JO URNA L O F C HRO MA TO G RA PHY A ELSEVIER Journal of Chromatography A, 688 (1994) 135-152 Pulsed discharge helium ionization detector Universal detector for inorganic and organic compounds at the low picogram level W.E. Wentwortha3*, Huamin Cai”, Stanley Stearnsb zyxwvutsrqponmlkjihgfe “Chemistry Department, University zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of Houston. 4800 Calhoun Road, Houston, TX 77204- 5641, USA %alco Instruments Co., Inc.. Houston, TX 77055, USA First received 22 June 1994: revised manuscript received 13 September 1994 zyxwvutsrqponmlkjihgfedcb Abstract The pulsed discharge helium ionization detector is a universal ionization detector with sensitivity in the low picogram range. The response is approximately constant for saturated hydrocarbons on a per gram basis. Unsaturated and aromatic hydrocarbons have lower sensitivities. by about lo-20%. Heterocyclic substituents such as oxygen, chlorine and bromine tend to lower the response on a per gram basis. The dependence of the response on various parameters such as pulse interval and power, voltage, flow-rate and detector volume has been investigated. The response is linearly related to concentration over five orders of magnitude. The detector volume can be made small enough for high-speed microbore chromatography. 1. Introduction In a previous publication the pulsed discharge helium ionization detector (PDHID) was intro- duced, and its capabilities in the analysis of permanent gases were demonstrated [ 11. In other applications -air pollution analysis, for exam- ple- the simultaneous anaIysis of inorganic and organic compounds is desired; nitric oxide and sulfur dioxide need to be detected as well as formaldehyde, aromatic hydrocarbons and halo- genated compounds. It is also important to analyze for trace water in organic streams, because water may be deleterious to the catalyst or process. In this paper we demonstrate the * Corresponding author. response of the PDHID to both inorganic and organic compounds. Smce the PDHID is sensitive and essentially non-destructive (ca. O.Ol-0.1% ionization) it can be used in conjunction with more selective detectors of comparable sensitivity. For exam- ple, the pulsed discharge source can be adapted to the electron-capture mode, yielding sen- sitivities on the femtogram level [2]. Also various emission detectors such as microwave-induced plas-ma [ 31, alternating current helium plasma, [4] capacitively-coupled plasma [5], radio fre- quency plasma [6] and helium discharge [7,8], could be used in conjunction with the universal PDHID to detect various elemental composi- tions and functional groups. (For a general discussion of element-specific chromatographic detection by atomic emission, consult the text 0021-9673/94i$O7.00 0 IO 94 Elsevier Science B.V. All rights reserved SSDI 0021-9673(94)00913-Y