USP Physical Parameters in Dissolution: What should you check?
When performing a dissolution test, everything revolves around accuracy and reproducibility. One of the most important pillars for this is mechanical calibration and the control of the USP physical parameters (physical parameters). If these parameters fall outside the specifications, this can alter the hydrodynamic mix in the vessel, which directly leads to erroneous or non-reproducible test results.
Whether you are working with a Pharmatest USP/EP Device 1 (baskets) or Device 2 (paddles), you must strictly and regularly check the following physical parameters.
1. Centering the axis (Wobble)
The shaft must rotate perfectly straight. If a shaft wobbles, this creates unwanted turbulence in the dissolution medium, which can artificially accelerate the dissolution rate.
- What to check: The wobble of the rotating shaft and the basket/paddle.
- USP limit: Maximum 2.0 mm total result (run-out) over a full rotation, measured at the prescribed points.
2. Centering of the shaft in the vessel (Vessel Centering)
The shaft must hang exactly in the geometric center of the dissolution vessel. A shaft positioned too close to the vessel wall drastically alters the fluid dynamics.
- What to check: The distance from the axis to the inner wall of the vessel at various points.
- USP limit: The axle may be at most 2.0 mm deviate from the exact center of the barrel.
3. Verticality of the shaft and the vessel (Verticality / Alignment)
Both the shafts and the vessels themselves must be perfectly perpendicular to the base plate.
- What to check: The angle of the shafts and the vessels using an accurate digital spirit level.
- USP limit: The deviation may not exceed 0,5° of the vertical axis.
4. Height of the paddle or basket (Clutch Height / Tool Height)
The distance between the bottom of the paddle or basket and the bottom of the vessel is crucial for the flow under the dosing mold.
- What to check: The exact distance from the bottom of the stirring element to the inner bottom of the vessel.
- USP limit: Must be exactly 25 mm ± 2 mm are.
5. Rotational Speed (RPM)
The speed at which the paddles or baskets rotate determines the mechanical energy delivered to the medium.
- What to check: The actual rotational speed of the shafts with a certified tachometer.
- USP limit: The speed must be within ± 4% lie outside the set value (for example, between 48 and 52 RPM with a setting of 50 RPM).
6. Temperature of the medium
The solubility of an active substance is strongly dependent on temperature.
- What to check: The temperature in each individual vessel before and during the test.
- USP limit: The medium must be stable on 37 °C ± 0.5 °C be held (unless otherwise stated in the monograph).
7. Quality and condition of the vessels (Vessel Integrity)
Scratches, imperfections, or distortions in the glass of the vessel can affect the hydrodynamics. In addition, the vessels must be clean and free of residue.
Why is the inspection of Pharmatest equipment so efficient?
Modern dissolution testers of Pharmatest are designed to meet the strictest USP and EP guidelines to comply. Thanks to advanced features such as centered barrel mounts and self-aligning shafts, the risk of mechanical deviations is minimized.
The golden rule: Perform periodic mechanical calibration (MQ) and visually check critical parameters before each run. This guarantees the reliability of your data and prevents costly Out-of-Specification (OOS) investigations.