Gas purifiers are necessary 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 several types of contaminants. Still, the gas purifiers will never be in a position to convert low purity gases into high purity gases. For this reason important factor, it is necessary 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
Various types of gas purifiers can be found in the market. While headspace sampler remove just one specific contaminant, other types remove multiple contaminants simultaneously from the gas stream. You have to reflect on several factors during the selection process of gas purifiers, considering your specific applications. These factors will include the potential contaminants present in 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, skin tightening and, and moisture traps will be the most common purifiers used in majority of the gas chromatography (GC) applications. Oxygen traps are normally filled with metal catalysts. Oxygen is considered as 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 larger than methane. Still, the molecular weight and size of the organic contaminants will have a definite effect on the capacity of the hydrocarbon trap to an excellent extent but it will also think about trap efficiency somewhat.
Activated charcoal possesses a higher capacity to trap larger hydrocarbons which are greater than C4, compared to smaller hydrocarbons, which are lesser than C4. Moisture traps are often filled with unique molecular sieves. When put through 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 may fit the cavity. Water fits perfectly into this cavity but this trap will also be able to remove gases like skin tightening and, sulfur dioxide, hydrogen chloride, and chlorine or other gases which have effective diameters lesser than water.
Procedure for Contaminants Affecting Gas Stream
If you wish to know how the contaminants affect the gas stream, you have to follow the road that the carrier gas takes to find yourself in 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 various other fittings. Each one of these areas is a potential culprit to introduce contaminants in to the gas stream. This leads not only in degrading the outcomes of chromatography but additionally 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 result is baseline noises, spikes, and drifts.
It is advisable to install gas purifiers in a vertical position as wall mounted types to avoid channeling. Channeling occurs once 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.
