There are many varieties of chromatography that are used in sample purification. The purpose of the chromatography will determine which method is appropriate for this process.
The two most common forms in laboratory use are gas chromatography and liquid chromatography. Each has its own benefits and drawbacks, which will be covered in detail below.
Gas Chromatography can be defined as the separation of a mixture by passing it over a column containing solid stationary phase particles, or beads, with each particle coated with chemically active groups or coatings specific to the components in the mixture to be separated out.
Here is the guide to interpret your experimental data to determine which diacetylferrocene isomer forms.
In gas chromatography, a mixture of compounds is passed through a packed high pressure column.
As the compounds pass through the column, they interact with the solid stationary phase at regular intervals. This interaction changes the mobility or retention time of the compound, which is now “frozen” in place on the column and can be visualized by a detector.
Here are some points discussed Should The Chromatography Serve To Purify The Sample-
1. Advantages
Gas chromatography is the fastest and most sensitive of all chromatographic techniques.
It is relatively inexpensive and has a wide range of applications. The list of applications goes on and on: drug screening, food quality control, environmental monitoring, and so forth.
Gas chromatography has 3 main advantages over other sampling techniques:
It provides a rapid readout of the composition of a mixture as it passes through the column. It can measure values as low as parts per billion (ppb).
It provides accurate recovery from low recovery mixtures with high recovery mixtures. It can be used to analyze thousands or even millions of compounds simultaneously.
It has the highest resolution of all chromatographic methods.
2. Disadvantages
Gas chromatography does have its limitations, however. It is not the best choice for analyzing very polar compounds such as carbohydrates and nucleotides that have a tendency to condense onto column packing materials.
Additionally, it is not the best choice for measuring volatile compounds because of their low volatility and high water solubility, which will elute before reaching a detector.
The main disadvantage of gas chromatography is the cost of instrumentation required for this analysis method. Separating compounds using chromatography is one thing, but making the chemicals on the packing material functional again is another.
The concentrated chemical on the packing materials can be recycled many times, but it is still quite expensive to do so.
For example, the columns for GC are fairly expensive items that have to be changed out periodically due to wear and tear.
3. Calibration of Gas Chromatography
The amount of separation achieved by gas chromatography will depend on many factors, including the injection time used to make the sample mixture pass through the column, criteria used to define sample mixtures, efficiency losses due to impurities along with coating residues on the column surface after each cycle of operation and finally instrument calibration factors.
However, if the injection time is set to be longer than half the retention time of the compound being analyzed, then a reasonable separation can be achieved.
Generally, if a valid calibration curve is calibrated first with known standards and a comparison is made with a gas chromatograph method of analysis, an accuracy of ±20% or better can be expected.
Losses in GC operations include:
The loss of solvent from the column during an injection.
The loss of volatiles from the column during every injection due to leakage past retention time windows. Spray-drying interaction between mechanical spray drying nozzle and column wall.
4. Advantages of gas chromatography over other sample purification techniques
One of the major advantages of GC over other chromatographic methods is that it can quickly scan the molecular composition of a mixture for detection or quantification of certain compounds.
It is easily modified to allow for fast run times, more samples compared to other methods, and more sensitivity. However, it is not always an ideal choice if the composition must be scanned analytically.
This is more common in environmental monitoring programs where large quantities of unknown chemicals are suspected to be present.
GC has been successfully applied to screening very small amounts of unknown compounds in soil samples collected from all over the world.
GC has become increasingly popular in environmental monitoring because of its fast scan times, high sensitivity, and ease of use.
Liquid chromatography is the separation of a mixture by passing it over a column containing solid stationary phase particles or beads with each particle coated with chemically active groups or coatings specific to the components in the mixture being separated out.
