Premeation Calibration tube

[atharwasim]

Dears
We are using Premeation Tubes for calibration of trace sulfer GC, now calibration mixture supplier has proposed us to use Gas Mixture with 10 PPM sulfer balanced in nitrogen, he essures one year stability. Shall we move to the Gas Mixture or there are some possible complication. Question is why are we using Premeation Tube for Sulfer component not Gas Mixture.

Please advise

[Ron]

Historically it has been very difficult to produce a sulfur standard mixture that is stable for an extended period of time. There have been improvements in the last few years in the deactivation of storage containers, and it is now possible to get standards that are stable for longer periods of time. The question of using permeation tubes or cylinders comes down to concentration. A 10 ppm standard should be stable in most cases for a year or more if stored in the proper material. Sub-ppm standards are best prepared with a permeation tube, since these standards are very difficult to prepare and certify.