The relative influence of derivatization and normalization procedures on the compound-specific stable isotope analysis of nitrogen in amino acids.

The overall accuracy and precision of δ15 N-AA measurements were improved following both compound-specific calibration and scale-normalization, as was the comparability of δ15 N-AA measurements of individual amino acids between derivatization techniques across organisms. The mean difference of scale-normalized δ15 N-AA values across all organisms between the two derivatization techniques was 0.19‰, much less than the typical analytical error associated with δ15 N-AA measurements (±1‰). CONCLUSIONS: Adoption of standardized calibration procedures will be important to establishing reproducibility in δ15 N-AA measurements, particularly across derivatization techniques. It is both technically practical and desirable for users of CSIA-AA to adopt practices in quality control and assessment similar to those outlined for BSIA, including the compound-specific calibration of δ15 N-AA values, followed by scale-normalization. Copyright © 2017 John Wiley & Sons, Ltd.