Development of 100 μmol mol−1 Cl2 Standard Gas Mixture for Accurate Calibration of Ambient Cl2 Sensors and Stack Emission Monitors

Abstract

To accurately measure Cl2 mixing ratio using stack emission monitors and leak monitoring sensors in a workplace, it is essential calibrating monitors and sensors periodically using a Cl2 standard gas mixture. Because there is no reliable analytical technique for Cl2, an international standard for high-pressure Cl2 gas mixtures has not been established. A novel approach for the quantification of Cl2 was developed using quadrupole mass spectrometry (QMS) with an expanded uncertainty of 0.7 μmol mol−1. A 100 μmol mol−1 chlorine (Cl2)/N2 gas mixture was produced through a two-step procedure involving dilution of Cl2 with N2 in high-pressure aluminum cylinders. To check the consistency between 100 μmol mol−1 Cl2 gas mixtures in different cylinders, Cl2 gas mixtures were quantified using the QMS based approach. It was found that four cylinders of 100 μmol mol−1 Cl2 gas mixtures prepared in 2016 agreed within 0.7 μmol mol−1. The long-term stability of 100 μmol mol−1 Cl2 gas mixtures was assessed through changes in the Cl2 mixing ratio over a one-year. It was found that the 100 μmol mol−1 Cl2 gas mixture was stable within ±0.7 μmol mol−1 over one year. Finally, 100 μmol mol−1 Cl2/N2 gas mixture was successfully developed in a high pressure cylinder with an expanded uncertainty of 2.0 μmol mol−1 (k = 2; 95% confidence level).