College of Marine Science, University of South Florida, 140 Seventh Avenue South, St. Petersburg, FL 33701, United States.
Talanta. 2013 Nov 15;116:217-22. doi: 10.1016/j.talanta.2013.05.014. Epub 2013 May 20.
This work examines the transmission behavior of aqueous dissolved methane, nitrogen, argon and carbon dioxide through two types of membranes: a polysiloxane nano-composite (PNC) membrane and a conventional polydimethylsiloxane (PDMS) membrane. Transmission properties at 30 °C were examined by membrane introduction mass spectrometry (MIMS) at nearly constant gas partial pressures in NaCl solutions over a range of ionic strength (0-1 molal). Gas flow rates were examined as a function of dissolved gas concentrations using the Setschenow equation. Although MIMS measurements with PDMS and PNC membranes produced signal responses that were directly proportional to aqueous dissolved gas concentrations, the proportionalities varied with ionic strength and were distinctly different for the two types of membranes. With the exception of carbon dioxide, the PNC membrane had membrane salting coefficients quite similar to Setschenow coefficients reported for gases in aqueous solution. In contrast, the PDMS membrane had membrane salting coefficients that were generally smaller than the corresponding Setschenow gas coefficient for each gas. Differences between Setschenow coefficients and membrane salting coefficients lead to MIMS calibrations (gas-flow vs. gas-concentration proportionalities) that vary with ionic strength. Accordingly, gas-flow vs. gas-concentration relationships for MIMS measurements with PDMS membranes are significantly dependent on ionic strength. In contrast, for PNC membranes, flow vs. concentration relationships are independent (argon, methane, nitrogen) or weakly dependent (CO2) on ionic strength. Comparisons of gas Setschenow and membrane salting coefficients can be used to quantitatively describe the dependence of membrane gas-flow on gas-concentrations and ionic strength for both PDMS and PNC membranes.
这项工作研究了两种膜（聚硅氧烷纳米复合材料（PNC）膜和常规的聚二甲基硅氧烷（PDMS）膜）中溶解甲烷、氮气、氩气和二氧化碳的传输行为。通过在氯化钠溶液中接近恒定的气体分压下使用膜进样质谱（MIMS），在 30°C 下检查了传输特性，范围为离子强度（0-1 摩尔）。使用 Setschenow 方程研究了气体流速作为溶解气体浓度的函数。尽管 PDMS 和 PNC 膜的 MIMS 测量产生的信号响应与水溶液中溶解气体浓度直接成正比，但比例关系随离子强度而变化，并且两种类型的膜明显不同。除二氧化碳外，PNC 膜的膜盐系数与水溶液中气体的 Setschenow 系数非常相似。相比之下，PDMS 膜的膜盐系数通常小于每种气体的相应 Setschenow 气体系数。Setschenow 系数和膜盐系数之间的差异导致 MIMS 校准（气体流量与气体浓度的比例）随离子强度而变化。因此，PDMS 膜的 MIMS 测量中气体流量与气体浓度的关系显著依赖于离子强度。相比之下，对于 PNC 膜，流量与浓度的关系独立（氩气、甲烷、氮气）或弱依赖（CO2）于离子强度。气体 Setschenow 和膜盐系数的比较可用于定量描述 PDMS 和 PNC 膜的膜气体流量对气体浓度和离子强度的依赖性。
