Reversed-phase liquid chromatography coupled on-line with capillary gas chromatography

Automated on-line comprehensive two-dimensional LC×GC and LC×GC-ToF MS: Instrument design and application to edible oil and fat analysis

After a successful off-line feasibility study, the automation of comprehensively coupled liquid chromatography and gas chromatography (LC x GC) has been studied. Important aspects to consider when developing automated LG x GC include the relative speeds of the two dimensions, the compatibility of the LC eluent (type and flow rate) with the GC dimension, and the column loadabilities. Because the GC separation is relatively slow, the LC instrument has to be operated in the stop-flow mode. Two interfaces for transferring large numbers of subsequent LC fractions to the GC were constructed: one based on a six-port switching valve, and one which uses a dual side-port syringe. Both interfaces were found to perform fully acceptably. The actual transfer of the LC fraction to the GC was realised using a standard split injector to vaporise the compounds and LC eluent. Gas phase splitting was applied to match LC mass load and GC column loadability. The standard deviations of the peak areas obtained in this way were better than 7% (n = 6). The reliability of the system was demonstrated by the problem-free analysis of large series of oil and fat samples, with the focus on both intact triglycerides and their fatty acid methyl esters (FAMEs). Finally, the hyphenation of the automated LC x GC system to a sensitive and rapid-scanning time-of-flight mass spectrometer was realised. By using LC x GC-ToF MS, the information density of the chromatograms could be improved even further, which allowed easy identification of individual compounds as well as compound groups.

On-line coupled liquid chromatography-gas chromatography

On-line coupled liquid chromatography-gas chromatography (LC-GC) is a powerful technique that combines the best features of LC and GC and is ideal for the analysis of complex samples. This review describes the unique features of on-line coupled LC-GC. The different interfaces and evaporation techniques are presented, along with their advantages and disadvantages. Guidelines are given for selecting a suitable LC-GC technique and representative applications are noted.

Introduction of large volumes of water-containing samples into a gas chromatograph. Improved retention of volatile solutes through the swing system

The swing system is designed for introducing large volumes of water-containing samples into a gas chromatograph. Sample evaporation and solvent-solute separation are performed in separate compartments. This widens the application range to compounds of higher volatility. Sample evaporation takes place in a hot chamber packed with Carbofrit. Solvent-solute separation is performed in a cascade of increasing powers of retention. While high boiling solutes are retained in an oven-thermostatted retaining precolumn, the more volatile components are retained by a packed bed of sorbents of increasing powers of retention situated in a programmed temperature vaporiser. For elution, the gas flow is reversed and the solutes are discharged from the heated packed bed through the retaining precolumn into the separation column.

On-line combination of aqueous-sample preparation and capillary gas chromatography

Methods currently in use to combine the preparation of aqueous samples on-line with capillary gas chromatography (GC) comprise heartcut-orientated reversed-phase liquid chromatography-GC and analyte-isolation-orientated analyte extraction-GC. These approaches either use techniques in which water is directly introduced onto the GC column, or an indirect approach in which water is eliminated, i.e., by solid-phase extraction, solid-phase microextraction or liquid-liquid extraction, prior to introduction of the analytes onto the GC column. The latter type of approach is much more successful and user-friendly, and many applications have been reported.

On-line combination of aqueous-sample preparation and capillary gas chromatography

An overview is presented of methods currently in use to combine the preparation of aqueous samples on-line with capillary gas chromatography. Two approaches can be distinguished: heartcut-orientated reversed-phase liquid chromatography-gas chromatography (GC) and analyte-isolation-orientated analyte extraction-GC. These approaches either use techniques in which water is directly introduced onto the GC column, or an indirect approach in which water is eliminated, i.e., by solid-phase extraction, solid-phase microextraction or liquid-liquid extraction, prior to introduction of the analytes onto the GC column. The latter type of approach is much more successful and user friendly, and many applications have been reported.