5-6) Non-Degassing Methods
Though they are not degassing methods, placing the mobile phase bottle higher and installing a bubble trap can potentially reduce the inflow of bubbles into the solvent delivery pump.
Elevating the Mobile Phase Bottle
Elevate the mobile phase bottle above the solvent delivery pump, as shown in Figure 31. This applies a little pressure to the pump inlet, which can reduce malfunctions of the IN backflow check valve (irrelevant if the backflow check valve is functioning properly), somewhat compress any bubbles that enter the pump inlet, and provide other benefits. Buoyancy also makes it more difficult for small bubbles in the suction tube to enter the pump.
Since there are many benefits to elevating the mobile phase bottle, we recommend it even if using an online degassing unit.
A bubble trap can be installed between the mobile phase bottle and solvent delivery pump (Figures 32 and 33) to prevent bubbles flowing through the suction tube from entering the solvent delivery pump. To draw the mobile phase into the trap (to suck bubbles out of the trap), connect a syringe to the syringe port.
Disadvantages of this method include (1) replacing the mobile phase takes time (requires drawing at least 10 to 20 times the internal volume of liquid through the trap), (2) it cannot be used for inlets to pumps used for mixing low-pressure gradients (because it prevents creating proper gradients), and other factors. Therefore, there is no point using a trap if an online degassing unit is used.
This page is a partially revised html version of LCtalk Special Issue 5 (1991).