Quantitative determination of fluorine in spent grain and brewery yeast

Previously published studies have shown that fluorine could present a health risk for humans. In this context, legislative regulations define the fluorine limits in many commodities, including brewery by‐products, such as spent grain and brewery yeast used as a feed. A method for the determination of fluorine in these by‐products using gas chromatography with flame ionization detection is therefore proposed. The first step is based on extraction of fluorine with 1 mol/L hydrochloric acid solution simulating acidic stomach surroundings. Then, fluorine is derivatized by trimethylchlorosilane to form trimethylfluorosilane (TMFS), which is subsequently extracted in liquid–liquid mode. TMFS is then analysed by gas chromatography–flame ionization detection; n‐pentane is used as an internal standard for fluorine quantification. The recovery of the method was >96%. The results also showed a high correlation coefficient (R > 0.999) in the calibration range studied (0–2000 mg/kg). The precision of the method, expressed as the relative standard deviation, was 13%. The limit of quantification was 0.02 mg/kg. This method was used for pilot screening of fluorine in 16 grain and 12 yeast samples. The resulting concentrations of fluorine ranged between 1.5 and 20.0 mg/kg, levels far below the legislative limits. Copyright © 2015 The Institute of Brewing & Distilling