The osmometer is divided into: ice point osmometer, dew point osmometer, vapor pressure osmometer, and colloid osmometer. First, determine the type of sample to be tested. Samples that can freeze below 0 point are You can choose the freezing point osmometer, the macromolecular biological sample, you need to choose the vapor pressure osmometer, the colloid osmometer is suitable for measuring the vasodilating force, and the dew point osmometer is mainly used to test the osmotic pressure of the plant leaves.
Then, depending on the sample size of the laboratory, it is decided whether to select a multi-sample or a single-sample model.
The freezing point osmometer is also called: molar concentration osmometer, molar concentration meter, osmolality meter, crystal osmometer, ice point osmometer, etc., which is currently the most widely used.
For the freezing point osmometer, the way of inducing crystallization is related to the stability of the measurement, and it must be ignored when selecting. According to the "2010 Pharmacopoeia" regulations, there are two ways to induce solution crystallization by the freezing point osmometer, which is the oscillation method and the metal probe method (generally called the secondary needle method). The difference between the two is:
- The osmometer measurement results of the oscillating method induced crystallization are relatively reliable and stable. This technique of inducing crystallization only contacts the sample with a thermal probe, and the component that induces crystallization of the solution does not come into contact with the sample, thereby eliminating the possibility of cross-contamination of the sample, so the test result is relatively more stable. The best oscillating method to induce crystallization of the freezing point osmometer is the freezing point osmometer of Advanced Instrument of the United States and YASN of the United Kingdom.
- An osmometer for crystallization induced by a secondary needle . The secondary needle-induced crystallization is characterized in that the metal probe or the secondary needle is introduced into the sample each time during the test to induce solution crystallization. When choosing such brands, it is also necessary to consider the problem of cross-contamination of samples, so the most important thing is whether the secondary needles that induce crystallization are easy to wipe to reduce the possibility of cross-contamination. Some manufacturers hide the secondary needles, which is inconvenient to wipe. After using the instrument for a period of time, the parallelism of the test results will be worse.
In addition to the above-mentioned key technical factors affecting measurement accuracy and repeatability, another factor that cannot be ignored is the cost of consumables. Common consumables for osmometer include: calibration solution and sample cup.
The sample cup of a small sample size (2.5ml) osmometer is made of glass, and it can be reused for full cleaning. Most osmometers have a sample volume of between (25 ul and 100 ul) and the sample cup is a disposable plastic tube. Most manufacturers require the use of a dedicated sample cup supplied by the original manufacturer. Then, before purchasing the host, you must ask the unit price of the sample cup to avoid the problem that the use cost of the sample tube is too high after the purchase. It is recommended to choose an open sample cup as much as possible.
Calibrators are also commonly used consumables. To ensure the accuracy and repeatability of the instrument, all manufacturers recommend periodic calibration of the instrument with the specified calibration solution. The price of the calibration solution should also be determined before purchasing the host for the same reason.
Another important component is the sample probe for measurement. Sample probes are not a common consumable and come standard with only one. The probe is the core component and is expensive. There are two types of sample probes used in current osmometers: one is made of glass and the other is made of stainless steel (such as Osmolab One from YASN, UK). The manufacturer of the glass probe requires that the action be gentle and avoid touching the damaged probe. The stainless steel probe is much easier and can be safely wiped, which avoids the problem of leaving the sample and improves the measurement repeatability. From the standpoint of durability, the two probes are judged high. Therefore, don't forget to ask your supplier when purchasing, what kind of material is the probe of the osmometer?
In addition, it is necessary to consider factors other than products, such as the after-sales service of the supplier, the warranty period of the product, etc. It is also important to know in advance that there is no harm in advance.
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