Pharmaceutical Analysis Question Bank

Pharmaceutical Analysis Question Bank

QUESTIONS & ANSWERS BANK

PHARMACEUTICAL ANALYSIS(B.PHARMA)

1. Explain ways to minimize the errors.

Ans: determinate errors can often be reduced by one of the following methods

a. Calibration of apparatus and application of corrections.

all instruments ( weights, flasks, burettes, pipettes, etc) should be calibrated and the appropriate corrections applied to the original measurements.

b. Running a blank determination

consists of carrying out a separate determination of the sample being omitted. the object is to find out impurities or to determine the excess of standard solution necessary to establish an endpoint. a large blank correction is undesirable.

c. Running a control determination

this consists of carrying out a determination under as nearly as possible identical experimental conditions upon the quantity of standard substance which contains the same weight of the constituents as is contained in the unknown sample.

the weight of the constituent in the unknown can then be calculated from the relation

Result found for standard/ Result found for unknown= weight of the constituent in standard/x

where,

x is the weight of the constituent in unknown

d. Use of the independent method of analysis

in some instances the accuracy of the result may be established by carrying out the analysis in an entirely different manner.

e. Running of parallel determinations.

these serve as a check on the result of a single determination and indicate only the precision of the analysis. the values obtained for constituents that are present in not too small an amount should not vary among themselves by more than three parts per thousand. if larger variations are shown, a determination must be repeated until satisfactory concordance is obtained.

f. Standard addition

A known amount of constituent being determined is added to the sample which is then analyzed for the total amount of constituent present. the method is usually applied to Physico-chemical procedures such as polarography and spectrophotometry.

g. Internal standard

This procedure is of particular value in spectroscopic and chromatographic determination. it involves adding a fixed amount of reference material to series of known concentrations of the material to be measured.

Pharmaceutical analysis Question bank

h. Amplification methods

Determination in which a very small amount of material is to be measured may be beyond the limits of the apparatus available. the amplification of quantity may then be within the scope of apparatus or method available.

i. Isotopic dilution

A known amount of elements being determined containing radioactive isotope is mixed and the element is isolated in pure form which is weighed or otherwise obtained.

2. Distinguish between Accuracy and Precision

Accuracy

  1. the accuracy of a determination may be defined as the concordance between the data and true or most probable value
  2. accuracy is the agreement between the data and true value
  3. it is usually expressed in terms of errors.
  4. accuracy expresses correctness of measurement
  5. it is based on single-factor
  6. it focuses on systemic error

Precision

  1. precision may be defined as the concordance of series of measurements of the same quantity
  2. precision is a measure of agreement among values in a group of data
  3. it is usually reported as average deviation standard deviation or range
  4. precision expresses the reproducibility of measurements
  5. it is based on more than one factors
  6. it focuses on random errors.

3. Distinguish between Absolute and Relative errors.

Absolute error

  1. the difference between the mean and true value is known as the absolute error

Relative error

  1. the relative error is found by dividing the absolute error by the true value
Pharmaceutical analysis Question bank

4.What is a significant figure? give example

Ans:  A significant figure is a digit that denotes the amount of quantity in the place in which it stands. the digit zero is a significant figure except when it is the first figure in the number.

example

thus in quantities 1.2680gm and 1.0062gm, the zero is significant, but in quantity 0.0025kg the zeros are not significant figures; they serve only to locate the decimal point and can be omitted using the proper choice of units.

e,g. 2.5gm the first two numbers contain five significant figures, but 0.0025 contains only two significant figures.

2. in the case of number 4  3 2 the figures signify that there were 4 hundred 3 tens and 2 units and are therefore all significant.

5. Explain the significance of quantitative analysis in quality control.

Ans: quantitative analysis is of enormous importance in science and industry.

for example, the chemical formula of an unknown substance is found from the percentage contents of its constituents found by analysis.

chemical analysis is the most important method of investigation and is widely used in all branches of science which are related to chemistry.

quantitative analysis means the estimation of an active constituent from the sample.

it is otherwise called by term assay by which we can determine the purity of the sample from its constituents.

modern medicines for human use are required to meet exact standards which relate to their quantity, safety, and efficacy.

the evaluation of safety and efficacy and their maintenance in practice is dependant upon the existence of adequate methods for quantity control of the product.

Pharmaceutical analysis Question bank

Gravimetric analysis

Questions and answers

1.Define electrogravimetry and state equation of ohms law.

Ans:- Electrogravimetry is the electroanalytical method based on the electrolysis of an analyte.

the equation of ohm’s law-     I= E/R OR E=IR

where I= current in amperes

E= potential difference in volts

R=resistance in ohms.

 

2. Define a) solute b) solvents

Ans:-

a) it is a dissolved substance

b) it is a component in which the solute is dissolved.

Pharmaceutical analysis Question bank

3. Write a note on the partition coefficient.

Ans:- If two solvents are in contact with each other and a solute in both solvents is added to it, then that substance will distribute itself in both solvents in such a way that the ratio of the concentration of two solutions remains constant, this is called as distribution coefficient or partition coefficient.

4. Explain the theory of electrogravimetry.

Ans:- electrogravimetry is the electroanalytical method based on the electrolysis of an analyte. electrogravimetry is mainly used for the gravimetric determination of metals.

an electrochemical cell consists of two electrodes immersed in one or more solutions. A cell may be a galvanic ( voltaic) cell or electrolytic cell.

Galvanic cell:- such cells give electrical energy to the external system.

Electrolytic cell:- in such cells electrical energy is supplied from an external source to the cell.

Back potential:- during electro-gravimetric operation a galvanic cell is formed as the products form on the electrodes.

when the current is switched off, the products tend to produce a current in a direction opposite to the electrolysis current.

Cathode:- it is the electrode of which reduction occurs. in an electrolytic cell, it is connected to the negative terminal while in a galvanic cell it is connected to the positive terminal.

Anode:-it is the electrode at which oxidation occurs. it is the positive terminal of an electrolysis cell or the negative terminal of a galvanic cell.

Polarisation:- polarisation is an electrode phenomenon that may affect either or both of the electrode in a cell. the degree of polarisation varies widely and will be influenced by;

1.size, shape, and composition of electrodes.

2.the composition of the electrolytic solution.

3.the temperature and stirring rate.

4.the current level.

5.the physical state of the species involved in the cell.

Concentration polarization:- electron transfer between a reactive species in a solution and electrode can take place only from a thin film of solution located immediately adjacent to the electrode surface.

reactants are transported to the surface of an electrode by three mechanisms:-

a) Diffusion: diffusion occurs when there is a concentration difference between two regions of a solution. in this process, the ions or molecules move from the more concentrated region to the dilute region.

b)Migration: migration is a process in which ions or molecules move under the influence of an electric field. rate of migration of ions increases as the electrode potential increases.

c) Convection: convection is the mechanism of transport of ions or molecules through a solution as a result of stirring, vibration, or temperature gradient.

d) Kinetic polarisation: in kinetic polarisation the magnitude of the current is governed by the rate of electron transfer between the reactants and the electrode rather than the mass transfer.

5.Explain types of extraction.

Ans:        the extraction method using extracting liquid can be classified into two categories:

a.Solid-liquid extraction & b. liquid-liquid extraction

in both these types of various devices is adopted for the complete separation of one or more active constituents from a given mixture. these methods are given as :

a. Solid-liquid extraction:– in the solid-liquid extraction method, the separation, and isolation of the desired constituent is based upon the solubility phenomena. extracting solvents is chosen which will have the highest solubilizing power for the desired constituent. since active material present in solid is extracted out by using liquid phase it is called solid-liquid extraction. now for achieving extraction different techniques are adopted.

Pharmaceutical analysis Question bank

a)Maceration

b)Percolation

c)Continuous percolation

d)Soxhlet extraction

these methods are most widely adopted for isolation and separation of active constituents from crude drug or crude drug preparation.

b.liquid-liquid extraction:– solvents extraction technique is basically a liquid-liquid extraction method in which a solution (usually aqueous) is brought in contact with another solvent(usually organic) essentially immiscible with each other by extraction and separation of phases one or more solutes are transferred into the second solvent. the separation is generally effected using separating funnels and bringing two to three extractions with a fresh charge of extracting solvents. the separation by this method is simple, rapid, and quantitative.

The liquid-liquid extraction method is based on Nernst law which states that ” the ratio of activities of a solute material in a pair of two immiscible liquids at equilibrium is a constant” according to this law if two solvents are in contact with each other and a solute or a substance that is soluble in both solvents is added to it. then that substance will distribute itself in both solvents in such a way that the ratio of the concentration of two solutions remains constant. this is called as distribution coefficient or partition coefficient. thus, according to the law, C1/C2=K

where

c= reference to concentrations 1 and 2 refer to the different solvents and k as distribution coefficient.

6. Explain the theory of liquid-liquid extraction.

Ans:     Solvents technique of extraction is basically liquid-liquid extraction method in which a solution ( usually aqueous) is brought in contact with another solvent(usually organic) essentially immiscible with each other by extraction and separation of phases one or more solutes are transferred into the second solvent. the separation is generally effected using separating funnels and bringing two to three extractions with a fresh charge of extracting solvents. the separation by this method is simple, rapid, and quantitative.

the liquid-liquid extraction method is based on Nernst law which states that ” the ratio of activities of a solute material in a pair of two immiscible liquids at equilibrium is a constant” according to this law if two solvents are in contact with each other and a solute or a substance that is soluble in both solvents is added to it. then that substance will distribute itself in both solvents in such a way that the ratio of the concentration of two solutions remains constant. this is called as distribution coefficient or partition coefficient. thus, according to the law,

C1/C2=K

where  C1= concentration of the first solvent

C2=concentration of the second solvent

K=partition or distriution constant

C1 & C2 can be replaced by Cu & Cl which refers to concentration in the upper and lower phase

accordingly,    Cu/Cl=K

IF we consider P as a fraction of solution upper phase & Q as a fraction of the same solute in lower phase, then P can be calculated as,

P= amount present in upper phase/ total amount of solute

P= Cu × V2

the total amount of solute= CuVu+ClVl

7.describe the applications of electrogravimetry

ans: applications of electrogravimetry:

  1. Electrogravimetry is limited to the separation of easily reduced cations.
  2. It is used in the analysis of electrolytic analytical solutions.
  3. For deposition of electronegative metals more electropositive metals must be absent.
  4. Quantitative electrodeposition of analytical samples typically takes an hour to an hour.
  5. At the completion of electrolysis, to prevent the metal from spontaneously going back into the solution, the electrode is removed from the solution.

 

Pharmaceutical analysis Question bank

Diazotization titration