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Effects of Current- and Voltage-Regulated Supplies on Temperature Variation of Graphite Atomizer in Atomic Absorption Spectrophotometry

Recently atomic absorption spectrophotometry with the graphite electrothermal atomizer has been useful for trace analysis. However, this method is inferior in reproducibility to that utilizing the flame atomizer. This poor reproducibility reported is due to variations of the atomizer temperature and of the nature of the heated graphite surface. It is important to note that during experiments with a graphite atomizer, gradual vaporization of carbon occurs and leads to smaller cross sectional area; and hence, to higher electrical resistance for the atomizer. Thus, the atomization temperature of heated graphite atomizer for the constant current controlled by the current-regulated supply (CRS) would increase with an increase in the number of operations. At the same time the constant voltage controlled by the voltage-regulated supply (VRS) would decrease because the increase in the resistance directly reduces the current through the atomizer. Montaser and Crouch reported that the power-regulated supply with a power transistor yielded superior results in reproducibility for the temperature of the graphite braid atomizer which is current-regulated. However, it is difficult to construct the power-regulated supply for the graphite tube atomizer control because of higher current required.