headspace sampler are necessary because they help in providing a clean gas stream, that may 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 span of the column. Gas purifiers are like insurance policies to protect the instrumentation along with other analytical columns from different types of contaminants. Still, the gas purifiers will never be able to convert low purity gases into high purity gases. Due to 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 fit your Applications
Various types of gas purifiers are available in the market. Although some gas purifiers remove just one single specific contaminant, other types remove multiple contaminants simultaneously from the gas stream. You have to think about several factors during the selection process of gas purifiers, considering your specific applications. These factors includes 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 Found in Gas Purifiers
Oxygen, hydrocarbon, carbon dioxide, and moisture traps will be the most common purifiers found in most the gas chromatography (GC) applications. Oxygen traps are usually filled with metal catalysts. Oxygen is recognized 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 usually packed with activated charcoal, that may absorb organic compounds that are larger than methane. Still, the molecular weight and size of the organic contaminants will have a definite influence on the capability of the hydrocarbon trap to a great extent but it may also reflect on trap efficiency somewhat.
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 often packed 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 carbon dioxide, sulfur dioxide, hydrogen chloride, and chlorine or other gases which have effective diameters lesser than water.
Procedure for Contaminants Affecting Gas Stream
If you want to understand how the contaminants affect the gas stream, you need 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 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 additionally 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 will get degraded easily when 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 effect 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 once you install the gas purifier in a horizontal position. Gas purifiers are available as compact panels having multiple purifiers or single panel which has multi-absorbent capabilities.