Pharmaceutical Analysis
2nd sessional important questions
Pharmaceutical analysis is primarily concerned with the determination of active ingredients, contaminants, excipients, content homogeneity, solubility, dissolving rate, and stability in drugs, raw materials, and pharmaceutical formulations.
Only if the wavelength employed is not interfered with by other species may direct analysis of target chemicals be performed. Derivative spectrophotometry, chemometrics, or a chemical derivative obtained through reactions such as redox, ion pairing, metal ion chelation, azo dye derivatization, Schiff base creation, and charge transfer complex synthesis can all be used to analyse mixtures of components.
Important questions
Question - Definition of Gravimetry and principle ?
Answer - gravimetric analysis is method of quantitative determination of an analyte based on the mass of a solid the quantitative determination of a substance by precipitation followed by isolation and weighting of the precipitate is called gravimetric analysis.
Principle -- the principle of gravimetric analysis is based upon the isolation of compound from solution by precipitation method and determination of mass of that compound after drying it it is quantitative method of analysis . First of all the census is precipitated then it is washed to remove impurities with a suitable solvent ,filtered ,dried and finally determined the mass of that compound by weighing method.
Question - define Redox Reaction
Answer - Redox tiration --- redox titration is based on the redox reaction between analyte and titrant in oxidation reduction method of titration or reducing substances titrated with a standard solution of an oxidizing agent or an oxidizing substances titrated with a standard solution of a reducing agent .
E=E°+2.303RT/nF . log10 [OX]/[red]
Question - define conductometry and its principle ?
Answer - Conductometry is the simplest of the electro analytical techniques found by kolthoff in 1929. Conductivity is the ability of the medium to carry electric current according to ohm's law the voltage set up across the solution is proportional to the flowing current
G=1/R
Principle - in the conductometric titration during the course of titration the conductivity of solution changes due to difference in ionic conductivity of science one iron is replaced by another ion that result in difference in conductivity by plotting the graph of the change in conductance as a function of the volume of tyrant added endpoint is detected.
Question - Define Iodometry and its principle
Answer - Iodometric and iodimetric titration is redox type of titeration where the iodine is liberated it is indirect titration
Principle - iodometry is commonly used to analyse the concentration of the oxidizing agent in water sample to a known volume of sample and access but known amount of iodide is added which the the oxidizing agent oxidise the iodide to iodine iodine dissolve in the iodide solution to give brown colour tri iodide ions this solution is further against standard thiosulphate solution by using starch indicator to give iodide starch indicator is used because it can absorb treated iodine and change the colour of solution from yellow to dark blue.
Question - Define Complexometry titration and its principle ?
Answer - Simple metal iron is transformed into a complex ion is known as complexometric titration this technique metal ions are titrating with the complexing agent or chelating agent equivalence point is determined by using metal indicator for electro metrically complexometric titration is also known as silver metric titration ethylene diamine tetra acetic acid EDTA is known as complexing agent complexing agent react with metal ions to form a complex known as chelate.
Principle - the principle of complexometric titration is based on acid base titration in complexometric titration the free metal ions form a complex with ligand like acid base titration metal ion act as Lewis acid as it accept electron from the ligand and ligand act as a Lewis base .
Question - Define Oxidation , Reduction , Oxidising agent and Reducing Agent ?
Answer - Oxidation - oxidation is the process in which oxygen is gained by a substance for example magnesium is oxidised when it react with oxygen to form magnesium oxide
2Mg + O2 -> 2MgO
In other terms oxidation is loss of electrons for example sodium losses electron after oxidation positive charge represent electron deficiency.
Na -> Na+ + e-
Reduction --- reduction is the process in which oxygen is lost by a substance for example copper oxide can be reduced to form copper if it is reacted with hydrogen.
CuO + H2 -> Cu + H²O
Another term for reduction is the gain of electrons
Cu2+ + 2e- -> Cu
Oxidizing agent -----an oxidizing agent is a substance that oxidizes other substance and it get reduced . Common oxidizing agents are oxygen ,potassium permanganate ,sodium peroxide etc .
Reducing Agent ----- a reducing agent is a substance of oxidation reduction reaction which reduces the other substances by giving out electrons to the substance and its itself get oxidized . For example the reducing agents are generally sodium oxalate ferrous sulfate etc .
Question - write about Indicators ?
Answer - Indicator is a substance which is used to determine the endpoint of the reaction .
Types of Indicators
1 . Acid base indicators - acid base indicators are the substances which show colour changes of solution as the pH of solution varies they are usually weak acid or bases .
Theories of acid base indicators
1 . Ostwald's theory
According to ostwald's theory the colour change of any indicator is due to its ionization . the unionized form of indicator has different colour then it ionized form.
Phenolphthalein -phenolphthalein is a colourless weak acid but after dissociation in water gives pink colour Anions . under the acidic condition the concentration of anion is less hence it is colorless while under alkaline condition concentration of the anion is more to produce pink colour .
Methyl orange - it is a very weak base and can be represented as MeOH .it is ionized in solution to give Me+ and OH- ions, methyl orange gives red colour in acidic medium and yellow colour in basic medium .
2 .. Quinonoid Theory
According to quinonoid theory acid base indicators exist in two tautomeric form having the different structure which are in equilibrium .
One form is benzenoid form and the other is Quinonoid form, in acidic medium phenolphthalein exist in benzenoid form and in the basic medium it form quinonoid structure which has pink colour in acidic solution methyl orange gives quinonoid form having the red colour and benzenoid form in alkaline solution which has yellow colour .
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| Quinonoid form and benzenoid form |
3. Indicator range -- at a low pH of weak acid indicator is present in the undissociated form and the solution has the colour of undissociated form of weak acid as the pH increases the dissociation take place and concern of increases therefore the intensity of the colour of the indicator increases as the ideal indicator is one which shows the distant colour change over a low pH range .
Indicator are the substances which show colour change after completion of chemical reaction there are used in acid base titration .
2 ... Redox indicators -- Redox indicator which is used in the redox titration a Redox indicator has a different colour in different oxidation state that is it has one colour in oxidising medium and one different colour in oxidising and reducing form .
Type of visual indicator are used in redox titration
1. Self indicator
2. Internal indicator
3. External indicator
Question - Define potentiometry and the principle ?
Answer - it consists of measuring the potential or EMF of a solution using a set of indicator and reference electrons .
The potential of solution depends upon the nature and concentration of ion of the drug substances the potential is measured in mV using the potentiometer which have an indicator and reference electrode .
Indicator electrode - indicator electrode respond to the changes in the EMF or the pH of a solution most commonly indicator is used is glass electrode
Reference electrode - reference electrode is one which has a standard potential on its own and its potential does not change to which ever solution it is dipped into.
Example - saturated calomel electrode .
Principle -- When the pair of electrodes are placed in the sample solution or analyte it shows the potential difference between two electrodes by addition of the titrant or by the change in the concentration of ions.
Question - Define diazotization with its principle and mechanism .
Answer -The principle of diazotization titration is based upon the reaction between primary aromatic amine present in the sample and the sodium nitrate in the presence of acid such as hydrochloric acid to obtain a diazonium salt . Sodium nitrite and acid is added to the solution of amine at 0-5 degree Celsius . The amine react with nitrous acid to form nitrosamine which is followed by tautomerization and the water molecule is lost to form the diazonium ion
Mechanism of reaction
Step 1 - when sodium nitrate is reacted with the hydrochloric acid sodium chloride and nitrous acid are formed .
NaNO2 + HCl -> NaCl + HNO2
Step 2 --- the obtained nitrous acid is reacted with the primary aromatic amine to form the diazonium salt . The excess of nitrous acid is removed by the addition of ammonium sulfamate solution .
R - NH2 + HNO2 -> R - N = NH + H20
Question - Define Redox titration with nernst equation and indicator used in redox titration .
Answer - Redox titration is based on the Redox reaction between analyte and titrant in oxidation reduction method of titration a reducing substance is titrated with a standard solution of an oxidizing agent or an oxidizing substance is titrated with a standard solution of a reducing agent.
For such a system of the most equation take place the form where E is the formal potential at the specified concentration.
n is the number of electrons involved in the half reaction.
R is the gas constant 8.314 J mol-1K-1
T is the absolute temperature
F is the Faraday constant 96500 c
E° is the standard electrode potential and is characteristic of a particular system.
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| Nernst equation |
The solution potential can be calculated if we know the concentration of the two forms also knowing the chemical reaction involved and the potential of the solution we can use nernst equation to evaluate the relative concentration of oxidized and reduced
form.
Redox indicators -- Redox indicator which is used in the redox titration a Redox indicator has a different colour in different oxidation state that is it has one colour in oxidising medium and one different colour in oxidising and reducing form .
Type of visual indicator are used in redox titration
1. Self indicator
2. Internal indicator
3. External indicator
Self indicator ----- in permanganatometric titration potassium permanganate changes colour at the endpoint and is called self indicator.
External indicator ------these indicators are not added internally to the reaction medium but are used externally as in the form of small droplets on white tile for example potassium ferricyanide is used as an external indicator in the chromatometry
Internal indicator ------ internal indicators are the substances which are added in the flask in case of chromatometry the indicators such as 1% di phenylamine is added in reaction mixture such indicator are called internal indicator .
Types of redox titration
1 . Permanganate titration - a large number of reducing agent may be determined directly by titration with standard potassium permanganate and many oxidizing agents may be determined indirectly .
2 . Cerimetry titration - it is also called cerimetric titration or cerate oximetry it is volumetric method of analysis Ferroin is used as an indicator and the cerium sulphate is used as standard solution .
3 . Dichromate titration - potassium dichromate is a primary standard in the estimation of ferrous iron, potassium ferricyanide is used as external indicator the estimation is based on the oxidation of ferrous ions to ferric iron by potassium dichromate in acidic medium .
4 . Iodometry - iodometry is a Redox type of titration where the iodine is liberated it is in direct titration
5 . Bromatometry - potassium bromate is primary standard oxidizing agent used in redox titration mixture of potassium bromate and potassium bromide in sulphuric acid is used in back titration of organic compound bromine is released in the reaction solution is back titrated with sodium thiosulfate by using starch as the indicator .
Question - What is Conductivity cell ?
Answer - conductivity measuring the cell consists of an electrode pair voltage is applied across these two electrode the metre measure the flowing current and calculate the conductivity .
When a direct current is applied to the electrodes the positively charged ions migrate to the negatively charged electrode analogous to this the negatively charged ions move in the inverse direction to the positively charged and this can lead to accumulation of ions near the electrode surface and 2 the chemical reactions. This electrolysis affect the composition of the solution and therefore also the conductivity to prevent the undesirable electrolysis reaction alternating current is used for the conductivity measurement with the alternating current the ions do not migrate in one direction they oscillate with the rhythm of the applied frequency about their position.
Question - Define Polarography and its principle ?
Answer - polarography is an electrochemical method of analysis polarography involves the measurement of current voltage cause when the voltage is applied to the electrode in most in the solution dropping Mercury electrode is used as indicator electrode consisting of a Mercury drop hanging at the orifice of a fine for glass capillary Mercury flows through the capillary from the Mercury reservoir at the rate of a few mg per second the lifetime of each drop is usually 3 to 5 second . Each drop form a new electrode, its surface is practically unaffected by processes take places on the previous drop hence each drop represented well reproductive electrode with the fresh clean surface the second electrode is a reference electrode its potential remain constant during the Measurement the potential at the indicator electrode varies in the course of measurement of the current voltage curve because of the damage of the applied voltage.
Question - Types of electrodes in potentiometry
Answer - types of electrodes
1 . Reference electrode
a) Normal Hydrogen Electrode (NHE)
--- It is fundamental electrode and is used as standard in the pH measurement, it can be used over wide pH range it exhibits no salt error .
b) the silver / silver chloride reference electrode
--- the silver silver chloride electrode is a reference electrode of the second kind where the metal is in the contact with the slightly soluble salt containing the metal which into an is in contact with the solution containing the common anion the ions in the solid paste and those in the liquid phase are in equilibrium .
c) calomel electrode -- calomal electrode is the mercury mercurous chloride electrode the potential of the caramel electrode on the hydrogen scale has been found to vary with the concentration of potassium chloride solution used the reduction potential for the various KCL concentration at 25 degree Celsius
Indicator electrodes
a) glass electrode -- this is very useful electrode for determination of hydrogen ions or the pH of solution it involve no electronic change but allow transfer of h ion through its membrane.
b) metal indicator electrode--metal indicator electrode are the system that use specific metal electrode as the indicator electrode in an electrochemical measurement .
Question- discuss the construction of silver/silver chloride reference electrode ?
Answer - construction - the electrode assembly consists of silver metal electrode in the contact with the solid silver chloride immersed in an Aqueous chloride salt solution saturated with silver chloride all these are contained in a small vessel quickly made up of glass tubing a typically separator is small porous ceramic plug sealed into the end of the glass tubing .
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