In the past, the photometric blue number method has been used for determination of alpha amino N in order to characterize the technological value of sugar beet in Germany. Since the late eighties, a new fluorometric method using OPT for determination has been adopted for analytical and environmental reasons, i.e. replacement of toxic lead acetate as clarifying agent by aluminium salts. Aluminium sulphate in comparison to lead acetate has no significant effect of the value alpha amino N, whereas using the fluorometric OPT method consistantly higher values are achieved when compared with the blue number method. The Reinefeld formula is used to estimate the technological quality of sugar beet in Germany. In this formula, the content of alpha amino N is considered, which has been measured by the blue number method. In order to take the systematic effect of the new method into account, a simple factor is applied to convert fluorometric into blue number values in most beet laboratories. Scientifically speaking, the application of a regression would be appropriate. By the application of a factor instead of a regression differences may arise due to different mathematical ways of correction. These artificial differences may be crucial when absolute values of a amino N are compared.
