Flow-injection solvent extraction without phase separation: Fluorimetric determination of thiamine by the thiochrome method

Two modes of liquid–liquid extraction in flow-injection systems were compared and applied to the fluorimetric determination of thiamine (Vitamin B1). The first included phase segmentation, but fluorescence was measured without phase separation. In this mode, thiamine was detected at concentrations higher than 8 μg/l with a linear application range of 30–2000 μg/l, an R.S.D. of 1.9% (150 μg/l, n = 10) and a sampling frequency of 60/h. In the second mode, a single segment of organic solution was injected into the aqueous stream and fluorescence was also measured without phase separation. Using this mode, concentrations of thiamine higher than 1 μg/l were detected, with a linear application range between 5 and 280 μg/l, an R.S.D. of 2.4% (150 μg/l, n = 10) and a sampling frequency of 60/h. The two forms were applied to the analysis of thiamine in pharmaceuticals.