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An Ion moblllty detector (IMD) for gas chromatography has been modltled to accept the use of a photolonlratlon source. Photolonlratlon offers a number of advantages over the commonly employed 63Ni lloll lncludlng the lack of reactant Ions, which are seen with the secondary lonlratlon source, enabllng use of the entire Ion rnoblllty spectrum1 from 0 to 20 ms for observatlon of product Ions. Test compounds contlnuousiy bled Into the detector are used to compare pertormance of the standard ""I foll to that of a low-pressure 10.0-eV krypton photolonlration lamp. Due to uncompkated fragmentatlon patterns produced via photoloniratlon, the tunable selectlve capabllitles of the dettsctor are enhanced. Selectlve moblllty monltorlng Is used to detect toluene, mesitylene, and naphthalene In a mixture of aromatlc compounds of slmllar structure following Separation on a fused slllca capillary column.Ion mobility spectrometry (IMS) has long been recognized as a potentially useful technique for eelective detection of organic compounds after separation by gas chromatography (1-7). First introduced in 1970 by Cohen and Karasek (8,9), the ion mobility spectrometer consists of two basic units: a 63Ni foil in an ionization cell analogous to that found in an electron capture detector (ECD) and an atmospheric pressure ion drift tube maintained at either a positive or negative uniform electric field gradient of 150-250 V/cm. Ions produced in the ionization cell are accelerated down the electric field where they are separated according to their mobilities in a countercurrent flow of nitrogen pas. As discussed by Revercomb and Mason (IO), a number of factors including the mass, size, and charge of an ion determine its mobility at atmospheric pressure.The prime advantage of IMS as a GC detection method is that the instrument imay be easily tuned to monitor ions of a preselected mobility, thereby tailoring response characteristics to fit the needs of a given separation problem. Ion mobility spectrometry can often provide selective detection between compounds of the same elemental content but differing in structural composition. Despite these advantages, however, IMS has not enjoyed wide-scale popularity as a GC detection technique largely due to limited success a t interfacing the instrument with chromatographic columns.A new GC detector based on the principles of IMS has been developed in this laboratory specifically to eliminate many of the limitations preventing use with high-resolution separations (11). Known as the ion mobility detector (IMD), this instrument has been used to selectively detect a wide range of compounds including substituted naphthalenes in gasoline (11) and terpenes in orange extract (12) using the positive ion mode and 2,4-dichlorophenoxyacetic acid in soil extracts (13) using the negative ion mode. Investigations into the response characteristics of the IMD have shown it to be extremely sensitive to organic compounds. Minimum detectable amounts are typically in the low picogram range and detector response is expone...

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