Flow-injection spectrophotometric determination of nanogram levels of iron(III) with N,N-dimethylformamide.

A simple and fast flow-injection spectrophotometric method has been described for the determination of iron(III). The method is based on the measurement of absorbance intensity of the complex that is formed between iron(III) and N,N-dimethylformamide (DMF) at 310 nm. The carrier stream was just a mixture of water and DMF at ratio 5% (v/v). The method is highly selective; most of the 30 metal ions and anions tested did not effect on the determination of iron(III) even when present up to 1000-fold excess over iron(III). The calibration graph for iron(III) obtained under optimized conditions were linear in the range 5 - 90 ng ml(-1) with a detection limit of 0.1 ng ml(-1) for a 20 microl injection volume. The reproducibility was satisfactory, with a relative standard deviation of 2.4% (n = 5) in the range of 5-90 ng ml(-1) of iron(III). The sampling rate was over 60 h(-1). The developed method was succesfully applied to the determination of total iron in river water, seawater, hot spring water and iron alloy samples. The accuracy of the method was evaluated using the standard addition method and checked by the certified reference metal alloy samples.