Abstract: This invention relates to an improved method and apparatus for preventing cross-contamination of biochemical test wells included in a microtiter test plate which comprises the covering of the biochemical test wells with a porous barrier that has been impregnated with an approximately 10% (W/V) solution of a solid, water soluble compound and then dried before use, the impregnating material being one selected form a group of chemical compounds consisting of inorganic acid phosphates, the acid salts of amino acids and the polycarboxylic organic acids which are relatively non-volatile, non-hygroscopic and non-toxioc to humans and bacteria while remaining effective to neutralize alkaline gases without attacking the barrier material.

Abstract: This invention relates to a porous barrier impregnated with an acidic compound positioned in overlying relation atop the biochemical test wells portion of an antibiotic microtiter test plate effective to intercept and neutralize volatile alkaline products evolved through bacterial growth taking place therein before they can diffuse and contaminate nearby test wells and produce erroneous pH-sensitive color tests. The invention also relates to an improved method for preventing cross-contamination of the biochemical tests being carried out in test wells adjacent microtiter test wells, the contents of which are being analyzed for antibacterial activity, which consists of covering the biochemical test wells with a porous medium impregnated with an acidic compound capable of neutralizing gaseous alkaline products resulting from bacterial growth in wells containing sub-inhibitory antibiotic levels thereby protecting the biochemical tests from erroneous pH-sensitive indicator color changes.