Preparation of Accurate, Low-Concentration Gas Cylinder Standards by Cryogenic Trapping of a Permeation Tube Gas Stream
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- 作者：Lyn Gameson ; George C. Rhoderick ; Franklin R. Guenther
- 刊名：Analytical Chemistry
- 出版年：2012
- 出版时间：March 20, 2012
- 年：2012
- 卷：84
- 期：6
- 页码：2857-2861
- 全文大小：256K
- 年卷期：v.84,no.6(March 20, 2012)
- ISSN：1520-6882
文摘
National and international measurements are underpinned by accurate, low concentration standards. These standards are typically produced gravimetrically, or volumetrically, by a series of dilutions of the pure material by the balance gas. This blend technique is time-consuming and may involve the handling of pure, hazardous material. These problems have been overcome by developing a novel blend technique whereby the process gas stream, from an appropriate permeation tube, was cryogenically trapped in an aluminum cylinder. The permeation rate of the component is monitored by real time mass determinations using a magnetic suspension balance system. With the combination of the real-time calculated permeation rate, plus the use of a dilution system, a one step production of a very low concentration of the minor component in nitrogen gas can be achieved. This method was used to prepare low 渭mol/mol standards of propane, a known stable compound. Analysis of a conventional gravimetrically prepared 10 渭mol/mol propane standard and a cryogenically prepared standard via a permeation gas stream resulted in agreement between the two of <0.1% at 10 渭mol/mol, confirming the accuracy of the permeation method. After confirmation of the validity of the permeation/cryogenic trapping system, the propane permeation tube was replaced with a methyl mercaptan tube (a toxic, reactive compound) in balance nitrogen. After cryogenically trapping the methyl mercaptan output stream from the permeation system into a cylinder, the output stream and the cylinder gas mixture were analyzed. The results showed agreement of <0.6% for methyl mercaptan at 5, 10, 15, and 20 渭mol/mol to the expected blend concentration, thereby demonstrating the validity of the method.