Physiological saline plays an indispensable role in medical care, scientific experiments, and certain everyday situations. It is a sodium chloride solution with an osmotic pressure essentially equal to that of human blood plasma, maintaining the normal morphology and function of cells. Distilled water, after special treatment, has high purity, making it an ideal raw material for making physiological saline.
Preparing the necessary materials and tools
To make physiological saline, you first need to prepare the appropriate materials and tools. For materials, you will need distilled water and pharmaceutical-grade sodium chloride (what we commonly call table salt, but it must be high-purity pharmaceutical salt; ordinary table salt may contain other additives and is not suitable for making physiological saline). Tools include a precise electronic scale, a clean glass container (preferably sterilized), a stirring rod (which can be made of glass or plastic), a graduated cylinder, and filter paper or a filter membrane for filtration (if higher purity is required). The electronic scale is used to accurately weigh the sodium chloride, the graduated cylinder is used to measure the volume of distilled water, the stirring rod is used to fully dissolve the sodium chloride in the distilled water, the glass container is used to hold and mix the solution, and the filter paper or membrane can further filter out any possible tiny impurities.
Accurately Weigh Sodium Chloride
Physiological saline solution has a specific concentration requirement, generally a 0.9% sodium chloride solution. This means that 100 ml of solution contains 0.9 grams of sodium chloride. Therefore, we need to accurately weigh the sodium chloride based on the total amount of physiological saline solution to be prepared. For example, to prepare 500 ml of physiological saline solution, according to the ratio, the required mass of sodium chloride is 500 × 0.9% = 4.5 grams. When using an electronic scale, first zero it, then carefully pour the pharmaceutical-grade sodium chloride onto weighing paper, gradually adding it until the required weight is reached. Minimize the spillage of sodium chloride during the weighing process to ensure accuracy.
Measure an Appropriate Amount of Distilled Water
After weighing the sodium chloride, the next step is to measure an appropriate amount of distilled water. Again, using the example of preparing 500 ml of physiological saline solution, in addition to the 4.5 grams of sodium chloride, you will need to measure approximately 500 ml but slightly less than 500 ml of distilled water, as the volume of the solution will increase after adding sodium chloride. When measuring distilled water using a graduated cylinder, place the cylinder on a level surface and keep your line of sight level with the lowest point of the concave meniscus of the liquid inside the cylinder. This ensures accurate volume readings. Pour the measured distilled water into a clean glass container prepared earlier.
Dissolving Sodium Chloride
Slowly pour the weighed 4.5 grams of sodium chloride into the glass container containing distilled water, then gently stir with a stirring rod. Be careful to stir gently to avoid creating too many bubbles, and stir in one direction only. This will help the sodium chloride dissolve in the distilled water more quickly and evenly. During stirring, you can observe the sodium chloride gradually disappearing, and the solution becoming clear and transparent. If you find undissolved sodium chloride particles in the solution, continue stirring for a while until completely dissolved. If a small number of particles remain undissolved after stirring for a long time, it may be due to too much sodium chloride or the distilled water being too cold, reducing its solubility. In this case, add a small amount of distilled water and continue stirring.
Adjusting the Solution Volume and Making Up to Volume
After the sodium chloride is completely dissolved, the solution volume may not yet reach the required 500 ml. At this point, using a graduated cylinder or other suitable measuring instrument, distilled water is slowly added to the solution while continuously observing the volume change until the lowest point of the concave meniscus is tangent to the 500 ml mark. This process is called volume adjustment, and the accuracy of volume adjustment directly affects whether the concentration of the physiological saline meets the standard. After volume adjustment, gently stir the solution again to ensure a uniform concentration.
Filtration and Sterilization (Optional)
If higher purity is required for the physiological saline, such as for medical injections, filtration and sterilization can be performed. Filtration can be done using filter paper or a filter membrane, passing the solution through a filtration device to remove any small impurities and undissolved particles. Sterilization can be achieved using high-temperature, high-pressure sterilization. The container containing the physiological saline is sealed and placed in an autoclave, maintained at a specific temperature and pressure for a period of time to kill any microorganisms present in the solution. However, if the distilled water used has already undergone rigorous sterilization and aseptic techniques are strictly followed during the preparation process, this step can be omitted.
Through these steps, we can successfully prepare physiological saline from distilled water. During the preparation process, it is crucial to strictly adhere to the operating procedures and ensure accuracy at every step. This is essential to producing physiological saline solution that meets the required standards and satisfies diverse usage needs. Whether for routine care or scientific experiments, properly prepared physiological saline solution can fulfill its intended purpose.
