Accuracy in Trace Analysis

Most analytical measurements are not absolute but depend on the correlation between physical phenomena and some intrinsic property, e.g., concentration. Therefore, calibration is an indispensable part of analytical chemistry. Unfortunately, calibrations are not free from interference by the environment. This disturbing environment can be the micro-environment, components in the sample that influence the calibration line. As a rule this interference is usually constant, though not always (e.g., separation processes). The macro-environment, however, changes continuously. Temperature, pressure, chemicals, and man are stationary only during a short time. These influences will be seen as random fluctuations or, when autocorrelated, as drift. One approach is to monitor the properties of the calibration system internally by incorporating a calibration system and a measuring system. By monitoring the calibration system, the results of the unknown can be corrected. Kalivas and Kowalski [1] described the solution for the multicomponent situation, using the generalized standard addition method (GSAM). By treating drift as a time dependent component they obtain the equation