Gravimetric Preparation of Toluene CGMs in Nitrogen Gas: Verification and Stability Assessment

This research paper presents the preparation, verification and stability evaluation of a toluene calibration gas mixtures (CGMs) in nitrogen gas via gravimetric method. These toluene gas mixtures are prepared gravimetrically i. e., by wt. mixing of high-purity gases according to the International Organization for Standardization, ISO 6142, and are validated as per ISO 6143. Toluene gas mixtures within the range of 5 to 20 mu mol/mol are prepared and traceability with SI, 'International system of units', amount of substance, the ' mole ', through mass-based measurements is achieved. The verification of prepared CGMs was carried out using a GC-FID (gas chromatography with flame ionization detector) technique, and the outcomes demonstrated a consistent linear correlation between instrumental response and gravimetric amount fraction for all gas mixtures, which confirmed the accuracy and reliability of CGMs. The gravimetric uncertainty of the prepared gas mixtures, as projected in terms of amount fractions, is below 1 % relative, while the analytical uncertainty is in the range of 2-3 % relative at a confidence level of k=1. The stability study investigation over a period of one year demonstrated that the mole fraction of toluene remained consistent throughout the entire duration, which indicated the long-term stability of the CGMs. The study uses a gravimetric method, traceable to the SI unit 'mole', for toluene CGMs preparation. ISO 6142 guidelines are followed, with modifications including the introduction of 1/3rd N2, gas-tight syringe use, and a V-shape injection method to minimize condensation. GC-FID verification following ISO 6143 confirms their reliability, and a year-long stability assessment reveals remarkable stability. image