A NEW CALIBRATION APPROACH BASED ON LINEAR CORRELATION AND
ITS APPLICATION IN SPECTROSCOPY

G. Galbács1, I. Horváth1, I.B. Gornushkin2, B.W. Smith2, J.D. Winefordner2, Z. Galbács1

1Dept. of Inorg. and Anal. Chem., University of Szeged, 6701 Szeged, POB 440, Hungary
2Dept. of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, USA




We have recently introduced [1] a new, semi-quantitative calibration approach for the percentage level concentration range. Our current paper describes the proposed calibration approach and its application in laser induced plasma spectroscopy (LIPS) and diode array UV/Vis absorption spectroscopy in detail. The method is based on the observed dependence of the linear correlation coefficient (r) on the analyte concentration in binary samples. The linear correlation coefficient is calculated between masked spectra of a range of certified standards and the spectrum of a reference sample (the analyte in a pure form), and the resulting curve is used for calibration. It was found, that a quadratic function can be adequately used to fit the points.

There are at least two reasons why this approach can be of particular interest. First, r is known to be insensitive to the linear transformation of any or both of the two data sets for which it is calculated. This means that the shape and position of the proposed calibration curves are not affected by detector sensitivity or baseline level variations, as long as these affect the spectra uniformly. In other words, once recorded, these calibration curves can be stored and used for a certain experimental setup for a long time. Second, the fluctuation of the linear correlation coefficient calculated for two spectra is observed to be generally smaller than the fluctuation observable on any of the analytical lines in the same spectra.

Our presentation characterizes the proposed calibration method providing mathematical and simulational data and describes its possible extension to multicomponent samples. In the application part, the new method is compared to the conventional direct calibration through applications and is found to outperform it in terms of both precision and accuracy.
 

[1] G. Galbács, I.B. Gornushkin, B.W. Smith, J.D. Winefordner: Semi-quantitative analysis of binary alloys using laser induced breakdown spectroscopy and a new calibration approach based on linear correlation, Spectrochim. Acta B (2001), in press