Determination of iron(III) in pharmaceutical samples using dialysis in a sequential injection analysis system

The use of membranes for on-line separations in flow-through dialysers as part of flow systems is extremely useful for automated sample preparation. Iron(III) was separated from a sample matrix by dialysis in a sequential injection system. The dialysed iron was complexed with tiron and the resulting complex was monitored spectrophotometrically at 667 nm. The influence of various parameters, including pump speed for both the donor and recipient streams, sample volume, reagent volume, dialysis time and the effect of multiple flow reversals, on dialysis efficiency was studied. The system proved to be feasible for the determination of iron in pharmaceutical samples which are usually turbid and contain undissolved organic particles. The system is fully computerised and is able to monitor iron(III) in samples at a frequency of 8 samples per hour with a relative standard deviation (RSD) of <1.50% in the linear calibration range (100–1000 mg l−1). The 3σ detection limit is 45.0 mg l−1. Although the sample frequency of the proposed sequential injection system is much lower than that of conventional flow injection systems, the volume of sample used is much smaller and the consumption of reagents is much lower, which is more cost effective. Using the feature of multiple flow reversals, the percentage dialysis can be improved to up to 4.5%, which compares well with the 4% obtained with conventional flow injection analysis.