GC037 Sample Inlets and Sampling Devices

The most common way to introduce a sample is using a micro syringe and the sample is a liquid. The sample system should permit the sample to be introduced rapidly and quantitatively onto the column. Three types of inlets are the most common for capillary columns: split, split less and on-column. In practice is impossible to introduce the whole sample instantaneously, but it is desirable to introduce it as a sharp symmetrical band. The difficulty of achieving this can be seen by analyzing an example. A 1.0 µL liquid sample of benzene vaporizes to 600 µL after heating in the injector. If the flow rate is 1 mL/min, then 36 seconds would be needed to carry the whole sample onto the column. Hence, sampling and the size of the samples are critical aspects of chromatography.

The smallest possible sample size should be used to obtain the maximum resolution and peak shape. On the other hand, the more components present in the sample, the larger the sample size may need to be. For trace work and for preparative-scale work is best to use big samples. The column will be “overloaded” with the major peaks; however, the trace peaks will be larger and the result of seeing or measuring them will be achieved.

Quick guidelines for sample size in each type of column:

Regular analytical packed: sample size of 0.2-20 µL

High efficiency packed: sample size of 0.01-2 µL (using splitting techniques)

Capillary (open tubular): sample size of 0.01-3 µL (using splitting techniques)

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