Process Gas Chromatographs. Tony Waters

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Part One PGC fundamentals

      1975 Beckman Model 6800 Air Quality Chromatograph.

      Figure 1.1 A Classic Process Gas Chromatograph.

      Source: Beckman Historical Collection, Box 58, Folder 28. Science History Institute, Philadelphia. https://digital.sciencehistory.org/works/474299142 Reproduced with permission of Rosemount, Inc.

      “We cannot teach people anything; we can only help them discover it within themselves.”

       Attributed to Galileo Galilei 1564–1642

      Why study this?

      Part One introduces the art and science of gas chromatography (GC) as applied to the industrial process instrument.

      These four chapters explain how a GC column works, why the compounds in the injected sample form the characteristic peak shape, how one peak becomes separate from another peak, and how we can predict the position and shape of peaks on a chromatogram from known patterns of peak timing and width.

      The text presents this information in an easy‐to‐read and mostly non‐mathematical manner. Yet it shuns simplistic analogies of what happens inside a GC column because they tend to mislead rather than to inform. Instead, it offers a challenging insight into real chromatographic behavior.

      The knowledge gained here is a necessary preparation for understanding the function of the hardware devices and software techniques introduced in later chapters of the book. For those who aspire to be proficient in the application or troubleshooting of process gas chromatographs, mastery of these concepts is not optional.

1 An introduction

      “Books on gas chromatography, of which there are many, usually start by reviewing the historical development of the science, so we won't do that here. Instead, we'll start by understanding the basic technique: what a chromatograph does and how it does it. To read the fascinating history of chromatographic science, see the beautiful book by Ettre (2008)”.

Chromatographic separation

      Let's start by looking briefly at the various forms of chromatography.

      Chromatography by itself is not a complete analytical technique. It's just a way to separate one kind of molecule from another kind of molecule. Of course, for those reading this book, the reason for separating those molecules is to measure them alone, without interference from other molecules. This is the analytical use of chromatography.

      While analytical measurement is the main use of chromatography, it is not the only one. Some laboratory‐scale and industrial‐scale processes use a chromatographic separation to isolate extremely pure batches of valuable chemicals. This usage is known as preparative chromatography, and it works with much larger quantities of material than analytical chromatography does. This textbook focuses on analysis, so it doesn't further discuss the preparative use of chromatography.

      When used as part of an analytical technique, chromatography is a very effective way to separate the measured compounds from each other and from all the other chemical compounds present in the analyzed material. After all desired compounds have been isolated, another device measures each one independently.

      Keep in mind, then, that chromatographic analysis is always a two‐stage process: first separation, then measurement.

There are many ways to produce a chromatographic separation, and they involve all possible combinations of gases, liquids, and solids. While quite different in practice, these various forms of chromatography share some common features. СКАЧАТЬ