A Pre-Filter for Removing Suspended Solids from HPLC Samples In the HPLC analysis of solid pharmaceutical dosage forms, it is frequently desirable to suspend a portion of the finely powdered tablet or the contents of a capsule in a measured volume of mobile phase. An aliquot of this suspension may then be introduced directly onto the chromatograph using a valve and loop injector. This procedure is advantageous since it obviates the necessity of finding a solvent pair suitable for the extraction of the drug from the dosage matrix or of filtering the suspension before the chromatographic step, either of which is time consuming and can result in sample losses. However, it has been our experience that when these suspnsions are injected with the valve and Loop device, a number of the smaller partieles are introduced into the system and are carried to the head of the column where they either block the flow of the mobile phase or alter the chromatographic separation by acting in effect a.a precolumn. We have been able to eliminate this problem by using an easily constructad pre-filter attached to the inlet of the injector. The filter body consists of a 5 s X Us-in. stainless steel union with Swagelakfittings. Into the union a small quantity of silanized glass wool is packed tightly enough to restrict the passage of the smaller particles of the suspension hut not so tightly that excessive suction is required to fill the sample loop. One end of the filter is attached to the &-in. inlet tubing of the valve injector. To the other end there is fitted a length of Xs-in. stainless steel tubing long enough to reach well into the sample container. The fittings should be firm enough to prevent the entry of air into the stream so that suction may be maintained when the loop is filled. This device has been emdoved successfullv in our undereraduate course in Analvtical Pharmaceutical Chemistrv. ~~~~~~~~-~~ Sixty pairs of students were reqiired to prepareand analyze a k p e n s i o n of powderedisonimid tablets. After hundreis of injections, no clogging of the rolumn uas noted nor was there degradation in the ehromatopaphic response. ~
Rutgels Uuiversity-Busoh Campus College of Pharmacy New Bruuswick. New Jersey 08903
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Leonard C. Bailey
