MEASUREMENT OF ATMOSPHERIC FORMALDEHYDE USING A DROP COLLECTOR AND IN-SITU COLORIMETRY

A sensitive and affordable approach is described for the in-situ measu rement of ambient formaldehyde. Air is sampled around a 100 microliter aqueous drop containing 3-methyl-2-benzothiazoline hydrazone. After a desired period of sampling (typ. 5 min) and a waiting period of 10 mi n for the reaction to be completed, a second reagent (FeCl3) is added to the drop by means of a conjoined conduit. A blue product is formed and is read after an additional 10 min of reaction by a fiber-optic/li ght emitting diode based photodetector. A fresh drop is then formed an d the process begins anew. As demonstrated here, the limit of detectio n is similar to 6.25 mu g m(-3) HCHO but can be significantly improved by using longer sampling times and a sampling rate higher than 100 mi min(-1) used in most of this work. This is the first example of a chr omogenic drop sensor that utilizes sequential reagent addition.