Instrumentation

GC-MS

Sample Preparation

GC-MS is a combined acronym for two experimental techniques: gas-liquid chromatography (GC) and mass spectrometry (MS). These acronyms are also applied to the instruments used for each technique: gas-liquid chromatograph (GC) and mass spectrometer (MS).

GC-MS samples are typically complex mixtures. A mixture is injected into the GC and separated into its components. As each component exits the GC, it enters the MS and is ionized. A single compound can produce ions of many different masses and the full assortment of ions constitutes a compound’s mass spectrum. In favorable cases, the heaviest ion has the same mass as the compound itself, and the compound’s molecular weight can be established. Carey, Chapter 13.22, and Padias p. 98-106 contain more information on mass spectrometry and GC-MS.

Instructions (under construction) are provided here for the Reed College under construction GC-MS. This instrument is extremely sensitive and only small amounts of material should ever be put through this instrument. Samples should be extremely dilute (typically x mg volatile compound dissolved in xx mL solvent), and only a small volume (typically x mL) of sample should ever be injected into the instrument. Non-volatile compounds should never be put in the GC-MS.

Recording and printing your GC-MS data

Students may only use the GC-MS instrument under the direct supervision of an instructor or lab assistant.

Before students can use the GC-MS, the instructor should see to it that all electronics have been turned on, all systems have been checked and are in operating order, the MS has been tuned to maximum sensitivity and resolution, and an appropriate parameter for data acquisition has been loaded into the computer (Chem 201/202 students uses a file named under construction that contains settings for both the GC and MS.)

Once the instrument has been properly set-up, students may inject samples into the GC and initiate data runs for themselves. They should also workup data, print Total Ion Count (TIC) vs. time data, and print the mass spectrum of each major peak.

To operate the GC-MS and obtain MS data for your compound:

under construction