Determination of free l- and d-alanine in hydrolysed protein fertilisers by capillary electrophoresis

The objective of this study was to determine the degree of racemisation of hydrolysed protein fertilisers (HPFs) using an inexpensive and easy to handle analytical method for qualitative control of the products. Using a polyacrylamide coated capillary and a run buffer containing 0.1 M Tris–borate+2.5 mM EDTA-Na2+0.1% sodium dodecylsulfate+10 mM β-cyclodextrin a quantitative separation of d- and l-alanine (Ala) was made from an not treated HPF sample derivatised with dansyl chlorine by capillary electrophoresis. The d-Ala:[d-Ala+l-Ala] ratio, called degree of racemisation (RD), was calculated. The analysis of ten commercial HPFs has shown that more than 60% of HPFs have an RD ≥40%, while only one product has shown an RD <5%. These results showed that most of the HPFs on the market are obtained with strong hydrolytic processes and high contents of d-amino acids are probably less effective as plant nutrients or even potentially dangerous to plants.