The Scale of Scrutiny

| Home | | Pharmaceutical Technology |

Chapter: Pharmaceutical Engineering: Mixing

Whether or not materials are satisfactorily mixed depends on the subsequent operations in which the mixture plays a part.


THE SCALE OF SCRUTINY

Whether or not materials are satisfactorily mixed depends on the subsequent operations in which the mixture plays a part. Any mixture, if examined on a small-enough scale, will show regions of segregation. An acceptable degree of mixing is related to subsequent operations in a process sequence. Danckwerts introduced the term “scale of scrutiny” to describe the minimum size of the regions of segregation in a particular mixture, which would cause it to be regarded as insufficiently mixed (Dankwerts, 1953). For example, if a tablet is to contain 0.1 g of drug A and 0.1 g of drug B, the powder from which the tablets are to be made must be sufficiently mixed so that on drawing a sample of 0.2 g from the mixture, the sample will contain, within narrow limits, the correct amounts of A and B. The way in which A and B are dispersed within the sample may be of no importance so long as the tablet is not divided. The scale of scrutiny is here determined by the weight of the tablet.

In general, a small scale of scrutiny is applied if the unit size of the product is small and if too much or too little of one component is very undesirable.

Two further useful concepts may be introduced here to describe unmix-edness: the scale of segregation and the intensity of segregation. The scale of segregation is a measure of the size of the regions of unmixed materials. In the example given above, the intensity of segregation shows the extent to which A has been diluted with B and vice versa. These two concepts are usually inter-related. A high intensity of segregation can be tolerated so long as the scale of segregation is small. Alternatively, a larger scale of segregation may be tolerated if the intensity of segregation is reduced.

Contact Us, Privacy Policy, Terms and Compliant, DMCA Policy and Compliant

TH 2019 - 2024 pharmacy180.com; Developed by Therithal info.