Extended range background correction in continuum source atomic absorption spectrometry

Abstract

A novel analogue to digital converter (ADC) range switching procedure has been developed which allows the extension of the background correction capability of continuum source atomic absorption spectrometry through reduction of the error associated with quantisation noise. The procedure is based on the use of two channels of the ADC for the acquisition of data. One channel operated at a gain of × 1 and the other at a gain of × 10. Signals from both channels were recorded simultaneously during data acquisition and stored in a dual data buffer. The data reduction routine was switched between the data acquired by both channels via a threshold algorithm based on the intensity of the continuum source as the data were collected. Hence data were taken from the × 10 data buffer when the intensity of the continuum source was very low due to background absorbance. This avoids the use of data from the × 1 channel of the ADC which had resolution problems at low transmitted lamp intensity levels and gives greater quantisation noise. This paper describes this system and illustrates the improvement obtained when using the gain switching procedure for the measurement of continuum source atomic absorption signals in the presence of high levels of background absorption caused by a sodium chloride matrix.