A Multiparameter Gas-Monitoring System Combining Functionalized and Non-Functionalized Microcantilevers.

The aim of the study is to develop a compact, robust and maintenance free gas concentration and humidity monitoring system for industrial use in the field of inert process gases. Our multiparameter gas-monitoring system prototype allows the simultaneous measurement of the fluid physical properties (density, viscosity) and water vapor content (at ppm level) under varying process conditions. This approach is enabled by the combination of functionalized and non-functionalized resonating microcantilevers in a single sensing platform. Density and viscosity measuring performance is evaluated over a wide range of gases, temperatures and pressures with non-functionalized microcantilevers. For the humidity measurement, microporous Y-type zeolite and mesoporous silica MCM48 are evaluated as sensing materials. An easily scalable functionalization method to high-throughput production is herein adopted. Experimental results with functionalized microcantilevers exposed to water vapor (at ppm level) indicate that frequency changes cannot be attributed to a mass effect alone, but also stiffness effects dependent on adsorption of water and working temperature must be considered. To support this hypothesis, the mechanical response of such microcantilevers has been modelled considering both effects and the simulated results validated by comparison against experimental data.

On-line systems for continuous water and gas isotope ratio measurements.

New continuous on-line techniques for water and air extracted from ice cores are developed. Water isotope ratio determination on any of the water phases (water vapour, water, ice) is of great relevance in different research fields, such as climate and paleoclimate studies, geological surveys, and hydrological studies. The conventional techniques for water isotopes are available in different layouts but all of them are rather time-consuming. Here we report new fast on-line techniques that process water as well as ice samples. The analysis time is only approximately 5 min per sample which includes equilibration and processing. Measurement precision and accuracy are better than 0.1 per thousand and 1 per thousand for delta18O and deltaD, respectively, comparable to conventional techniques. The new on-line techniques are able to analyze a wide range of aqueous samples. This allows, for the first time, to make continuous isotope measurements on ice cores. Similarly, continuous and fast analysis of aqueous samples can be of great value for hydrological, geological and perhaps medical applications.Furthermore, a new technique for the on-line analysis of air isotopes extracted from ice cores is developed. This technique allows rapid analyses with high resolution of the main air components nitrogen, oxygen, and argon. Measurement precision is comparable to precisions obtained by conventional techniques. It is now possible to measure delta15N and delta18O(atm) over entire ice cores helping to synchronize chronologies, to assess gas age-ice age differences, and to calibrate the paleothermometry for rapid temperature changes. This new on-line air extraction and analyzing technique complements the water methods in an ideal way as it separates the air from the melt-water of an ice sample. The remaining water waste flux can directly be analyzed by the water methods.

Continuous extraction of trapped air from bubble ice or water for on-line determination of isotope ratios.

We describe a new continuous extraction system for trapped air from bubble ice or water for on-line determination of the isotopic composition of the main air components nitrogen and oxygen (delta15N, delta18O, and delta17O). Studies of the composition of air from bubbles trapped in polar ice are providing fundamental information about ancient atmospheric composition and, therefore, are an important tool to learn more about Earth's climate. The new system proved to work reliably for standard air admixed and subsequently removed from a water stream. The precision (1 SD) of standard measurements is approximately 0.04/1000 for delta15N, approximately 0.1/1000 for delta18O, and approximately 0.15/1000 for delta17O. Ice measurements with the new on-line system are promising. Continuous measurements of nitrogen as well as oxygen isotope ratios can be performed with a spatial resolution of approximately 3 cm and nearly the same precision as for the standards. However, the measured delta values of ice are generally lower, as compared to ice measured with conventional techniques, as a result of a time-dependent dissolution process of air in water associated with kinetic fractionation, which affects standard and sample differently. By modeling the dynamics of the this dissolution process, we found a reason for the lack of accuracy and propose an improvement of the system that will lead to a better accuracy of the ice measurements.