Used commonly in quantitative and qualitative analysis, filter papers must be closely matched to the application according to the physical characteristics of the filter paper. There are many sizes, materials, types, and grades of filter paper available for a variety of applications. Whatman® filter papers use only the highest quality raw materials for high reproducibility and high uniformity. Whatman® cellulose filter papers are manufactured from high-quality cotton liners that are treated to achieve an α-cellulose content >98%. A wide selection of Whatman® filter papers are available to suit numerous laboratory applications. Pre-pleated (folded) filter paper is also available for convenience.
Qualitative filter papers are what most users would consider general purpose filter papers, designed for use in analytical separations and qualitative analytical techniques for the determination and identification of particles, contaminants, or material components. Qualitative papers are categorized by paper grades based on various properties including thickness, weight, and particle retention. The most common qualitative paper grades are 1-6, 595, 597, 598, and 602, which have applications across multiple industries.
Quantitative filter papers are designed for sample preparation and gravimetric analysis, and are typically selected based upon the level of surface toughness and ash content required for the filtration procedure. Quantitative papers are acid treated to reduce ash, often to less than 0.01%. This low ash content is useful for quantitative analyses. After filtration or sample collection, the filter paper can be ignited and burned off, leaving very little residue that could interfere in downstream measurements.