To develop standard toxic gas mixtures, it is essential to identify adsorption characteristics of each toxic gas on the inner surface of a gas cylinder. Thus, this study quantified adsorbed amounts of the four toxic gases (NO, NO₂, SO₂, and HCl) on the inner surface of aluminum and nickel coated manganese steel cylinders. After eluting adsorbed gases on the inside of cylinders with ultra pure water, a quantitative analysis was performed by an ion-chromatograph. To evaluate the reaction characteristics of the toxic gases with cylinder materials, quantitative analyses of Ni, Fe, and Al were also performed by an inductively coupled plasma-optical emission spectrometry(ICP-OES). It was found that amounts of NO, NO₂, and SO₂ adsorbed on the inner surface of aluminum cylinders were less than 1.0 % at the level of 100 μmol/mol mixing ratios whereas the signal for most heavy metal elements were below their respective detection limits. This study found that amounts of HCl adsorbed on the inner surface of nickel coated manganese steel cylinders were less than 5% at the level of 100 μmol/mol mixing ratio, while amounts of Ni(86 μmol) and Fe(28 μmol) were detected in the same cylinders. It was revealed that the adsorption mainly took place via the reaction of HCl with inner surface material of nickel coated manganese steel cylinders. On the other hand, in the case of aluminum cylinders, amounts of the adsorption were determined to be less than 1 % at the level of HCl 100 μmol/mol mixing ratios whereas most of Ni, Fe, and Al were detected levels similar to their limits of detection. As a result, this study found that aluminum cylinders are more suitable for preparing HCl gas mixtures than nickel coated manganese steel cylinders.
To develop a 100 μmol/mol 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 μmol/mol HCl gas mixtures agreed within 0.2 μmol/mol. A previous study showed that 0.29 μmol/mol of HCl was adsorbed on the inner surface of aluminum cylinders that contained 100 μmol/mol HCl gas mixtures. The long-term stability test showed that the 100 μmol/mol HCl gas mixture in the aluminum cylinder decreased by 0.8 μmol/mol over 2 years, whereas that in the nickel-coated manganese steel cylinder decreased by 6 μmol/mol. This result suggested that the nickel-coated manganese steel cylinder is not suitable for developing 100 μmol/mol HCl gas mixtures. From the verification test between gas cylinders and the long-term stability test, the 100 μmol/mol HCl standard gas mixture in the aluminum cylinder was successfully developed with an expanded uncertainty of 1.65 μmol/mol (k=2, 95 % confidence level). The 100 μmol/mol 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 with in an expanded uncertainty of 1.5 %.