Thursday, December 20, 2018

Wilhelmy Plate Method of Surface Tension

A thin plate is utilized to determine equilibrium interfacial and surface tension on the air-liquid or liquid-liquid interfaces. The vertically oriented plate is for the interface and the force is applied to measure the surface tension. This is a universal method which is mainly appropriated for surface tension testing at long intervals. A known perimeter is connected to vertical plate balance and because of wetting, the force is measured.


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Drop weight method of measuring surface tension

Stalagmometer has been the most frequently used methods for finding out the surface tension. Numerous drops of liquid emitted from the glass capillary of stalagmometer have weighed, if the weight of liquid is known about every drop, we are able to count the leak droplets to the determination of the surface tension. The drop at the tip of the glass capillary is placed in a vertical position and has been formed gradually on the tip, The pendant drop turns to begin separation while its weight goes to the magnitude balance. The Volume depends on the characteristics of the liquid.
This method is utilized for interfacial tension determination in the form of interface edge, a liquid of density is pumped to another liquid which has different density and the drops number of every liquid in the air and the interface is calculated. alternatively, drop weight is calculated.


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Determination of surface tension by capillary rise method

This is the most established method used to determine surface tension, in this method, the surface tension presence of the liquid/gas interface is taking fluid in a thin tube, generally a capillary made up of glass, and this occurrence was used to determine the surface tension of the liquid. For this cause, a thin round capillary is deep in the liquid which is already tested. If the liquid molecules have strong interaction among the capillary walls, the capillary end is deep in the solution. The height reaching the liquid in a capillary is associated with the surface tension.


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Surface tension by drop number method

In this method of surface tension, a liquid drop is permitted to form on the capillary lower end, in the surface tension upper forces of tension supported to the outer periphery of the tube. The drop mass is dragged it down, when the force is balanced the drop are brakes at the bottom of the working device there is a glass in which the capillary is called a stalagmometer. 

The drop breaks when forces are balanced.  Working equipment has a glass in the lower part with the capillary this called as a stalagmometer. Then the surface tension is detected by calculating the number of droplets for the specified liquid.



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Surface Tension Measurement Methods

Surface tension is the power or force that the particles or molecules are pushed together on the fluid surface and creates a layer. Due to the particle attraction in the surface layer by the liquid bulk, it is the tension of the liquid surface film which goes to decrease the surface area. The surface tension is assessing the consolidate energy which is present in an interface. The molecules of the fluid are attracting each other and the molecule interplay in the liquid bulk is balanced by the similar attractive force in every direction.
The Surface tension can be determined by the following techniques.
  • Drop Number Method
  • Capillary Rise Method
  • Drop Weight Method
  • Spinning Drop Method
  • Wilhelmy Plate Method
  • Du Noüy Ring Method
  • Bubble Pressure Method
  • Pendant Drop Method

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Isotonic Buffers

The solution will affect isotonicity in addition to any compound because there is a property of the number of particles in the isotonicity solution. The osmotic pressure of the solution can be influenced by the drug as well as by every buffer compounds which is included in formulations, however, these compounds have been added after; it is probable that the solution would not be isotonic. It might be important to include additional sodium chloride to the solution in isotonicity.


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Definition of Isotonicity

There is an event called osmosis if the use of a semi-permeable membrane to isolate the solutions of various soluble concentrations. In which the molecules of solvent traverse the membrane from the lower concentration to higher concentration to set the concentration balance. The movement drives by the pressure that is called osmotic and is governed by the particle numbers in the solution. The particle number is fully determined by the solution concentration if the solution is non-electrolyte. If the solution is electrolyte then the particles are number determined by the solution concentration and the degree of dissociation.
The clinical importance of all this is to make sure that the solution of isotonic or Iso-osmotic does not harm the tissue or while administering it does not produce pain. The solutions that have fewer particles and pouring osmotic pressure less than 0.9% called as hypotonic and those solutions contain high osmotic pressure are called as hypertonic. Painful swelling of the tissues produces, when the administration of a hypotonic solution, since the water passes by the administrative site through blood cells or tissues. As water is pulled from the biological cells in an effort to dilute the hypertonic solution, it reduces the tissues. The administering effects of the hypotonic solution are generally graver than the solution of hypertonic since the breaking cells cannot be repaired. To adjust the Isotonicity of pharmaceutical solution several methods are used. The sodium chloride equivalent method is one of the most widely used methods.


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Wednesday, December 19, 2018

pH Determination Methods

a pH is a short form for the potential of hydrogen. This is a numeric value that is allocated to the solution which indicates the solution that it is acidic or basic. pH ranges from 0 to 14, if the pH is less than 07, then it is defined as acidic while it greater than 7 pH then it is defined as basic and 7 pH is neither acidic nor basic. pH is the most commonly used parameter and there are numerous methods available to measure the pH of the solution.

Here are mentioned some methods used for pH measurement
pH paper or Indicator papers:
This is an easy and cheap way, which provides an indication of acidity or alkalinity, although this is not providing a precise measurement. The pH paper is coated with organic dyes which indicate with the color change. Litmus paper is also used to check the acidity or alkalinity of the solution. 
pH meters:
The pH meter is a scientific instrument it is widely used to determine the exact pH, the pH meter is determining the difference in electrical potential among an electrode and a reference electrode. It is available in small to medium sizes; easy to use, read on display, as well as the additional printer facility is available.
pH Indicators:
If we do not need to know the exact numerical pH value of the solution, but only knows that the solution is acidic or basic in such case a pH indicator is useful. A pH indicator is a compound which is contingent on the nature of the solution environment, the solution causes different colors.
If the pH of the solution is less than 2, it shows a vibrant red color, if the pH of the solution is around 5, it shows gold or yellow color.


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pH Determination By Colorimetric Method

A colorimetric method of pH determination is depicted to measure the pH of a liquid/ aqueous solution with the 0-01 pH unit accuracy. It is emphasized that the obvious pH measured by sulphone- phthalein indicators is not in the same amount as it gets electrometrically. The progress of glass electrodes, involved in the pH meter, has certainly made the electrometric method the most common way of pH measurement. 
Since it can be applied in a highly diluted solution, colloids, and colored solution, where the indicators are inconvenient, in addition to these particular cases, the indicators provide some benefits, and it appears to us a mistake to regard that the electrometric method is a standard, and always the most precise method. The simple comparator is used, about 0-01 pH unit of reproducibility readily gives by an indicator. 

Commonly asked questions on pH determination are as follows.

Which different methods are used for determination of pH?
Two types of methods are used for the determination of pH, the colorimetric method and the electrochemical method.

Can the colorimetric method be used to determine the pH of water?
Yes, we can use the colorimetric method used to determine the pH of water

Which method is the most accurate in pH determination?
The electrometric method of pH determination i.e. pH meter is the most accurate type of measurement and are broadly used.


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How to Calculate LOD and LOQ

LOD as per the Signal-to-Noise Ratio:
The signal-to-noise ratio is determined by comparing the measured signals with analytes, with which the sample has low concentrations with blank specimens and the analyte can be detected reliably by establishing a minimum concentration.
LOD as per the visual evaluation:
The identification limit is calculated by analysis of analyte with recognized sample concentration and by setting up the lowest level on which the sample can be consistently detected.
LOD as per the standard deviation of response and the slope:
The LOD can be expressed as - LOD=3 X SD/Slope.
LOQ (limit of quantification)
LOQ as per the Signal-to-Noise Ratio:
The signal-to-noise ratio is determined by comparing the measured signals from the analytes, with which the sample has low concentrations with the blank sample and by setting up at least concentration on which the sample can be constantly quantified. 10:1 a normal signal-to-noise ratio.
LOQ as per the visual evaluation:
LOQ is analyzing by analysis of analyte with recognized concentration and by setting the least level of the analyte to quantify with suitable precision and accuracy.
LOQ as per the standard deviation of response and the slope:
The LOQ can be expressed as - LOQ=3 X SD/Slope.


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Advantages and disadvantages of conductometry

Conductometry means the measurement of the conductivity of the ionic compounds. The conductivity meter consists of a conductivity cell made up of platinum and Wheatstone bridge circuit which use for the measurement of solution conductance.
 The advantages of conductometric titrations are mentioned as follows.
  • The measurement process of conductivity is simple.
  • Broad selectivity.
  • Indicators are not required, since changes of solution conductance measured by the conductivity meter.
  • It is suitable for the turbid suspensions, diluted, and colored solution.
  • By graph plotting, the endpoint can be determined.
  • Provide accurate results with minimum errors.
  • Suitable for the analysis of weak bases, weak acids, a combination of strong & weak acids
  • Throughout the titration, the temperature is maintained constant.
The disadvantages of conductometric titrations are mentioned as follows.
  • High concentration is not possible to measure with this method.
  • A Solution is required to be diluted for measurement.
  • Less accurate than other methods.
  • Changes in salt level enhanced conductivity in the solution mask.
  • Less satisfactory than other methods.
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Applications of Conductometry

The basic function of the conductometry is to measure the efficiency of each aqueous solution in the carry of electrical current.
Applications of Conductivity are mentioned as follows. 
  • Water purity can be determined by conductometry. 
  • The solubility of sparingly soluble salts, such as sulfate, lead sulfate, and barium is determined by the conductivity. 
  • It can be used for the determination of salinity of sea water. 
  • The alkalinity of fresh water can be determined by conductometry 
  • It can be used for the determination of the ionic product of water. 
  • It can be used for the conductometric titration. 
  • It can be used for the determination of chemical equilibrium in ionic reactions. 
  • The purity of de-ionized and distilled water can determine by conductometry. 
  • It can be used for the determination of the basicity of organic acids. 
  • Used in the quantitative analysis of the compounds. 
  • It can be used for the determination of deuterium ion concentration in water. 


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The basic principle of conductometry

Conductivity measurement is one of the most important needs of today's laboratories. Laboratories that are involved with water and wastewater analysis, pharmaceutical manufacturing, bulk drug manufacturing, biotechnology, environmental analysis, soil analysis, metal processing, food processing, and  Agro manufacturing, etc. In that various characteristic like quality control, pollution control, process monitoring and managing require performing conductivity measurement regularly.
Conductivity is the measure of the ability of the material to carry out electrical current. Siemens “g” is the conductance basic unit and which is reciprocal of resistance and that measured in ohms. Conductivity measurement of the sample solution provides the degree of electrical conductivity in the definite quantity of the solution. The electrical conductivity of the solution is similar to the number of ions available in it and therefore the conductivity measurement of a solution will give a reading of the solution.
The principle by which the system measures the conductivity is simple. There are two conductivity plates are situated in the sample and potentially apply to them (usually ac voltage) and after that, the current is measured. By voltage and current values, conductivity can be determined. Constant specific conductivity can be determined to multiply the conductivity by electrode cell. This constant is calculated by the formula as below,

Gt = Gt cal { 1 + a (t - t cal) }
Where Gt is Conductivity at any temperature in °C
G tcal is Conductivity at calibration temperature in °C
a is the Temperature coefficient of the solution
t cal is calibration temperature.

By considering the temperature coefficient of the sample with the modern conductivity meter, this change can be remunerated automatically or manually. For accurate conduct measurement, automatic temperature compensation (ATC) with different temperature sensor is required and the standard and sample must be measured at the same temperature. Conductivity is also used for determining the total dissolved solids (TDS) and salinity.


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Factors affecting conductivity
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