Glass microfiber filter papers are widely used in many different industries for routine applications such as filtering large particulates and as a pre-filter for membrane filtration. They are manufactured from borosilicate glass microfibers and are available both containing binders and binder-free. This overview will cover binder-free papers only. Quartz microfiber filters are made from micro-quartz fibres and their main application of use is in air and smoke monitoring.

Qualitative filter papers are considered general-purpose filter papers, these are ideal for is a vast range of applications in and out of the laboratory. Composed of cellulose fibre, these filters are manufactured from high-quality cotton linters treated to maximize alpha-cellulose as it is the most stable form of cellulose, with the highest degree of polymerization.  

The grading of qualitative filter paper is based on various properties which includes particle retention, thickness, and weight. Unlike quantitative filter papers, where ashless grades can be burned off for analytical applications, qualitative papers are more suited for general purpose filtration use. The most common qualitative paper grades used from Whatman are 1-6, 595, 597, 598, and 602.  These filter papers have applications across multiple industries. Below are summaries of the grade properties and their common uses.

Please note that Whatman is a colloquial name used for products supplied by Cytiva 

Whatman quantitative filters are designed for gravimetric analysis and the preparation of samples for instrumental analysis. They are available in three formats designed to meet your specific needs.

Ashless: 0.007% ash maximum for Grades 40 to 44 and a maximum of 0.01% for the 589 Grades - very pure filters suitable for a wide range of critical analytical filtration procedures.

Hardened low ash: 0.015% ash maximum - treated with a strong acid to remove trace metals and produce high wet strength and chemical resistance. These filters are particularly suitable for Büchner filtration where the tough smooth surface of the filter makes it easy to recover precipitates.

Hardened ashless: 0.006% ash maximum - acid hardened to give high wet strength and chemical resistance with extremely low ash content. The tough surface makes these filters suitable for a wide range of critical filtration procedures.

Grade 42: 2.5 μm (slow filter paper)
A world standard for critical gravimetric analysis with the finest particle retention of all Whatman cellulose filter papers. Typical analytical precipitates include barium sulfate, metastannic acid, and finely precipitated calcium carbonate.

Please note that Whatman is a colloquial name used for products supplied by Cytiva 

For a more comprehensive filter choice for your application Cytiva have provided a filter selection guide.

For more information on the wider range of filter paper grades available in the Whatman range, download the Filter Paper and Membranes guide.