SOURCES OF SYSTEMATIC-ERRORS IN CHEMICAL SENSOR CHEMOMETRICS

Systematic errors can occur in every chemical analysis independent of the method used. In general, the risk of systematic errors can be dimi nished by separation steps prior to the determination procedure. In se nsor measurements systematic errors can be noticed only by analysing r eal samples with a known concentration of the analyte with a great var iety of matrices. The sources for such errors are manifold, although e xcellent reproducibility of the results is shown. The main reason for a systematically biased result in the field of chemo- and biosensors l ies in the influence of the sample matrix on the sensor signal, which ought to be produced by the analyte only. Examples of strong matrix in terferences on different sensor principles are presented and a classif ication of the most prominent systematic errors known in analytical ch emistry is given. Apart from problems related to a lack of selectivity , which lead to a co-sensing of interferents, the matrix often influen ces the sensitivity (slope of the calibration curve) and/or the level of the blank signal in an unpredictable manner. Compensation methods, like the well-known blank-signal subtraction or differential sensor me asurements, work properly only if certain conditions are fulfilled. Th e principle of signal additivity has to be proven and the invariance o f the sensitivity has to be demonstrated in any case and for different matrices. With sensor arrays these requirements must be fulfilled as well.