Validated flow-injection method for rapid aluminium determination in anti-perspirants

A flow-injection (FI) method for the rapid determination of aluminium in anti-perspirants has been developed. The method is based on the spectrophotometric detection at 535 nm of the complex formed between Al ions and the chromogenic reagent eriochrome cyanine R. Both the batch and FI methods were validated by checking the parameters included in the ISO-3543-1 regulation. Variables involved in the FI method were optimized by using appropriate statistical tools. The method does not exhibit interference from other substances present in anti-perspirants and it shows a high precision with a R.S.D. value (n = 6) of 0.9%. Moreover, the accuracy of the method was evaluated by comparison with a back complexometric titration method, which is currently used for routine analysis in pharmaceutical laboratories. The Student's t-test showed that the results obtained by both methods were not significantly different for a significance level of 95%. A response time of 12 s and a sample analysis time, by performing triplicate injections, of 60 s were achieved. The analytical figures of merit make the method highly appropriate to substitute the time-consuming complexometric method for this kind of analysis.