Qualitative Analysis of Acetophenone, Naphthalene, and Hexadecane by GC-Triple-Quad-MS Using MRM

The use of mass spectrometry (MS) is becoming widespread and rather routine in all levels of industry, government, and academia. Coupled with chromatographic methods, this powerful instrumental technique can be used to elucidate the composition of a complex sample and definitively identify constituents while offering the benefits of high-precision quantitative analysis and low detection limits. These attributes, as well as its growing employment, emphasize the need for the undergraduate student to gain practical experience with this instrumental technique. Additionally, it is critical that students observe first-hand the abilities and contrasts of MS analysis versus MS−MS analysis or triple-quadrupole (Q1q2Q3) multiple reaction monitoring (MRM) analysis. The focus of this experiment was the qualitative analysis of a sample containing three compounds: acetophenone, naphthalene, and hexadecane using a Q1q2Q3 GC–MS in single-quad full-scan mode, Q1q2Q3 in full-scan mode, and Q1q2Q3 in MRM mode. The analytes were specifically chosen to range from extensive fragmentation (molecular ion of low stability) to minimal fragmentation (molecular ion of high stability). Students utilized the MS NIST library to identify the unknown peaks after analysis using the first quadrupole in full-scan mode. They further compared different injection volumes and observed the effect of injection volume on the band shapes and the signal to noise ratio. The students then compiled a table of precursor ion MS peaks from the single-quad full-scan mode. The sample was next analyzed using Q1q2Q3 in full-scan mode, and students compiled a table of product ion MS peaks. These were translated to transition ion pairs and compared to instructor-chosen transition ion pairs used in the final MRM analysis. This laboratory exercise allowed the students to use modern instrumentation and analytical techniques to investigate the potential of second stage mass spectrometry, increasing their technical ability and understanding of this critical scientific tool. Moreover, they were able to observe first hand the power of the NIST library for unknown analytes as well as the potential advantages of MRM when selectivity and low detection limits are critical.