The Use of Gas Chromatography and Mass Spectrometry To Introduce General Chemistry Students to Percent Mass and Atomic Mass Calculations

Abstract

A general chemistry laboratory experiment is described that introduces students to instrumental analysis using gas chromatography−mass spectrometry (GC−MS), while simultaneously reinforcing the concepts of mass percent and the calculation of atomic mass. Working in small groups, students use the GC to separate and quantify the percent composition in a mixture of dichloromethane and chloroform dissolved in toluene by the injection of known quantities of each pure substance dissolved in toluene and the determination of the individual instrumental response factor. The relative abundances of the chlorine-35 and chlorine-37 isotopes can also be determined from several different groupings on the mass spectra of the compounds, allowing for the calculation of the atomic mass of chlorine. This collaborative-learning experiment enhances student understanding through the hands-on use of chemical instrumentation and helps to develop their problem solving skills in the analysis of several different types of experimental data.

Separation of Caffeine from Beverages and Analysis Using Thin-Layer Chromatography and Gas Chromatography–Mass Spectrometry

“…They also print a mass spectrum for the solvent (dichloromethane), measure the height of the 35 Cl and 37 Cl peaks with a ruler, and calculate the percent abundance of each of these isotopes from this data. Pfennig and Schafer also report an alternate method for calculation of the percent abundance of chlorine by GC–MS. Our method is able to detect caffeine in the coffee, as well as substances likely added as flavoring agents to the coffee, such as vanillin, by the comparison of the sample spectrum to the mass spectral library.…”

“…GC–MS is one of the most versatile tandem methods for quantitative and qualitative identification of sample components. Its use in the general chemistry laboratory curriculum has become more common in recent years, demonstrating the suitability of incorporating such instrumentation into an introductory course. − This experiment has been conducted with over 3500 on-campus and dual credit General Chemistry I students at MWSU. The detection of caffeine in beverages using high-performance liquid chromatography (HPLC), including coffee, , soft drinks, and energy drinks; nuclear magnetic resonance (NMR) of energy drinks; and UV–visible spectrophotometry (UV–vis) of coffee extracts has been reported for use in the instructional laboratory.…”

Headspace GC–MS Analysis of Halogenated Volatile Organic Compounds in Aqueous Samples: An Experiment for General Chemistry Laboratory

“…Additionally, HVOCs are attractive as an experimental subject because they can be rapidly separated by GC and contain an interesting mixture of isotopes that are easy to observe and quantify with a low-resolution mass spectrometer. 1,7 The main learning goal of the HVOC−GC−MS experiment is to help students understand the nature of isotopes and the practical consequences of atoms occurring in nature as different stable isotopes. In this lab, students explore the halogen isotope content of the HVOCs by obtaining experimental evidence for multiple Cl or Br isotopes using GC−MS with headspace sampling.…”

“…According the National Energy Technology Laboratory, “HVOCs are the most significant organic contaminants in groundwater associated with disposal sites in the United States.” The frequent appearance of these compounds as environmental pollutants should spark the interest of chemistry, biology, and civil and environmental engineering students. Additionally, HVOCs are attractive as an experimental subject because they can be rapidly separated by GC and contain an interesting mixture of isotopes that are easy to observe and quantify with a low-resolution mass spectrometer. , …”

“…In this lab, students explore the halogen isotope content of the HVOCs by obtaining experimental evidence for multiple Cl or Br isotopes using GC–MS with headspace sampling. The subject of isotopes and the use of GC–MS in the study of isotopes have been described for other general chemistry experiments, − and several studies have described other kinds of GC–MS experiments for the general chemistry lab. , The novel components of this study are (i) the rapid sampling method that makes the experiment practical for large general chemistry classes and (ii) a large-scale investigation of the impact of the experiment on the students’ perceived learning gains in terms of content understanding, skills, and attitudes. An online student assessment of the learning gains (SALG) instrument was used to compare the students’ perceptions of skills, understanding, and attitudes toward laboratory science before and after performing the experiment…”