First, what is osmotic pressure?
The semipermeable membrane is separated, one of which is the solvent water, and the other is the solution, and the water permeates through the semipermeable membrane to the solution side. The pressure applied to the solution side to prevent the movement of water is called the osmotic pressure. The reason why the movement of water stops is that the pressure is equal to the chemical potential energy of the water passing through the membrane. The solution osmotic pressure П of the molar concentration Cs is approximately П = CsRT (R: gas constant, T: temperature). If the molar concentration is used, a larger measured value than the theoretical value can be obtained. There is a relationship between the plant cells with well-developed liquid cells and the cell volume V.
However, in cells with many cytoplasms such as animals, the cell volume of the inactive part (non-aqueous phase) is subtracted from V. The above formula is also established. In plant cells, cytoplasm and cell fluid maintain osmotic pressure balance. The osmotic pressure of the cytosol limits the water content of the cytoplasm and affects the physicochemical properties such as cytoplasmic viscosity. In addition, osmotic pressure can also cause expansion pressure to regulate cell growth and expansion. The cells have the effect of regulating the osmotic pressure, which is called osmoregulation. As with animal body fluids, the osmotic pressure of the internal environment of the impregnated tissue also has a large physiological impact. The osmotic pressure can be expressed by air pressure, freezing point osmometer drop (?) or osmolality.
Second, how to choose osmometer?
1. The freezing point osmometer is measured by the principle of freezing point and low pressure. The test results are good in repeatability and linear. Freezing point low pressure technology is the accepted standard for osmometer production in most laboratories in the world.
The dew point osmometer uses the principle of boiling point rise, and the water vapor pressure technology heats the solution to evaporate it to measure the osmotic pressure of the sample. Compared with the freezing point osmometer, the test result is not as accurate as the freezing point and the repeatability is also poor.
2. Freezing point osmometer test probe Wipe cleaning is simple and convenient, requires little maintenance, and has a long service life. Under normal use, zui can be used for ten years or longer.
The dew point osmometer is a vapor-sensing measurement produced by evaporation of a sample of a thermocouple condensation solution. The thermocouple needs to be cleaned after every 100 samples tested. The instrument has a large maintenance workload and high maintenance costs. Since the thermocouple is inside the instrument, the instrument needs to be disassembled during cleaning, and the thermocouple is easily broken and needs to be replaced frequently.
3. The freezing point osmometer uses semiconductor refrigeration, and the physical properties of the semiconductor itself do not require routine maintenance, and the life is long.
The dew point osmometer is heated by electric heating wire, and its service life and accuracy are lower than that of the freezing point osmometer.
4. The freezing point osmometer design is mainly used in clinical research and detection of life-related fluids such as body fluids, blood and urine in mammals. It has been recognized by many clinical researchers and drug researchers.
The dew point osmometer is mainly used for ecological research and is suitable for plants and invertebrates.
The dew point osmometer cannot be used to detect samples of volatile solutions such as ethanol and ether, especially those that are easily decomposed by heat, and the freezing point osmometer can.
5. The freezing point osmometer is easy to operate, requires no routine maintenance, and has a long calibration cycle.
The dew point osmometer needs to be calibrated frequently.
