P. Schulze Lammers

Online measurement of odorous gases close to the odour threshold with a QMB sensor system with an integrated preconcentration unit

Today odour measurement close to the odour threshold can be performed only by classical olfactometry. Classical olfactometry is an expensive and time-consuming method that is not suitable for continuous monitoring as needed by operators of compost facilities. This paper describes a system consisting of a quartz microbalance (QMB) sensor array with an integrated preconcentration unit which is able to measure odorous gases below the odour threshold. The system is developed for use in connection with biofilters in biological waste utilisation (compost facilities). The system is highly sensitive to the main odorous components of waste gas, e.g. limonene, 2-butanone or ethyl acetate. Moreover, the system evinces linear behaviour over a wide range between the odour threshold and some hundred parts per million. It was evaluated both in the laboratory and in field measurements, and it shows very good sensitivity and stability about the tested time in the field measurements (2 weeks).

A QMB-based temperature-modulated ammonia sensor for humid air

Abstract A temperature-modulated sensor for ammonia based upon two quartz microbalances (QMBs) has been developed. One sensor element is coated with the tris-diethylammonium salt of 4,4′,4″-[benzene-1,3,5-triyl-tri(ethin-2,1-diyl)tribenzoic acid (SPCA) [D. Meinhold, Thesis, Institute of Organic Chemistry, Mining Institute of Technology, Freiberg/Saxony, Germany, 1999.], which serves to detect ammonia, but shows a cross-sensitivity to humidity. To compensate for the influence of the latter, a sensor element coated with poly[ethylene imine] (PEI) functions as a humidity sensor.

A humidity-independent ammonia sensor based on a quartz microbalance: a test under agricultural conditions

Abstract Sensor-arrays consisting of multiple quartz microbalances (QMB) each coated with different cryptophanes (CPH), macrocycles (MC) (U. Schramm, T. Rechenbach, P. Boeker, S. Winter, C. Roesky, R. Pollex, E. Weber, P. Schulze Lammers, J. Bargon, Ammonia sensor based on carboxylic-acid functionalized cryptophanes and macrocycles, Proceedings of the EUROSENSORS XII Conference, 1998, pp. 533–536), or heterocalixarenes (E. Weber, J. Trepte, K. Gloe, M. Piel, M. Czugler, V.Ch. Krartsov, Yu.A. Simonov, J. Aiptrowsky, E.V. Ganin, Heterocalixarenes featuring the benzimidazol-2-one subunit synthesis and X-ray structural studies of solvent inclusion, J. Chem. Soc., Perkin Trans. 2 (1996) 2359–2364) have been used to detect ammonia under agricultural conditions. As with almost all other QMB-based ammonia sensors, when using only one ammonia-sensitive sensor element on the array, the response of this initial device to ammonia fluctuated significantly due to a pronounced sensitivity to humidity. This cross sensitivity to humidity has been compensated using a heterocalixarene as a coating on one additional element of the array which thus functions as a humidity sensor. Combined with a partial least-square (PLS) analysis, this combination yields a robust humidity-independent ammonia sensor for agricultural applications.

Temperature dependence of an ammonia sensor in humid air based on a cryptophane-coated quartz microbalance

Abstract A cryptophane-coated sensor for ammonia based upon a quartz microbalance has been developed and the influence of the operating temperature and humidity have been evaluated. Whereas the time constant of the sensor reaction decreases at higher temperature, a lower temperature yields a higher sensor signal. To characterize the interference of relative humidity on the determination of the ammonia concentration, we have constructed a scheme of isotherms based upon measurements using pulses of a carrier gas (purge-pulse (PP) method). This scheme of isotherms enables us to explain and estimate the efficiency of the PP and of the alternate temperature-pulse (TP) method.

Near real time detection of hazardous airborne substances.

A fast near real-time monitoring system for hazardous airborne substances, such as chemical warfare agents (CWA) is presented and limits of detection (LOD) for five CW simulants are determined. A tandem thermal desorber (TTD) continuously collects and pre-concentrates air. The pre-concentrated samples are then separated in a fast gas chromatographic (GC) run of 6.9min. and detected by a time-of-flight mass spectrometer (TOFMS). The GC-TOFMS signals are evaluated using chemometric methods for deconvolution and target identification. The high toxicity of nerve agents requires extremely low detection limits; for some as low as 100 ng/m(3) (10 ppt). The combination of TTD, TOFMS and chemometric data evaluation methods enables the system to fulfill this requirement. Calibration measurements for five different CWA simulants show lower limits of detection in the range of 10 ng/m(3)-60 ng/m(3) (1-11 ppt). In addition, the ability to detect trace concentrations of real CWA is demonstrated with a measurement of 30 pg Sarin on column. Several other real CWA measurements are shown, like sulfur mustard in diesel, lewisite under humid conditions and VX. As part of this work the influence of stationary film thickness on peak tailing of organophosphates is investigated for peak shape optimization.