The dilute solution has the following dependency: the vapor pressure of the solution decreases, the boiling point of the solution increases, and the freezing point of the solution decreases. Measuring any of these properties can indirectly obtain osmotic pressure. However, among these measurement methods, only the vapor pressure does not need to change the image shape of the solution. Adding a non-electrolytic non-electrolyte solutes to the water to make a dilute solution (≤0.2mol•Kg-1). At this time, part of the liquid surface occupied by the pure water molecules is occupied by the solute molecules, and the solute molecules It hardly volatilizes, so the number of water molecules that escape from the surface per unit time is reduced. When the evaporation and condensation reach equilibrium again, the vapor pressure of the solution is lower than the vapor pressure of the pure water at the same temperature, that is, the vapor pressure of the solution decreases. The Raoult FM law shows that at a certain temperature, the vapor pressure drop of the non-volatile non-electrolyte dilute solution is proportional to the mass molar concentration of the solution, regardless of the type and nature of the solute.
According to this principle, located in the US state of Ultah Wescor company in 1973 to design and manufacture the world's first osmotic pressure dew point instrument, bring revolutionary progress from the measurement volume molar concentration (Osmolarity) of.
How the VAPRO® osmometer works and steps:
Step 1: After the sample is placed, the temperature and vapor pressure are naturally balanced in the closed vaporization chamber. The thermocouple senses the exact temperature of the vapor above the sample, and the microprocessor sets the temperature to 0 degrees, or the measured reference temperature. ( TA )
Step 2: Then, the thermocouple is cooled down to the dew point ( TD ) with Peltier refrigeration , and the water droplets begin to condense on the surface of the thermocouple.
Step 3: The microprocessor allows the condensed water to control the temperature of the thermocouple. The heat released by the condensation of water raises the temperature of the thermocouple, and finally stops coagulation at a certain temperature. This steady state can be reached one minute after the sample is placed.
The fourth step: the stable temperature is the dew point temperature ( TD ). At a resolution of 0.0003 degrees Celsius, the final instrument displays a reading that is proportional to the dew point temperature reduction. Because the dew point temperature drop is a function of vapor pressure, the instrument can be calibrated and the measurement results directly show the world-wide osmolality unit (mmol / kg).
working principle:
The dew point osmometer measures the dew point temperature of the substance to be tested through the thermocouple head, and obtains the vapor pressure value through a functional relationship. By calibration, it can be displayed as the concentration unit of the osmometer (mmol/kg).
application:
The osmotic pressure of the cell culture fluid is measured, and the osmotic pressure of the plant leaf or the tissue and plant tissue section is measured.
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