Gas purifiers are necessary because they help in providing a clean gas stream, which can guarantee the quality 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 insurance policies to protect the instrumentation and other analytical columns from several types of contaminants. Still, the gas purifiers will not be able to convert low purity gases into high purity gases. For this reason important factor, it’s important to select the right grade of gases with different purity levels for proper used in gas chromatographic applications.
Selection of Right Gas Purifier to fit 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 should reflect on several factors during the selection process of gas purifiers, considering your unique applications. These factors will include the potential contaminants within the gas stream, the limitations on flow and pressure, levels 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 will be the most common purifiers used in most the gas chromatography (GC) applications. Oxygen traps are usually filled with metal catalysts. Oxygen is considered 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 usually filled with activated charcoal, that may absorb organic compounds that are bigger than methane. Still, the molecular weight and size of the organic contaminants will have a definite effect on the capability of the hydrocarbon trap to a great extent but it may also reflect on trap efficiency to some extent.
Activated charcoal possesses a higher capacity to trap larger hydrocarbons which are greater than C4, in comparison 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 will 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.
Process of Contaminants Affecting Gas Stream
If you want to know how the contaminants affect the gas stream, you have to follow the road that the carrier gas takes to get into the gas chromatograph. This path is applicable for detector fuel gases also. The gases begin from a gas tank or a special gas generator. The gas travels through long lengths of tubes, pressure gauges, valves, and various other fittings. headspace sampler of these areas is a potential culprit to introduce contaminants into the gas stream. This leads not only in degrading the results of chromatography but also shortens the life 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 can get degraded easily if they are exposed to oxygen or moisture, especially at high temperatures. These contaminants will also compromise detector performance. Because the detectors actually ‘see’ these contaminants, the result is baseline noises, spikes, and drifts.
It is advisable to 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 are available as compact panels having multiple purifiers or single panel that has multi-absorbent capabilities.