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4.38 ANALYTICAL FILTRATION BY FILTER PAPER

4.38 ANALYTICAL FILTRATION BY FILTER PAPER

      The following considerations are provided as a guide when filtration is utilized in the assay.

      Only high quality filter paper should be used to assure maximum filtering efficacy. For analytical work, pleated filter paper folded in a special way or prepleated filter paper should be used to increase filtering speed and prevent tearing at the apex.

      The steps in folding a pleated filter paper are illustrated in the figure below.

      When the filter paper has been accurately pleated and creases emphasized by pressure, it is then carefully opened and placed in a dry funnel. Pour the assay preparation into the dry filter (in case the solutionvolume has been adjusted). The stream should be delivered upon one of the sides. The first appropriate millilitres of the filtrate should be discarded in order to eliminate insofar as possible contamination of the assay preparation by free fibres associated with most filter paper and to maintain the concentration of the assay preparation.

      In folding a filter paper, care should be observed not to extend the creases entirely to the apex, but to end them at a distance of about half an inch from it, because the point at which all the creases converge would be thereby so weakened that the weight of the assay preparation may rupture the filter paper. 

APPENDICES • 4.38 ANALYTICAL FILTRATION BY FILTER PAPER
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หมายเหตุ / Note : TP II 2011 PAGE 469