![]() Such a column could produce about the same resolution as the narrow-bore column in about twice the time, and it is compatible with the larger injection volumes produced by direct injection. megabore column with the same phase ratio and direct injection. Without an on-column or split–splitless inlet on-hand, the chromatographer could choose to sacrifice speed of analysis by using a longer 60-m, 0.53-mm i.d. ![]() For example, analysis of a trace-level sample might best be performed with splitless or on-column injection onto a 25-m, 0.25-mm i.d. Where they have the methodological latitude, they also can solve this dilemma by modifying preparation procedures to make the sample compatible with available inlet systems, or by choosing a different, more compatible column. Sometimes none of the suitable inlet systems is available, in which case the analyst might have to choose between compromising the injection or upgrading their chromatographic equipment. ![]() There often is more than one choice of appropriate injection technique, of which only one might be available in a particular laboratory or instrument. The type of sample and its concentration, taken along with the column and detector, determine which types of injection will give the best results. In GC, samples can be liquids, solids, or gases. Chromatographers measure an injection's success by the degree to which it preserves the relative sample composition while not interfering with separation, and by how well the injection process repeats from run to run. On the way to the column, the sample undergoes volume, concentration, temperature, and pressure changes that convert it into a condition that is more or less compatible with the separation that follows. This transformation consists of two principal steps: transfer from the outside into the inlet and transfer from the inlet into the column. Gas chromatography (GC) inlets transform a sample from its physical state outside the chromatograph into a state suitable for separation inside the column.
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