A manifold for the automatic dilution of concentrated solutions in flame atomic absorption spectrometry

A fully computer-controlled manifold is described which enables the automatic dilution and measurement of solutions which are too concentrated to be measured by direct aspiration in FAAS. The sample solution is propelled by a peristaltic pump equipped with two pump tubes of different diameters, the difference between the nebulizer uptake rate and the flow rate supplied by both tubes being compensated by solvent provided through a T-piece. The absorbance is averaged and the pump turning speed automatically increased or reduced until an absorbance value within the linear response of the spectrometer is obtained. To furnish very high dilution, the system automatically reverses the direction of the flow moved through one of the pump tubes, so that the net flow delivered by the pump is the difference between the flows propelled through the two pump tubes. In these circumstances, in addition to absorbance, the module of the Fourier transform obtained from the absorbance-time profile can be used as the analytical signal. Calibration is performed by use of a single standard solution. In this way, it is possible to determine copper in the 1-10,000 microg mL(-1) range with an RSD of 1.3-3%. Copper, zinc, calcium, and magnesium were determined in different samples to check the reliability of the procedure.