Microdetermination of vitamin B1 in the presence of vitamins B2, B6, and B12 by solid-phase UV spectrophotometry

A very sensitive, selective, and rapid spectrophotometric method for the determination of vitamin B-1 in the presence of vitamins B-2, B-6, and B-12 was carried out in the UV region without performing a previous separation. Vitamin B-1 was selectively and strongly sorbed on Sephadex CMC-25 ion exchanger at pH 4.80 and its intrinsic absorbance measured directly in the solid phase at 247 and 320 nm. The apparent molar absorptivity ranged from 5.63 x 10(5) to 2.19 x 10(7) Lmol(-1) cm(-1), depending on the sample volume used (from 10 to 1000 mt). A procedure (for five different sample volumes) was here proposed. Thiamin could be determined in the concentration ranges 0.5-5.5 mu g mL(-1) (10-mL sample volume) up to 12 - 170 ng mL(-1) (1000-mL sample volume) with detection limits ranging from 80.0 to 3.0 mu g L-1 and RSDs from 1.5 to 2.6%, respectively. The method showed an excellent selectivity against other compounds of the B complex with similar spectral features and which did not cause interference. The method was satisfactorily applied to the determination of vitamin B-1 in pharmaceutical preparations.