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RECEIVED for review July 20, 1983. Accepted September 1, 1983. The authors thank the New York State Racing and Wagering Board Equine Drug Testing and Research Program for financial support. Part of this work was first presented at the 31st Annual Conference on Mass Spectrometry and Allied Topics, Boston, MA, May 8-13, 1983; Paper 343.
Gas-Nebulized Direct Liquid Introduction Interface for Liquid ChromatographyIMass Spectrometry James A. Apffel,* Udo A. Th. Brinkman, and Roland W. Frei
Department of Analytical Chemistry, Free University, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands Evert A. I. M. Evers
Department of Organic Chemistry, Free University, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
The design of a direct liquid introduction (DLI) LC/MS interface Is described. This system uses a jet of helium gas to aid the nebulization of the vaporizing LC effluent and sample Into the MS source. The effects of several operating variables, such as probe tip position, mobile phase composttion and flow rate, and source temperature are discussed. The performance of the unit is evaluated in terms of the variance Contribution to the total peak width, repeatability, linearity, detection limits and the applicability for a range of samples including phenyiurea herbicides, polycyclic aromatic hydrocarbons, drugs such as ciobaram and ranltidine, and catecholamines.
In the last several years, the field of on-line high-performance liquid chromatography/mass spectrometry (LC/MS) has grown from the desire for LC detector specificity comparable to that available in gas chromatography/mass spectrometry (GC/MS) into an analytically applicable technique (I). As an LC detector, the mass spectrometer offers a number of advantages over conventional detector systems, including simultaneous use as both a universal and specific detector and the capability of yielding molecular weight and confirmatory identification information. On the other hand, LC offers not only the possibility of separating nonvolatile and thermally labile compounds for subsequent MS analysis but also use of LC pretreatment, preconcentration, and cleanup techniques not practical with GC. Interfaces used in coupling these two analytical techniques fall into two basic categories: transport interfaces and direct liquid introduction (DLI) interfaces. A number of systems have been used in the DLI approach for introducing the LC effluent into the MS source. These include the formation of
liquid jets through either a viscous flow capillary (2) or 1-5 pm diaphragms (3) and vacuum nebulization interfaces (4). In the vacuum nebulization interface, the LC column effluent is nebulized from a capillary tip by a flow of gas into an intermediate vacuum chamber before entering the MS through an orifice (46). While the diaphragm systems have shown the most impressive results, the diaphragms themselves are expensive and are subject to wear (7). The narrow capillaries (
