Laboratory degassers are used to filter or remove gases from solvents and samples. The primary methods employed include vacuum degassing, flow degassing and helium degassing. Flow degassers function via a gentle flow of dry gas over the surface of the sample particles. This function serves to quickly wick moisture and other contaminants away from the sample. In many cases, needle valves are employed, which allow careful control of flow rate while avoiding elutriation (blowing out) of fine powders.
Vacuum degassers remove atmospheric interferences and diffused gases from solvents, mobile phases, and reagents during use. Within these degassers, water trickles through the system where its flow is interrupted up by a packed filtration medium. The water flow is broken down into a very thin film, which allows gases to escape at an enhanced rate. An internal vacuum system inside the filter increases the rate at which gases can be extracted from the sample.
Solvent or membrane degassers remove gaseous components such as O2, N2, and CO2 from solvents by passing the solvent through a special fluoropolymer membrane tube with the pressure outside the tube reduced. This is a popular degassing method, because membrane separation is carried out under such mild conditions, that the process has virtually no effect leaving the composition of the solvent relatively unchanged. In addition, it is highly efficient, yielding results similar to that of degassing by the helium sparging method.
In helium degassers, the dissolved air within the solvent is expelled by continuously passing helium through the solvent. This is the most effective method of degassing and is particularly recommended for trace analysis, and for avoiding the fluorescence quenching due to the affect of dissolved oxygen on the analytes. The disadvantages associated with helium degassing are the high price of helium, and the fact that the helium can release more volatile solvent components, like tetrahydrofuran, over a period of time. This can give rise to changes in retention times.
Other important configurations to consider include the vacuum rating of the degasser, the number of input channels in the device, and the maximum flow rate per channel. The more channels that degassers have, and the higher the flow rate, the more rapidly the devices can dissipate gases from a sample.