Filter Paper Aperture and Size

Filter paper is a kind of paper with good filtration performance. The paper is loose and has strong absorption properties to liquid. The filter paper commonly used in the analytical laboratory is used as a filter medium to separate the solution from the solid. Filter paper mainly includes quantitative analysis filter paper, qualitative analysis filter paper, and chromatographic qualitative analysis filter paper.

Quantitative analysis of filter paper, divided into fast, medium, and slow speed categories, on the filter paper box with leucorrhea (fast: Quantitative Ashless Filter Paper Grade: BIO-41), blue belt (medium speed: Quantitative Medium Flow Filter Paper Grade: BIO-40), red belt (slow speed: Quantitative Laboratory Filter Paper Grade: BIO-42 ) for the classification. The shape of the filter paper is round and square. The specifications of the circular paper are 5.5cm, 7cm, 9cm, 11cm, 12.5cm, 15cm and 18cm, 18.5cm, 24cm, 27cm. The square quantitative filter paper has 60 cm x 60 cm and 30 cm x 30 cm.

The type and specification of the qualitative analysis filter paper are basically the same as the quantitative analysis filter paper, indicating fast, medium speed, and slow speed, but printed with fast, medium speed, and slow speed. The chromatographic qualitative analysis filter paper has a filtration speed of 35 seconds or less and less than or equal to 70 seconds and less than or equal to 140 seconds.

Filter paper is categorized by its pore size or aperture, which refers to the size of the openings in the paper that allow liquids or particles to pass through while retaining larger particles. The aperture size is usually expressed in micrometers (µm) or millimeters (mm) and determines the size of particles the paper can effectively filter.

1. Aperture (Pore Size)

Fast: 80 to 120 microns aperture
Medium speed: 30 to 50 microns pore size
Slow speed: hole diameter is 1 to 3 microns

There are several categories of filter paper based on aperture size:

  • Coarse or Fast Filtering: This type of filter paper has larger pores (around 80-25 µm) and is used for rapid filtration of larger particles and precipitates.
  • Medium Filtering: Medium-pore filter paper typically has a pore size range of 25-10 µm. It is commonly used for general filtration, separating crystalline substances, and collecting fine precipitates.
  • Fine Filtering: Fine-pore filter paper has smaller pores (around 10-2.5 µm) and is used for filtering finer particles and materials.
  • Very Fine Filtering: This type of filter paper has very small pores (below 2.5 µm) and is used for filtering very fine particles, colloids, and microbial cultures.

The choice of aperture size depends on the nature of the particles you want to separate, the clarity of the filtrate required, and the speed of filtration.

2. Size

Filter paper comes in various sizes, usually denoted by its diameter. Common sizes include 70 mm, 90 mm, and 125 mm. The choice of size depends on the filtration apparatus you’re using and the volume of liquid you’re filtering. Larger sizes are suitable for filtering larger volumes of liquid, while smaller sizes are used for smaller quantities.

When selecting the appropriate size of filter paper, consider the diameter of the filtration apparatus (funnel or holder) you’re using. The filter paper should fit snugly without folding or creasing.

Keep in mind that the aperture size and diameter of filter paper are related but distinct characteristics. You’ll need to choose both the right aperture size to suit your filtration needs and the appropriate size to fit your equipment.

Remember to always check the manufacturer’s specifications and guidelines for the filter paper you’re using, as well as any specific filtration requirements for your experiment or application.