Evaluation of emulsions & suspensions

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evaluation of emulsions and suspensions for m.pharm students

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Evaluation of emulsions & suspensions :

Evaluation of emulsions & suspensions By:- ravi kumar Aditya college andhra university

Emulsions :

Emulsions Emulsions are thermodynamically instable . Garret “stable emulsion, would maintain the same number of sizes of particles of the dispersed phase per unit volume of wt of the continuous phase. The total interfacial energy must be in variant with time to conform to this definition.”

Instability in emulsions :

Instability in emulsions 1. Creaming a. Cream up (rises) b. Cream down (sediments) 2. Flocculation (Reversible aggregation). 3. Coalescence (irreversible aggregation

Evaluation of emulsion :

Evaluation of emulsion It involves two parameters namely Physical parameters Chemical parameters

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PHYSICAL PHARAMETERS : The most parameters commonly measured to assess the effect of stress conditions on emulsions include. 1 . Phase separation. 2 . Viscosity /Rheology studies. 3 . Electrophoretic properties. 4 . Particle size analysis &particle count.

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1. PHASE SEPARATION : The rate of phase separation after aging of an emulsion may be observed visually (or) by measuring the vol. of separated phase. Phase separation It is not been described in literature. It involves with drawl of the small specimens of the emulsion from the top & the bottom and compares the composition of the two samples by appropriate analysis of Water content. 2. Oil content (or) 3. Any suitable constituent (e.g.: preservative) The amount of coalescence observed at room temp. depends on the conc. of emulsifier. At 1. Conc. (<0.1% w/v) → Visible coalescence occurs →After 1 month only 2. High conc. (2 to 5% w/v) →Visible coalescence is negligible→ even after 2 years also

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2 .viscosity For shelf life studies of emulsions, changes in viscosity during aging (but not absolute viscosity) are very important. →Emulsions are non Newtonian liquids. The various viscometers used for the determination of viscosity of emulsions are: Cone plate type. Viscometers with coaxial cylinder (easiest). Penetrometer (Highly viscous emulsions). Brook field viscometer, with Helipath attachment (for the detection of creaming & sedimentation before it becomes visibly apparent). → the best way of using viscosity determination for the prediction of shelf life is to relate them to changes in particle size.

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S.NO Type of emulsion Changes in n on storage at room temp. 1. w/o η, drops quickly & continuous to drop for some time (5 to 15 days at RT) 2 o/w η, increases immediately, & continuous to increase linearity. Essesment of shelf life: IDEAL SHELF LIFE. Typical shelf life. Questionable shelf life. → the best way of using viscosity determination for the prediction of shelf life is to relate them to changes in particle size.

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3) ELECTROPHORETIC PROPERTIES: A)ZETA POTENTIAL. 1. Moving boundary method (slower). 2. Electrophoretic method (faster) → Micro electrophoresis apparatus. Critical value of zeta potential 20 to 50 mv. B)ELECTRICAL CONDUCTIVITY; Electrical conductivity measurement is a tool for the evaluation stability shortly after preparation. APPARATUS: Nuro amperometer pH – electrodes Diameter – 0.4mm → o/w (or) w/o → current up to 15 to 50 Distance between – 4mm at RT (or) 37 c

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S.NO TYPE OF EMULSION ELECTRICAL CONDUCTIVITY 1. o/w (fine). Resistance Low → stable. High → instable ( droplet aggregation) 2. w/o (fine). Conductivity. No → stable. Yes → instable (droplet coagulation)

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4. PARTICLE SIZE NUMBER ANALYSIS : In the evaluation of emulsions. → Avg. particle size (or) are critical. → Particle size distribution of the droplets. Various methods, gives different avg. particle sizes Microscopic methods. (e.g.: microscopic, macrometer ). Electronic counting methods. (e.g.; coulter counter). Light scattering & related reflectance. 3 ) LIGHT SCATTERING & RELATED REFLECTANCE : Principle: The change of reflectance at wavelength, at which the colored internal phase partially absorbs the incident light, has been found to be inversely proportional, to a power of the particle diameter. R=C/D (or) log R = -K log D + log C → (logarithmic plot 1) Where,

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R = % reflectance. D = surface avg. particle diameter. C&K are constants, characteristic of emulsion. Procedure: Loyd : Has employed a relationship between reflectance of colored emulsions and the surface area diameter of the dispersed phase . To evaluate: 1.Emulsion stabilizers. 2.Kinetics of emulsion coalescence. The o/w emulsions, containing 5 vol of the dispersed phase, the oil phase was colored with red dye, scarlet B. Reflectance → of the emulsions was determined by at 450 mṵ (wavelength). Surface avg particle diameter of internal phase was determined by microscope

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It simulates the first order reaction and can be used to estimate the physical stability of an emulsion at extended storage periods. Practical Re Commendations for shelf life predictions of emulsions; Instability of emulsions under stress conditions can be related to normal shelf life. The stress conditions normally employed for evaluating the stability of emulsions include. 1.Aging & temp. 2.Centrifugation . 3.Agitation .

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1.Aging and temp S.NO AGE STORAGE TEMP. LIMITS 1. 60 to 90 days 45/50 ᵒc Emulsion should be stable with no visible signs of separation. 2. 5 to 6 months. 37 ᵒc 3. 12 to 18 months. 25 ᵒc /RT.

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2.Freeze thaw cycle s.no age Storage tempearture Freeze thaw cycles limits No.of cycles b/w temp 1 1 month 4ᵒc 2 or 3 -20ᵒc and +25ᵒc There should be no visible signs of separation 2 NLT48 hrs - 6 or 8 Refrigeration temp

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3.centrifugation Centrifugation at rpm Temp Limit 2000 to 3000 Room temp No signs of determination DURATION TEMP LIMIT 24 TO 48 HRS On a reciprocating shaker (Approx 6o cycles per min) Room temp & at 45ᵒc The emulsion should not be adversely effected 4 .Agitation

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Additional testing (for emulsions): During the testing period, at reasonable time intervals the following characteristics are to be monitored Physical tests: Change in electrical conductivity. Change in light reflection. Change in viscosity. Change in particle size. Change in chemical composition. In addition to these physical parameters Evaluation for microbial contamination (during storage, due to microbial activity redistribution (or) micellization of the preservative may takes place).

Various methods for evaluation of suspensions are:

Various methods for evaluation of suspensions are Sedmentation method Rheological method Electrokinetic method Particle size changes (freeze thaw cycle) Redispersibility

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s.no I.P.Q.C TEST APPARATUS TEST PROCEDURE ACCEPTABLE LIMITS 1 Sedmentation volume Measuring cylindera F=Vu/Vo F=sedimentation vol Vu+the ultimate vol.of the sediment Vo+the intial volume of the total suspension F=1;Ideal suspension F=0;instable suspension F,value range 0 to 1 ↑F; ↑physical stability of suspension

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s.no I.P.Q.C TEST APPARATUS TEST PROCEDURE ACCEPTABLE LIMITS 2 Rheological methods Brookfield viscometer mounted on helipath stand with T-bar spindle High yield value/viscosity at rest. 1. Desirable rheological characteristics. Thixotrophy (↓viscosity; ↑shear force). (↑ pourability , ↓sedimentation, Aggregation, caking) 2. Un desirable rheological characteristics. Pseudo plastic Dilatants Rheopexy (↑viscosity; ↑shear force).

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s.no I.P.Q.C TEST APPARATUS TEST PROCEDURE ACCEPTABLE LIMITS 3 Electro kinetic techniques/Electrophoretic method. Micro electrophoresis apparatus Determination of zeta potential(or) migration velocity of the particles with respect to the surface electric charge. Critical value of zeta potential 20 to 50mv.

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s.no I.P.Q.C TEST APPARATUS TEST PROCEDURE ACCEPTABLE LIMITS 4 Particle size changes./Freeze thaw cycling technique 1 .Occular grid counting. 2.Photo micrographs 1. It applies stress to suspension for stability testing. 2. It promotes particle growth. 3.It alerts the changes in →Absolute particle size. →Particle size distribution. →Crystal habit. Pharmaceutical susp . (10 to 100ṵm).

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s.no I.P.Q.C TEST APPARATUS TEST PROCEDURE ACCEPTABLE LIMITS 5 Redisperssibility . Mechanical shaker device which simulates the human arm motion The 100ml measuring cylinder containing suspension after sedimentation was rotated through 360 at 20rpm. End point: basement is clear of sediment. ↓time required; ↑ redispersibility

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