Injection temperature effects using On-column and split sampling in capillary gas chromatography

The effect of sample injection temperature on quantitation is examined for on‐column and conventional split modes of sampling in capillary gas chromatography. Discrimination effects can be observed even with on‐column injection if the injection temperature is too far above the boiling point of the solvent (or that of a major low boiling constituent(. This is attributed to higher boiling components being left behind in the syringe needle, and a set of simulation experiments are described to illustrate this effect. Various discrimination patterns using conventional split injection were observed, depending on temperature of injection. Apart from syringe needle effects, discrimination is probably due to the preferential venting of higher boiling components as liquid sample droplets, which can have a lifetime greater than the time of transit to the splitter. With such a two‐phase system, involving variable droplet size, the flow distribution in the splitter will be critical to uniform sampling. The use of combination on‐column/split sampling, with the appropriate temperature control to provide sample uniformity to the splitter is discussed as an advantageous alternative to conventional split sampling.