Application of the inverse Zeeman effect to background correction in electrothermal atomic-absorption analysis

Abstract

An electromagnet was placed around a specially designed graphite furnace atomiser and the Zeeman effect generated in the atomised sample was used to correct for background absorption generated by the matrix. The optical polarisation properties inherent in the Zeeman effect were utilised to generate two signals, one corresponding to the absorption of the atomic line plus background and the other to the background alone. A simple theoretical treatment was developed that related the observed atomic absorbance to a parameter dependent on magnetic flux density. This parameter, designated R in this work, is a function of the atomic line profile and the Zeeman splitting pattern of the line. The purpose-built apparatus incorporated facilities for simultaneous background correction by both the Zeeman and conventional deuterium-arc techniques.

Measurements were made of the dependence of R on magnetic flux density for silver, gold, cadmium, chromium, mercury, potassium, magnesium, manganese, sodium, nickel and lead in the range 2–9 kG. A reduction in the analytical sensitivity of up to 35% arising from the Zeeman correction procedure was found in some instances. Calibration graphs for lead and nickel were linear with concentration change over two orders of magnitude but were found to invert at high concentrations (about 300 µg ml^–1). Using the Zeeman correction system, a background absorbance of 2.0 was compensated to better than 0.005, while that achieved by a well adjusted deuterium arc system was approximately 0.02.