Standard Grades

Grade 1: 11µm

The most widely used filter paper in the Whatman range. Medium retention and flow rate. Extended range of circle sizes from 2 to 50cm diameter. Sheets and strips also available.

This grade covers a wide range of laboratory applications and is frequently used for clarifying liquids. Traditionally the grade is used in qualitative analytical separations for precipitates such as lead sulphate, calcium oxalate (hot) and calcium carbonate.

In agriculture, it is used for soil analysis and seed testing procedures. In the food industry, Grade 1 is used for numerous routine techniques to separate solid foodstuffs from associated liquid or extracting liquid and is widely used in education for teaching simple qualitative analytical separations.

In air pollution monitoring, using circles or rolls, atmospheric dust is collected from an airflow and the stain-intensity measured photometrically. For gas detection, the paper is impregnated with a chromogenic reagent and colour formation quantified by optical reflectance.

Grade 2: 8µm

Slightly more retentive than No. 1 with a corresponding increase in filtration time (i.e., slightly slower filtration speed). More absorbent than No. 1. Also available in folded (prepleated) form as Grade 2V. In addition to general filtration in the 8µm particle size range, the extra absorbency is utilised, for example, to hold soil nutrient in plant growth trials. Also used for monitoring specific contaminants in the atmosphere and in soil testing.

Grade 3: 6µm

Double the thickness of No. 1 with still finer particle retention and excellent loading capacity; more precipitate can be held without clogging. The extra thickness gives increased wet strength and makes this grade highly suitable for use in Büchner funnels. The high absorbency is particularly valuable when the paper is used as a sample carrier.

Grade 4: 20-25µm

Extremely fast filtering with excellent retention of coarse particles and gelatinous precipitates such as ferric hydroxide and aluminium hydroxide. Very useful as a rapid filter for routine cleanup of biological fluids or organic extracts during analysis. Used when high flow rates in air pollution monitoring are required and the collection of fine particles is not critical.

Grade 5: 2.5µm

The maximum degree of fine particle filtration in the qualitative range. Capable of retaining the fine precipitates encountered in chemical analysis. Slow flow rate. Excellent clarifying filter for cloudy suspensions and for water and soil analysis.

Grade 6: 3µm

Twice as fast as No. 5 with almost as fine particle retention. Often specified for boiler water analysis applications.