Gas standards, how standard are they

Difficulties involved in establishing a primary gas standard for ultrahigh-purity gases are discussed. Four examples are given which show that suppliers of primary-standard gases often do not meet certified impurity standards. Problems of gas-mixture stability that create difficulties with respect to certified standards are examined, and it is suggested that a central standardization authority be established to remedy the existing situation where many private industries maintain their own arbitrary standards. For obtaining a primary standard, it is proposed that a series of internal-standard correlations among many different chemical and physical methods be undertaken. Recommendations regarding standard reference materials are offered for users of certified calibration gases.