Higher surface area allows intimate contact of the drug with the dissolution ﬂuids in vivo & increases the drug solubility & dissolution. 2. Absorption & Drug action: Higher the dissolution, faster the absorption & hence quicker & greater the drug action.
of shape also Principle of operation 1. Optic or electronic measures 2. Two dimensional projection 3. Projection screen or circles 4. Image analysing programs 5. Measures 6. Feret diameters 7. Equal circles 8. Size range-‐ 0.001-‐1000 µm 9. Gives number average, or area average
information • Reasonable amount of sample Drawbacks • Statistic relevance “tedious” if image analyse can not be used • Risk for bias interpretation • Diﬃcult for high concentrations • Sample preparation might be diﬃcult
method. It is widely used as a method for the particle size analysis. Range of analysis: The International Standards organization (ISO) sets a lowest sieve diameter of 45 µm and since powders are usually deﬁned as having a maximum diameter of 1000 µm, this could be considered to be the upper limit. In practice sieves can be obtained for size analysis over a range from 5 to 125 000 µm. 0.001 0.01 0.1 1 10 100 1000 ISO Range Particle diameter (µm)
20 minutes is arbitrary and BS 1796 recommends sieving to be continued until less than 0.2% material passes a given sieve aperture in any 5 minutes interval Advantages: 1. This method is very simple 2. Not expensive 3. Easy to operate Disadvantages: 1. Not too much precise method. 2. Not applicable for all disperse systems.
Can be divided into two main categories according to the method of measurement used. 1. One of the type is based on measurement of particle in a retention zone. 2. Another type uses a non-retention measurement zone. One of the most popular of the pipette methods was that developed by Andreasen and Lundberg and commonly called the Andreasen pipette.
Counter Method (Electrical stream sensing zone method) is a sophisticated method. It is a precise and accurate method. Range of analysis: 0.001 0.01 0.1 1 10 100 1000 Coulter counter Particle diameter (µm)
250µ are free ﬂowing but as size falls below 100µ it is cohesive; collection of powder will be either A. Monodisperse ( having particles of same size ) or B. Polydisperse (having particles of more than one size) Particle shape : Spheres have minimum contact & hence optimal ﬂow; particle ﬂakes have high surface to volume ratio & poor ﬂow Packing geometry : • Characterization by porosity & bulk density • Bulk density is always less than true density-‐ due to interparticle pores/voids
Apart from fundamental properties, there are derived properties. These are based on fundamental properties. 1. Porosity 2. Packing arrangements 3. Densities of particles: Dense particles are less cohesive than less dense particles of the same size & shape 4. Particle volume: Bulk volume, Tap volume, Void volume. Instrument used for measurement is coulter counter
adsorption and dissolution rate studies and can be studied by A. Adsorption method B. Air permeability method Here the principle is “resistance to the ﬂow of a ﬂuid through a plug of powder is the surface area of powder. “Greater the surface area, the greater will be the resistance to ﬂow. The instrument used is Fisher subsieve sizer. when a mixture of helium and nitrogen is passed through the cell, containing powder. Here nitrogen is absorbate gas and helium is inert and is not adsorbed on surface. An instrument used to obtain data for calculation of surface area is Quantasorb
properties: Powders may be free-‐ﬂowing or cohesive. Factors those aﬀect ﬂow properties are a) particle size, b) shape, c) porosity, d) density, e) texture. 8. Compaction 9. Angle of repose: [θ = tan-‐(h/r)] 10. Carr’s Index: (Tapped density -‐ Poured density) x 100 Tapped density 11. Hausner’s ratio: Tapped density Poured density
with ﬂowmeter How to improve ﬂow? 1. Alter particle size & size distribution 2. Alter particle shape or texture 3. Alter surface forces 4. Formulation additives 5. Vibration assisted hoppers 6. Force feeders
µ = = r h θ tan h r θ 1. Shape: Spherical particles flow better than needles. 2. Size: Very fine particles do not flow as freely as large particles. a. 250-2000 µm: flow freely if the shape is amenable b. 75-250 µm: may flow freely or cause problems c. less than 100 µm: flow is problem with most substances.
an indication of poor ﬂowability. • The Hausner ratio (H) is related to the Carr index (C), another indication of ﬂowability, by the formula H = 100 / (100 − C) • A Carr index greater than 25% is considered to be an indication of poor ﬂowability, and below 15%, of good ﬂowability
material, and is measured as a fraction, between 0–1, or as a percentage between 0–100%. It is deﬁned by the ratio: Vv Φ = -‐-‐-‐-‐ VT where VV is the volume of void-‐space (such as ﬂuids) and VT is the total or bulk volume of material, including the solid and void components.