Basic Gas Chromatography

Harold M. McNair, James M. Miller, Nicholas H. Snow

• Editore: Wiley
• Anno: 2019
• ISBN:
  9781119450788
• Edizione: 3
• Argomento: Physical Sciences
• Categoria: Analytic Chemistry

Basic Gas Chromatography, Third Edition provides a brief introduction to GC following the objectives for titles in this series. It should appeal to readers with varying levels of education and emphasizes a practical, applied approach to the subject.: This book provides a quick need-to-know introduction to gas chromatography; still the most widely used instrumental analysis technique, and is intended to assist new users in gaining understanding quickly and as a quick reference for experienced users.

The new edition provides updated chapters that reflect changes in technology and methodology, especially sample preparation, detectors and multidimensional chromatography. The book also covers new detectors recently introduced and sample preparation methods that have become much more easily accessible since the previous edition.

1
INTRODUCTION

It is hard to imagine an organic analytical laboratory without a gas chromatograph. Gas chromatography (GC) is the premier technique for separation and analysis of volatile compounds. It has been used to analyze gases, liquids, and solids, with the latter usually dissolved in volatile solvents. Both organic and inorganic materials can be analyzed, and molecular weights can range from 2 to over 1000 Da.

Gas chromatographs continue to be the most widely used analytical instruments in the world. Efficient capillary columns provide high resolution, separating more than 450 components in coffee aroma, for example, or the components in a complex natural product like peppermint oil as seen in Figure 1.1. Sensitive detectors like the flame ionization detector can quantitate 50 ppb of organic compounds with a relative standard deviation of about 5%. Automated systems can handle more than 100 samples per day with minimum downtime, and all of this can be accomplished with an investment of about $20,000.

Figure 1.1. Typical gas chromatographic separation showing the high efficiency of this method.

Source: Courtesy of Phenomenex, Inc.

A BRIEF HISTORY

Chromatography began at the turn of the century when Ramsey [1] separated mixtures of gases and vapors on adsorbents like charcoal and Michael Tswett [2] separated plant pigments by liquid chromatography (LC). Tswett is credited as being the “father of chromatography” principally because he coined the term chromatography (literally meaning “color writing”) and scientifically described the process. His paper was translated into English and republished [3] because of its importance to the field. Today, of course, most chromatographic analyses are performed on materials that are not colored.

GC is that form of chromatography in which a gas is the moving phase. The important seminal work was first published in 1952 [4] when Martin and James acted on a suggestion made 11 years earlier by Martin himself in a Nobel Prize‐winning paper on partition chromatography [5]. It was quickly discovered that GC was simple, fast, and applicable to the separation of many volatile materials, especially petrochemicals, for which distillation was the preferred method of separation at that time. Theories describing the process were readily tested and led to still more advanced theories. Simultaneously the demand for instruments gave rise to a new industry that responded quickly by developing new gas chromatographs with improved capabilities.

The development of chromatography in all of its forms was thoroughly explored by Ettre, who authored nearly 50 publications on chromatographic history. There are three most relevant articles: one focused on the work of Tswett, Martin, Synge, and James [6]; one emphasizing the development of instruments [7]; and a third containing over 200 references on the early development of chromatography [8].

Today GC is a mature technique and a very important one. The worldwide market for GC instruments is estimated to be between $2 and $3 billion or more than 40,000 instruments annually.

DEFINITIONS

In order to define chromatography adequately, a few terms and symbols need to be introduced, but the next chapter is the main source of information on definitions and symbols.

Chromatography

The “official” definitions of the International Union of Pure and Applied Chemistry (IUPAC) are:

Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (stationary phase) while the other (the mobile phase) moves in a definite direction. Elution chromatography is a procedure in which the mobile phase is continuously passed through or along the chromatographic bed and the sample is fed into the system as a finite slug [9].

This type of chromatographic process is called elution. The various chromatographic processes are named according to the physical state of the mobile phase. Thus, in GC the mobile phase is a gas, and in LC the mobile phase is a liquid. Figure 1.2 shows a flow ch...