Semisolids Testing

Welcome to the Semisolids Testing section of our web site. Please select one of the categories below for further information:

Immersion Cell

An alternative to the Vertical Diffusion or Franz Cell for testing semisolids, the Immersion Cell is used with a special flat bottomed version of the 200 mL Small Volume Conversion Kit and a mini version of the conventional USP Apparatus 2 Paddle Method.

The PTFE Immersion Cell is designed to accommodate a 25 mm diameter membrane. It comprises four main parts:

  • A retaining ring which secures the membrane to the cell body.
  • A washer which holds the membrane in contact with the sample.
  • The membrane or skin and
  • The cell body which contains the compartment in which the sample to be tested is placed.

Vacuum Deaeration Apparatus

Air bubbles accumulating on the underside of the membrane concerned are the single largest source of problems in Vertical Diffusion Cell testing. For this reason it is essential that the receptor medium used to bathe the membrane is degassed prior to use if air bubbles, and hence impaired diffusion, are not to take place.

The Vacuum Deraeration Apparatus Model VDA is an inexpensive unit that has been designed to oviate this problem. USP Chapter <1092> suggests an oxygen concentration of less than 6 ppm as being effective as a marker for adequate deaeration of the dissoution media. The VDA System guarantees to reduce oxygen levels to below 4 ppm.

Vertical Diffusion Cell (VDC) Test System Model HDT 1000

The Vertical Diffusion Cell (VDC) Test System Model HDT 1000 has been specifically designed to accommodate 10 diffusion cells.

It comprises a heated aluminium block capable of accepting two rows of five cells.

A powerful magnetic stirrer is mounted beneath each test station.

The heating block approach to heating the diffusion cells eradicates the difficulties in use and “spaghetti” of tubing associated with its water-jacketed predecessors.

Vertical Diffusion Cell

The Vertical Diffusion or Franz Cell is a simple, reproducible test for measuring the drug release from creams, ointments and gels that is rapidly emerging as the apparatus of choice for the in vitro testing of topical semisolid dose forms and skin permeation studies.

Three different designs of VDC are included in USP <1724>, but the basic principle is the same in each case.

The cell comprises two parts (a) the sample holder containing the sample to be tested and (b) the reservoir of the diffusion cell itself containing the receptor medium.

Introduction to the testing of Semisolids

Creams, ointments, lotions and gels are topical drugs normally described as semisolid dosage forms. Unlike transdermal drug systems which are applied to the skin for systemic effects (the drug penetrates the skin whereupon it is then absorbed into the drug stream), topical drugs are applied to the skin for local action principally to counter dermatological problems.

Current USP thinking suggests two types of test to characterise semisolids, product quality tests (USP Chapter <3>) and product performance tests (USP Chapter <1724>).