Temperature-programmed Capillary Gas Chromatography Research Articles

Optimization of GC-MS Method for Analysis of Basil Essential Oils from Algeria: Design of Experiments and Exploratory Pattern Recognition

An optimization procedure for multistep temperature-programmed capillary gas chromatography was developed for the analysis of basil essential oil. The current study was planned after performing the following three steps: a preliminary chromatographic study, primary parameter screening, and final method optimization by using 23 factorial and Doehlert designs (DOE). The optimized conditions were obtained by using a split ratio of 1 / 2 , a gas flow rate of 1.3 mL/min, and a heating rate of 2°C/min. This set of conditions was later used for the optimization of the final method. The optimal experimental conditions were subsequently obtained by response surface optimization (isotherm duration = 6.2 min and slope = 1.06°C/min). The compositions of essential oils from six varieties of basil (Ocimum B. (1), Ocimum B. purpurescens opal (2), Ocimum B. minimum (3), Ocimum. B. cinnamon (4), Ocimum B. (marcellas) (5), and Ocimum B. Citriodora (6)) grown in four regions of Algeria (Ouargla, south of Algeria (O); Mostaganem, west of Algeria (M); Algiers, north of Algeria (A), and Constantine, east of Algeria (C)) were determined. A statistical study was performed based on hierarchical ascending classification and principal component analysis to elucidate the relationships between the basil varieties, their region of growth, and their essential oil composition. In addition to identifying several chemotypes, such as linalool, linalool/eugenol, linalool acetate, methyl eugenol, methyl chavicol, eugenol, methyl cinnamate E, and geraniol, a new compound, namely, octadecenamide (Z) (oleamide), was detected in the essential oil of Ocimum basilicum L. from Algiers (A1).

Mathematical method for the prediction of retention times of fatty acid methyl esters in temperature-programmed capillary gas chromatography.

An accurate method for identification of fatty acids in complex mixtures analyzed by temperature-programmed capillary gas chromatography is described. The method is based on a mathematical approach using regression curves obtained by plotting the relative retention times of fatty acid methyl esters (FAMEs) analyzed in isothermal and gradient temperature conditions. The method was applied to a complex biological sample (human milk), and it was possible to identify 64 fatty acids, including branched-chain and other fatty acids for which reference standards were not readily available. The identities of the majority of the peaks were confirmed by mass spectrometry. The relative residuals and the relative differences between estimated and measured relative retention times of individual FAMEs varied from 0.03 to 3.15% and from 0.0 to 2.9%, respectively. The method is useful for identification of fatty acids in routine analysis.

Comparison of Sample Preparation and Analysis Using Solid-Phase Extraction and Solid-Phase Microextraction to Determine Monohydroxy PAH in Urine by GC/HRMS

Sample preparation techniques using solid-phase extraction (SPE) and solid-phase microextraction (SPME) are compared for the analysis of monohydroxy polycyclic aromatic hydrocarbons (OHPAH) in human urine. Urine samples spiked with five carbon-13 labeled internal standards are first enzymatically hydrolyzed. Sixteen OHPAH from eight parent compounds (naphthalene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, benzo[ c ]phenanthrene, and benz[ a ]anthracene) are then extracted along with the internal standards by these two different techniques. The analytes are derivatized by a silylating reagent before final analysis. Final separation and detection are performed by temperature-programmed capillary gas chromatography (GC) and high-resolution mass spectrometry (HRMS). The two extraction techniques are compared for sample preparation time, cost, throughput, reinjection possibility, frequency of outliers, matrix interference, signal linearity, and method detection limit. SPE demonstrates major advantages over SPME for most of these aspects.

Comparison of Sample Preparation and Analysis Using Solid-Phase Extraction and Solid-Phase Microextraction to Determine Monohydroxy PAH in Urine by GC/HRMS

Sample preparation techniques using solid-phase extraction (SPE) and solid-phase microextraction (SPME) are compared for the analysis of monohydroxy polycyclic aromatic hydrocarbons (OHPAH) in human urine. Urine samples spiked with five carbon-13 labeled internal standards are first enzymatically hydrolyzed. Sixteen OHPAH from eight parent compounds (naphthalene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, benzo[ c ]phenanthrene, and benz[ a ]anthracene) are then extracted along with the internal standards by these two different techniques. The analytes are derivatized by a silylating reagent before final analysis. Final separation and detection are performed by temperature-programmed capillary gas chromatography (GC) and high-resolution mass spectrometry (HRMS). The two extraction techniques are compared for sample preparation time, cost, throughput, reinjection possibility, frequency of outliers, matrix interference, signal linearity, and method detection limit. SPE demonstrates major advantages over SPME for most of these aspects.

An equation for the calculation of retention indices in temperature-programmed gas chromatography with allowance for the nonlinear variation of the retention parameters ofn-alkanes

In view of the nonlinear variation of the temperature increments ofn-alkanes found previously, the accuracy of the calculations of the retention indices (I pr) of substances in temperature-programmed capillary gas chromatography carried out in terms of six known equations was verified. A new four-parameter equation was proposed, and a general method for the calculation of its coefficients, suitable for all stationary phases, based on the adjusted retention times ofn-alkanes was suggested. The coefficients of the equation for 12 temperature variation programs were determined. Using the homologous series of methyl esters of fatty acids as an example, it was shown that the proposed equation ensures the minimum error of determination ofI pr under various conditions. The equation also makes it possible to carry out interpolation and extrapolation calculations. The coefficients of the equation are found using the least-squares method based on data for any 4–5 referencen-alkanes.

Estimation of Air/Coating Distribution Coefficients for Solid Phase Microextraction Using Retention Indexes from Linear Temperature-Programmed Capillary Gas Chromatography. Application to the Sampling and Analysis of Total Petroleum Hydrocarbons in Air

The paper describes a method to quantify hydrocarbons in air exclusively on the basis of chromatographic parameters without the need for calibration. A simple technique is presented to estimate distribution coefficients (K) between air and the poly(dimethylsiloxane) solid phase microextraction (SPME) fiber coating using the linear temperature-programmed retention index system (LTPRI). There is a linear relationship (r(2) = 0.99989) between the log K for a series of n-alkanes and LTPRI, thus providing a means by which establishing a K for any peak in a chromatogram is possible given its published or experimentally determined LTPRI. This alternative approach to establishing K values significantly enhances and simplifies the use of SPME for sampling and analyzing air for quantification of compounds without the need for fiber calibration. Analysis of a group of 29 isoparaffinic compounds and a group of 33 aromatic compounds showed excellent agreement between their theoretical air to fiber distribution coefficients based on LTPRI and the experimentally obtained distribution coefficients. In addition, for a very complex mixture of organics such as gasoline, SPME can establish a total petroleum hydrocarbon in air level using LTPRI. This method was carefully evaluated, and the results were essentially identical between standard procedures and the proposed simple procedure described in the paper.

Retention index system for identification of polychlorinated biphenyl congeners in gas chromatographic analysis

A retention index system is proposed based on a series of individual PCB congeners: PCB8, PCB31, PCB44, PCB101, PCB138, PCB180, PCB194. The retention indices of 59 PCB congeners were determined using this system under different GC conditions. This index system is suitable for electron-capture detection in the examination of environmental samples by temperature-programmed capillary gas chromatography and will have universal applicability.

Design and use of a thermal conductivity detector at reduced pressure for temperature-programmed capillary gas chromatography

Based on a systematic study of the response characteristics of a thermal conductivity detector (TCD) at reduced pressure, a newly designed TCD was constructed and evaluated for use in temperature-programmed capillary gas chromatography. The effective cell volume is as low as 1.3 μl (physical volume 100 μl), and there is no dead corner along the sensing path. Capillary columns of I.D. ⩾0.25 mm can couple directly with the TCD without a make-up gas. The detector response time is less than 0.1 s, the linear dynamic range is about four orders of magnitude and the detection limit is about 10 ppm (v/v) for octadecane. In the split injection mode, a simple configuration of the capillary inlet system offers a constant carrier gas flow-rate through the column with temperature-programmed operation. Practical examples are given that demonstrate the applicability of this detector and the system.

Exposure of commuters to volatile aromatic hydrocarbons from petrol exhaust

Twenty-two volatile aromatic hydrocarbons were determined in the air of an automobile during commuting. Sampling was made on Tenax cartridges and laboratory determinations were carried out using thermal desorption combined with temperature-programmed capillary gas chromatography. Selected hydrocarbons representative of petrol exhaust were determined in the automobile and in an electric commuter train during eight parallel commuter trips. In the automobile, the concentrations of benzene were 35–70 μg/m 3 and those of total aromatic hydrocarbons 200–400 μg/m 3. The petrol exhaust levels were 5–10 times higher in the automobile than in the compartment of the commuter train.

Live retention database for identification in multi-step temperature-programmed capillary gas chromatography

A calculation procedure for multi-step temperature programmed gas chromatographic retention times and that was investigated over diverse temperature programme conditions is descibed. Thermodynamic parameters of components, calculated from their Kováts retention indices and the isothermal retention times of n-alkanes, are utilized in the procedure. The influence of column dead time and variations of Kováts retention indices is examined. The calculation accuracies are better than 1% in most instances. A live retention time database for multi-step temperature programming was constructed using this procedure.

Determination of MK-287, a new platelet-activating factor antagonist, in plasma and serum by gas chromatography chemical ionization mass spectrometry

MK-287 is a novel platelet-activating factor antagonist. A sensitive and specific gas chromatographic/mass spectrometric assay has been developed for the determination of the drug in serum and plasma. The assay utilizes an extraction with methyl-t-butyl ether and subsequent trimethylsilylation of the hydroxyl function. The gas chromatographic/mass spectrometric determinations are carried out with temperature-programmed capillary gas chromatography and ammonia negative chemical ionization mass spectrometry. The method has sufficient sensitivity, precision, accuracy and selectivity for the analysis of drug concentrations in clinical samples.

Interactive retention index database for compound identification in temperature-programmed capillary gas chromatography

A procedure is described and evaluated that allows the calculation of linear temperature-programmed retention indices from accurate Kováts retention indices on a given stationary phase and their temperature variation coefficients. The influence of experimental factors such as column film thickness, phase ratio and variation of Kováts retention indices, column dead time and carrier gas flow-rates are examined. The calculation accuracies are ≤ 0.5 retention index units in most instances. The applicability and limitations of the procedure are discussed.

Automated analysis of various compounds with a wide range of boiling points by capillary gas chromatography based on retention indices

A simple and reliable automated method has been developed for the analysis of various compounds with a wide range of boiling points by temperature-programmed capillary gas chromatography (GC). It consists of the identification based on corrected retention indices and the quantitation by a multi-internal standard technique. The full automation of the analysis was achieved by the connection of a GC system to a personal computer. Some factors affecting the reproducibility of retention indices and the quantitation are discussed. As an example of the application of the method, the analysis of a commercial cosmetic product was demonstrated.

INFLUENCE OF CROPPING TREATMENTS ON THE MONOSACCHARIDE CONTENT OF THE HYDROLYSATES OF A SOIL AND ITS AGGREGATE FRACTIONS

The influence of three cropping treatments on the quantitative and qualitative composition of the carbohydrate fraction of a silt loam soil and its water-stable aggregates was assessed. Three cropping treatments were considered: bromegrass (Bromus inermis Leyss.) grown continuously for 15 yr (B15), grain-corn (Zea mays L.) grown continuously using conventional tillage for 15 yr (C15), and grain-corn grown continuously for 13 yr followed by 2 yr of bromegrass (B13C2). Six water-stable aggregate size fractions ranging from 8.00–4.70 to 0.25–0.10 mm in diameter were separated from the soil by wet sieving. The carbohydrate fraction was extracted by acid hydrolysis, reduced, acetylated to alditol acetates and analyzed by temperature-programmed capillary gas chromatography. Total carbohydrate content was not significantly influenced by cropping treatment but was observed to increase as aggregate size decreased irrespective of cropping treatment. The carbohydrate content in the different aggregate size fractions was positively correlated with both organic carbon and clay contents. With the exception of xylose and mannose, the monomeric sugars behaved similarly to total carbohydrates. Based on the magnitude of the ratio of the content of mannose to that of arabinose plus xylose, the contribution of plant carbohydrates to the total carbohydrate fraction increased as aggregate size decreased in the B15 treatment, but decreased in the C13B2 and C15 treatments. No significant correlations existed between either the total carbohydrate content or the content of individual sugars, and the stability of aggregates in the soils from the different cropping treatments. Key words: Wet aggregate stability, soil organic matter, soil structure, crop rotation, corn, bromegrass

The precision of area and height measurements with flame ionization detectors in temperature-programmed capillary gas chromatography

The precision of area and height measurements with flame ionization detectors in temperature-programmed capillary gas chromatography

Use of kovats indices for prediction of retention temperatures in linear temperature-programmed capillary gas chromatography

Over 100 hydrocarbons present in gasoline have been identified by linear temperature-programmed capillary gas chromatography on OV-101 on the basis of

Calculation of retention indices in temperature-programmed capillary gas chromatography

Previously reported methods for calculating retention indices in temperature-programmed gas chromatography (TPGC) were restricted either to a simple linear temperature increase without a constant temperature stage, or to a complicated temperature programme operated at a constant mass flow-rate. The present method is applicable to complicated temperature programmes operated at constant pressure, which is the common practice in most applications of capillary GC.

Structure-retention studies of model ketones by capillary gas chromatography

The retention indices ( I) for a number of ketones were determined using linear temperature-programmed capillary gas chromatography. 2-Ketones were used as standards for the index calculations. The 95% confidence interval for triplicate determinations was found to be ± 0. 13 index unit. These retention indices and the zero-, first-, and second-order molecular connectivity factors for each compound were treated with multiple regression to yield equations to predict I. An interesting trend in the retention of symmetric ketones was noticed and rationalized on the basis of shielding of the carbonyl oxygen.

Use of equivalent chain lengths for the characterization of fatty acid methyl esters separated by linear temperature-programmed gas chromatography

C 12C 26 fatty acid methyl esters (FAMEs) were separated by glass capillary gas chromatography on SP 2340 as stationary phase, both isothermally in the temperature range 150–220°C and using linear temperature-programmed capillary gas chromatography (LTPCGC) with gradients of 0.5–3.5°C/min. The dependences of the equivalent chain lengths on temperature are linear. An equation as well as a graphic procedure are derived for the prediction of the retention temperatures of FAMEs separated by LTPCGC on SP 2340. Good agreement between predicted and experimental retention temperatures was found.

Gas-liquid chromatographic analyses : XXV. Branched-chain C 3–C 5 alkyl esters of halogenated acetic acids

The temperature-programmed capillary gas chromatography of branched-chain C 3C 5 alkyl esters of acetic and mono-, di- and tri-chloro- and -bromoacetic acids was studied on low-polarity (SE-30) and highly polar (OV-351) columns. The retention behaviour of the esters was compared with that of the corresponding alcohols, the retention indices and the retention index increments for the methylene units and the various halogen substituents were determined and the retention order of the individual components in the eight homologous series is discussed.