Ammonia was detected and determined by a piezoelectric quartz crystal sensor coated with a 2:1 (v/v) mixture of (A) commercial aqueous solution of glycolic acid (70 % w/w) combined with tetrakis(hydroxyethyl) ethylenediamine - THEED (3:4 v/v) and a saturated solution of (B) tannic acid in acetone. A large quantity of promising substances and their mixtures, under different proportions, were initially studied as possible films. The effects of flow rate, cell temperature, and the amount of coating were investigated, to establish the best experimental conditions. Studies on repeatability, sampling times and some possible interfering gases were performed. The analytical curves are linear over the concentration range (2.0-11 ppm v or 1.4-7.7 mg m3-) for four different sampling times (0.5; 1; 2 and 3 min), with good linearity correlation (r) varying between 0.9994 and 0.9980 and respective sensitivities ranging from 13.5 to 42.0 Hz / ppm v.
ammonia; piezoelectric sensor (QCM); glycolic-tannic acids-THEED coating
