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Application of Rotating Viscometer in the Pharmaceutical Industry

Author : Date : 11/15/2018 9:22:30 PM
One of the most important applications of rotational viscometers in the pharmaceutical industry is to measure the viscosity of pharmaceutical thickeners. The medicinal thickener is a kind of medicinal excipient, which is used to increase the viscosity of the liquid or the paste. For example, adjusting the viscosity of the liquid in the eye drop can make the eye drop stay in the eye for a long time; The ointment can be easily applied in the ointment. The main varieties currently used are alginate, glycerin, carboxymethyl cellulose (CMC), methyl cellulose (MC), polyvinylpyrrolidone (PVP), hydroxypropionyl cellulose (HPC), etc. Carbomer and Xanthan Gum are also used as drug thickeners.

In the second part of the Chinese Pharmacopoeia (Western Medicine), there is a requirement for viscosity control of some pharmaceutical agents. For example, in Appendix IF: Ointments and creams can be added with humectants, preservatives, thickeners, antioxidants, and permeable as needed. Skin enhancer. Ointments and creams should have a suitable viscosity, and pastes generally have a relatively high consistency. However, it should be easy to apply on the skin or mucous membranes, not melted, and the viscosity should be small with the seasons. The above formulations are also required to adjust the viscosity as required in Appendix IG (Ophthalmic Formulation), Appendix IQ (Auricular Formulation), Appendix IR (Nasal Formulation) and Appendix IU (gelling agent).

The method for determining the viscosity is specified: the viscosity is mainly represented by three kinds, kinematic viscosity, intrinsic viscosity and dynamic viscosity, and correspondingly, three kinds of viscometers are used for testing, and the rotational viscosity meter is used to test the dynamic viscosity. There are many types of rotary viscometers, including coaxial double barrel rotary viscometer, single cylinder rotary viscometer, cone and plate viscometer, rotor type rotary viscometer, and different types of viscometers can be selected according to actual needs. This appendix does not address the use of rotational viscometers.

In the Chinese Pharmacopoeia, the following excipients were tested for viscosity using a rotary viscometer: carbomer, methylcellulose, hypromellose, polyvinyl alcohol and polymethacrylic resin. However, the description of the test method is not sufficient. In contrast, the U.S. Pharmacopoeia test method for viscosity is very detailed, from the processing of the sample, to the type and size of the rotor of the viscometer for testing, because in the process of viscosity testing, in addition to the external environment (temperature, In addition to the effects of pressure and sample state, the measuring instrument, the viscometer, has a large influence on the accuracy of the measurement.

Similarly, there are not many types of pharmaceutical excipients in China's Pharmacopoeia. The detection methods of many products are not very complete. The US Pharmacopoeia stipulates that there are many drugs that need to be tested for viscosity, and the viscosity test method is also perfect. The choice of rotor type from rotary viscometer To test standards, etc., it also has a greater guiding significance for the production of drugs. Tables 1 and 2 are the types and methods of the agents that need to be tested for viscosity in the Chinese Pharmacopoeia (2005 edition) and the United States Pharmacopoeia (UPS28).

Construction and working principle of rotary viscometer

(1) Construction: The rotary viscometer consists of five parts: an electric motor, a constant speed device, a shifting device, a measuring device, and a bracket case. The constant speed device and the shifting device are collectively referred to as a rotating portion. An outer cylinder is fixed on the rotating member, that is, the outer cylinder rotates. The measuring device consists of a measuring spring part, a dial and an inner cylinder. The inner cylinder is fixed to the body by a torsion spring, and a dial is attached to the torsion spring. Usually the outer cylinder is called the rotor and the inner cylinder is called the suspended hammer.

(2) Principle: During the measurement, the inner cylinder and the outer cylinder are simultaneously immersed in the drilling fluid. They are concentric cylinders with an annulus of 1.17 mm. When the outer cylinder rotates at a constant speed, it drives the drilling fluid in the annulus to rotate. Due to the viscosity of the drilling fluid, the inner cylinder connected to the torsion spring is rotated by an angle. According to Newton's internal friction law, the angle of rotation is proportional to the viscosity of the drilling fluid, so the measurement of the viscosity of the drilling fluid is converted to the measurement of the angle of the inner cylinder. The size of the corner can be read directly from the dial, so this viscometer is also known as the direct reading rotary viscometer.

(3) Measurement principle: 1 relationship between shear rate and speed: 1 rev / min (common rpm) = 1.703s-1; 2 dial reading q (q is the degree on the circumference, the unit can be omitted) and scissors The shear stress t (in Pa) is proportional. When the designed torsion spring coefficient is 3.87'10-5, the relationship between the two can be expressed as: t=0.511
 

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