GC is an invaluable tool used for separation of compounds in a mixture followed by their qualitative identification and quantification. It finds major applications in analysis of petroleum &petrochemicals, pharmaceuticals, foods and beverages, flavours &fragrances, forensic investigations and environmental monitoring. GC chromatogram is also referred to as Gas Liquid Chromatograph or simply as Gas Chromatograph.
It comprises of individual components illustrated above. In essence the component parts are.
Gaseous carrier stream also referred to as mobile phase. Sample injector. Separation column. Detector. Data station. GC Schematic DiagramThe role of each of these component parts is described in detail in our free e- course on GC and will be elaborated further in the Certificate Programme which is due for launch later this year.Mobile phase – serves as carrier for the injected sample to the column and leads separated components to the detector. Time RetentionRt is retention time of peak.
It is qualitative indicator of presence of a compound in the mixture.W is the peak width at base. Narrower the peak width better is the chromatographic resolutionis time the mobile phase takes to pass through the column and reach the detector when no sample is injected.This post is a basic introduction to the GC chromatogram and also an elementary depiction of chromatographic output. Further details can be accessed by registering for the free E-learning GCcourse Certificate programme. Deepak BhanotDr Deepak Bhanot is a seasoned professional having nearly 30 years expertise beginning from sales and product support of analytical instruments.
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After completing his graduation and post graduation from Delhi University and IIT Delhi he went on to Loughborough University of Technology, UK for doctorate research in analytical chemistry. His mission is to develop training programs on analytical techniques and share his experiences with broad spectrum of users ranging from professionals engaged in analytical development and research as well as young enthusiasts fresh from academics who wish to embark upon a career in analytical industry.
GC is used as one test to help identify components of a liquid mixture and determine. It may also be used to separate and purify components of a mixture.
Additionally, gas chromatography can be used to determine, heat of solution, and activity coefficients. Industries often use it to monitor processes to test for contamination or ensure a process is going as planned. Chromatography can test blood alcohol, drug purity, food purity, and essential oil quality. GC may be used on either organic or inorganic analytes, but the sample must. Ideally, the components of a sample should have different boiling points. First, a liquid sample is prepared.
![Chromatograph Chromatograph](/uploads/1/2/4/1/124114840/542258040.png)
The sample is mixed with and is injected into the gas chromatograph. Typically the sample size is small - in the microliters range. Although the sample starts out as a liquid, it into the gas phase.
An inert carrier gas is also flowing through the chromatograph. This gas shouldn't react with any components of the mixture. Common carrier gases include argon, helium, and sometimes hydrogen. The sample and carrier gas are heated and enter a long tube, which is typically coiled to keep the size of the chromatograph manageable.
The tube may be open (called tubular or capillary) or filled with a divided inert support material (a packed column). The tube is long to allow for a better separation of components. At the end of the tube is the detector, which records the amount of sample hitting it. In some cases, the sample may be recovered at the end of the column, too. The signals from the detector are used to produce a graph, the chromatogram, which shows the amount of sample reaching the detector on the y-axis and generally how quickly it reached the detector on the x-axis (depending on what exactly the detector detects). The chromatogram shows a series of peaks.
The size of the peaks is directly proportional to the amount of each component, although it can't be used to quantify the number of molecules in a sample. Usually, the first peak is from the inert carrier gas and the next peak is the solvent used to make the sample. Subsequent peaks represent compounds in a mixture. In order to identify the peaks on a gas chromatogram, the graph needs to be compared a chromatogram from (known) mixture, to see where the peaks occur. At this point, you may be wondering why the components of the mixture separate while they are pushed along the tube. The inside of the tube is coated with a thin layer of liquid (the stationary phase). Gas or vapor in the interior of the tube (the vapor phase) moves along more quickly than molecules that interact with the liquid phase.
Compounds that interact better with the gas phase tend to have lower boiling points (are volatile) and low molecular weights, while compounds that prefer the stationary phase tend to have higher boiling points or are heavier. Other factors that affect the rate at which a compound progresses down the column (called the elution time) include polarity and the temperature of the column. Because temperature is so important, it is usually controlled within tenths of a degree and is selected based on the boiling point of the mixture.
Pavia, Donald L., Gary M. Lampman, George S. Kritz, Randall G. Engel (2006). Introduction to Organic Laboratory Techniques (4th Ed.).
Thomson Brooks/Cole. Pp. 797–817. Grob, Robert L.; Barry, Eugene F. Modern Practice of Gas Chromatography (4th Ed.). John Wiley & Sons. Harris, Daniel C.
Gas Chromatography'. Quantitative chemical analysis (Fifth ed.). Freeman and Company.
ISBN 0-7167-2881-8. Higson, S. Analytical Chemistry. Oxford University Press ISBN 978-0-19-850289-0.