App Note: Helium Degassing
The Helium Shortage and Degassing
Helium degassing has historically been the technique of choice because it is simple and effective. However, the price of helium, which is for degassing of reagents in Lachat's Flow Injection Methods, is going up. While it seems counter ‐ intuitive that gas sparging would remove dissolved gasses and not contribute to the problem, this technique saturates the solution with helium, while oxygen and nitrogen from dissolved air diffuse into the helium and are carried away by helium bubbles. This reduces out ‐ gassing on the chemistry manifold.
Although helium is the second most abundant gas in the universe, it is currently in short supply. As is typical when there is less of something that is needed, the price goes up. Party stores that provide helium balloons as well as hospitals (used for example to cool magnets used in MRI's) and research labs are all affected. It is possible that the world may run completely out of helium gas within 30 years
What can you do?
1) Prepare reagents a day ahead of time, and keep them at room temperature whenever possible. In some cases, this may mean preparing smaller volumes more often. Out ‐ gassing occurs naturally as reagents reach room temperature.
2) For heated chemistries in particular, increasing the length of the back pressure loop located after the flow cell can greatly reduce the number of air spikes. Don't add too much at once; generally increases of 50 cm at a time are best. Use the shortest length of coiled tubing that helps with out ‐ gassing without affecting flow on the manifold.
3) Vacuum degassing. This can also be an effective method of removing dissolved gas from solutions. The solubility of gas obeys Henry's law ‐‐ the amount of a dissolved gas in a liquid is proportional to its partial pressure. Placing a solution under reduced pressure makes the dissolved gas less soluble. Sonication in combination with stirring under reduced pressure can usually enhance the efficiency.
Care must be taken in cleaning glassware used for vacuum degassing to avoid cross contamination
when the reagent from one chemistry contains the analyte for another (for example, ammonium chloride buffer which has very high levels of ammonia that could cause problems for an ammonia chemistry)
In most cases, these steps will eliminate the need to degas and reduce costs.