CSIRO, Earth Science and Resource Engineering, Bentley, WA, Australia.
Anal Chim Acta. 2011 Oct 3;703(1):70-9. doi: 10.1016/j.aca.2011.07.015. Epub 2011 Jul 19.
Long-term environmental monitoring of organic compounds in natural waters requires sensors that respond reproducibly and linearly over a wide concentration range, and do not degrade with time. Although polymer coated piezoelectric based sensors have been widely used to detect hydrocarbons in aqueous solution, very little information exists regarding their stability and suitability over extended periods in water. In this investigation, the influence of water aging on the response of various polymer membranes [polybutadiene (PB), polyisobutylene (PIB), polystyrene (PS), polystyrene-co-butadiene (PSB)] was studied using the quartz crystal microbalance (QCM). QCM measurements revealed a modest increase in sensitivity towards toluene for PB and PIB membranes at concentrations above 90 ppm after aging in water for 4 days. In contrast, the sensitivity of PS and PSB coated QCM sensors depended significantly on the toluene concentration and increased considerably at concentrations above 90 ppm after aging in water for 4 days. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) showed that there is a change in the sorption mechanism at higher toluene levels for PS and PSB. Positron annihilation lifetime spectroscopy (PALS) studies were performed to investigate the free volume properties of all polymers and to monitor any changes in the free volume size and distribution due to water and toluene exposure. The PALS did not detect any considerable variation in the free volume properties of the polymer films as a function of solution composition and soaking time, implying that viscoelastic and/or interfacial processes (i.e. surface area changes) are probably responsible for variations in the QCM sensitivity at high hydrocarbon concentrations. The results suggest that polymer membrane conditioning in water is an issue that needs to be considered when performing QCM measurements in the aqueous phase. In addition, the study shows that the hydrocarbon response is concentration dependant for polymers with a high glass transition temperature, and this feature is often neglected when comparing sensor sensitivity in the literature.
长期监测天然水中的有机化合物需要响应重现性好、线性范围宽且不会随时间降解的传感器。虽然聚合物涂覆的压电传感器已广泛用于检测水溶液中的碳氢化合物，但关于其在水中长时间稳定性和适用性的信息却很少。在这项研究中，使用石英晶体微天平（QCM）研究了水老化对各种聚合物膜（聚丁二烯（PB）、聚异丁烯（PIB）、聚苯乙烯（PS）、聚苯乙烯-丁二烯（PSB））响应的影响。QCM 测量结果表明，在水中老化 4 天后，PB 和 PIB 膜在浓度高于 90ppm 时对甲苯的灵敏度略有增加。相比之下，PS 和 PSB 涂覆的 QCM 传感器的灵敏度显著依赖于甲苯浓度，并且在水中老化 4 天后浓度高于 90ppm 时灵敏度显著增加。衰减全反射傅里叶变换红外光谱（ATR-FTIR）表明，PS 和 PSB 在较高甲苯水平下的吸附机制发生了变化。进行正电子湮没寿命谱（PALS）研究以研究所有聚合物的自由体积特性，并监测由于水和甲苯暴露而导致的自由体积大小和分布的任何变化。PALS 未检测到聚合物膜的自由体积特性随溶液组成和浸泡时间的变化而发生任何显著变化，这表明粘弹性和/或界面过程（即表面积变化）可能是导致 QCM 在高碳氢化合物浓度下灵敏度变化的原因。结果表明，在水相中进行 QCM 测量时，需要考虑聚合物膜在水中的调节问题。此外，该研究表明，对于玻璃化转变温度较高的聚合物，烃类响应与浓度有关，而在文献中比较传感器灵敏度时，通常忽略了这一特征。
