Practical 3: Particle Size and Shape Analysis Using Microscope

Date

17th November 2014

Objective

To analyse the size and shape of particles and to observe and compare the size of particles under microscope.

Introduction

The bulk properties such as particles size and shape of the powder are determined by using the size of particles. There are various method that can be used to determine particle sizes and shapes. Microscopic analysis is the most widely used method in this case. It can determine the diameter, shape, and surface area that cannot be determined with the bare eye.  In this experiment, different sizes and shapes of sands are used. . In this experiment, various type of sands ( 150µ, 355µ, 500µ, 850µ, mixed ) and two different powders ( MCC and lactose ) are given to be analyze. Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.  It exists in various different sizes rangingfrom 0.0625 mm (or 1⁄16 mm) to 2 mm.  Fine sand is defined as particles between 0.02 mm and 0.2 mm while course sand as those between 0.2 mm and 2.0 mm. It is used in this experiment as it is inert, easy to obtain and economical.

Materials

Sands( 150µ, 355µ, 500µ, 850µ, mixed )
Lactose powder
MCC powder

Apparatus

Microscope

100 ml beaker

Spatula

Glass slide and cover slip

Procedure

1. Sands with sizes of 150µ, 355µ, 500µ, 850µ, mixed, lactose and MCC are placed in the different beakers by using spatula. The beakers are labeled according to the content.
2. The microscope was set up and ready to be use.
3. 150µ sand scattered on the glass slide and covered with the cover slip.
4. The sand was observed under the microscope using 4x100 magnification.
5. The particles were observed microscopically and the shape was determined.
6. Steps 3 to 5 were repeated by using 355µ, 500µ, 850µ, mixedsands, lactose and MCC powder.


Observations

Size of sand 150 microns  (4 X 4 magnification)
(The particles are irregular in shape)

 Size of sand: 355 µm (4X4 magnification)
(All the particles are small, same size and irregular in shape.)

Size of sand: 500 µm
(All the particles are larger than 355 µm, the size is almost same and the shape is irregular.)

Size of sand: 850 µm (4x4 magnifications)
(The particles are larger compare to 500 µm, particles that present on the upper position look larger and can be seen clearly while particles at the lower position look smaller. The shape of the particles is irregular and without a defined shape.)

 Lactose (4x4 magnifications)
(All particles are small; some of them have round shape while others are irregular in shape.)

Sand of various sizes (4x4 magnification)
(All the particles have different size; most of them have irregular shape with different number of edges and sides.)

 MCC (4x4 magnification)
(the particles are irregular in shape)

Questions

1. Briefly describe the various statistical methods that can be used to measure the diameter of a certain particle.

     There are several method that can be used to measure the diameter of a certain particle.One of the methods is Feret’s  diameter.Feret diameters denoted as Dfh ( horizontal) and Dfv (vertical).Feret diameters are defined as the distance between parallel tangentsFeret diameters are easy to measure and relate intuitively to a characteristic dimensions (eg : length) that may be important in processes.In the early work,Feret diameters were measured using a projection of a photographic negative on a piece of graph paper.Horizontal and vertical Feret diameters were read directly from the graph paper by counting  the squares between parallel tangents.The techniques ensured that both tangents in the horizontal and verticalndirections were parallel to one another,and the horizontal and vertical directions were perpendicular.If significant error in measurement could be tolerated,Feret diameters were measured directly from photographs rather than projeciting a negative onto a piece of graph paper.
Martin;s diameter method also used to determine the diameter of certain particle.Martin’s diameter is the mean chord length of the projected particle perimeter, which can be considered as the boundary separating equal particle area.Martin;s diameter is determined by drawing successive diameters through the centroid of the profile and computing bisected areas.Where the bisected areas are equal,the Martin diameter is defined as the length of chord bisecting the two equal areas.

Another method is projected area diameter which is measured based on the equivalent area to that of projected image of that particle. Projected area is two-dimensional area measurement of a three-dimensional object by projecting its shape on to an arbitrary plane. Besides, another useful method is the projected perimeter diameter which is based on the circle having the same perimeter as the particle. Both of these methods are independent upon particle orientation. They only take into account of 2 dimensions of the particle, thus inaccurate for unsymmetrical particle.

        The other method is by using Fourier analysis to provide an accurate quantification of particle morphology and texture. Three lower order Fourier descriptors, denoted “Signature Descriptors” provide measures of Elongation, Triangularity and Squareness, whilst an additional descriptor, denoted “Asymmetry” provides a measure of particle irregularity. They describe the overall shape of soil particles (defined as “morphology”). A summary of higher order descriptors provides textural information which is related to local roughness features (defined as “texture”).
               


2. State the best statistical method for each sample that you used.

As such, the best statistical method is Feret’s and Martin’s diameter. It is because both of these are the statistical diameter which is the average over many different orientations to produce a mean value for each particle diameter. This will give an average value of diameter in more orientation and giving an average diameter value which is more accurate. Besides, since it is accessing the three-dimensional image of particle, we can use the electron microscope that considering the orientation and shape of the image.

Discussion

       At the most basic level, we can define a particle as being a discrete sub portion of a substance. For the purposes of this guide, we shall narrow the definition to include solid particles, liquid droplets or gas bubbles with physical dimensions ranging from sub-nanometer to several millimeters in size. The most common types of materials consisting of particles are powders and granules for example pigments, cement, pharmaceutical ingredients. Secondly suspensions, emulsions and slurries and example are. Vaccines, milk, mining muds. Thirdly aerosols and sprays with asthma inhalers, crop protection sprays as the example.

  We had conducted an experiment on particle size and shape analysis by using a microscope. From this experiment, we had determine a various size and shape of  150µ, 355µ, 500µ, 850µ, mixed, lactose and McCaw also least that particle size and shape play such an important rule. By far the most important physical property of particulate samples is particle size. Particle size measurement is routinely carried out across a wide range of industries and is often a critical parameter in the manufacture of many products. Particle size have direct influence on reactivity or dissolution rate, stability in suspension, efficacy of delivery, texture and feel appearance, flow ability and handling viscosity, packing density and porosity.


     As well as particle size, the shape of certain particles can also have a significant impact upon the performance or processing of the materials. Many industries are now also making particle shape measurements in addition to particle size in order to gain a better understanding of their products and processes. Some areas where particle shape can have an impact include reactivity and solubility ,powder flow and handling ,ceramic sinter properties ,abrasive efficiency, texture and feel Particle shape can also be used to determine the state of dispersion of particulate materials, specifically if agglomerates or primary particles are present.

The ability to analyze and characterize particle size and shape can significantly improve the manufacturing efficiency and product performance. Thus, we can use of microscopy and image analysis as the most reliable technique to characterize particle shape, size and volume distribution. From this practical, it is found that the overall shape of the sand is asymmetrical. One of the methods used to measure a particle is the projected area diameter which is measured based on the equivalent area to that of projected image of that particle. Another method is the projected perimeter diameter which is based on the circle having the same perimeter as the particle. Both of the methods do not account the 3 dimensional shape of particle (orientation). They only consider the 2 dimensions of the particle, thus it is inaccurate for unsymmetrical particle.

        During the experiment, we put different types of sand on slide to be directly observed them using a light microscope. The sand should be spread evenly and just thin layer to avoid agglomeration that will affect the observation. We observed that the particles are irregular in shape. The size analysis is carried out on two-dimensional image of particles which are generally assumed to be randomly oriented in 3-dimensional and they are viewed in their most stable orientation.


Conclusion

Different types of sands have different size and shape which can be analyzed by using  a light microscope. We are able to determine the overall distribution of shape and size of this particle which are asymmetrical and irregular.


References

1. http://golik.co.il/Data/ABasicGuidtoParticleCharacterization(2)_1962085150.pdf
2. http://www.surfaceanalysis.ru/surface/categors/1f/74/content_128015234686.pdf
3. http://www.nature.com/nature/journal/v162/n4113/abs/162329b0.html

Analyzing by using microscope:

Practicle 3: Sieving

Date

17th November 2014

Objectives

To determine the particle size and the size distribution of both powders.

Introduction

A sieve is a device for separating wanted elements from unwanted material or for characterizing the particle size distribution of a sample, typically using a woven screen such as mesh or net. Sieves are the most commonly used devices for particle size analysis. The sieving process is comparatively inexpensive, simple in concept and easy to use. In sieving process, we use lactose and microcrystalline cellulose (MCC) by using sieve nest.

Apparatus and Materials

Lactose

 microcrystalline cellulose (MCC)

 weighing machine

 mechanical sieve shaker with stack of sieves

Procedures

1. 100g of lactose was weighed

2. A 'sieve nest'  was prepared in ascending order and assigned appropriate sieve size.

3. The lactose powder was put into the sieve.

4. Then, lactose powder was sieved for 20 minutes.

5. The results obtained was recorded and a graph on powder particle size distribution was built.

6. The process was repeated with MCC.

Results

Size (diameter) of aperture  (µm)	Particle size range (µm)	MCC		Lactose
		Weight (g)	Frequency (%)	Weight (g)	Frequency (%)
<50	0<x≤50	60.0473	59.9483	4.9536	4.9675
50	50<x≤150	34.1569	34.1006	93.1901	93.4518
150	150<x≤200	3.2373	3.2320	1.2056	1.2090
200	200<x≤300	1.7847	1.7818	0.3625	0.3635
300	300<x≤425	0.9293	0.9278	0.0082	0.0082
425	>425	0.0096	0.00958	0.0000	0.0000
Total		100.1651	100	99.7200	100

Graph

Discussion

Two types of materials which are lactose and microcrystalline cellulose (MCC) have been used in this experiment. Sieving methods is used to determine the particle size distribution. The stack of sieve nest, which have larger opening size above the smaller opening sizes, have the diameter of aperture of 50µm, 150µm, 200µm, 300µm, and 425µm.

The sieves are stacked on top of each other in ascending degrees of coarseness, and the powder to be tested is placed on the top sieve. The nest of sieves is completed by a well-fitting pan at the base and a lid at the top. The literature provides additional sources of information about the performance of sieving analysis. The nest of sieves is subjected to a standardized period of agitation, which causes the powder sample to distribute between the sieves. Agitation can be conducted using vibration, rotation–tapping, or ultrasound. The horizontal sieve motion loosens the powder packing and permits sub sieve particles to pass through. Vertical motion mixes the particles and brings more of the sub sieve particles to the screen surface. The sieving analysis is complete when the weight on any of the test sieves does not change by more than 5% of the previous weight on that sieve.

Based on the result of the experiment, the frequency of the MCC is higher at the range of particle size 0<x≤50 µm which is 59.9483. While the particle range for the lactose 50<x≤150 µm with the frequency 93.4518. This show that the particle of the lactose is bigger compared to the particle size of the MCC. This is also due to MCC and lactose is two different materials and it has different physical properties.

During the experiment, there is some error happen. The weight of the lactose and MCC is changed after the sieving process is done. The amount of the lactose is decreasing and this can be cause by the little amount of powder still left in the sieves and some of it is spilled out from the sieve nest when the powder was pouring into the weighing boat. The amount of the MCC is increasing might be due to the left powder at the sieve nest by the other group. This can affect the result obtained.


To avoid this happen, the container must be clean by the brush before using it again. The machine must be set up correctly to avoid the error along the process happen so that the experiment can be carried out without any problems.

Questions

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

The average particle size for both lactose and MCC are <50µm, 50µm, between 50µm and 150µm, between 150µm and 200µm, between 200µm and 300µm, between 300µm and 425µm, and >425µm.

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

The other methods to determine the size of particle are:
• Laser light scattering method
Light scattering is a non-invasive technique for characterizing macromolecules and a wide range of particles in solution. In contrast to most methods for characterization, it does not require outside calibration standards. In this sense it is an absolute technique.

• Dynamic light scattering method
Dynamic Light Scattering (DLS) is nowadays used on a routine basis for the analysis of particle sizes in the sub-micrometer range. It provides an estimation of the average size and its distribution within a measuring time of a few minutes.

• Coulter counter
A coulter counter is an apparatus for counting and sizing particles suspended in electrolytes. It is used for cells, bacteria, prokaryotic cells and virus particles.  A typical Coulter counter has one or more micro channels that separate two chambers containing electrolyte solutions. As fluid containing particles or cells is drawn through each micro channel, each particle causes a brief change to the electrical resistance of the liquid. The counter detects these changes in electrical resistance.

• Sedimentation methods
Sedimentation method is a widely used analysis method that produces extremely high resolution size distributions of microscopic to sub-microscopic particles. The normal measurement range for the method is from about 0.02 micron (20 nanometers) to about 30 microns (30,000 nanometers), though it is possible with some types of materials to extend the range to below 0.01 micron or to 50 microns or more.

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

The particle size distribution of active ingredients and excipients is an important physical characteristic of the materials used to create pharmaceutical products. The size, distribution and shape of the particles can affect bulk properties, product performance, process ability, stability and appearance of the end product.


The link between particle size and product performance is well documented with regards to dissolution, absorption rates and content uniformity. Reducing particle size can aid the formulation of NCE’s with poor water solubility. Proper matching of active ingredient and excipient particle size is important for several process steps. Particle size analysis is an integral component of the effort to formulate and manufacture many pharmaceutical dosage forms.

Conclusion

Sieving process can be used as one of the method to determine the size of particles. After conducting the experiment, the distribution of particles can be known and the optimum production of drugs in medicine can be achieved in pharmaceutical phase.

References

1. http://images.alfresco.advanstar.com/alfresco_images/pharma/2014/08/22/f88b360d-1d82-4141-8d33-1643a3ec6357/article-40975.pdf

2. https://www.sympatec.com/EN/Science/Characterisation/13_DynamicLightScattering.html

3. http://www.wyatt.com/theory/theory/understandinglaserlightscatteringtheory.html

The particle size range of lactose and MCC is being weighed:

Practical 3: Phase Diagram Part B

Date

3rd November 2014

Objective 

To determine mutual solubility curve for phenol and water.

Introduction

Some liquids mix readily like perfect partners. Alcoholic beverages like whiskey, wine and beer, for example, are all mixtures of water and alcohol. Other liquids don't mix at all. If you shake a bottle full of oil and water, for instance, you can get them to mix but as soon as you return the bottle to the shelf, the two will separate. Liquids that don't mix and stay mixed are said to be immiscible.

Miscible liquids are liquids that are able to dissolve completely into each other, creating a new homogeneous solution. Miscibility is the ability of two different chemical compounds to mix completely. When two liquids are combined, it becomes impossible to distinguish one from the other. Instead, the combination becomes an entirely different solution. Examples of miscible liquids and compounds are water and alcohol, milk and water, soda and gin, wine and water, and vinegar and water.

Pouring grain alcohol into water results in a single liquid phase. No meniscus forms between the alcohol and the water, and the two liquids are considered “miscible”. Nearly any pair of liquids is miscible if only a trace amount of one of the liquids is present.

Many liquid mixtures fall between these two extremes. Two liquids are “partially miscible” if shaking equal volumes of the liquids together results in a meniscus visible between two layers of liquid, but the volumes of the layers are not identical to the volumes of the liquids originally mixed. For example, shaking water with certain organic acids results in two clearly separate layers, but each layer contains water and acid (with one layer mostly water and the other, rich in acid.)  Liquids tend to be immiscible when attractions between like molecules are much stronger than attractions between mixed pairs.

Phenol also known as carbolic acid, hydroxybenzene, and phenyl alcohol is produced at the rate of millions of tons per year, mostly from isopropylbenzene. Phenol is a starting material in the manufacture of plastic and drugs. It was used an antiseptic beginning in the 1860’s. However, phenol is poisonous. The phenol-water mixtures used in this lab are concentrated and dangerous by contact or ingestion.

Liquid water and phenol show limited miscibility below 70⁰C. In this experiment, miscibility temperatures of several phenol-water mixtures of known composition will be measured.




Chemicals

Phenol

Distilled water

Apparatus

Water Bath

Thermometer

Test Tube

Measuring Cylinder

Experimental Procedures:

1. Tightly sealed test tube containing amounts of phenol and water with different phenol concentration is prepared.

 

2. The tubes were heated in the water bath and being stirred and shaken. The temperature at which the mixture turned clear was recorded.

3. The tubes were removed from heat and allowed to cool at temperature at which the mixture became turbid and two layers were separated.

4. The average temperature of the two readings was determined. Some of the tubes were cooled rather than heated.

Results

Phenol Coposition ( %)	Volume of water (mL)	Volume of phenol (mL)	Temperature (ͦC)
			Single phase	Double phase	Average
8	18.4	1.6	48	39	43.5
11	17.8	2.2	59	55	57.5
25	15	5	65	63	64
35	13	7	67	66	66.5
50	10	10	69	68	68.5
63	7.4	12.6	66	64	65
70	6	14	64	64	64
80	4	16	42	41	41.5

Discussion

Phenol-water system exhibit partial miscibility. The curve shows limits of temperature and concentration within two phases. The region outside the curve contain systems having one liquid phase whereas region inside the curve contain systems having two liquid phases. At point a, the system contains 100% water. Increasing percentage by weight of phenol in water at 50 ͦC will result in forming two liquid phases until the total concentration of phenol exceeds 63 ͦC at that temperature, and a single phenol-rich liquid phase is formed. The maximum temperature at which two phases region exists is termed critical solution temperature. From the curve, the critical solution temperature is 66.8 ͦC, whereby any combinations of phenol and water above this temperature are completely miscible and yield only a single liquid phase.    

Phase rule is a useful device for relating the effect of the least number of independent variables like temperature, pressure and concentration upon the various phases (solid, liquid and gaseous) that can exist in an equilibrium system containing a given number of components. Phase rule can be expressed as F=C-P+2 where F is the number of degrees of freedom in the system, C is the number of components and P is the number of phases present.With a two-component condensed system having one liquid phase, F=3 because F=2-1+2. However, the pressure is fixed so F is reduced to 2, hence we have to fix both temperature and concentration to define the system. When two liquid phases are present, F=2 because 2-1+2=2, but F is reduced to 1 as pressure is fixed. Hence, only temperature is needed to define the system.

Some precaution should be taken in this experiment. When we sealed the tubes, we have to ensure that all the tubes are tightly sealed to prevent evaporation of phenol once the phenol is mix with water. Evaporation of phenol will affect the result of this experiment. . Besides, extra care must be taken as phenol is a carcinogenic compound. The results show a deviation of critical solution temperature. This may be due to the evaporation of some of the phenol. Also, the temperature may not be taken at the exact time when two phases exist or two phases are no longer seen.

Questions

1. Discuss the diagrams with reference to the phase rule.

The diagram obtained is a phase diagram for a two components condensed system having one liquid phase. Phenol and water are miscible with each other at a particular condition. By applying the phase rule, F=C-P+2 where F is the number of degrees of freedom in the system, C is the number of components and P is the number of phases present, the degree of freedom, F= 2-1+2=3. Since the pressure in the system is fixed which is 1atm, therefore F is reduced to 2. Hence, we only require two independent variables to define the phenol-water system completely which are temperature and concentration. Based on the graph we obtained, if the temperature is given, the composition of the mixture can be determined easily through the graph.

2. Explain the effect of adding foreign substances and show the importance of this effect in pharmacy.

Addition of foreign material to binary system results in ternary system. If material soluble only in one component or if the solublilities in both liquids are marked different, the mutual solubility of the liquid pair is decreased. Its upper consolute temperature is raised and lower consolute temperature is lowered. If the foreign substances are soluble in both liquids, the mutual solubility of the liquid pair is increased. Its upper consolute temperature is lowered and lower consolute temperature is raised. The increase in mutual solubility of two partially miscible solvents by another agent is known as blending. In pharmaceutical preparations, adding of foreign substances may form insoluble complexes and leads to inefficiency of biological availability of drug. This effect is also important to the industrial production of highly concentrated solutions of tar acids (phenols and cresols) used as disinfectants.

Conclusion

From the experiment, the mutual solubility of phenol and water can be influenced by the temperature and it will affect the critical solution temperature. Phenol is partial miscible with water and produce one liquid phase system at certain temperature and concentration when pressure is fixed. The critical solution temperature obtained from this experiment is 69˚C. 

References

1.   Sinko, Patrick J, Martin’s Physical Pharmacy and Pharmaceutical Sciences 5 th editon, Lippincott Williams & Wilkins, 2005, page 51.

2. http://jeplerts.wordpress.com/2008/12/21/partially-miscible-liquids-determination-of-mutual-solubility-of-phenol-water/

3. Dr. U. B. HadkarPhysical Pharmacy(9th Ed.) November 2008page 209-210

4. http://www.scribd.com/doc/116082090/The-Binary-System-Phenol‎