Cysteine can be difficult to analyze by LCMS because it is hard to ionize and also very sensitive to any metals in the instrument such as tubing, injectors, seals, joints etc. For this reason, we would strongly recommend using a metal free coated Cogent TYPE-C™ column.

Cystine, which is a disulfide bonded cysteine dimer can form and this may be helpful in your scouting and method development.