Does anyone know whether it is OK to use an inline vacuum degasser when operating electrochemical detection for acetylcholine. Somebody told me that the post column solid phase reactor with the immobilised enzymes on it needed some oxygen in which to work and the use of such an in line degasser would remove all dissolved oxygen thus reducing sensitivity? However continuous helium degassing is recommended by the manufacturers of the HPLC-ECD system. Any help gratefully received.

I´m not sure what will happen with the online degasser, but You will need traces of oxygen in Your reactor as it contains acetylcholine esterase and choline oxidase, the enzyme that produces the H2O2 determined by Your electrochemical detector.A typical online degasser removes dissolved oxygen to about 2 ppm remaining in solution. As it is quite critical for chromatography to remove gasses from your system I would think about adding some air by using a short piece of gas-permeable tubing behind the column.The problem is the void volume. Maybe someone else knows a better solution for this problem?

Under similar circumstances, when detecting carbohydrates using an ECD, oxygen from the sample can create large negative excursion with columns designed for separating carbohydrates at high pH. One solution which we've used successfully to deal with this problem is to place a length of Teflon tubing after the separation column which allows oxygen to pass into the column effluent, effectively eliminating negative excursion. You don't actually need very much tubing to accomplish this since Teflon is fairly oxygen permeable. 1-2 feet should be sufficient. Preferably, choose a thin wall tubing to maximize transport rate.