Flow manifold for automated on-line dilution of standards for flame atomic absorption spectrometry and its use in a null measurement method

Abstract

A flow manifold that automatically dilutes solutions presented to a flame atomic absorption spectrometer while maintaining a constant flow to the nebuliser is described. The manifold is based on a fixed-speed pump, together with a computer-controlled stream switching valve and pump. The computer is also used for data acquisition and handling. In addition to the production of solutions for a conventional calibration procedure, the system is also used for a novel calibration procedure whereby the stock standard solution is automatically diluted by a known factor until its absorbance matches that of the sample. This null measurement method avoids the need to fit a curve to a set of calibration points. The performance of both methods compares favourably with the conventional procedure with errors ranging from 0.0 to 4% and no significant bias at the 99% confidence level. Problems with pulsations in the flow caused by peristaltic pump rollers were encountered with the consequent difficulties of accurate flow-rate measurement. Attempts to improve the speed of the method by the use of flow injection introduction were not successful owing to these pulsations in the flow.