ABSTRACT

Chemical data preprocessing includes all calculations needed to prepare the chemical data for analysis. Necessarily, this includes instrumental calibration, determination of sample extraction recoveries, the precision, and the accuracy for a given analytical procedure. For instrumental analyses, calibration can be either by the external standard or the internal standard procedure, whichever is appropriate. When absolute calibration is not possible, meaningful comparisons of the relative levels of analytes in different samples can still be obtained. External standard calibration is appropriate when detector drift is not a problem, pure samples of the analytes are available for calibration of the instrument, sample extraction/preparation is very reproducible, and variations in injection volumes are minimized. Internal standard calibration is used when there is a good chance of variation being introduced in an analysis procedure. Internal standard calibration allows calculation of levels for many analytes when the response of each analyte is calibrated against that for the internal standard.