Abstract
The performance parameters of volatile fatty acids (VFAs) measurements were assessed for the first time by a multi-laboratory validation study among 13 laboratories. Two chromatographic techniques (GC and HPLC) and two quantification methods such as external and internal standard (ESTD/ISTD) were combined in three different methodologies GC/ESTD, HPLC/ESTD and GC/ISTD. Linearity evaluation of the calibration functions in a wide concentration range (10–1000 mg/L) was carried out using different statistical parameters for the goodness of fit. Both chromatographic techniques were considered similarly accurate. The use of GC/ISTD, despite showing similar analytical performance to the other methodologies, can be considered useful for the harmonization of VFAs analytical methodology taking into account the normalization of slope values used for the calculation of VFAs concentrations. Acceptance criteria for VFAs performance parameters of the multi-laboratory validation study should be established as follows: (1) instrument precision (RSDINST ≤ 1.5%); (2) linearity (R2 ≥ 0.998; RSDSENSITIVITY ≤ 4%; REMAX ≤ 8%; REAVER ≤ 3%); (3) precision (RSD ≤ 1.5%); (4) trueness (recovery of 97–103%); (5) LOD (≤3 mg/L); and (6) LOQ (10 mg/L).