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 charge 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 readily obtained when the proper conditions were used. Shot noise, which cannot be correlated, degrades the correlation between the analyte and the reference signal. The instrumentation used permitted the examination of the same spectral line signal of an element in adjacent orders of the echelle grating, thus providing a useful means of studying signal correlation and the effect of shot-noise. A signal which is generated from a linear combination of signals coming from a multi-element line 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 analytical signal was limited by flicker noise. Improvement factors of almost-equal-to 50 were observed when the signal contained a significant drift component. The precision of shot-noise limited signals was not improved by applying simultaneous internal standardization. Methods are described for discriminating between flicker noise, shot noise and drift in the analytical signal.