One of the most important applications of the rotary viscometer in the pharmaceutical industry is to measure the viscosity of pharmaceutical thickeners. Pharmaceutical thickeners are a kind of pharmaceutical excipients used to increase the viscosity of liquids or pastes. For example, adjusting the viscosity of liquids in eye drops can make eye drops stay in the eye longer; The ointment can make the cream easy to apply. 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), some requirements for the viscosity control of certain pharmaceuticals have been put forward. For example, in Appendix IF: Ointments and creams can be added with moisturizers, preservatives, thickeners, antioxidants and Skin promoter. Ointments and creams should have a suitable viscosity, and pastes generally have a relatively high consistency. However, they should be easily applied to the skin or mucous membranes, not melted, and the viscosity should be small with seasonal changes. In Appendix IG (ophthalmic preparations), Appendix IQ (ear preparations), Appendix IR (nasal preparations) and Appendix IU (gelling agents) also require that the above preparations should be adjusted as needed viscosity.
The method for determining the viscosity is specified in Appendix 39. The three methods for expressing the viscosity are kinematic viscosity, intrinsic viscosity, and dynamic viscosity. The corresponding three viscometers are also used for testing. Among them, the rotational viscometer is used to measure the dynamic viscosity. . There are many types of rotary viscometers, including coaxial double cylinder rotary viscometer, single cylinder rotary viscometer, cone-plate viscometer and rotor-type rotary viscometer. 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 use a rotational viscometer to measure the viscosity: Carbopol, methylcellulose, hypromellose, polyvinyl alcohol, and polymethacrylic resins. However, the description of the test method is not sufficient. In contrast, the United States Pharmacopoeia's test method for viscosity is very detailed, from the sample processing, 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 conditions, measuring instruments, viscometers, have a great influence on the accuracy of the measurement.
Similarly, there are not many types of excipients for Chinese medicine in the Pharmacopoeia of China, and the detection methods for many products are not very complete. The US Pharmacopoeia specifies that more drugs are required for viscosity detection, and the viscosity testing method is also relatively complete. The selection of the rotor model from the rotary viscometer To the test standards, etc., have a great guiding significance for the production of drugs. Tables I and II are the types and methods of the agents required for viscosity testing in the Chinese Pharmacopoeia (2005 version) and the United States Pharmacopoeia (UPS28).
Table 1 Drugs for viscosity testing in the Chinese Pharmacopoeia (2005 edition)
Pharmacy category
test temperature
Viscosity range
Carbom
25°C
15-30Pa.s
Methylcellulose
20°C
< 70% to 140% of the 100cp mark
>80%-120% of the 100cp tag value
Hypromellose
20°C
5-7.5cp
Polyvinyl alcohol
20°C
3-5cp
Polyacrylic resin
25°C
<50cp
Table 2 Medicaments for viscosity testing in the United States Pharmacopeia (UPS28)
Pharmaceutical name
Rotor
Speed ​​(RPM)
Viscosity range and temperature
Instrument range
Xanthan gum
LV#3
60
>600cP(24°C)
2000cP
Methacrylic acid copolymer dispersion
LV with ultra-low viscosity adapter
30
<15cP (20°C)
20cP
Methacrylic acid copolymer
LV#1
30
50cP-200cP (Depending on product) (25°C)
200cP
Magnesium aluminum silicate
LV#2, #3 or #4
60
Determined according to the type of agent (25°C)
#2–500cP,#3–2000cP,
#4-10,000cP
Alginate
LV#1
30
>15cP (75°C)
200cP
Ethyl cellulose water dispersion
LV with ultra-low viscosity adapter
Torque range 10%-90%
<150cP(25°C)
Variable
Dimethicone
>1000cP(25°C)
Microcrystalline cellulose and methyl
10%-90% of torque
20
No specific viscosity
Variable
Cellulose sodium
Carrageenan
LV#1
30
>5cP (75°C)
200cP
Carbom
RV#6
20
Viscosity is not specified (25°C)
50,000cP
Purified bentonite
LV#2
60
40cP <viscosity<200cP (25°C)
500cP
Ammonium polymethacrylate
LV with ultra-low viscosity adapter
30
<15CP (20°C)
20cP
Alkyl phenyl acid salt (C12-15)
RV#1
100
<100cP(25°C)
100cP
Colloidal oat
LV#1
60
1cP<viscosity<100cP (45°C)
100cP
Stannous fluoride colloid
LV#3
12
600cP<viscosity<170KcP (25°C)
10,000cP
In addition to the use of rotational viscometers for pharmaceutical excipients, it is also necessary to test the viscosity during the sol process of the capsule production process. The main ingredients of capsules are gelatin, glycerin and other medicinal materials. Different raw materials, gelatin, analysis of its physical and chemical properties, according to local conditions matching sol formulations, as far as possible to meet the production requirements and the relative quality of a constant glue. The quality of the sol process has been half or more of the decision of the completion of the batch of rubber production (production speed efficiency, the smoothness of the head, the waste rate, etc.). The main indicators of a batch of gelatin raw materials are: viscosity, freezing capacity, water content, transparency and so on. In order to control the quality, it is necessary to conduct a viscosity test, which includes controlling the quality of the raw material gelatin and the quality of the glue during the production process.
In addition to the quality inspection, the rotary viscometer also has many applications in the research and development of pharmaceuticals. Especially in the formula design of some ointments and injections, different formulae result in different rheological properties of the pharmaceuticals, resulting in the production and use of pharmaceuticals. Great influence. The formula design and rheology study of the pharmaceuticals are performed by a rotating viscometer/rheometer. The new viscometer/rheometer can also be controlled by a computer. Different data can be obtained according to different test conditions, which can be more comprehensive. The rheological behavior of the reagents is of great use value for the development and quality testing of some pharmaceuticals!