PRECISION-OPTIMIZATION OF WAVELENGTHS IN DIODE-ARRAY DETECTION IN SEPARATION SCIENCE

With the theoretically predicted relative standard deviation (RSD) of measurements as a criterion, the ultra-violet detection wavelengths ar e optimized in a capillary electrophoresis system equipped with a diod e-array, when analyte signals are baseline-separated in the time-direc tion and the measurements are the integration results in the time and wavelength directions. Some cold drugs and additives are taken as exam ples. The auto-correlation of an instrumental baseline at a diode (tim e-correlation) and the cross-correlation of measurements between diffe rent diodes (wavelength-correlation) are both taken into account for a better prediction of RSD. A simple method for estimating the waveleng th-correlation is presented with a theoretical proof. This paper also shows that the measurement precision is governed to a large extent by the zero level setting of the time integration which accumulates the i nstrumental output relative to the zero level. The optimum (minimum RS D) is selected from among the wavelengths (190 - 300 nm) and possible zero level settings. The validity of the RSD prediction is statistical ly verified.