What should be noted in blank experiments

What are the influencing factors of high blank content in crude protein determination?

Consider the following aspects:

1. The water used for preparing the solution has not been changed;

2. Check the recovery rate of the digestion furnace;

3. Check the recovery rate of the distiller;

4. Hydrochloric acid is not within its shelf life;

5. Is there a problem with the sulfuric acid used in the solution;

6. Check if the catalyst contains potassium nitrate.

Summary

Blank testing is an important part of laboratory quality control, and its accuracy is crucial for improving the accuracy of detection results. Taking the blank of spectrophotometry as an example, corresponding experimental pure water or organic solvent should be used as a reference, and blank experimental solution should not be used as a reference to avoid artificially reducing the blank value and masking the variation of the blank experimental value.

It is worth noting that laboratories that have passed metrological certification, due to regular calibration of testing instruments and glass measuring instruments, as well as comprehensive quality management measures, if the blank experimental values measured are too large, it is generally due to insufficient chemical purity, deterioration or contamination of the prepared test solution, and other reasons. The test solution should be prepared again, and the batch of samples should be reworked and retested until the blank experimental value is qualified.