In this study, analytical method validation has been done for the measurement of carbon dioxide/nitrogen (CO2/N-2) and methane/nitrogen (CH4/N-2) calibration gas mixtures using gas chromatography with flame ionization detector (GC-FID). Class-I calibration gas mixtures (CGMs) of CO2 (500 mu mol mol-1 to 1100 mu mol mol(-1)) and CH4 (2 mu mol mol(-1) to 130 mu mol mol(-1)) used in method validation process has been prepared gravimetrically following ISO 6142-1. All prepared gas mixtures have expanded uncertainty 1 % at coverage factor (k) of 2 with 95 % confidence. The following parameters are chosen for this case study which include selectivity, accuracy, precision, linearity, limit of detection (LOD), limit of quantification (LOQ), robustness, stability, and uncertainty. Different statistical approaches are taken into consideration for each parameter assessment. The results indicate that GC-FID is selective for CO2 and CH4. CGMs represent good repeatability and reproducibility having percentage relative deviation < 1 % among measurements. A good linear behaviour was observed for CGMs of CH4 and CO2 on basis of least square regression with R-2 value 0.9995 and 1, respectively. LOD and LOQ for CH4 are calculated 0.47 and 1.59 mu mol mol(-1) based on signal-to-noise ratio by taking its lowest concentration of 2.9 mu mol mol-1. The in-house validated method for GC-FID using CGMs for the measurement of greenhouse gases (CO2 and CH4) is found to be precise, accurate and fit for purpose.
