Dynamic system for the calibration of semi-volatile carbonyl compounds in air

A dynamic calibration system designed for generating accurate and precise c oncentrations of semi-volatile carbonyls in the ppb (v/v) (ppbv)-ppt (v/v) (pptv) range has been developed and tested. Alkanals from C-6 to C-9 were u sed as test compounds. Diffusion rates of their vapours from capillary tube s were determined theoretically and with two methods whose accuracy was ind ependently evaluated with liquid standard solutions. Methods selected for t esting the calibration system were those commonly used for the selective qu antification of carbonyls in air. One is based on the well-known reaction w ith 2,4-dinitrophenylhydrazine (DNPH), followed by the analysis of formed h ydrazones by HPLC-W. The other is based on the retention of carbonyls on gr aphitic carbon adsorbents, followed by MS detection of the sample injected into a capillary column by thermal desorption. A good consistency was found between the values of the diffusion rates determined by the two methods. T he scatter between the two methods was in the range of +/-10% when diffusio n rates of ca. 1 ng/s were attained. Experimental values closely approached those calculated by applying the equation describing the diffusion of a va pour in equilibrium with the liquid through a capillary tube. (C) 2000 Else vier Science B.V. All rights reserved.