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Celite® Analytical Filter Aid II (CAFA II)

Reporter EU Volume 18

Diatomaceous earth, a natural material comprising fossilized diatoms, has widespread commercial, industrial and agricultural applications. Diatoms themselves are single-celled or colonial eukaryotic algae found throughout both fresh water and marine environments. Their cell walls or frustules show a great diversity in form, with many being quite ornate (Figures 1 and 2).

Figure 1. Optical micrograph of various living diatoms (The Academy of Natural Sciences, Philadelphia, PA USA, used with permission)


Figure 2. SEM of Thalassiosira diatoms (Ivo Grigorov, Ph.D., www.sinia-planeta.com, used with permission)


In the chemical laboratory, diatomaceous earth is often employed as a filtration aid to remove particulate matter and clarify solutions. The silicate shell of the diatom and the calcining process provide high mechanical strength which reduces breakage and fines. The fusing process and the natural porosity of the frustules permit fast filtration rates.

The demands of analytical and other chemical applications dictate that the manufacturer pay strict attention to the composition, purity, extractables, and pore and particle size of the diatomaceous filtration media. One of the most respected and widely used commercial brands of diatomaceous earth is Celite®. Sigma-Aldrich offers Celite® Analytical Filter Aid II (CAFA II), a high purity material that replaces the original CAFA material. The production process has been refined to optimize the purity and consistency of CAFA II without compromising filtration effectiveness compared to the original CAFA material. In addition, World Minerals, the manufacturer of Celite®, moved the CAFA II process to a modern facility under ISO governance with batch tracking and record keeping designed for traceability and continuous quality monitoring.

CAFA II remains identical to the original material (CAFA) with respect to:

  • Intended use as an analytical filter aid
  • Filtration efficiency in the range of 0.5 - 1.0 micron
  • Diatomite composition (marine plankton)
  • Manufacturing location (World Minerals in Lompoc, CA, USA)

Any detectable changes in CAFA II over CAFA are within the boundaries of the original CAFA variability eliminating the need for change-control when switching to the new version.

Each batch of CAFA II is tested to ensure low extractables, optimal flow rate and clarifying properties as measured under standard conditions in special equipment. Test methodology and criteria are those defined by Advanced Minerals Corporation (the product development subsidiary of World Minerals) or the National Formulary. This extensive and relevant testing ensures that CAFA II will perform your most demanding filtration or clarification applications effectively and consistently.

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