Chapter 3 - Sample injection

Abstract

Component separation is affected both by the ratio of solute retention factors and by the width of solute peaks. Peak widths are influenced by the efficiency of the injection process: the shorter the length of column occupied by the injected sample, the shorter the band as it begins the chromatographic process; and the shorter the band as it completes the chromatographic process and is delivered to the detector, the sharper the peak generated by the detector and the better the separation. Direct injection into large-diameter columns, split injection, and split-less injection constitute the hot-injector vaporization methods. In split injection, the sample is introduced into a heated injector, where it undergoes rapid vaporization and thorough mixing of the volatilized components. The split-less mode of injection is used for injecting samples into small-diameter open tubular columns for analysis of trace levels of higher boiling solutes that can be injected in a low-boiling solvent. Direct injection technique is used for injecting into large internal diameter column. Programmed temperature vaporizing (PTV) injector can be used in split, split-less, or direct mode injector and employs an initial inlet temperature that is below the boiling point of all components, including any solvent.