Measurement of the 15 N/ 14 N ratio of phenylalanine in fermentation matrix by isotope ratio mass spectrometry

Objectives To determine the origin of 15 N-labeled phenylalanine in microbial metabolic flux analysis using 15 N as a tracer, a method for measuring phenylalanine δ 15 N using HPLC coupled with elemental analysis-isotope ratio mass spectrometry (EA-IRMS) was developed. Results The original source of the 15 N-labeled phenylalanine was determined using this new method that consists of three steps: optimization of the HPLC conditions, evaluation of the isotope fractionation effects, and evaluation of the effect of pre-processing on the phenylalanine nitrogen stable isotope. In addition, the use of a 15 N-labeled inorganic nitrogen source, rather than 15 N-labeled amino acids, was explored using this method. Conclusions The method described here can also be applied to the analysis of metabolic flux.