First international comparative study of volatile fatty acids in aqueous samples by chromatographic techniques: Evaluating sources of error

•We describe the state of practice in measurement of volatile fatty acids (VFAs).•Analytical improvement in measurement of VFAs by field analytical laboratories.•Human and calibration errors were the main causes of inaccurate measurements.•Improvement needs interlaboratory comparisons and certified reference materials.

This first international proficiency-testing scheme evaluated the analytical performance and the state of practice in measurement of volatile fatty acids in aqueous samples. Gas chromatography and high-performance liquid chromatography were used by 25 laboratories from 15 different countries. Two reference materials were selected for analysis. The performance of each laboratory was assessed by the internationally-accepted z-score. The overall performance was rather poor. Among the causes of poor analytical performance, human errors and inadequate calibration were probably the major problems encountered.