APPLICATIONS OF MULTIPLEX GAS CHROMATOGRAPHY TO THE DETERMINATION OF ORGANICS IN SOLID SAMPLES

摘要

A multiplex gas chromatographic technique for determining nicotine in cigarettes is described and multiplex gas chromatograms of volatiles from other solid samples are also presented. Direct headspace sampling, which is carried out in a sampler modified from an injector, provides a continuous gas sample stream for multiplex gas chromatography. Volatiles evaporating from the sample are picked up and carried by a carrier gas to a thermal desorption modulator and column. Concentrations to be determined are modulated by the modulator. The thermal desorption modulator is a short section at the head of the capillary column. The modulator section is coated externally with a thin electrically conductive film. An electrical current pulse applied to the thin film heats the modulator section and the stationary phase within it. When the stationary phase is heated and cooled, it releases and adsorbs substances into and from the flowing carrier gas. The signal form resembles a derivative of a chromatographic injection. Large-volume, continuously flowing or headspace samples can be accepted directly. The modulator is simple and effective and is used as both a trap and desorption device. Multiple modulation pulse signals applied during an extended sample introduction period result in a multiplex detector output signal, from which the chromatograms are recovered and computed by applying some fairly simple computational techniques such as cross-correlation. It is possible to determine volatiles in solid samples where the solid material is neither volatile nor soluble in a solvent. No sample pretreatment, preconcentration, extraction or distillation are required. Both the accuracy and precision achieved are fairly good. [References: 18]