Is there a significant difference in purity between domestic and imported ammonium sulfate for protein precipitation?

We have suffered losses during protein salting out, and the problem is not entirely due to imports or domestic production, but rather the instability of the batch provided by the supplier. Currently, Sigma or Sinopharm's premium grade purity is used regularly. When placing an order, it is required to provide a quality inspection report for the batch, at least including the ammonium sulfate content pH、 Heavy metals and burnt residues. The price of imported 500g/1kg is much higher than that of domestic products. For specific inquiries, domestic products come in 1kg and 500g packs, while imported products are mainly 500g/bottle. Suggest buying enough for the entire project at once to avoid changing batches midway. If the supplier cannot provide COA, switch to another one. After receiving the goods, first prepare a saturated solution to check the solubility and clarity, and then measure the pH. These simple indicators can help you quickly screen out batches with problems.

Excess host cell proteins are not necessarily the fault of ammonium sulfate. In our recombinant enzyme salting-out process, we tried many brands and ultimately found that the main variables were the rate of salt addition and pH control. It is recommended to first fix the buffer pH and temperature, then add ammonium sulfate slowly with stirring to avoid local supersaturation. If domestic analytical-grade ammonium sulfate has inconsistent pH, it can shift the precipitation window and cause poor reproducibility; heavy metals may affect the activity of certain enzymes, but if the enzyme is not metal-sensitive, the impact may not be obvious. You can first run a small experiment: use domestic and imported ammonium sulfate on the same batch of samples, collect precipitates within the same saturation range, and compare enzyme activity and purity. If the difference is small, domestic superior-grade purity is sufficient; if the difference is significant, then consider imported and write it into the SOP. It is best to retain the supplier's batch quality inspection reports for traceability.

Domestic analysis of pure and imported ammonium sulfate may not differ much in conventional content, but when doing recombinase salting out, the key is often in the consistency of heavy metals and pH. Imported molecular biological grades such as Sigma usually have clearer limits on heavy metals such as iron and copper, and have narrower pH controls, resulting in better batch repeatability. High-grade pure or specialized ammonium sulfate for protein purification in domestic plants is also sufficient, but pure analysis may not be suitable. It is recommended not to directly replace all of them first, and compare the same batch of lysate: domestic and imported parallel 30% -50% graded precipitation, see SDS-PAGE miscellaneous bands and enzyme activity. If the import significantly improves, consider locking the import, but give priority to batches that have regular agents in China and can provide a complete COA.