Volume 45, Number 1 (January - February 2000)

Key words:  sulfur hexafluoride  (SF6), trace analysis, head-space method, water samples, electron capture detector (ECD), hypercoulometric effect

The determination of SF₆ concentration in water using the head-space method is presented. The head-space extraction from water and enrichment of SF₆ in a trap filled with glass pellets placed in liquid nitrogen are presented. It was found that mathematical analysis of the head-space method allows for determination of conditions under which the extracted mass of SF₆ from water sample reach maximal value. The detection limits received for SF₆ are 0.0186 ± 0.0095 fg/cm³ H₂O and 0.0054 ± 0.0028 fg/cm³ H₂O for the measurement containers of volume 710 and 2340 cm³, respectively. During realisation of investigation the hypercoulometric effect for SF₆ in the electron capture detector (ECD) was confirmed. The determined values of the hypercoulometry factor are in the range from 4 to 10 and depend on purity of the carrier gas and on the detector supplying system.