Comparison of two-stage retention index monitoring capillary gas chromatography and selected ion monitoring capillary gas chromatography: Mass spectrometry as analytical tools

Two‐stage capillary GC with two‐stage retention index monitoring is an efficient analytical technique which can be used for detection and determination of small amounts of volatile compounds in complex mixtures of hundreds or thousands of other compounds. The system employs two capillary columns, coated with different stationary phases, connected on‐line with the aid of a micro valve; the first column acts as a pre‐separating unit from which unresolved fractions of interest are cut (transferred) into another column for final, interference‐free separation of the compounds to be determined. This technique has been compared with selected ion monitoring capillary GC‐MS using a hydrocarbon mixture as a test sample for comparing resolution, repeatability, and the practical usefulness of the techniques. Results indicate that two‐stage capillary GC is very useful for mixtures containing compounds which produce mostly non‐specific ions in the MS ion source whereas compounds producing specific ions can be easily analyzed by capillary GC – single ion monitoring MS even if they are not perfectly separated by a single capillary column.