Solid analytical column, large-volume injection

For many analytical methods using HPLC as the end step, the samples presented to the analyst cannot be injected directly into the instrument. For example, the sample may be a large volume of water where the analytes are present at low concentrations, a solid such as soil or foodstuffs, or a biological specimen where numerous other compounds are present. Sample preparation is therefore needed to isolate the analytes of interest, to pre-concentrate them in order to lower detection levels and also to protect the analytical column from substances which may potentially damage the bed of packing material. Despite many advances in instrumentation for HPLC, only rarely are samples (particularly complex samples) injected without some form of sample pre-treatment. 

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