Degassing Mobile Phase Solvents
Detrimental Effects of Dissolved Air (Oxygen) on Detection (1)
Problems related to bubble formation are easy to discover, by checking fluctuations of discharge pressure, characteristic noise in the baseline from bubbles, and so on. However, a more troublesome problem that is difficult to notice is the detrimental effects of dissolved air that does not form bubbles.
Detrimental Effects on Detection Caused by High Levels of Dissolved Oxygen
Of all dissolved gases, oxygen affects detection the most. Dissolved oxygen can cause all sorts of problems in solution inside the detector cell under various pressure/temperature conditions, even at levels below the saturated solubility.
i) Fluorescence Detection: When the dissolved oxygen level is high, detection response can decrease (O2 quenching) for certain fluorescent components, such as pyrene, naphthalene, and other polycyclic aromatics or tocopherols (vitamin E). In reality, the solvent background level decreases a little as well, but the drop in response is large. For example, the response for naphthalene can be about 1/4 of the response with dissolved oxygen removed.
ii) Electrochemical Detection: Particularly if measurements are below the reduction potential, high levels of dissolved oxygen can generate a reduction current detrimental to the S/N ratio.