Rapid extraction and direct spectrophotometric determination of iron(III) with thiothenoyltrifluoroacetone

To obtain NH₄F-HF etching agents with constant etching behaviour the concentration of NH₄OH in commercially available 40% NH₄F solutions has to be measured. By application of pH-indicators of the phenol type very small pH-deviations (0.007 pH) from the specified value (0% NH₄OH) can be measured. The specified value is simulated by the stable McIlvaine buffer. By determining the differences in optical absorption 0.01% NH₄OH can be measured in NH₄F solutions. Values found in practice are between 0.1– 0.3%.