Determination of aluminium in dental enamel by the carbon cup atomic-absorption method

Abstract

The possibility of using the carbon cup atomisation technique for the atomic-absorption determination of aluminium in dental enamel has been investigated. Various parameters that influence the sensitivity and accuracy of the measurements were studied by use of a standard electronic detection system (Varian AA-5; chart recorder f.s.d., 1 s) and oscilloscopic (Tektronix) recording of the absorption signal. The latter system enabled the atomic-and non-specific absorption signals to be studied as a function of the time of atomisation. Thus, increasing the rate of heating of the carbon cup in the atomisation step resulted in a substantial enhancement of the aluminium peak absorption signal. The presence of calcium in the solution (7·2 mg ml^–1, in the form of the phosphate) produced a two-fold increase in sensitivity for aluminium.

For routine determinations of aluminium in tooth material (in vitro) 10 mg of finely ground and homogenised sample are dissolved in 6 N nitric acid and the solution is diluted to 0·5 ml; 5-µl aliquots are sampled for a single determination. A single calibration graph obtained by the standard addition method is adequate for one set of samples. No correction due to non-specific absorption is necessary, but the blank value (nitric acid) should be checked from time to time.

The absolute sensitivity of the method (3·5 × 10^–11 g of aluminium) permits the determination of aluminium in tooth material both in vitro and in vivo at microgram per gram concentration levels with a general precision of 8 per cent.

In vivo analysis can be carried out on 300–600 µg of sample obtained by a chemical biopsy method. The main problem encountered in in vivo analysis lies in obtaining an aluminium-free support material for etching purposes. In addition, “clean room” facilities are recommended for improving the accuracy.