# partical size analysis Flashcards

what is the importance of particle size reduction (what does the size and surface area affect)

The rate of drug dissolution and release from dosage forms

Flow properties of granules and powders.

Proper mixing of granules and powders.

Physical stability for suspensions.

Grittiness for topical formulation (powder must beimpalpable).

Irritation of the eyes for

ophthalmic suspensions (small

particles must be used).

how many and what dimension do we measure when using spheres

1, the diameter

what is the equivalent diameter

an hypothetical sphere,which represents only an approximation to the true size of the irregular particle

give examples on different equivalent diameters

weight, volume, surface area, sedimentation, length, sieve diameter

are most powders monodispered or polydispersed?

polydispersed (multiple diameters in the powder)

how can we define the size distribution of a polydisperse?

the size distribution can be

broken down into different size ranges, which can be presented in the form of a histogram (or curve).

The histogram presentation allows also to compare the characteristics of two or more polydisperse powder samples.

When the number (or weights) of particles lying within a certain size range is plotted against a size range (or mean particle size), a frequency distribution curve is obtained.

what info can we take from the frequency distribution curve

the mode

when normally distributed

mean=median=mode

mean= average

mode= the highest frequency

median is the half

we can plot % of particles in each size range instead

what’s the difference between weight and number distribution?

number—– data collected by counting ( microscopy and coulter)

weight—- based on weight ( sedimentation and sieving)

we can convert number to weight assuming that the general shape and density of particles are independent

how can we see if the skewed distribution is normal ?

by using a log- normal distribution

what are the different distributions

a) Normal distribution: the mode separates the curves into two symmetrical halves.

b) Positively skewed: a frequency curve with an elongated tail towards the higher size range.

c) Negatively skewed: a frequency curve with an elongated tail towards

the lower size range.

d) Bimodal: the frequency curve containing two peaks (two modes).

what is the cumulative frequency distribution?

Cumulative % oversize:

The total percent of particles

with size higher than the lower

limit of each class interval

Cumulative % undersize:

The total % of particles with size

lower than the upper limit of

each class interval

we can take the median from it, and estimate the degree of skewness

what are the methods of particle size analysis

- Sieve analysis method.
- Microscopy.
- Sedimentation in a liquid or gas.
- Electrical sensing zone method
- Laser light scattering

what is the serving method

most widely used for being simple, cheap, accurate and rapid

uses different sieves, and we can find the sieve diameter from it

how is the sieve method used

we usually use dry powders

we can use wet sieving for suspensions and powders that agglomerates

Sieve analysis uses wire woven stainless steel meshes

with known aperture diameters which form a physical barrier to particle

Most sieve analysis use a stack or nest of sieves which has the smallest mesh above a collector tray followed by meshes that become progressively coarser towards the top of the stack of sieves.

The sieves are mounted on a mechanical shaker.

Powder is loaded on to the coarsest sieve at the top of the assembled stack and the nest is subjected to mechanical vibration.

After suitable time the particles that passes through one sieve and retained on the next finer sieve are collected and weighed.

Frequently the powder is assigned the size of the screen through which it passes, on which it is retained or the mean of the two values.