91Ó°ÊÓ

(a)

Split injection is recommended if the sample contains $>0.1\%$ of the analyses of interest Meanwhile, split less injection is applied for samples that has less than $0.01\%$analyses and requires trace analysis. Lastly, for samples that decay above their boiling points, on-column injection is preferred. It is also recommended for quantitative analysis.

(b)

In solvent trapping, the solvent condenses at the start of the column because the initial column temperature is set $40\mathrm{C}$below the boiling point of the solvent. Solutes are then confined in the solvent as they catch up with the condensed plug of solvent. This method results to sharp chromatographic peaks, wherein the first peaks of interest should have boiling points 30 C greater than that of the solvent. The chromatography in solvent trapping starts when the column temperature is increased to vaporize the solvent trapped at the column head.

Cold trapping is another technique of condensing solutes in a narrow band at the beginning of the column. In this method, the initial column temperature is set at 150C lower than the boiling temperature of the solutes being considered. The solutes with high boiling points are trapped in a narrow band at the start of the column, while the solvent and components with low boiling points are quickly removed.

Chromatography of the high-boiling solutes is initiated by rapidly heating the column. Meanwhile, for low-boiling solutes, cryogenic focusing is needed and the initial column temperature is set below room temperature.