REAL-TIME INTERNAL STANDARDIZATION FOR INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY USING A CUSTOM SEGMENTED-ARRAY CHARGE-COUPLED-DEVICE DETECTOR

The use of real-time internal standardization for inductively coupled plasma atomic emission spectrometry (ICP-AES) was investigated using a new echelle spectrometer equipped with a custom segmented-array charg e coupled device detector. The simultaneous data acquisition system is useful for the study of the degree of correlation in the line signals for a multi-element line set. Precision values below 0.1% RSD were re adily obtained when the proper conditions were used. Shot noise, which cannot be correlated, degrades the correlation between the analyte an d the reference signal. The instrumentation used permitted the examina tion of the same spectral line signal of an element in adjacent orders of the echelle grating, thus providing a useful means of studying sig nal correlation and the effect of shot-noise. A signal which is genera ted from a linear combination of signals coming from a multi-element l ine set was used as the reference signal for internal standardization. Results with this synthetic signal were compared with the use of a Sc reference line. Precision improvements as large as a factor of three were observed with simultaneous internal standardization when the anal ytical signal was limited by flicker noise. Improvement factors of alm ost-equal-to 50 were observed when the signal contained a significant drift component. The precision of shot-noise limited signals was not i mproved by applying simultaneous internal standardization. Methods are described for discriminating between flicker noise, shot noise and dr ift in the analytical signal.