Micro-determination of phosphate in enamel biopsy samples using the malachite green method

A simple and sensitive malachite green method was adapted for the determination of phosphate in enamel demineralizing solutions. Comparison with other methods indicates that malachite green was about 60 times more sensitive than Fiske and Subbarow's method and 10 times more than that of Chen et al. The high sensitivity of this method allows very small biopsy samples to be used. The linearity is good between the tested range of 0.025-3.0 mM P. The relative standard deviation was low and amounted to 1.4% in duplicate determinations. No statistical differences in phosphate concentration of enamel biopsy samples determined by the three methods were found. Fluoride concentration up to 80 micrograms/ml did not interfere with phosphate determined by the malachite green. For sampling enamel, the acid-etch technique was used, and the fluoride concentration at successive demineralization runs was monitored using fluoride-ion electrode.