Determination of N-nitrosoproline and N-nitrososarcosine in malt and beer

A rapid and sensitive method is described for the determination of N-nitrosoproline and N-nitrososarcosine in malt and beer. It consists of extraction of the sample with methanol, cleanup on commercially available extraction tubes, and preparation of the methyl ester derivatives by treatment with diazomethane or BF sub(3)-methanol. The final determination is carried out by gas-liquid chromatography using a thermal energy analyzer detector. The average percentage recoveries of both the compounds added to malt and beer were highly satisfactory (84-90%). The average levels of N-nitrosoproline detected in 11 malt (both old and recent) and 28 beer samples (mostly recent) were found to be 24.1 ppb (range 5.6-113.3) and 1.7 ppb (range trace-6.0), respectively. Only two samples of malt contained traces (< 1 ppb) of N-nitrososarcosine. In view of the noncarcinogenicity of N-nitrosoproline in experimental animals, these findings are unlikely to pose any hazard to human health.