Technical Notes Gas Chromatograph Injection Liner for Continuous Analyte Admission into a Mass Spectrometer Thomas N. Corso, Colleen K. Van Pelt, and J. Thomas Brenna* Division of Nutritional Sciences, Cornell University, Savage Hall, Ithaca, New York 14853 An inexpensive modification to a gas chromatography injector liner is reported that facilitates continuous admis- sion of analyte into a gas chromatograph/ mass spectrom- eter (GC/ MS) for methods development. The MS meth- ods development liner can be made by making simple modifications to commercially available liners and fits into standard injectors in place of the normal liners without any need to break vacuum in the MS. The injector temperature and gas flow rates are adjusted to provide appropriate analyte levels in the MS, which can be admitted under conditions identical with those of real analyses, including co-admission of column bleed. The device is particularly useful for development of tandem MS methods in GC/ MS/ MS instruments, which are configured with the GC as the sole sample inlet. Tandem mass spectrometry (MS n ) is one of the most powerful methods for structural and quantitative chemical analysis. The recent commercial availability of MS n capabilities for low-cost tabletop gas chromatograph/ mass spectrometers (GC/ MS), based on quadrupole ion traps, has widely expanded the range of applications of MS n . 1-3 Optimization of ionization and detection parameters is straight- forward for single-stage MS experiments, so that tuning based on standards such as perfluorotributylamine provides satisfactory results for a wide range of analytes. MS n parameters involve isolation and dissociation steps, which are closely linked to analyte chemical characteristics, and consequently often require consider- able effort to obtain optimal results. 1 High-performance magnetic sector and quadrupole MS instruments are typically equipped with multiple sample inlets to the MS, including a heated inlet or probe from which a constant stream of analyte can be admitted for tuning purposes. Low-cost ion trap-based GC/ MS instruments are frequently equipped with the GC as the sole sample inlet to the MS. As a result, MS n methods must be developed by optimizing tuning conditions during the short period of time that analyte is eluting from the GC column. Numerous parameters are relevant for ion trap tandem MS analysis, including rf amplitude during ionization, isolation mass window and time, collision-induced dissociation (CID) amplitude, rf, time, type, and bandwidth, rough and fine ejection amplitudes, prescan type, modulation range and rate, and low and high isolation rf offsets. At least one commercial manufacturer has incorporated software-based routines to rapidly cycle through some of the settings for several parameters so that optimization can be done on eluting GC peaks. However, cycling through several parameters is time-consuming because of the requirement for multiple injections, and interpretation of results is uncertain because analyte concentration changes continuously. We report here a simple and inexpensive GC injection liner that makes it possible to admit sample continuously into any GC/ MS instrument which requires no instrumentation hardware modifications. Because the intact GC injector system is used, actual experimental conditions, including column bleed and flow rates, are maintained during parameter optimization. EXPERIMENTAL SECTION Hardware. Electron impact (EI), chemical ionization (CI), and collision-induced dissociation (CID) were performed on a Varian (Walnut Creek, CA) Saturn III QISMS ion trap equipped with a wave board and MS n software. The chromatograph setup consisted of an HP5890 Series I GC (Hewlett-Packard) equipped with a split/ splitless injector and a DB5 fused-silica capillary column (J&W, Folsom, CA), 30 m × 0.25 mm, and 0.5- μm film thickness. Samples and Conditions. Analytes were purchased from Sigma Chemical Co. (St. Louis, MO) and used without further purification. In the first experiment, 100 mg of >98% methyl myristate (methyl tetradecanoate, Me14:0) was deposited into the modified development liner. For the second experiment, ap- proximately 200 mg of >95%R-tocopherol was deposited into the modified development liner. These analyte amounts were chosen for convenience only, and significantly lower amounts have been used. The R-tocopherol was analyzed in EI mode, and the Me14:0 was analyzed in CI mode with ethanol as the CI reagent. Conditions common to all analyses were as follows: electron multiplier voltage, 1.4 kV; emission current, 10 mA; manifold (ion trap) temperature, 295 °C; axial modulation, 4.0 V; and acquisition time, 1 s. * To whom correspondence should be addressed. Phone: (607) 255-9182. Fax: (607) 255-1033. E-mail: jtb4@ cornell.edu. (1) March, R. E., Todd, J. F. J., Eds. Practical aspects of ion trap mass spectrometry, Volume III: Chemical, Environmental, and Biomedical Ap- plications; CRC: Boca Raton, FL, 1995. (2) Strife, R. J.; Simms, J. R. J. Am. Soc. Mass Spectrom. 1992 , 3, 372-377. (3) Johnson, J. V.; Yost, R. A.; Kelley, P. E.; Bradford, D. C. Anal. Chem. 1990, 62, 2162-2172. Anal. Chem. 1998, 70, 1030-1032 1030 Analytical Chemistry, Vol. 70, No. 5, March 1, 1998 S0003-2700(97)00928-1 CCC: $15.00 © 1998 American Chemical Society Published on Web 01/10/1998