The purpose of this work was to develop a method which enables the automatic determination of a-amino-N in sugar beets and sugar factory juices. For this reason the method of Stanek and Pavlas has been tested and some sources of errors could be eliminated. It was found that, for the determination of the copper-amino- acid-complex, best results were obtained in the range of wavelengths between 530 and 650 nm. The concentration of the solution exerts an influence on the absorption maximum. Different pH-values can cause further errors. With the original method no constant conditions for a constant pH-value could be effected. In the original method no precautions are taken to keep a constant pH-value. The adjustment of constant pH at value 6,0 however, brings results which are comparable with those obtained by other methods. The modified method then was compared by tests with the ninhydrin-method of Moore and Stein. For sugar beets and for raw – and thick – juices produced in the laboratory, statistical evaluation showed a good agreement of the results. The thin juices contain still ammonia originating from hydrolisis of amids during juice purification, which falsifies results of the ninhydrinHmethod. If condenser water is used for extraction, it is to be expected that also in raw juice samples, results of ninhydrin-method are influenced by ammonia.
The modified method has been successfully applied for evaluation of beets with automatic analysis apparatus since two years.
Proceedings: CITS 1971
pdf download: CITS1971-539-553.pdf