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Limit of discrimination, limit of detection and sensitivity in analytical systems

1994; Elsevier BV; Volume: 287; Issue: 1-2 Linguagem: Inglês

10.1016/0003-2670(94)85109-3

1873-4324

Ricard. Ferrus, Maria Rosa Egea,

Chemical and Physical Properties in Aqueous Solutions

The limit of discrimination is the minimum increase in analyte amount in the test portion which secures, with a high probability, analytical signals significantly different from those given by the original analyte amount. The analyte addition technique is applied to measure the limit of discrimination. The Hubaux and Vos methodology for measuring the limit of detection is followed to obtain the limit of discrimination from the plot of analytical signal vs. added analyte amount. According to Currie, the limit of discrimination in the matrix blank is the limit of detection. When matrix blanks are not available, the limit of detection can still be measured as the limit of discrimination in the solvent, provided that matrix effects are absent. This absence can be shown by compariosn of the limits of discrimination in the laboratory sample, in an analyte solution giving about the same signal as the laboratory sample and in the solvent. This check is not possible in analytical systems showing a sensitivity change near the limit of detection. An extension of the Hubaux and Vos methodology is proposed for measuring the limit of detection in the presence of strong sensitivity changes. Four analytical methods showing sensitivity changes to different extents are applied for the sake of demonstration to determine the sulphate ion concentration in tap water. The Hubaux and Vos, Kaiser and method detection limit methodologies are compared. The differences between the analytical signal, analytical result and analyte amount standard are emphasized. Bias introduced by the calibration standards can be shown through erratic regression residuals.