Short Communicationspeak represents either sinigrin itself or an other impurity from the sample overlapping with sinigrin. So it is evident, that glucotropaeolin is a better internal standard than sinigrin for the determination of glucosinolate content of oilseed rape by HPLC.HPLC methods will only detect intact glucosinolates. Glucosinolates degraded either enzymatically by myrosinase or thermally will not be determined by this method. In both cases the HPLC method detects a lower glucosinolate content. Figures 2 A and 2 B show the HPLC-chromatograms of a rapeseed sample untreated (A) and after heating to 110°C for 60 min (B). It is evident that the glucosinolate content in chromatogram B is lower. Especially the indolyl-glucosinolate 4-OH-glucobrassicin (peak 9) is very sensitive to heat and 50 % has already been destroyed. The alkenyl-glucosinolates are more stable and only 10 % of these have been lost.
The reproducibility of py-GCis also strongly affected by the sample application technique. A fast heat transfer between the Curie wire and the sample, for instance, by pressing a thin sample film into the Curie wire improves the reproducibility [2]. As a consequence of the small sample size, a severe problem could be the sample homogeneity. lnhomogeneous samples can sometimes be homogenized by milling in a mortar with or without the addition of liquid nitrogen.
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