Evaluating GC/MS Performance

Alcaraz, A ; Dougan, A

Lawrence Livermore National Laboratory

关键词: Hydrocarbons;    37 Inorganic, Organic, Physical And Analytical Chemistry;    Tuning;    Mixtures;    Air;   

DOI  :  10.2172/1036861
RP-ID  :  UCRL-TR-226415
RP-ID  :  W-7405-ENG-48
RP-ID  :  1036861

美国|英语

来源: UNT Digital Library

【 摘 要 】

Evaluating the chemical background in the GC/MS system (system background) and solvent purity. This procedure will allow the analyst to verify that the GC/MS is free of chemical interferences or contamination and verify the solvent being utilized is free of interferences - Conduct a GC/MS analysis without injecting a solvent (system background) and Conduct a GC/MS analysis inject 1uL of CH2Cl2 solvent (Solvent background). GC conditions: (1) Injector Temperature (C): Injector Temperature is typically set at 250; (2) Transferline Temperature (C) - The Transferline Temperature is typically set at 280 C; (3) Constant flow (Sec./cm2) - This value, in seconds per cubic cm. Typically, set at 32; (4) Splitless mode (Sec.) - This value, in seconds, is the time before the purge valve opens. Typically, set at 45 seconds; (5) Starting Temperature (C): The Starting Temperature value can be set at 40 C; (6) Hold Time 1 (Min.) - Hold Time 1 is the amount of time, in minutes at the Starting Temperature that Ramp 1 Temperature is held. Typically set at 3 minutes; (7) Ramp 1 Rate (C/Min.) - Ramp 1 Rate is the temperature rise per unit time and has a typically value of 8 C per minute to 300 C; and (8) Hold Time 2 (Min.): Hold Time 2 is the amount of time, in minutes at the final Temperature that Ramp 1 Temperature is held. Temperature is held at 300 C for 3 minutes. MS conditions: Electronic - 40 to 500 amu, Scan Range - 30-600 m/z, Scan time - 0.7 sec, Mass Resolution - 07u, and Electron energy 1 - 70 eV. The total ion chromatograms (TIC) from a bakeout and solvent should be void of any large chromatographic peaks (see figure 1). Autotune using the PFTBA calibrant: First selecting the autotune option and click on standard autotune. The software program will generate final tune report similar to figure 2. If there are any MS tuning problems (e.g., dirty source, air leak, etc.) the tuning process will fail. Be sure to save the tune file before proceeding to the next step. Run an 'Air and Water Check': By selecting View - Diagnostics/Vacuum Control - Vacuum - Air and Water Check. A Yes/No dialogue box will appear; select No (use current values). It is very important to select No! Otherwise the tune values are drastically altered. The software program will generate a water/air report similar to figure 3. Evaluating the GC/MS system with a performance standard: This procedure should allow the analyst to verify that the chromatographic column and associated components are working adequately to separate the various classes of chemical compounds (e.g., hydrocarbons, alcohols, fatty acids, aromatics, etc.). Use the same GC/MS conditions used to collect the system background and solvent check (part 1 of this document). Figure 5 is an example of a commercial GC/MS column test mixture used to evaluate GC/MS prior to analysis.