Aquametry (from lat. aqua - water and Greek. metreo - measure, define a set of methods for determination of water in various biological materials. The fastest and most accurate is the volume of the analytical method for the determination of water by titration with Fischer reagent (a mixture of iodine, sulphur dioxide and pyridine, dissolved in methyl alcohol), vigorously absorbing water
(2H2O + SO2 + J2 = H2SO4 + 2HJ).
The reaction products (sulphuric acid and hydrogen iodide) contact pyridine. Under the charge of reagent calculate the water content of the sample. The end of titration determined by a colour change - from Canary yellow to reddish-brown coloring of iodine). In stained samples the end of titration determined by Electrometry.
For preparation of 1 l of reagent Fisher dissolve in a bottle with a glass stopper 84,7 g of iodine in 269 ml dry pyridine. The solution adds 667 ml dry methyl alcohol, the mixture is cooled with ice, then it carefully pour 45 ml of liquid (pre condensed in a calibrated vessel) sulphurous anhydride. The flask is closed, and the mixture is shaken, until it becomes homogeneous. Opening for a moment tube, equalize the pressure in the bottle with atmospheric and maintain reagent 1-2 days.
Before each use, check the title of reagent Fisher standard solution of water. To do this in measuring liter flask accurately weighed 15 ml of distilled water and add dry methyl alcohol to the mark. Solution store in a dark place. When defining title Fischer reagent 10 ml of standard solution of water is placed in a flask with a glass stopper, 250 ml and titrated reagent Fischer until a steady painting of iodine.
Determination of water can be produced in gaseous, liquid and solid organic and inorganic samples, for which they dissolve (or mixed) in the dry methyl alcohol or pyridine; solid sample is then ground.