Pressurized Solvent Reservoir for High-pressure Liquid Chromatography Trapped air bubbles in reciprocal displacement pumps used for high-pressure liquid chromatography hamper analysis and necessitate the employment of tedious solvent degassing techniques,' especially when mixed organic, aqueous solvent systems are used in the mobile phase. Standard techniques for solvent degassing include immersion in an ultrasonic bath, gentle heating of the mobile phase up to the boiling point, or pulling a slight vacuum on the mobile phase to remove dissolved gas. We have devised a solvent reservoir for high-pressure liquid chromatography (HPLC) which slightly pressurizes the mobile phase before entry into the pumping system and also filters the liquid at the same time. This apparatus is shown in the figure. The system consists of a 250-ml or 500-mlErlenmeyer flask equipped with a two-holed rubber stopper into which is inserted a length of 5 s in. inside diameter Teflon@TFE tuhing (VRW Scientific) and a piece of glass tubing on which is attached an atomizer bulb. At the end of the Teflonmtubing is inserted a4-micron porous metal filter element (Alltech Assoc.). The filter element is insertedinto the liquid in the flask so that the filter restsat the bottom, near one edge of the flask. The Erlenmeyer flask is then clamped on a ring stand above the pump, and the flask is tilted to a 30" angle so that the filter rests a t the lowest point in the flask. The Teflona tubing is primed using the atomizer bulb, and after attachment of the tuhing to the inlet of the pump, a positive pressure can be maintained for solvent flow by occasionally pressurizing the air above the solvent in the Erlenmeyer flask. Due to the valve system in conventional atomizer bulbs, the solvent flow will not be disturbed even if the solvent reservoir is not pressurized. There are a number of advantages for the useof thissolventreservoir system. First, andmost importantly, solvent degassing can all but be eliminated by maintaining a positive pressure for the solvent in the pump at all times. Although solvent degassing using an ultrasonic bath (Bransonic 12) has been employed on occasion, it can be dispensed with altogether using this system. Filtering of the solvent can be eliminated since the solvent is automatically filtered, thereby increasing the lifetime of expensive and hard-to-get-at filters contained in the check valves and solvent inlet head of the pump. The system filter can easily be cleaned by baek-washing with a wash bottle. This procedure is usually performed between each solvent changeover, first with a distilled water and then with an acetone wash bottle, followed by drying using a stream of Nz gas. Also, one can virtually use every milliliter of expensive solvents since the filter a t the bottom of the flask allows no air to enter the inlet tube until all the solvent has been used up, and the last few milliliters remaining in the inlet tube can be pushed into the pump inlet by applying back pressure. If trapped air does lodge in the pumping chamber, it can quickly and easily be expelled by allowing the pump to continue pumping at a slow flow rate (-1.0 mllmin), while opening the outlet of the pump t o provide zero pressure on the pump, and heavily pressurizing the solvent inlet. The trapped air buhhle can then be flushed out of the pump. Finally, this apparatus can be cheaply and easily assembled out of standard laboratory equipment. The use of Erlenmeyer flasks to contain the mobile phase aids in its preparation, since mixing or adjusting its pH can he accomplished in the same flask.
' Saitoh, K. and Suzuki, N.,Anal. Chem.,51,1877 (1979).
John J. Naleway Marquene University 535 North 14th Street Milwaukee. W153233
1078
Journal of Chemical Education
