Design, construction, and applications of an automated microprocessor-controlled gas chromatograph fraction collector-olfactometer.

摘要

A novel device for automated gas chromatography (GC) fraction collection and olfactometry is described. Using glass-lined stainless steel desorption tubes packed with adsorbent material, GC fractions are collected at ambient or sub-ambient temperature (--40°C) and subsequently either thermally desorbed directly into the GC and gas chromatograph-mass spectrometer (GC-MS) or extracted with solvents for rechromatography, infrared spectroscopy (IR), ultraviolet spectroscopy (UV), nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) analysis. The GC fraction collector is useful in the isolation of chromatographically close eluting compounds for their further detection. In addition, the instrument is able to isolate and concentrate low concentrations of individual sample constituents that are otherwise below the limit of detection of the MS and do not meet the sample quantity required for analysis by other techniques such as fourier transform infrared spectrometry (FTIR) and NMR. In the same manner, this device is able to isolate minor components that co-elute with.;larger ones which can obscure their spectrum. The system can be operated in the automatic mode to facilitate the collection of up to 12 fractions per sample by entering the desired trapping parameters, tube trapping sequence, and trapping time into a menu driven, user friendly microprocessor controller which drives all of the operating components of the unit. To ensure trapping in the desired GC retention time window, the control computer initiates a simultaneous start of the GC program and the internal timer of the collector so that both times are synchronized. The computer can also be instructed to mark the area in the chromatogram where the trapping takes place so that these marks can either be used as references during GC analysis or correlated to odor active regions when performing gas chromatography-olfactometry (GC-O). To conduct GC-O, a sniff port that was specifically designed for this system is attached to the unit. Unlike other preparative GC system, this unit was designed eliminating cold spot areas, dead volume areas, and outgasing materials, all of which are sources of contamination.;Several experiments were carried out to determine the collection efficiency of the unit and to demonstrate its capabilities. A recovery efficiency of 86% was obtained by using the internal standard quantitation method that used iso-octane as the standard compound and Tenax-TARTM as the adsorbent material. The trapping accuracy of the instrument in the automatic mode was successfully demonstrated by its ability to trap twelve desired fractions from a standard mixture of paraffin compounds. Accurate trapping and isolation of two closely spaced fractions such as those observed with deuterated and non-deuterated counterparts were successfully achieved. Precise multiple trappings of a single fraction taken from a complex mixture resulted in the isolation of milligram amounts of the purified component and enabled NMR and FTIR spectra of the component to be recorded. The sniff port was used for the identification of a trace level off-odor that was present in a polyethylene (PE) resin sample. Aided by GC-fraction collection (GC-FC), the off-odor was isolated and concentrated until a sufficient amount of the responsible component was obtained to perform GC-MS.