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A Novel Indirect Spectrofluorimetric Method for the Ultra Trace Analysis of a Highly Toxic Metalloid—Antimony in Aqueous Medium and Its Application to Metallurgical, Medicinal, and Biological Samples

ABSTRACT An inexpensive, virtually specific, non‐extractive method for the determination of antimony (III) at trace and ultra trace levels (5 ng mL−1–1 µg mL−1) in 0.09–0.45 (M) sulfuric acid has been developed. A known excess of chromium (VI) is allowed to quantitatively oxidise antimony (III) in the presence of iodine as catalyst, followed by addition of known excess of murexide (ammonium purpurate), where the unreacted chromium (VI) quantitatively quenches the fluorescence of murexide in acid medium, and measurement of the fluorescence intensity (λex = 336 nm, λem = 424 nm). The measurement is repeated without antimony (III) addition and the increase in fluorescence intensity gives the concentration of antimony (III) with the help of a calibration graph. The method is very precise and accurate (S.D. = ±0.2248 and R.S.D. = 0.2249% for the determination of 0.1 µg mL−1 of antimony (III) in 11 replicates). Relatively large excesses of over 35 cations and anions do not interfere. The method has been successfully applied for antimony determination in various complex matrices, certified reference materials (alloys), commercially available solder and lead samples, medicinal and biological samples.