Calibration of a multipoint sampling system connected with a photoacousticdetector

Photoacoustic detection of gases in the air phase in combination with a mul tipoint sampling device transfers about 100 mt of air from each sample loca tion to the next one, causing a considerable disturbance when small systems are sampled. In reactive systems, such as trace gas exchange in soil sampl es, a correction is required to determine the kinetic behavior of the syste ms. But this kinetic behavior is required in turn to calculate the correcti on in a repeated sampling sequence. A model was developed for reaction kine tics (zero-order or first-order) within closed systems and the sample trans fer between these systems by a CBISS MK2 multipoint sampling system, connec ted with a Bruel & Kjaer photoacoustic detector. By regression, the reactio n kinetics is determined, and by simulation of the system in the absence of sample transfer, corrected data are generated. Comparison of experimental and modeled data revealed that part of the sample is transferred directly t wo systems further. In addition, a slight memory effect of the detector was revealed. These effects were accounted for in the model. If the correction is not made, biased results are obtained for the reaction kinetics.