Consistency measurement in the pharmaceutical and cosmetic industry

One of the leading measurement methods used for quality monitoring in the pharmaceutical industry is consistency measurement by means of a penetrometer. Using this method, involving small sample quantities and short analysis times, precise statements can be made as to the quality of the measured sample. 

What information does a consistency measurement give?

Ointments with a low consistency, for example, can be more thoroughly applied on the skin and more easily absorbed. On the other hand, a substance with a high consistency can be used to cover a wound effectively.

In the production of pharmaceutical and cosmetics, finished products are constantly tested for quality. Consistency measurements are also performed on raw materials when they arrive, as well as during production routines, whereby considerable time pressure builds up as further processing of the product is often dependent on the result of the test measurement. This means that the consistency measurement must be both extremely reliable and also quick, and only use small sample volumes, as the samples are often expensive and only available in small quantities.

In addition to inspection measurements on incoming goods and finished product declarations, knowledge concerning the consistency of a substance is important for many handling processes such as:

  • Kneading
  • Pumping
  • Pressing
  • Mixing
  • Filling
  • Spraying
  • Spreading

The energy balance of these processes is significantly determined by optimizing the consistency parameters.

How does a penetrometer work?

Fig. 1: Penetrometer for consistency measurements

Typically, a penetrator vertically pierces the sample in a free fall for a certain interval with a precisely defined weight. The resulting penetration depth is a measurement for the consistency of the substance.

The method according to the European Pharmacopoeia 2.9.9. allows consistency measurements with a standard cone or a micro-cone.

In general, the measurement with the micro-cone is preferred based on the following advantages:

  • Very small sample volume of 4 mL. This results in short temperature-stabilization intervals. Ideal in case of a limited sample volume in the development phase of new products.
  • Broad range of application, from viscous liquids to hard pastes.
  • Thanks to the separated sample cup, it is easy to fill without air bubbles.

Alongside consistency measurements, pharmaceutical production monitoring and quality control frequently makes use of: