As we know when we treat a protein with SDS, it breaks non covalent bonds to form primary structure. But how it adds negative charges uniformly on all constituent amino acids?
In SDS-PAGE, proteins are separated in a palyacrylamide gel based on their molecular weight. Proteins are amphoteric molecules, i.e. they have both positive and negative charges. To make them move in a single direction, a uniform negative charge is created on them. https://www.sciencedirect.com/topics/nursing-and-health-professions/polyacrylamide-gel-electrophoresis
The SDS–protein complexes all contain about the same negative charge because the SDS swamps out all of the protein charges. Since the charges are all the same, the proteins all separate from one another strictly on the basis of their sizes. https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/sodium-dodecyl-sulfate
This paper also can be helpful:
Article Analysis of RNA by Analytical Polyacrylamide Gel Electrophoresis
Dipanshu Ghosh
Sir, you can check the following references
https://www.nature.com/articles/s41598-018-20669-7
Article Detergent binding explains anomalous SDS-PAGE migration of m...
Article On the Mechanism of SDS-Induced Protein Denaturation
If the problem persists then check the following
Encyclopedia of surface and colloid science