Quantitative determination of total free-amino acid in Nervilia fordii (Hance) Schltr. by ninhydrin colorimetric method.

Objective Based on the α-amino acids and ninhydrin color reaction principle,the ninhydrin colorimetry was used to determine quantitatively the amount of the free amino acids in Nervilia fordii(Hance) Schltr..Methods The reference of leucine was defined as the standard solution and absorbance was detected at 568 nm.The method focused on how to find out and what was the optimal conditions for the color reaction which reflected the amout of the free amino acids calculated by lambert-beer law.Results The optimal coditions was as following as pH value of buffer solution used in the test was at 5.0 with the volume of 1.0 mL,the volume of reagent used in the test was of 2.0 mL,all the tests were performed at 100 ℃ water bath and lasted for 19 min,and then cooled for 10 min before the ninhydrin colorimetric test.Conclusion This method is accurate,sensitive and reproducible.It is charaterized by simplicity and practicability.