How to manage standard titration solutions

There is no need to add temperature correction when using it, because you have already added temperature correction and burette correction when calibrating its concentration. The shelf life of different solutions is different. The shelf life of hydrochloric acid, sulfuric acid, sodium hydroxide, EDTA potassium permanganate, etc. is two months. Ferrous ammonium sulfate is calibrated once a week, so the shelf life of different solutions is different. When the shelf life has passed, it must be recalibrated. How much waste would it be to discard it and not use it?

How to control the storage environment?: Is there a special room for storing standard solutions? Are temperature correction values ​​added when using air conditioners and dehumidifiers? ： The correction value must be added, because the environment affects the expansion of the buret. How long is the general validity period?: According to different standard solutions, the storage time is different. After the expiration date, should the unused solution be discarded or should it be re-calibrated and continued to be used? According to the situation of the solution, use part A and part B.

For general reagents, such as sulfuric acid and sodium hydroxide, they can be used after recalibration after the expiration date, but some special ones cannot be used and must be prepared again!

In fact, general chemical analysis is not scientific research analysis, and the requirements are not too high. Generally, the validity period of acid is three months, that of alkali is two months, and that of iodine is one month. Some must be prepared for immediate use. If the validity period has passed, it should be recalibrated. The storage conditions are generally light-proof, dry, and ventilated. It would be better if there is air conditioning to keep it at 20 degrees.

Strengthen calibration management. There are two main methods for calibrating standard titration solutions.: GB/T 5009.1-2003 and GB/T 601-2002. Many laboratories like to use GB/T 601. When asked why, they were told that the Technical Supervision Bureau taught GB/T 601 during training, so they used it. However, there are traps in GB/T 601 * * of! ! ! For example, when calibrating the sodium thiosulfate standard titration solution, weigh the reference material potassium dichromate to a mass of about 0.1-0.2g. GB/T 601-2002 stipulates that when the weighing value of the reference substance is less than or equal to 0.5g, it needs to be accurate to 0.01mg. What does this mean? That is to say, you have to use the GB/T 601-2002 standard to calibrate the sodium thiosulfate standard titration solution. When weighing the reference potassium dichromate, you must use an electronic balance with a sensitivity of 0.01 mg (one hundred thousandth balance). Otherwise, it is a deviation from the method and it is a non-compliance. You will be asked to buy the balance back within 2 months! ! ! The price is tens of thousands of yuan for domestic products and more than 100,000 yuan for imported products. It's not over yet. GB/T 601-2002 also requires temperature correction of the burette, and range analysis for single-person four-parallel tests and double-person eight-parallel tests. The deviation requirements are very strict. It is impossible without a 1/100,000 balance. You must buy it. Moreover, this kind of balance also has requirements for the balance platform and ambient temperature and humidity, and also involves environmental monitoring issues. Therefore, I personally suggest that laboratories in the food field should use GB/T 601 with caution and adopt GB/T 5009.1 as much as possible. Although this standard also cites GB/T 601, it partially cites it and does not cite the latter's range analysis and burette temperature correction requirements. To be honest, there is no need for such precision in food analysis. In addition, a friendly reminder that some standards specify that the standard titration solution should be calibrated in accordance with GB/T 601 (such as GB/T 5530), which is difficult to avoid.

We usually calibrate titration solutions prepared with non-standard substances when making samples, unless they are particularly stable solutions such as potassium dichromate.