Question

Examples of medications analyzed using each of these analysis methods:(potentiometic titrations) and ( conductometric titrations)....and explain the reasons why certain medications are better analyzed using one of these methods more than the other????

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Answer 1

Conductometric titration :

Conductometric titration is a laboratory method of quantitative analysis used to identify the concentration of a given analyte in a mixture. Conductometric titration involves the continuous addition of a reactant to a reaction mixture and the documentation of the corresponding change in the electrolytic conductivity of the reaction mixture. It can be noted that the electrical conductivity of an electrolytic solution is dependant on the number of free ions in the solution and the charge corresponding to each of these ions.

Conductometric titrations using silver nitrate (AgNO3) as a titrant were used for determination of hydrochloric acid content of ciprofloxacin HCl , propafenone HCl and sotalol HCl , metformin HCl , verapamil HCl , propranolol HCl , mebeverine HCl and diltiazem HCl , where AgCl was precipitated.

Potentiometric titration :

volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function of the added reagent volume. Types of potentiometric titrations for the determination of analytes in photoprocessing solutions include acid-base, redox, precipitation, and complexometric.

Potentiometric titrations are preferred to manual titrations, since they are more accurate and precise. They are also more easily adapted to automation, where automated titration systems can process larger volumes of samples with minimal analyst involvement.A titration curve has a characteristic sigmoid curve. The part of the curve that has the maximum change marks the equivalence point of the titration. The first derivative, ΔE/ΔV, is the slope of the curve, and the endpoint occurs at the volume, V', where ΔE/ΔV has the maximum value.

potentiometric titration are done for medicines such as nimisulide,diphenhydramine hydrochloride,ziprazidone hydrochloride(anti psychotic),captopri(anti-hypertensive drug),ibuprofen etc.

Advantages of the conductometric titration process

• This process is very useful in the titrations of very dilute solutions and weak acids.
• The end-point of this method of titration is very sharp and accurate when compared to a few other titration processes.
• This type of titration is applicable for solutions that are coloured or turbid, and for which the endpoint of the titration with normal indicators cannot be observed easily by the human eye.
• Conductometric titration has numerous applications in acid-base titrations, redox titrations, precipitation titrations, and complex titrations.

Disadvantage of Potentiometric titration

• Typically, up to several hundred milligrams of sample is required for accurate titration of a pharmaceutical compound, depending on its molecular weight and number of titratable functional groups. However, such large amount of material is often difficult to obtain in the early stages of drug discovery and development. There is a need to scale down the titration method with minimal amount of material.
• The primary disadvantage of Potentiometric titrations is that they are highly pH sensitive. Even a small extra addition of the titrant could change the pH drastically. Also, there could be errors while preparing the solutions or any contamination. Even exposure of the electrode to air or other substances before it is dipped into the solution can vary the pH reading.

conductometric end-point detection to be markedly superior to the conventional potentiometric pH electrode based procedure in the case of a monoprotic strong acid –monoprotic strong base titration . Conductometric autotitrations of a hydrochloricacid analyte with a sodium hydroxide titrant showed positive errors of 0.1 % and 0.8% at drop delivery rates of 0.5 and 5 drops per second compared with 4.3% and 19.9% for autotitrations monitored with a pH electrode based on the data.That these large positive errors observed in potentiometric titrations were due to the inherently sluggish response of pH electrodes.