Any action applied to the sample before the analytical procedure. Such actions include the addition of preservatives, separation procedures, storage at low temperature, protection against light and irradiation, loading, etc.
Source:
PAC, 1989, 61, 1657. 'Nomenclature for automated and mechanised analysis (Recommendations 1989)' on page 1661 (https://doi.org/10.1351/pac198961091657)