A guide to Whatman quantitative filter paper grades

Quantitative filter paper

In Part 1 of this series, we reviewed the various, mostly general purpose, qualitative filter paper grades, each with a distinct set of properties. In this part, we review quantitative filter paper grades: the analytical papers supporting quantitative analyses in various industries. First though, let’s clarify the differences between qualitative and quantitative filter paper grades.

Qualitative vs quantitative filter paper

Both qualitative and quantitative filter paper grades contain a high percentage of alpha cellulose. We use these high-quality fibers in all Whatman cellulose filter paper.

Where they differ is in ash content: the non-volatile substances in the material. While qualitative papers might contain ash in the region of 0.06%, quantitative papers are acid treated to reduce ash, often to less than 0.01%.

This low ash content is useful for quantitative analysis. After filtration or sample collection, the filter paper can be ignited and burned off, leaving very little (but predictable) residue, simplifying downstream measurements.

Quantitative filter papers come in three major variations: ‘ashless’, ‘hardened low ash’, and ‘hardened ashless’, which we’ll review next.

Ashless filter paper

Visit Whatman ashless filter paper product pages here.

There are two groups of ashless paper: Grades 40 to 44 have 0.007% ash maximum, and the variations of grade 589 have 0.01% ash maximum, making both suitable for critical analytical uses, summarized below.

Table 1 shows the specific properties of each grade of ashless quantitative paper.

Grade 40
Of the quantitative papers, Grade 40 is the classic general purpose ashless paper, with medium speed and retention. Some typical applications include:

• Gravimetric analysis for substances/contaminants in cements, clays, iron, and steel.
• Separating solid matter in general soil analysis
• Quantitation of sediments in milk
• Analytical grade clean-up for atomic absorbance spectroscopy
• Collection of trace elements and radionuclides from the atmosphere

Grade 41
This is the fastest quantitative ashless paper. It’s suited for filtering coarse particles and gelatinous precipitates. It also performs well in quantitative air pollution analyses.

Grade 42
The finest particle retention of all Whatman cellulose filter papers makes Grade 42 exceptional for critical gravimetric analysis. Typical precipitates filtered include:

• Barium sulfate
• Metastannic acid
• Finely precipitated calcium carbonate

Grade 43
This filter paper sits between grades 40 and 41 in terms of particle retention but has twice the flow rate of Grade 40. It’s very useful when you need a good balance between particle retention and speed. Applications include:

• Foodstuffs analysis.
• Soil analysis
• Particle collection for XRF analysis (air pollution monitoring)
• Inorganic analysis in construction, mining, and steel industries

Grade 44
This paper is a thinner version of Grade 42, minimizing ash weight for each sample. It still retains very fine particles and benefits from almost twice the flow rate.

Grade 589/1
Also known as the Black Ribbon Filter, this paper has a high flow rate. It’s needed for numerous quantitative standard methods that involve filtering coarse precipitates, and is available prepleated (Grade 589/1 ½). Common applications include:

• Determination of ash content in foodstuffs
• Testing the fineness of cement (Blaine test)

Grade 589/2
The White Ribbon Filter captures medium fine precipitates at medium speed and is available prepleated (Grade 589/2 ½). Common applications include:

• Determination of sand content in foodstuffs.
• Identification of flour grade
• Analysis of aqueous suspensions in the paper industry

Grade 589/3
This Blue Ribbon Filter suits fine precipitate filtration. It has a slow flow rate, balanced by its high efficiency for particle collection. It’s used in routine analytical methods, such as the quantitation of insoluble contaminants in animal and vegetable fats and oils.

Table 1. Summary of typical properties for ashless cellulose filter paper grades

Hardened low ash filter paper

Visit Whatman hardened ashless filter paper product pages here.

The hardened low ash grades all have high wet strength and chemical resistance from the addition of a small quantity of chemically stable resin. They are well suited for Büchner filtrations as they allow the straightforward recovery of precipitate from the filter surface.

Table 2 provides a summary of typical properties for these grades of hardened low ash paper.

Grade 50
A small pore size and slow flow rate make Grade 50 well suited for the retention of very fine crystalline precipitates. Its hardened glazed surface doesn’t shed fibers and can withstand wet handling and precipitate removal by scraping. It’s well suited for:

• Vacuum filtration on Büchner and 3-piece filter funnels
• Carrying integrated circuits

Grade 52
Like Grade 50, the general-purpose Grade 52 has a high wet strength. It differs by having a medium pore size, providing medium retention and flow rate through its very hard surface.

Table 2. Summary of typical properties for hardened low ash cellulose filter paper grades

Hardened ashless filter paper

The hardened ashless grades also have high wet strength and chemical resistance. They are all designed for gravimetric analysis and the acid hardening process used in their manufacture results in extremely low ash content (< 0.005%) for accurate filtration results.

Table 3 shows properties of the three hardened ashless grades.

Grade 540
This is the most general-purpose grade of hardened ashless paper, with medium retention and flow rate. Grade 540 has a hard surface and strong resistance to acid and alkali. It’s commonly used for:

• Gravimetric analysis of metals in acid and alkali solutions
• Collecting hydroxides after precipitation by strong alkalis

Grade 541
A larger pore size than Grade 540 makes Grade 541 suitable for filtering coarse and gelatinous precipitates from acid and alkali solutions in gravimetric analysis. Typical applications include filtration of:

• Fiber in foodstuffs
• Gelatin in milk and cream
• Chloride in cement
• Chloride and phosphorous in coal and coke

Grade 542
A very hard and strong material, providing high wet strength and chemical resistance. The small pore size means Grade 542 has a slow flow rate but can retain fine particles under demanding conditions. It’s often used for gravimetric metal determination.

Table 3. Summary of typical properties for hardened ashless cellulose filter paper grades

Other guides and resources:

Guide to qualitative filter papers

Whatman Filter Selector Tool

Whatman Methods & Standards Search Tool

Laboratory Filtration Principles and Chemical Compatibility Chart (PDF)