Common Reagents Prone to Freezing

**Author:Orginal from Internet

Reagents freezing can pose a range of risks to chromatography experiments and, in severe cases, may lead to laboratory safety issues. So, which common reagents are prone to freezing?

Glacial acetic acid is commonly used to adjust the pH of the mobile phase; however, in winter, it freezes due to low temperatures, which affects the efficiency of our experiments. The freezing point of such reagents is generally above 10°C, or even close to room temperature; consequently, they solidify and freeze when the room temperature drops slightly in winter. Many laboratory staff, having overlooked these characteristics, handle them carelessly, which not only renders the reagents ineffective and causes the bottles to shatter, but may also pose safety risks. Such reagents are commonly found among acids, sulphonic acids and similar compounds.

2. Glacial acetic acid (freezing point 16.6°C): Upon freezing, it forms a white, ice-like solid; its volume expands slightly, which may cause the reagent bottle to burst. When handling, it is recommended to thaw the solution slowly in a water bath at 25–35°C. Tighten the cap to prevent water ingress; the water temperature must not exceed 40°C to avoid evaporation of the glacial acetic acid. Before thawing, gently loosen the cap to release pressure and prevent splashing caused by increased internal pressure. Once completely thawed, shake well before use; freezing does not affect its purity.

3. MSO (dimethyl sulfoxide, freezing point 18.4 °C): It freezes more readily than glacial acetic acid, solidifying at slightly below room temperature (below 18 °C), and takes on a white crystalline form upon freezing. To thaw, use a water bath at approximately 40°C, gently heating until completely transparent and clear; open flames and direct heating in high-temperature ovens are strictly prohibited. DMSO contracts in volume upon freezing but returns to its original volume upon thawing; there is no need to worry about changes in concentration.

4.Formic acid (also known as ant acid, freezing point 8.3°C): Although its freezing point is slightly below 10°C, it tends to freeze easily at room temperature in winter or when stored at 4°C, taking on a viscous consistency when frozen. There is no need to heat it; simply leave it at room temperature (15–25°C) to thaw naturally. Avoid heating it at high temperatures, as this may cause the formic acid to evaporate. Once thawed, shake well before use.

5. Crystalline oxalic acid (hydrated oxalic acid): Although it has an extremely low freezing point, it forms a large number of crystals at low temperatures; whilst this may appear to be freezing, it is in fact the formation of crystals. No heating is required for handling; simply place the reagent bottle in a dry environment at room temperature to allow it to dissolve naturally, taking care to avoid humid conditions which may cause increased crystallisation. Once dissolved, shake well and ensure there are no visible crystalline particles before use.

1.Avoid rapid heating at high temperatures: Direct heating using open flames, high-temperature ovens, boiling water baths, etc., may cause the reagents to evaporate. Furthermore, thermal expansion of the reagents can lead to a sudden rise in internal pressure, resulting in splashing or the shattering of the vial. This risk is particularly high with reagents such as glacial acetic acid and DMSO.

2.Glacial acetic acid and formic acid are commonly used in chromatography experiments as mobile phase additives; high-concentration aqueous solutions can be prepared in advance and simply diluted as required.

3. In HPLC experiments, DMSO is commonly used as a sample solvent; it can be substituted with DMF. Precise temperature-controlled storage: Store high-freezing-point reagents separately in a constant-temperature cabinet maintained at 18–25 °C, strictly controlling the ambient temperature to prevent excessively low room temperatures in winter; clearly label the freezing point of each reagent; strictly prohibit refrigeration or freezing; and display storage temperature reminders to prevent operational errors.