I am achieving 92% loading with Fmoc-Cys(trt)-OH with the same protocol and only 40% with Fmoc-Cys(Acm)-OH. Already, I had coupled other standard amino acids with loading efficiency more than 80%. Initially, I think that Fmoc-Cys(Acm) was not pure, but both HPLC and TLC analysis had shown 99% purity. What could be the reason for this?