A case study for in-house method validation of gas chromatography technique using class-1 calibration gas mixtures for greenhouse gases monitoring

In this study, analytical method validation has been done for the measurement of carbon dioxide/nitrogen (CO₂/N₂) and methane/nitrogen (CH₄/N₂) calibration gas mixtures using gas chromatography with flame ionization detector (GC-FID). Class-I calibration gas mixtures (CGMs) of CO₂ (500 µmol mol⁻¹ to 1100 µmol mol⁻¹) and CH₄ (2 µmol mol⁻¹ to 130 µmol 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 R² value 0.9995 and 1, respectively. LOD and LOQ for CH₄ are calculated 0.47 and 1.59 µmol mol⁻¹ based on signal-to-noise ratio by taking its lowest concentration of 2.9 µmol 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.