Hi,

RNA precipitation using lithium chloride (LiCl) is a commonly used method for purifying RNA from biological samples. The protocol typically involves adding LiCl to a solution containing RNA and other contaminants such as proteins and lipids. The addition of LiCl causes the RNA to become more negatively charged, which makes it more likely to bind to the positively charged LiCl ions and form a precipitate. The RNA can then be pelleted by centrifugation and washed to remove any remaining contaminants.

The pH of the solution can affect the efficiency of LiCl precipitation, as the charge on the RNA molecules is pH dependent. A pH around 8 is usually considered optimal for LiCl precipitation of RNA, as it allows the RNA to have a negative charge, but not too much to avoid unwanted side effects like binding to other materials, creating a more stable pellet and good washing conditions.

If your sample is in 10 mM MES buffer pH 6.0, you might not have enough negative charge on the RNA molecules to allow them to bind efficiently to the LiCl. In that case, adding Tris buffer to adjust the pH to around 8 would be a good idea, as it would provide the RNA molecules with a more negative charge.

You can experiment with different buffer systems and pHs to see what works best for your specific sample and downstream applications.

It's also worth noting that adding Tris buffer to adjust pH is not the only way to adjust the pH for successful LiCl precipitation, you can also consider using other buffers or acid/base to adjust the pH.

Regards

Mohammad Alzeyadi thank you for the thorough reply and insights.