Practical 4-Sieving (Part B)

PRACTICAL 4: SIEVING

PART B

Title

Particle Size and Shape Analysis Using Microscope.

Objective  

1. To determine the percentage of different grain sizes contained within a soil.

2. To analyse and interpret the shape of particles with seven different samples.

3. To observe and compare the size of particles for each sample.

Date

17^th November 2014.

Introduction

The analysis of particle size and shape is very important in the field of pharmaceutical science. The size and shape of the particles can give an effect to the bulk properties, product performance, processability, stability and appearance of the end product. Particle size analysis is an integral component of the effort to formulate and manufacture many pharmaceutical dosage forms. The understanding of the characteristic of particularly the active ingredients and excipients (pharmacologically inactive substance) always being used in the formulation of drugs is thus indeed important.

In this experiment, 5 different types of sands, MCC and lactose are being analysed to study the size and shape of the particles. Different types of particles have difference with respect to their sizes and shapes. MCC, or its full name, Microcrystalline Cellulose, is one of the most important and widely-used excipients. It acts as a key diluent for drug formulations and an essential component for almost every kind of oral dosage, including tablets, capsules, sachets, pellets and others, as well. Lactose, the milk sugar is another important excipient which is used to help form tablets due to its excellent compressibility properties. It can used to form a diluent powder for dry-powder inhalations as well. Lactose may be listed as lactose hydrous, lactose anhydrous, lactose monohydrate, or lactose spray-dried.

The analysis of particle size and shape can be done by several methods where each applying different working principle such as sieve method, laser light scattering method, dynamic light scattering method, sedimentation method and microscope method. The particle size and shape in this experiment are observed using microscope.

Experimental Methods

Chemicals

5 different types of sands and powders (MCC, Lactose).

Apparatus

Microscope, slide, spatula, beaker and weighing boat.

Procedures

1. A microscope was used to analyse 5 different types of sands and powders (MCC, Lactose) with particular emphasis on the size and shape of the particles.

2. The particles observed microscopically were sketched and the general shape for the particular material was determined.

3. The magnification that were used in sketching the particles were noted.

Results

Questions

1. Explain in brief the various statistical methods that you can use to measure the diameter of a particle.

    Various measure of the size of irregularly shaped particles as seen in profile under the microscope have been used, chosen according to their theoretical significance or practical ease of measurement. Example of statistical diameters are useful measures of central size tendency and are computed from some measured property that is a function of size and related to a linear dimension. Irregular particles that has assigned size depends strongly on the method of measurement .Method of assignment of numerical value for the diameter, surface area or other perimeter has been established. Mean particles diameter is the most important single statistical parameter because if the proper diameter is chosen, the various other parameter of interest such as specific surface area, number, mean particle weight often may be calculated.

2. State the best statistical method for each of the samples that you have analysed.

The best statistical method for each of the samples that have been analysed is by histogram.

Discussion

            In this experiment, the characteristic of different particles are observed and studied in regard to their size and shape using microscope. Particles being observed are sands with different size (150 micron, 350 micron, 500 micron, 850 micron and various size), lactose and microcrystalline cellulose (MCC). Microscopy is used as a sizing method as it allows the direct visualization and measurements of small particles. Light microscope is used where it works according to the principle of passing the visible light transmitted or reflected from the sample through a single or multiple lens to allow the magnification of sample’s view. In this case, 4 x 10 magnification (the product of objective-eyepiece combination) is chosen because it gives the best magnification view to observe the particles.

            The shapes and sizes of different particles are distinct from each other. All the sand particles have irregular shape with pointed edges but their sizes vary. The size of sand particles increases following the sequence of 150 microns, 350 microns, 500 microns and 850 microns. The sand particles with various types have varying sizes. Meanwhile, the MCC and lactose have granular shape without sharp edges and they are far smaller than even the 150-micron sand particles. When comparing the MCC and lactose, some of the MCC particles are acicular while the lactose particles are more rounded. The particles are dispersed evenly on the slide when doing the microscopy to avoid agglomeration which may affect the observation. When doing the size and shape analysis using microscope, we are actually observing them as two-dimensional image whereby similar particles may appear to be different due to different orientation. However, we assume the particles are randomly oriented and viewed in their most stable orientation.

            For the size analysis of non-spherical particle (which in our case are all the particles being observed), there are several equivalent diameters can be used to define them. Among the important and suitable ones are Feret’s diameter, Martin’s diameter and projected area diameter. They are diameters defined on the basis of the projected image or the two-dimensional image of particle. Martin's diameter is the averaged cord length of a particle which equally divides the projected area while Feret's diameter is the averaged distance between pairs of parallel tangents to the projected outline of the particle. The diameter of a sphere having the same projected area as the particle is termed the projected area diameter. Martin's diameter and Feret's diameter of a particle depend on the particle orientation under which the measurement is made. Thus, to obtain a statistically significant measurement for these diameters, a large number of randomly sampled particles which are measured in an arbitrarily fixed orientation is required.

            One of the precautionary steps taken in the experiment is the careful handling and transferring of the particles from the weighing boat to the slide for microscopy by using spatula. This is to prevent the particles from mixing with other particles not under study such as dirt and dust and affect the accuracy of result.

Conclusion

   In conclusion, different particles have different size and shape and these characteristics are indeed important to be understood well especially comes to the formulation of drugs in the field of pharmaceutical industry to allow the optimum efficacy of the drugs. To analyse particle size and shape, microscopy is a useful method to be used where the light microscope allows the direct observation of the particles being studied.

Reference

Anon. Chapter 1: Size and Properties of particles. http://158.110.32.35/CLASS/IMP-

CHIM/PGSF21-42.pdf [1st December 2014].

Anon. Lactose. http://www.drugs.com/inactive/lactose-157.html [1^st December 2014].

DFE pharma. New synergies, new values. http://www.dfepharma.com/en/excipients/mcc.aspx    

[1st December 2014].

HORIBA. Particle Characterization in the Pharmaceutical Industry.

http://www.horiba.com/scientific/products/particle-characterization/applications/

pharmaceuticals/ [1st December 2014].

Practical 4-Sieving (Part A)

PRACTICAL 4: SIEVING

PART A

Title:

Particle Size and Size Distribution.

Objective

To determine the particle size and the size distribution of lactose and microcrystalline cellulose (MCC).

Date

17th November 2014.

Introduction

            Sieving is a process of using an instrument with a meshed or perforated bottom, used for separating the coarse part from the fine part of loose matter, for straining liquids and so on, especially one with a circular frame and fine meshes or perforations. Sieve analysis is used to obtain the particle size distribution of a solid material by determining the amount of powder retained on a series of sieves with different sized apertures.

Particles are three-dimensional objects. In order to provide a complete description of a particle, three parameters are required — length, breadth and height. Thus, it is impossible to describe a particle using a single number that equates to particle size. Therefore, most sizing techniques assume that the material being measured is spherical because a sphere is the only shape that can be described by a single number, its diameter, thus simplifying the way particle size distributions are represented.

In this practical, lactose and microcrystalline cellulose, two common excipients used in tablet formulations are used. Powder form of lactose can be graded depending on particle size distribution, density and how easily it flows. The properties of lactose that makes them suitable as a pharmaceutical filler in tablets and capsules are cost effective, highly available, physically and chemically stable and are able to form tablets under compression. Lactose wettability enables it to form a dissolved layer around drug and retard the drug dissolution rate.

Microcrystalline cellulose is a commonly used excipient in the pharmaceutical industry. It has excellent compressibility properties and is used in solid dose forms, such as tablets. Tablets that are formed are hard but dissolve quickly. Microcrystalline cellulose is the same as cellulose, except that it meets USP standards. It is also found in many processed food products, and may be used as an anti-caking agent, stabilizer, texture modifier, or suspending agent among other uses. According to the Select Committee on GRAS Substances, microcrystalline cellulose is generally regarded as safe when used in normal quantities.

Experimental Method

Chemicals

Lactose powder and microcrystalline cellulose (MCC).

Apparatus

Beaker, weighing boat, laboratory test sieve (with 425μm, 300μm, 200μm, 150μm, 53μm sieve nest), spatula, electronic balance and electrical motorized sieve shaker (Octagon 2000 digital sieve shaker).

Procedures

1. 100g lactose was weighed.

2. The sieve nest was prepared in descending order (largest diameter to the smallest, from top to bottom).

3. The powder was placed at the uppermost sieve and the sieving process was allowed to proceed for 20 minutes.

4. Upon completion, the powder collected at every sieve was weighed and the particle size distribution was plotted in the form of a histogram.

5. The above process was repeated using MCC.

Results

1)      Lactose

Sieve opening	Mass of lactose remained in each sieve/ g ( W sieve)	% retained = (W sieve/ W total) x 100%	Cumulative % retained	% passing= 100% - cumulative % retained
< 53 µm	0.7625	(0.7625/100) x 100% = 0.7625%	0.7625	100 – 0.7625= 99.2375
53 µm	18.7789	(18.7789/100) x 100% = 18.7789%	0.7625 + 18.7789 = 19.5414	100 – 19.5414 = 80.4586
150 µm	48.9482	(48.9482/100) x 100% = 48.9482%	19.5414+48.9482 = 68.4896	100 – 68.4896 = 31.5104
200 µm	0.7261	(0.7261/100) x 100% = 0.7261%	68.4896 + 0.7261 = 69.2157	100 – 69.2517 = 30.7483
300 µm	8.6303	(8.6303/100) x 100% = 8.6303%	69.2157+ 8.6303 = 77.8460	100 – 77.8460 = 22.1540
425 µm	22.0313	(22.0313/100) x 100% = 22.0313%	77.8460+22.0313 = 99.8773	100 – 99.8773 = 0.1227

Theoretical weight of lactose = 100g

Experimental weight of lactose:

0.7625+ 18.7789 + 48.9482+ 0.7261 + 8.6303 + 22.0313 = 99.8773 g

Mass loss during sieving : (100 – 99.8773) / 100 x 100 = 0.12 %

2)      MCC

Sieve opening	Mass of MCC remained in each sieve/ g ( W sieve)	% retained = (W sieve/ W total) x 100%	Cumulative % retained	% passing= 100% - cumulative % retained
<53 µm	3.7321	(3.7321/100) x 100% = 3.7321%	3.7321	100 – 3.7321 = 96.2679
53 µm	89.6964	(89.6964/100) x 100% = 89.6964%	3.7321+89.6964 = 93.4285	100 – 93.4285 = 6.5715
150 µm	4.0674	(4.0764/100) x 100% = 4.0764%	93.4285+4.0764 = 97.5049	100 – 97.5049 = 2.4951
200 µm	1.6289	(1.6289/100) x 100% = 1.6289%	97.5049+1.6289 =99.1338	100 – 99.1338 = 0.8662
300 µm	0.0957	(0.0957/100) x 100% = 0.0957%	99.1338 +0.0957 = 99.2295	100 – 99.2295 = 0.7705
425 µm	0.0018	(0.0018/100) x 100% = 0.0018%	99.2295 + 0.0018 = 99.2313	100 – 99.2313= 0.7687

Theoretical weight of MCC = 100g

Experimental weight of MCC:         

3.7321 +89.6964 + 4.0674 + 1.6289 + 0.0957 + 0.0018 = 99.2313 g

Mass loss during sieving : (100 – 99.2313)/100 x 100 = 0.77%

Questions

1.  What is the average particle size for both lactose and MCC?

The average particle size is less than 150 µm for both lactose and MCC. This is because most of the lactose and MCC powder were found in the sieve nest with aperture size of less than 150 µm.

2.  What other methods can you use to determine the size of particle?

•         Aerodynamic method (APS, Impactors, etc)
•          Optical method (optical counters, light scattering analyzers, etc)
•           Electrical sensing zone method (Coulter Counter)
•           Electrical mobility and condensation method (DMA+CNC)
•           Electron microscopy 

3. What is the importance of particle size in a pharmaceutical formulation? 

For solid or suspension delivery systems, bioavailability is often directly related to particle size because it controls dissolution/solubility characteristics. Dissolution rate is directly proportional to particle surface area (Noyes-Whitney equation), so a finer particle size promotes faster drug dissolution. Particle size distribution is also relevant as a narrow distribution produces more uniform dissolution. Formulations with even a small number of relatively large particles may take some time to dissolve completely, but this may be the design intent.

For suspensions, stability is an important issue because if the active ingredient settles there is a greater chance of non-uniform delivery. Stokes' Law relates settling velocity to the physical characteristics of the fluid and the size of particles in the suspension. The relationship here is a strong one: velocity correlates with the square of particle diameter. For suspension stability, a very low settling velocity is preferable and is more easily achieved with finer particles.

Perhaps less obviously, particle size may also affect a formulation's behaviour during processing and, ultimately, its content uniformity, which is critical. Take, for example, the widespread operation of direct compression tableting; particle size can influence segregation behaviour, the ease with which powder flows through the press and the compressibility of a formulation. In turn, these factors affect the consistency of tablet weight and composition, how the press operates and the mechanical properties of the finished product.

Discussion

Sieve analysis is one type of mechanical analysis which determines the size range of particles present in lactose and microcrystalline cellulose (MCC), expressed as a percentage of the total dry weight or mass. Sieve analysis consists of shaking the lactose sample through a set of sieves that have progressively smaller openings. As a stack of sieves are prepared, the sieve that has larger opening size are placed above the ones that having smaller opening size. This means that the sieve that has diameter of aperture of 425 µm will be placed above followed by 300 µm, 200 µm, 150 µm, 53 µm and <53 µm. 

Theoretically, the smaller the size aperture of the sieve nest, the more the powder we can get from the sieve nest. From the mass of powder remained in each sieve nest, we can calculate the retained percentage as well as passing percentage. By comparing both the graph of MCC and lactose, we know that the particle size of MCC is smaller than lactose. It seems that MCC is affected more than lactose due to the physical vibration that has been applied on the particles, since the hardness of the surface of the particle contributes to the reduction of particle size. The results from this experiment were slightly inaccurate as the weight of lactose and MCC was inaccurate since there was still some powder left in the sieves after the process is carried out.  Besides that, some of powders may have spilled out from the container since the machine was not closed correctly. This also affects the result obtained.

The results of sieve analysis were generally expressed as the percentage of total weight of lactose and MCC that passed through different sieves. From the results, the total mass sample after sieving was smaller than the total mass before sieving where 0.1227 g and 0.7687 g were lost. This is probably because the small particles of lactose and MCC were lost when the sieves were being vibrated. The lactose and MCC used were then collected back and weighed. It was found that after sieving, there were 0.12 % and 0.77% loss of lactose and MCC respectively.

Therefore, the total mass was corrected by adding the mass retained with the corrected mass of lactose and MCC. In the formulation, the uniformity of the particle size of the powder and also the roundness play important roles in the pharmacodynamic properties of the medicine. It will affect the absorption rate and stability of the formulation.

Conclusion

Based on the histogram graph, we can conclude that the particle size of MCC is smaller than lactose. It was proven when the cumulative percentage retained for lactose was 99.8773% while the cumulative percentage retained for MCC was 99.2313%.

Reference

Pa

Particle Size Is Important: Particle Analysis Techniques. http://www.pharmaceutical-int.com/article/particle-size-is-important-particle-analysis-techniques.html [12^th December 2014].

Sieve Analysis Test. http://www.uta.edu/ce/geotech/lab/Main/sieve/index.htm#sthash.WEysNnzz.dpuf [12^th December 2014].