Gas purifiers are essential because they help in providing a clean gas stream, which can guarantee the grade of the gas chromatographic analysis and the reliability of the results. Further, such gas purifiers minimize detector noise and prolong the life of the column. Gas purifiers are like plans to protect the instrumentation along with other analytical columns from various kinds of contaminants. Still, the gas purifiers will not be able to convert low purity gases into high purity gases. Because of this important factor, it’s important to select the right grade of gases with different purity levels for proper use in gas chromatographic applications.
Selection of Right Gas Purifier to Suit Your Applications
Numerous kinds of gas purifiers are available in the market. Although some gas purifiers remove just one specific contaminant, other types remove multiple contaminants simultaneously from the gas stream. You need to reflect on several factors during the selection procedure for gas purifiers, taking into consideration your unique applications. These factors includes the potential contaminants within the gas stream, the limitations on flow and pressure, degrees of gas purity required, desired convenience in replacement of spent gas traps, and space availability.
Common Traps Used in Gas Purifiers
Oxygen, hydrocarbon, carbon dioxide, and moisture traps are the most common purifiers used in most the gas chromatography (GC) applications. Oxygen traps are normally filled with metal catalysts. Oxygen is recognized as probably the most detrimental contaminating gas in every analytical columns. Oxygen is capable of producing irreversible oxidation damage, especially to polar stationary phases. Hydrocarbon traps are typically filled with activated charcoal, which can absorb organic compounds which are bigger than methane. Still, headspace sampler and size of the organic contaminants could have a definite effect on the capacity of the hydrocarbon trap to a great extent but it may also reflect on trap efficiency to some extent.
Activated charcoal possesses an increased capacity to trap larger hydrocarbons which are greater than C4, compared to smaller hydrocarbons, which are lesser than C4. Moisture traps are usually packed with unique molecular sieves. When subjected to extensive heating, the crystalline structures are forced to reduce their hydration or water content. This opens a cavity which gets filled readily with any compound that can fit the cavity. Water fits perfectly into this cavity but this trap may also be in a position to remove gases like carbon dioxide, sulfur dioxide, hydrogen chloride, and chlorine or other gases that have effective diameters lesser than water.
Procedure for Contaminants Affecting Gas Stream
If you wish to understand how the contaminants affect the gas stream, you should follow the path that the carrier gas takes to get into the gas chromatograph. This path is applicable for detector fuel gases also. The gases start from a gas tank or a special gas generator. The gas travels through long lengths of tubes, pressure gauges, valves, and different other fittings. Every one of these areas is a potential culprit to introduce contaminants into the gas stream. This leads not merely in degrading the outcomes of chromatography but also shortens the life span of the column of CG.
Major contaminants like oxygen, hydrocarbons, and moisture are capable of wreaking havoc with the columns and detectors of CG. The packed and capillary columns will get degraded easily if they face oxygen or moisture, especially at high temperatures. These contaminants will also compromise detector performance. Because the detectors actually ‘see’ these contaminants, the effect is baseline noises, spikes, and drifts.
You should install gas purifiers in a vertical position as wall mounted types to prevent channeling. Channeling occurs when you install the gas purifier in a horizontal position. Gas purifiers can be found as compact panels having multiple purifiers or single panel that has multi-absorbent capabilities.
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