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June 22, 2018

Whatman paper filtration 101 – Part 3: Folding

By Giles Barton , Global Lead Product Specialist – Lab Filtration

Part 3 of this series describes various filter paper cone folding techniques. Read on to see the options for getting a good seal over your conical funnel.


How to fold filter paper

Following on from the last blog in this Paper Filtration 101 series, let’s look at the options for folding a filter paper cone for use with a conical funnel.

As we’ve come across previously, paper filtration appears to be a simple technique. However, there are so many options, and different people often use different methods for the same purpose. Are some methods more suitable than others, or should you just go with what you know?

In this blog, we’ll explore various filter paper folding techniques. While you may already know some of them, you might also learn a new technique that could improve your conical filtration.

The 60° filter paper funnel

Many conical filter funnels have an angle of about 60°. Folding a filter paper cone so that it beds well down into the funnel, creating a good seal when wet, makes for an efficient filtration step. Very often users will fold the paper cone with the same 60° angle. You can achieve this by simply folding the filter paper into four quadrants, creating a 60° apex when the paper is folded out into a cone.

But is the simplest option suited to every user and situation? While the aim is consistent—a perfect seal when the paper is wet—and the technique is partly down to personal preference, you might find one of the alternatives below gives you a better seal.

Filtration paper folding techniques

We’ve put together a table with some of the most common folding techniques. The choice might depend on your personal preferences, but one of these methods will hopefully help you create a paper filter cone for successful filtration. You can also watch our helpful video on gravity filtration: How to fold/pleat cellulose filter paper.

Folding method

Comments

Quadrant folded

Fold the paper into exact quadrants.
Diagram of exact quadrant folding technique
(Diag 1)

Standard, very common technique

Quadrant folded

Fold the paper into quadrants, then open to form a semicircle, identifying the center line.

Next, make two further folds, either in the same or opposite direction.

The result is a 60° cone when the paper is opened out.
Diagram of 60 degree cone quadrant folding technique
(Diag 2)

Allows the paper to filter in a more balanced manner than standard quadrant technique

Has certain disadvantages, especially if the precipitate tends to creep

Quadrant folded

Fold the paper into quadrants.
Make an extra fold at a slight angle from the center.
The result is an angle at the apex of the cone slightly more than 60°.
Diagram of quadrant folding with angle at apex technique
(Diag 3)

Can provide a better fit when wet and loaded with precipitate

Quadrant folded

Fold the paper into quadrants,
Tear off the corner of the outer fold
Diagram of quadrant folding with tear technique
(Diag 4)

Enables the rim of the filter paper cone to seal better against the glass funnel than a standard quadrant fold

Tearing the corner is better than cutting as it tends to stagger the two thicknesses of paper.

Pleated/Fluted paper

Pleating

Fold the paper into exact quadrants.

Make a further two folds bringing the outer edges in two the center line.

Open the folded circle and invert.

Push alternate folds into the center, making a neatly pleated arrangement.
Diagram of pleated/fluted paper folding technique
(Diag 5)

Watch our videoHow to fold/pleat cellulose filter paper

Pleating filter papers is a very widely performed technique and offers improved flow characteristics compared to conventional quadrant folding


Table 1. Different methods for folding a filter paper cone

Back to the filtration funnels

Hopefully these folding techniques provide useful alternatives when you next come to conical filtration.

Coming back to funnels, just like the filters, there are several options that could suit your application. Each type of funnel will suit various techniques to a greater or lesser degree. Options include:

  • Precision 60° funnel or similar with a smooth glass-like surface made from stainless steel or polymers, such as polythene
  • Funnels with a fluted or grooved surface
  • Funnels with long or short stems of varying bore

In the next blog in our series we’ll continue looking at funnels, but specifically those for vacuum filtration with flat disc filters. Read on for guidance on choosing the right funnel for your application.

If you’ve missed a blog, or want to skip ahead, check out the other blogs in this series to learn about other aspects of filtration in more detail. Our filter selector tool can also help guide you through finding the right filter for your application.

For Samples or to contact a Specialist