Flow injection method for antimony(III) based on its enhancement of the molybdenum blue reaction

A simple flow-injection methodology is described for the determination of antimony using spectrophotometric detection. The method is based on the enhancing effect of antimony in the molybdenum blue reaction. Phosphate and heptamolybdate reagents are premixed and pumped as a reagent stream, into which the antimony sample is injected. This allows the formation of a mixed heteropoly complex, which is then rapidly reduced by ascorbic acid to form the intense blue complex, the absorbance of which is monitored at 660 nm. A continuous-flow procedure is used and 120 samples can be processed per hour. The measurement range is 0–100 mg l^?1 antimony, with a detection limit of 0.5 mg l^?1. The relative standard deviation is 0.65–2.1% in the range 20–5 mg l^?1. Arsenic and silica cause interferences of ?4% and +4.6%, respectively, when present at concentration equal to that of the antimony.