time-weighted average; range 3-48 micrograms/m3) and 91 micrograms/m3, respectively. The DMBA concentrations in the urine samples were below the detection limit. After reduction of the urine samples the DMBA concentrations (U-SumDMBA) ranged from 0.02 to 0.22 mg/l. There was significant correlation between the exposure to DMBA and the U-SumDMBA. This observation suggests that the U-SumDMBA in urine samples collected at the end of a shift is a useful indicator of occupational exposure to DMBA.

Optimization of Gas Chromatographic Analytical Methods for Toxic Compounds in Air

This is a review article concernning the development of a gas chromatographic analytical method for the analysis of 70 air toxic compounds. Not only the operating conditions, but also the column system is optimized. Optimization of the GC analytical methods for air toxic compounds is based on a unified method with a system comparising two columns. An optimization strategy with stepwise temperature programming has been used to achieve optimum separations. Two sets of usual GC instruments with specially developed software, Chromatogram Analyzer, have also been used for this purpose. Some essential retention data and typical results are presented in this paper.

A survey of ethyl carbamate in beverages, bread and acidified milks sold in Denmark.

A sensitive gas-chromatographic method of analysis using mass specific detection has been applied to a study of ethyl carbamate in the Danish diet. Beverages and foods which were assumed to give a major contribution to the exposure of the Danish population to this potentially carcinogenic compound were investigated. Average values, ranges obtained for concentrations of ethyl carbamate and the number of analyses were 534 micrograms/l (< 5-5000 micrograms/l, n = 22) in spirits, 30 micrograms/l (7-61 micrograms/l, n = 14) in fortified wines, 7 micrograms/l (< 3-29 micrograms/l, n = 57) in wine, 3 micrograms/l (0.2-6.6 micrograms/l, n = 50) in beer, 3.5 micrograms/kg (0.8-12 micrograms/kg, n = 33) in bread and 0.2 microgram/kg (< 0.1-0.3 microgram/kg, n = 19) in yogurts and other acidified milk products. It is estimated that the average daily intake of ethyl carbamate is approximately 2 micrograms per person. The 5% of Danish males who have the highest alcohol intake probably consume more than 7 micrograms of ethyl carbamate per day.

Sorption and Diffusivity Measurements of Cyclohexane+Benzene and Cyclohexene+Toluene Mixtures in Polyurethane Membranes. Model Calculations of the Pervaporation Process

AbstractData of vapor sorption measurements of the solvents cyclohexane, benzene and toluene in polyurethane (PU) membranes are presented. Vapour sorption isotherms have been obtained from equilibrium data. Kinetic sorption data have been used for determining diffusion coefficients of the solvents in the membrane material. Further measurements of the individual solubilities of liquid cyclohexane+benzene and cyclohexane+toluene mixture components in PU‐membrane material have been carried out using the so‐called swelling density method and a gaschromatographic analytical method. Vapor sorption isotherms as well as solubility data of the liquid mixtures can be described with the UNIQUAC‐model in good agreement with experiments. All results obtained for solubilities and diffusion coefficients are used for predictive calculations of fluxes and separation diagrams in the pervaporation process of cyclohexane+benzene and cyclohexane+toluene mixtures through PU‐membranes. The basis of these model calculations is the solution‐diffusion model. Predicted results of pervaporation agree well with experimental data taken from literature provided diffusion coupling of the components permeating the membrane is taken into account.

Validation of a method for gas chromatographic analysis of eicosapentaenoic acid and docosahexaenoic acid as active ingredients in medicinal products

A gas chromatographic method for the determination of all‐cis‐5,8,11,14,17‐eicosapentaenoic acid (EPA) and all‐cis‐4,7,10,13,16,19‐docosahexaenoic acid (DHA) as active ingredients in medicinal products was developed and validated. In accordance with the rules governing medicinal products in the European Community, the method establishes relations between label claims of active ingredients and known reference standards. A routine for examining instrument status is proposed. The relative standard deviation was 1% (n=26) for determination of the empirical response factors of EPA ethyl ester and DHA ethyl ester relative to the internal standard, C23:0 methyl ester. This experiment included two columns and EPA and DHA standards from two different suppliers and was carried out over a five‐month period. Repeatability (n=6) for low and medium concentrates of glycerides and high concentrates of ethyl esters, expressed as coefficient of variation, was 4, 0.7 and 0.7%, respectively. Accuracy (n=6) determined as percent recovery was better than 98% for all sample types. Analytical results from a twelve‐month stability study of the high concentrate are shown.

Capillary Column Gas Chromatographic Method for Analysis of Encapsulated Fish Oils and Fish Oil Ethyl Esters: Collaborative Study

Abstract A gas chromatographic (GC) method using a capillary column for analysis of encapsulated fish oils and ethyl esters was studied collaboratively in 21 laboratories. Each collaborator analyzed 6 soft-gelatin encapsulated samples; 5 were trlacylglycerol oils (one was a blind duplicate), and one was an ethyl ester concentrate of omega-3 (n-3) polyunsaturates. Constituent fatty acids of the oils were converted to methyl esters by base-catalyzed transesterlflcatlon of the oils; any free acids in the oils were esterlfied by subsequent reaction with BF3/CH3OH. The ethyl ester concentrate required no further derlvatlzation. Results were reported as area percentages of 24 analytes of nutritional or biochemical interest. In addition, weights (mg/g sample) of EPA (all-c/s-5,8,11,14,17-elcosapentaenolc acid or 20:5n-3) and DHA (all-c/s- 4,7,10,13,16,19-docosahexaenoic acid or 22:6n-3) were determined through the use of the internal standards, respectively, methyl tricosanoate (23:0) and ethyl 23:0, for the methyl and ethyl esters. The only instrumentation specifically required was a flexible fused silica capillary GC column coated with a bonded polyglycol such as Carbowax-20M, an oxygen scrubber Installed In the carrier gas supply line, and a flame Ionization detector (FID). Most of the collaborators experienced little difficulty In applying the method, and, of 2526 values reported, only 4.3% were identified as outlier values. The reproducibility relative standard deviations (RSDR) compared favorably in most instances with, or were substantially better than, those of 2 earlier collaborative studies of fish oils. Because the variances were homogeneous, standard deviations and relative standard deviations determined on the area percent analyses of the blind duplicate oils were pooled to give the following mean values: sr = 0.15, RSDr = 4.88%, sR = 0.41, and RSDR = 12.91%. Analytes that rarely occur at greater than 0.5% In marine oils (22:0,22:4n-6,22:5n-6,24:0, and 24:1) were not Included in these calculations. The method was adopted first action by AOAC International as an American Oil Chemists' Society (AOCS)-AOAC method.