METHOD OF DETERMINING TRACE CONCENTRATIONS OF AMMONIA Russian patent published in 2009 - IPC G01N27/12 G01N31/00 

FIELD: chemistry.

SUBSTANCE: invention relates to determination of ammonia content in gas, liquid and solid media. The method involves use of piezocrystal bulk acoustic wave resonators with a sorbent film on electrodes, taking a sample, preparing the sample for analysis, putting the analysed sample into a detection cell, recording the analytical signal, plotting an analytical curve ΔF=f(C_NH3) and determination of ammonia content. Test objects are gas, liquid and solid media which contain 0.01-10 mg/m³ ammonia. There is a stage for preparing the sample for analysis: the solid phase is ground up, put into a weighing bottle, heated to 40°C, passing 500-1000 m³ air through it at a rate of 40-50 cm³/min, and then the obtained gaseous mixture or analysed gas phase with volume 500-100 cm³ is passed through an alkaline solution of tetraethylmethylenediamine with mass ratio of 1-5% at a rate of 40-50 cm³/min. For analysis of liquid media, a 10 cm³ sample is taken, 0.1 cm³ of concentrated solution of tetraethylmethylenediamine is added, mixed, 5 cm³ is taken from the obtained mixture during preparation for analysis of solid, gaseous or liquid phase and kept in a weighing bottle with a polyurethane plug for 15 minutes. 1 -2 cm³ is taken from the equilibrium gas phase over the solution and put into the detection cell. Concentration of ammonia in the analysed liquid sample is found from analytical curve ΔF=f(C_NH3) (dwg.), plotted at peak response of the piezocrystal resonator with a film in standard gaseous mixtures. Concentration of ammonia in the solid and gaseous phases is further found using formula (1) C_s=(C_a.p. · V_a.p.)/V_s, where C_s - is concentration of ammonia in the sample, C_a.p. - is concentration of ammonia in aqueous phase, found using the analytical curve, V_s - is volume drawn gaseous sample, V_a.p. - is volume of aqueous phase.

EFFECT: high selectivity, sensitivity and accuracy of analysis.

6 ex, 1 tbl, 1 dwg