Generation of gaseous mixtures of ethene Elz ˙ bieta Przyk, Piotr Konieczka, Jolanta Szczygelska-Tao, Jan F. Biernat, Jacek Namies ´nik Chemical Faculty, Technical University of Gdan ´sk, 11/12 Narutowicza St., 80-952 Gdan ´sk, Poland Generation of gaseous mixtures of ethene on the basis of thermal decomposition of compound bonded to silica gel surface – Single and multipoint calibration of a thermal decomposition-gas chromatography system The paper presents a new method of determination of a volatile component (ethene) of gaseous standard mixtures obtained by thermal decomposition of a suitable sur- face compound. This method is based on a simple mathematical relationsphip (func- tion of a single variable). The amount of the analyte generated (under given, chosen conditions of thermal decomposition) per unit of mass of the source material has been determined exclusively on the basis of measuring the standard generation time. Key Words: Gaseous mixtures; Surface compounds; Silica gel, chemical modifica- tion; Thermal decomposition; Calibration; Ethene Ms received: May 17, 2000; accepted: November 2, 2000 1 Introduction Silica gel is widely used, both in analytical chemistry and in other areas of science. One such application is as an intermediate in the generation of standard gas mixtures. The approach utilizes the thermal decomposition of sur- face compound bonded to silica gel [1]. The concentration of an analyte in a stream of a generated standard mixture depends on the mass of the modified silica gel bed (sur- face coverage), its thermal decomposition temperature, and the diluting gas flow rate. Therefore, a mathematical relationship must exist between the instantaneous con- centration of the analyte in the gaseous standard mixture and the parameters of the thermal decomposition process [2, 3]. Such relationships, however, are often complicated (functions of several variables), and their practical appli- cation is difficult. For these reasons, this paper proposes a practical new way of determining the amount of an ana- lyte generated as a component of a standard gas mixture, the latter being utilized for either single point or multipoint calibration of a measuring device. 2 Experimental 2.1 Reagents Silica gel (MN-Kieselgel 60, 35 – 70 mesh; specific surface area 200 m 2 g –1 ; Macherey-Nagel, Duren, Germany) was modified [4]. The modified silica gel contains compound bonded to its surface, which, under high temperature con- ditions (above 1108C), undergo decomposition or chemi- cal transformation yielding ethene, according to the equa- tion shown in Figure 1. 2.2 Apparatus and procedure Weighed samples of modified silica gel (l 0.00001 g) were placed in glass tubes (10063.5 mm ID), which were in- ternally silanized prior to use to minimize interactions be- tween the tube wall and the analyte [4]. The tubes with the modified gel were placed inside a cus- tom-made thermal desorber, which served as a sampling device and was connected to the GC/FID system via a four-port valve. Depending upon its position, the valve re- directed a stream of carrier gas either through the thermal desorber or directly onto the front of a GC column. The 226 Correspondence: Prof. Jacek Namies ´nik, Chemical Faculty, Technical University of Gdan ´sk, 11/12 Narutowicza St., 80-952 Gdan ´ sk, Poland. E-mail: chemanal@pg.gda.pl Fax: +48 58 347 2694 J. Sep. Sci. 2001, 24, 226–229 Figure 1. Scheme of thermal decomposition of surface com- pound yielding ethene. i WILEY-VCH Verlag GmbH, D-69451 Weinheim 2001 1615-9306/2001/0303–0226$17.50+.50/0