DETERMINATION OF CARBOXYLIC-ACID VAPOR BY A THICKNESS-SHEER-MODE ACOUSTIC-WAVE SENSOR COATED WITH CROWN-ETHERS

The frequency response sensitivities for 39 organic vapours by thickne ss-sheer-mode (TSM) acoustic wave sensors coated with monobenzo-15-cro wn-5 (B15C5), monobenzo-18-crown-6 (B18C6) and dibenzo-30-crown-10 (DB 30C10) have been reported. It shows that crown ethers are the most eff icient adsorptively active material for sensing carboxylic acid vapour , particularly B15C5 can be used for sensing formic acid vapour. The B 15C5 based sensor possesses good reproducibility, high stability and s hort response time with wide linear detection range and a low detectio n limit down to 0.0201 mg l(-1) (about 5.70 ppm, V/V) of formic acid v apour while coating with 12 mu g of B15C5. There is no significant int erference from other organic vapours except for some nitrogen containi ng compounds such as diethylamine, pyridine and N,N-dimethylformamide, and carboxylic acid homologues such as acetic and propionic acids. Th e effect of humidity is easily controllable. Compared with acid-base t itration method, the sensor can be used for the determination of HCOOH vapour with recovery rate of 98.4 similar to 103.8%, the analytical r esults are in good agreement with those obtained by the more time cons uming acid-base titration method. (C) 1997 Elsevier Science B.V.