An experimental study has been performed to determinethe factors affecting the stability of hydrogen sulfidecalibration mixtures at concentrations below 1 ppm.Quantitative data was obtained that illustrates that material selection and surface treatment are major factorsaffecting the shelf life of low concentration reactive gasmixtures. With the proper material selection and surfacetreatment, hydrogen sulfide and carbonyl sulfide standardmixtures on the order of 50−100 ppb can be maintainedfor at least 18 months.