Determination of thiamine and its esters in beers and raw materials used for their manufacture by liquid chromatography with postcolumn derivatization.

Thiamine and its mono- and pyrophosphate esters were determined in beer and the raw materials used for its manufacture (brewer's yeast, malt, raw grain, and hops) after separation using reversed-phase liquid chromatography. The method used fluorescence detection and a new amide-based stationary phase, which avoids the need to form ion pairs, leading to narrower peaks and a simpler mobile phase. Analyses were performed by isocratic elution with a phosphate buffer mobile phase and using a postcolumn derivatization system based on the oxidation of thiamine to fluorescent thiochrome with potassium ferricyanide in alkaline solution. Only thiamine was found in the beers and raw products, especially in brewer's yeast and malt. A stability study pointed to a faster decrease in the thiamine content of samples stored at room temperature and in sunlight.