File Name: difference between gas chromatography and hplc .zip
Gas chromatography is a term used to describe the group of analytical separation techniques used to analyze volatile substances in the gas phase. In gas chromatography, the components of a sample are dissolved in a solvent and vaporized in order to separate the analytes by distributing the sample between two phases: a stationary phase and a mobile phase. The mobile phase is a chemically inert gas that serves to carry the molecules of the analyte through the heated column.
Although most analysts already know which approach they need to use for analysis, this is occasionally a topic of discussion. While this blog post is not meant to give an absolute answer for each specific application, I hope to provide some tips to steer you in the general direction towards a solution, if this is your dilemma.
I will focus here on characteristics of the analyte compound, which should be the primary concern. Other factors, such as cost and detection methods will not be discussed in this blog post. First of all, the analyte must be volatile.
This is because it will need to exist in a vapor state in order to partition between the carrier gas stream mobile phase and the stationary phase inside the column.
For this reason, most GC analytes are smaller compounds with a molecular weight of less than An example of a compound that works well for GC analysis is naphthalene, which has a boiling point of Although we have many examples of analyses that include naphthalene, here is a chromatogram that represents one of the most common applications EPA method :.
In order for partition to occur in the vapor state, the molecule must also remain intact. Ideally, it should not decompose upon heating. In other words, it must be thermally stable not thermally labile. Often in cases like this, GC analysis can be done if the compounds are derivatized. There are some compounds that could be analyzed equally well by GC or LC. Bisphenol A is a good example of this. Here is a link to example chromatograms for both LC and GC analyses of this:.
Sometimes analytes that need to be derivatized for GC analysis do not need derivatization for LC. Chlorophenoxy acid herbicides are a good example of this. Here is an example of GC analysis for these herbicides derivatized to methyl ester form :.
Although there are many examples of compounds that can be done either way, LC is considered more universal and generally does not require derivatization as often. Analytes for LC need to be soluble in a suitable mobile phase, but they do not need to be volatile at all. As a result, compounds range from small to very large. As is the case for GC, most applications for LC are for organic molecules. Although it may be possible under certain circumstances for some inorganic compounds to be analyzed by LC, this would be beyond the scope of what Restek products can accomplish and will not be discussed here.
LC analysis is usually more difficult for the smallest of molecules, particularly if they coincide with the solvents in the mobile phase, for example methanol, acetonitrile or water. Also, compounds that exist as gases at room temperature cannot be analyzed by LC, or at least it would not be practical.
In LC, to allow partitioning between the liquid mobile phase and the stationary phase inside the column, a compound must be reasonably soluble in the mobile phase and it must have some affinity toward the stationary phase. As discussed in the guide, four of the primary mechanisms are dispersion, polarizability, hydrogen-bonding and cation exchange. As in GC, an analyte for LC also must remain intact and not decompose. Fortunately, thermal stability is not a concern for LC, since analysis can usually be performed at or near room temperature.
I mentioned earlier that riboflavin does decompose upon heating. We find that riboflavin is analyzed fairly easily by LC, though, as shown in the following chromatogram:. While decomposition is not common with LC analyses, ionization in aqueous solution occurs quite often.
Consequently, such analytes are affected dramatically by the pH of the mobile phase. To control these affects, most analysts will use buffer in the mobile phase. If interested in reading more on this topic, please refer to the following:. When should you use a buffer for HPLC, how does it work and which one to use? A good tool to use that is at your disposal is Restek Searchable Chromatogram Library. To look for example analyses for compound s of interest, simply type their name or CAS number in the search box.
You may see examples for the analysis done by LC or GC, or perhaps both. If the compounds of interest tend to decompose, become reactive or are difficult to detect, you may see examples of the analysis done by derivatization. You can follow any responses to this entry through the RSS 2. You can leave a response , or trackback from your own site. Name required. Mail will not be published required. Please type "d77e9c":.
Leave this field empty please:. Restek Corporation, U. All Rights Reserved. Sorry, your message could not be sent at this time. Please try again later, or contact Restek or your local Restek representative via phone. Which LC column should I use for my method? August 24th, by Nancy Schwartz. To use GC for analysis: First of all, the analyte must be volatile.
To use LC for analysis: Analytes for LC need to be soluble in a suitable mobile phase, but they do not need to be volatile at all. If interested in reading more on this topic, please refer to the following: When should you use a buffer for HPLC, how does it work and which one to use? Thank you for reading. Leave a Reply Click here to cancel reply.
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Author s : Puthiyaveettilparambu Y. DOI : Background: A major class of nitro-explosives being used in military and commercial purposes belongs to organic compounds containing nitro NO2 groups like nitrobenzene, nitrotoluenes, and nitramines. Apart from being energetic materials, these substances are inherently toxic to human beings. These substances may find their way into different environmental matrices from the site of their military or commercial applications.
A general question that comes up in your mind is how our HPLC and GC are different from each other and what factors decide suitability of one over the other. Liquids are generally mixtures of solvents of compatible polarities whereas in gas chromatography the mobile phase is a single high purity gas. Gas chromatography separations are mainly carried out on compounds ranging in molecular weights up to a few hundreds. Such compounds separate on differences in their volatilities and remain stable at high temperatures. On the other hand compounds separated on HPLC have higher molecular weights ranging from a few hundreds to several millions for large polymers and biomolecules. Such compounds can be analysed at room temperature only because at elevated temperatures they tend to degrade.
Post a Comment. Difference between GC and HPLC Techniques Gas Chromatography and High Performance Liquid Chromatography both are used to detect the components of the compounds but both are used for different purposes because both have differences in their working and use. Gas Chromatography and the High Performance Liquid Chromatography system are separation techniques used in obtaining specific eluents from an analyte basing on the compounds in the analyte distribution between the two phases Mobile phase and Stationary phase. The mobile phase is the part in chromatography which moves and it usually contains the sample while the stationary phase is one which does not move and contains adsorption material. Chromatography is a larger analytical technique in chemistry. In modern-day analytical chemistry, Gas Chromatography and the High Performance Liquid Chromatography system are the major techniques used in Analytical Chemistry.
High-performance liquid chromatography. Gas Chromatography. Method. Separate, identify and quantify compounds depending on the interactions between the.
Many chemical compounds, including drugs and metabolites, can be analyzed by either gas chromatography GC or high-performance liquid chromatography HPLC. Because both techniques function under the same basic principles of compound separation, identification, and quantification, it can sometimes be tricky to choose one over the other. GC responds to substances that can experience a change in matter to the gas phase with heat — that is, volatile compounds. Therefore, GC is limited to compounds that are low in molecular weight and stable at high temperatures.
High-performance liquid chromatography HPLC , formerly referred to as high-pressure liquid chromatography , is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to pass a pressurized liquid solvent containing the sample mixture through a column filled with a solid adsorbent material. Each component in the sample interacts slightly differently with the adsorbent material, causing different flow rates for the different components and leading to the separation of the components as they flow out of the column.
Liquid chromatography LC is a separation process used to isolate the individual components of a mixture. This process involves mass transfer of a sample through a polar mobile phase and non-polar stationary phase. The device is a column packed with the porous medium made of a granular solid material i.
Chromatography is an important biophysical technique that enables the separation, identification, and purification of the components of a mixture for qualitative and quantitative analysis. Proteins can be purified based on characteristics such as size and shape, total charge, hydrophobic groups present on the surface, and binding capacity with the stationary phase. Four separation techniques based on molecular characteristics and interaction type use mechanisms of ion exchange, surface adsorption, partition, and size exclusion.
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