A RENEWABLE LIQUID DROPLET AS A SAMPLER AND A WINDOWLESS OPTICAL-CELL - AUTOMATED SENSOR FOR GASEOUS CHLORINE

A droplet of a reagent solution is formed at the tip of a tube centered in a cylindrical chamber through which a gas sample is aspirated, The solution is continuously pumped; the drop grows, falls, and another drop grows again. The droplet serves not only as a reproducible collector for the sample gas flowing around it but also as a reactor for a chromogenic reaction and as a windowless optical cell, The design and characteristics of this dynamically growing/falling droplet-based gas sensor system are described; the performance parameters are attractive relative to a static drop, In particular, such systems can be internally calibrated for any humidity effects: at a constant pumping rate, the drop period/frequency is a predictable function of sample relative humidity. The feasibility of the sensor is demonstrated by the fully automated and continuous determination of gaseous chlorine using tetramethylbenzidine solution as a chromogenic collection liquid. At levels relevant to industrial hygiene monitoring, an 18 mu L droplet-based sensor equipped with a light-emitting diode photodiode-based detector shows a relative standard deviation of 1.2% (pCl(2) similar to 900 ppbv, drop period 1.1 min) while the corresponding blank standard deviation is equivalent to similar to 1 ppbv, There appears to be a great potential for such drop-based collectors with in situ photometric or electrochemical signal transducers as automated sensor devices in biphasic measurements (trace gases, solvent extraction, etc.).