Detector Systems in Capillary Gas Chromatography

Abstract

SummaryExpressIons for the minimum detectabie amount 0 0 and the minimum analyte concentration Co as functlons of the chromatographic parameters are derlved for both mass and concentratlon sensltlve detectors. The effects of pressure drop, column inner diameter, and film thickness are given.The minimum analyte concentration for mass flow sensitlve detectors, Cam, can be reduced conslderably by selecting the carrier gas velocity weil above lts optimum value (related to Hml n ), however, at the cost of long columns and long analysis times. For 0 0 the improvements can be neglected, and 80 the analysis can best be performed at Uopt.When the flow rate In the detector, F d, is equal to the column flow rate F c, the maximum permissible detector volume of concentration sensitlve detectors is proportional to d c 2 up to d c 3 , and so narrow bore columns requlre detectors of extremely sm all volume. Make-up gas has to be added when the actual volume is too large, th us worsening the detectability. Another approaCh, vacuum operation of the detector cell, appears to be very attractive. On the other hand, when wide bore columns are used in comblnation with smaU volume concentration sensltive detectors, very smaU values of Qoc and Coc are obtalnable when the abundant carrier gas can be removed betare entering the detector cell.Digital nolse filtering can furtherreducethe obtalnable 0 0 and Co values, especially for broad peaks and thus for wide bore columns.

Trace analysis of halogenated hydrocarbons in gaseous samples by capillary gas chromatography. Part II: Quantitative aspects and ECD calibration

“…The chromatographic equipment and sample introduction system was identical to that described in part I [1].…”

“…It was first recognized by Molina * For Part I,see [1] and Rowland in 1974 that these compunds play an important role in the catalytic destruction of stratospheric ozone [2]. Despite much effort to clarify the transport and photochemistry of chlorine containing species, until now, there is still unsufficient proof whether CFC's contribute significantly to the destruction of the ozone layer [3,4].…”

Pressure-Tunable Column Selectivity for High-Speed Vacuum-Outlet GC

“…Vacuum-outlet gas chromatography ( GC ) involves the use of a vacuum pump to pull carrier gas and injected samples through a capillary separation column. − Vacuum-outlet techniques are useful for increasing analysis speed and for reducing detector dead time for some closed-cell detectors. − When the outlet of a column is connected directly to the ion source of a mass spectrometer, the column outlet pressure is typically less than 10 -4 Torr. However, conventional GC/MS is conducted using relatively long capillary columns.…”