Measurements are carried out with the potentiometric technique, with the measurement of equilibrium potentials of an ion-selective electrode placed into the solution of the analysed ion underlying it. The measurement techniques are applied to natural cow milk as per the GOST Р 52 054−2003, thermo-processed milk as per the GOST Р 52 090−2003.
The milk is analysed for the contents of the following:
1. Contents of sodium ions to detect adulteration with soda in order to reduce the milk acidity.
The average mass concentration of Na+ ions in natural procured raw milk amounts to (50±10) mg/100 cm3. The value of mass concentration above 60 mg/100 cm3 is an indication that the milk is forfeited with soda (for the milk of healthy cows).
2. Contents of ammonia ions to detect adulteration with ammonia hydroxide in order to reduce the milk acidity.
The average mass concentration of ammonia ions in natural procured raw milk amounts to (1.5±0.5)mg/100 cm3. The value of mass concentration above 2 mg/100 cm3 is an indication that the milk is probably adulterated with ammonia hydroxide.
3. Contents of calcium ions. By the contents of calcium ions in milk, we can estimate the thermal stability of milk. The milk being analysed is thermally stable (for the sterilisation temperature +140оС) if the mass concentration of Са2+ ions in it is within the range from 3.0 to 7.0 mg/100 cm3.
The measurements are carried out in accord with the methodologies put forward by the All-Russian Research and Development Institute for Dairy Products named after D.I. Mendeleev Federal State Unitary Enterprise.