Capillary columns in series for the gas chromatographic analysis of essential oils

Summary By connecting capillary columns of different polarity in series and by changing the temperature program gradient, a system of variable polarity is obtained. The working conditions can be adjusted to optimize separations of complex mixtures. Application to the analysis of essential oils of: lavender, thyme, lemon petit grain, bergamot, and tangerine, are reported.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday.     

Preparation and gas chromatographic characterization of dibenzyl crown ether stationary phases

Summary Two crown ethers, di(tert-butylbenzo)-propyl-15-crown-5 polysiloxane (PSO-DTB-15C5) and dibenzo-propyl-15-crown-5 polysiloxane (PSO-DB-15C5) have been synthesized and coated onto fused-silica capillary columns. The chromatographic characteristics, including column efficiency, polarity, phase transition temperature, operating temperature range and selectivity, were studied.Excellent selectivity was obtained for the separation of polar position isomers, especially phenol and dinitrotoluene isomers. The separation mechanism is discussed.     

Liquid and gas chromatographic separation of isomeric methylated dibenzothiophenes

Trace amounts of a dibenzothiophene (DBT) series in complex matrices were detected by gas chromatography with flame photometric detection (FPD) after purification and isolation by normal-phase high performance liquid chromatography. The gas chromatographic behavior of eleven methylated DBTs was studied on six common stationary phases. Complete resolution of the four monomethyl DBT isomers was only achieved on a capillary column coated with a methylphenylsilicone phase gummified in situ by heat-curing. The determination of the relative distribution of the four monomethylated isomers is proposed as a powerful method for monitoring oil pollution in marine environment.     

Large diameter open tubular columns in gas chromatographic analysis

Large diameter open tubular columns provide the packed column chromatographer with a simple route to higher resolution gas chromatography. They can be operated in a high-flow (lower resolution) mode that permits their direct substitution for a packed column, or they can be operated in a low-flow (higher resolution) mode that maximizes separation at the cost of longer analysis times. Inlet design and column installation can influence both the chromatographic results and quantiative reliability. Make-up gas is not required in the high-flow mode, and its benefits in the low-flow mode are restricted to enhanced detector sensitivity, provided the outlet end of the column resides in the detector jet (FID). The columns seem fully compatible with all common modes of detection.     

Quantitative gas chromatography using a new automated derivatizer

In the gas chromatographic analysis of complex biological samples, the most time-consuming and error-prone steps are the pretreatment required for isolation and purification of the compounds of interest and, for most analytes, the derivatization to chemically and thermally stable compounds with high volatility. These wet-chemical steps are usually carried out manually, and for routine analysis of large numbers of samples they are often rate-limiting. A dedicated automated derivatizer has been constructed, the employment of which significantly reduces the time required for manual labor and increases the reproducibility of derivatization and hence the accuracy of analysis.     

Optimizing gas chromatographic separations

While separations based on the use of stationary phases specifically designed to maximize solute alphas can, in the strictest sense, be precisely optimized only under specific isothermal conditions, the approach has previously been used even with temperature programmed separations. Selectivity can by further “tuned” by (1) differential variations in the carrier gas velocity through dissimilarly coated coupled columns, and (2) temperature variations in columns of at least moderate polarity. This paper explores the latter approach.     

Quantitative capillary gas chromatographic analysis

Summary The attainment of precise quatitative analytical data using open-tubular (capillary) columns in standard, commercially available gas chromatographic instrumentation is demonstrated. Key elements in the design and proper utilization of the instrumentation are discussed. The function of the various sample introduction systems is elaborated and their quantitative performance demonstrated. The extra-column contribution to band-spreading is determined and the resultant data is used assessing the suitability of commercial instrumentation for highspeed capillary gas chromatography. The quantitative analysis of a sample containing some eleven components in less than thirty seconds is shown.Dedicated to Dr. L. S. Ettre on his sixtieth birthday.     

Dynamic headspace capillary gas chromatography: A versatile analytical technique

The applicability of dynamic headspace analyses for viscous liquids and solid samples is demonstrated. Some comments on the usefulness of this technique for quantifying volatiles in polymeric matrices are made.     

Capillary gas chromatographic analysis of pyrrolidinedithiocarbamate metal chelates

Pyrrolidinedithiocarbamate (PDTC) chelates of Zn(II), Cu(II), Ni(II), Co(III), Fe(III), Mn(II), Cr(III), and VO(II) were analysed by capillary GC on a DB-1701 column (30 m x 0.25 mm id) with flame ionisation detection (FID). Linear calibrations were attained within "1-30 microg/mL" for Ni(II), Fe(III), Mn(II), Cr(III), Cu(II), and VO(II), and within "2-50 microg/mL" for Co(III) and Zn(II). The limits of detection were in the "150-500 ng/mL" range, corresponding to 15-50 pg amounts reaching the FID system. The optimised method was applied to the determination of Cu(II) and Ni(II) in coins, and that of Zn(II), Cu(II), Ni(II), Fe(III), Mn(II), Cr(III), and VO(II) in pharmaceutical preparations with relative standard deviations within 1.1-5.2%. The results obtained are in good agreement with sewage water samples and the declared values for the pharmaceutical formulations, or with the results of AAS of metal contents in coins, pharmaceutical preparations, and sewage water samples.     

Automatic system for rapid analysis of volatile compounds by purge-and-cold-trapping/capillary gas chromatography

A system for automatic analysis of volatile compounds by purge-and-cold-trapping/capillary gas chromatography is described. It is suitable for analysis of volatile compounds in a wide variety of samples, such as water, food products and environmental samples. Possibilities and limitations of the system are evaluated in relation to several parameters. The efficiency of different types of cryogenic trap (open tubular, coated, packed) is also investigated; it depends on purge-flow rate, temperature of trapping, and total purge volume. Examples of the analysis of volatile compounds in foods and water are given.     

Capillary gas chromatography of esters correlations between structure and retention index

Summary The retention index of twenty different homologous series of esters have been determined experimentally on polar (Carbowax 1540) and non-polar (squalane) columns. General equations to calculate retention index have been established by statistical methods. The influence of the length and inductive effect of acid and alcohol chains and the relative position of the carboxylic group are discussed.     

On-line multidimensional chromatography using packed capillary liquid chromatography and capillary gas chromatography

The introduction of selected fractions from a liquid chromatograph into a gas chromatograph has been described; however, analyses were performed by off-line experiments requiring collection and reinjection of the separate fractions or by on-line procedures where disadvantageously, only a fraction of the separated peak or a well resolved component in a mixture could be introduced into a gas chromatograph. This disadvantage is overcome by the apparatus and method described in this paper, which utilizes a multidimensional chromatography system employing a high efficiency, packed capillary LC column coupled on-line to a capillary gas chromatograph. The liquid chromatograph (so designed) can act as a highly efficient clean-up or chemical class fractionation step prior to introduction into the gas chromatograph, significantly reducing sample preparation times in many applications. Thus minor components in a complex matrix can be determined without prior sample clean-up, an example of which is the determination of polychlorinated biphenyls in a complex hydrocarbon matrix.     

Gas chromatographic separation of sugars by on-column injection on glass capillary columns

Sugars were separated gas chromatographically on short apolar glass capillary columns by using cold, on-column injection (OCI) techniques. After silylation, oligomers up to the hexasaccharides could be efficiently separated in resonable retention times. Response factors of silylated sugars were determined as a function of varying sample amounts and concentrations. The optimum injection amount was found to be 1 μl in heptane as solvent.     

Ketoimine modified silica as an adsorbent for gas chromatographic analysis of olefins

New adsorbents for capillary complexation GC have been proposed. The adsorbents contain free ketoimine groups which enable binding copper(II) and chromium(III) chlorides. The adsorbents obtained have been characterised by elemental analysis, differential scanning calorimetry and electron spin resonance. The specific interactions between the adsorbent and adsorbate molecules have been characterised by retention parameters (retention index - I, specific retention volume - Vg, molecular retention index - deltaMe). Attempts were also made at separating mixtures of olefins.