Aquametry

Abdullah Al NomanDaffodil International

University.Bangladesh.

Aquametry

AQUAMETRY AQUA- means water METRY- means measurement

Aquametry is a analytical process to measure the water present in any product.

Determining micro quantities of water by the use of Karl Fischer Reagent by the application of current is known as aquametry. It is also been known as amperometry.

Importance of water determination

Quantitative determination of water is important because many drugs contain water:

As a solventAs absorbed waterAs water of crystallizationAs an adulterant

Physical properties of a drug or a raw material are modified by its water content. Pharmaceutical procedures of granulation, tablet formation & coating operations are affected by water content.

Methods of Water Determination

Methods of Water determination can be oftwo types

1. Thermal Methods:

Loss on drying

Azeotropic Distillation Method

2. Chemical Methods:

Karl Fischer Titration

Importance of aquametry

1.Quantitative Determination of Water in pharmaceutical products is important.because H2O may be present in the products as – Solvent Absorbed water. water of Crystallization

2.This is important, because – Physical properties of a drug or raw material is modified by the presence of H2O

3. Physical stability of the product may be hampered in presence of water. So , we should determine whether it possesses water or not.

4. Water content of drugs may also be important for other reasons i.e- when crude drugs

The principle of Karl Fischer titration

Fundamental Reaction The fundamental principle behind the Karl Fischer Titration is based on the Bunsen reaction between iodine and sulphur dioxide in an aqueous medium shown below:

I2+ SO2+2H2O → 2HI+ H2SO4

Karl Fischer discovered that this reaction could be modified to be used for the determination of water in a non-aqueous system containing an excess of sulphurdioxide. He used a primary alcohol (methanol) as the solvent, and a base (pyridine) as the buffering agent. So the reaction changed into

py. I2+ py ·SO2+H2O+ py → 2py ·HI+ py ·SO3

Preparation of Karl Fischer titration

Into a glass- stoppered flask (about 750 ml capacity) anhydrous methanol (400 ml,containing not more than .03% water ) is placed and pure dry pyridine(80 g) is taken.

Flask is immersed in a freezing mixture and slowly sulphur dioxide is passed into the cold solution , with continuous agitation, until the increase in weight is 20 g .

Finally iodine is added (45 g) , and shaked well to dissolve and the mixture is allowed to stand for 24 hr before use.

Advantages of Karl Fischer Titration

Karl Fischer Titration Method is very popular for a large practical advantage which it holds over other moisture determination technique,

These includesEasy Sample PreparationHigh Accuracy and PrecisionIndependence of presence any volatile materialsNearly Unlimited Measuring RangeShort Analysis DurationSmall Sample Quantities requiredSuitability for analysing-

SolidsLiquidsGases

Application

Soil quality: The appearance of large information banks on soil properties in Europe was provoked by necessity of increasing of agricultural production economics, i.e. the commercial price of soil as the production medium.

Quality of food materials and products: Moisture content affects food quality, i.e. texture, taste, appearance and stability of foods depends on the amount of water they contain. A knowledge of the moisture content is often necessary to predict the behavior of foods during processing, e.g. mixing, drying, transportation, flow through a pipe or packaging, storage stability or shelf-life