Development of 100 μmol mol−1 HCl primary standard gas mixtures in high-pressure cylinders

To develop a 100 mu mol mol(-1) hydrogen chloride (HCl) primary standard gas mixture in a high-pressure cylinder, pure HCl gas was diluted in two or three steps with pure N-2 in high- pressure aluminum and nickel-coated manganese steel cylinders. To check the consistency between the HCl gas mixtures in the different cylinders, the HCl mixing ratios were analyzed by Fourier transform infrared spectroscopy. Four cylinders of 100 mu mol mol(-1) HCl gas mixtures agreed within 0.2 mu mol mol(-1). A previous study showed that 0.29 mu mol mol(-1) of HCl was adsorbed on the inner surface of aluminum cylinders that contained 100 mu mol mol(-1) HCl gas mixtures. The long-term stability test showed that the 100 mu mol mol(-1) HCl gas mixture in the aluminum cylinder decreased by 0.8 mu mol mol(-1) over 2 years, whereas that in the nickel-coated manganese steel cylinder decreased by 6 mu mol mol(-1). This result suggested that the nickel-coated manganese steel cylinder is not suitable for developing 100 mu mol mol(-1) HCl gas mixtures. From the verification test between gas cylinders and the long-term stability test, the 100 mu mol mol(-1) HCl standard gas mixture in the aluminum cylinder was successfully developed with an expanded uncertainty of 1.65 mu mol mol(-1) (k = 2%, 95% confidence level). The 100 mu mol mol(-1) HCl standard gas mixture was validated using an online ion chromatograph with a liquid Cl- certified reference material (CRM). The HCl gas mixture agreed with the liquid Cl- CRM within an expanded uncertainty of 1.5%.