Difference Between Gas Chromatography and Mass Spectrometry

The key difference between gas chromatography and mass spectrometry is that gas chromatography is important in separating components in a mixture, whereas mass spectrometry is useful in calculating the exact molecular weight of the sample components.

Generally, gas chromatography is used along with mass spectrometry because we can separate components in a mixture using gas chromatography and can identify those components using mass spectrometry.

CONTENTS

1. Overview and Key Difference
2. What is Gas Chromatography
3. What is Mass Spectrometry
4. Side by Side Comparison – Gas Chromatography vs Mass Spectrometry in Tabular Form
6. Summary

What is Gas Chromatography?

Gas chromatography is an analytical technique in which a mobile phase and a stationary phase is used where the mobile phase is in the gas state. A chromatographic technique is an analytical test used to separate, identify, and sometimes quantify the components in a mixture. There are two types as gas-solid chromatography and gas-liquid chromatography.

In gas-solid chromatography, the stationary phase is in the solid-state and the mobile phase is in the gaseous state. Here, gas-solid chromatography is used for the separation of volatile components in a mixture. This technique includes both the mixture and the mobile phase in the gaseous state. The mobile phase and the mixture we are going to separate combine with each other, and then this mixture passes through the solid stationary phase. The stationary phase is applied to the inner wall of a tube known as the chromatographic column. The molecules of the stationary phase can interact with the molecules in the mobile phase.

In gas-liquid chromatography, the stationary phase is in the liquid state while the mobile phase is in the gaseous state. There, the stationary phase is a nonvolatile liquid. We need to apply this stationary phase on the inner wall of a tube known as the chromatographic column. Then, the inner wall act as a solid support for the stationary phase. In this technique, the mobile phase is an inert gas such as Argon, Helium, or Nitrogen.

What is Mass Spectrometry?

Mass spectrometry (often denoted by MS) is a technique in analytical chemistry that measures the mass-to-charge ratio of ions. The final result of this technique is given as a mass spectrum that appears as a plot of intensity. Moreover, we need to draw this plot as a function of the mass-to-charge ratio. In mass spectrometry, the instrument we are using for the measurement is a mass spectrometer. When we introduce our sample into this instrument, the sample molecules undergo ionization. During this ionization, choosing the proper ionization technique is very important because it has a great impact on the end result. If we use a reagent gas, e.g. ammonia, it will cause ionization of sample molecules to form either only positive ions or only negative ions, depending on the setup of the instrument.

Positive ionization in mass spectrometry involves the formation of positive ions for the determination of the mass-to-charge ratio of the sample molecules. We call this positive ion mode in mass spectrometry. We can denote this positive ion as M-H⁺. In this technique, we can detect ions in a high yield.

Negative ionization in mass spectrometry involves the formation of negative ions for the determination of the mass-to-charge ratio of the sample molecules. We call this negative ion mode in mass spectrometry. Furthermore, we can denote this negative ion as M-H^–. In this technique, we can detect these ions in a high yield.

What is the Difference Between Gas Chromatography and Mass Spectrometry?

Gas chromatography is an analytical technique in which a mobile phase and a stationary phase is used where the mobile phase is in a gas state. Mass spectrometry (often denoted by MS) is a technique in analytical chemistry that measures the mass-to-charge ratio of ions. Therefore, the key difference between gas chromatography and mass spectrometry is that gas chromatography is important in separating components in a mixture, whereas mass spectrometry is useful in calculating the exact molecular weight of the sample components.

The below infographic summarizes the difference between gas chromatography and mass spectrometry in tabular form.

Summary – Gas Chromatography vs Mass Spectrometry

Often we are using gas chromatography followed by mass spectrometry in order to separate the components in a desired mixture followed by their identification. The key difference between gas chromatography and mass spectrometry is that gas chromatography is important in separating components in a mixture, whereas mass spectrometry is useful in calculating the exact molecular weight of the sample components.

Reference:

1. “Gas Chromatography.” Chemistry LibreTexts, Libretexts, 15 Aug. 2020, Available here.

Image Courtesy:

1. “Gas chromatograph” By en:user:rune.welsh – Own work (CC BY-SA 3.0) via Commons Wikimedia

2. “Mass spectrometry protocol” By Philippe Hupé – Emmanuel Barillot, Laurence Calzone, Philippe Hupé, Jean-Philippe Vert, Andrei Zinovyev, Computational Systems Biology of Cancer Chapman & Hall/CRC Mathematical & Computational Biology , 2012 (CC BY-SA 3.0) via Commons Wikimedia