For Hg speciation by HPLC-ICP-MS, I prepared a Mobile Phase with 0.1% (m/v) of L-Cysteine free base + 0.1% (m/v) of L-Cysteine.HCl.H2O, pH 2.3, and I would like to know the main reason why both L-Cysteines are mentioned. Any specific reason?
It is mainly to maintain pH at 2.3. If you like, you can take 0.2% of either free base or the hydrochloride and then adjust the pH with HCl or NaOH, but that is extra work.
Agree with the previous answer. In addition most columns will destroy if your pH is lower for example if you use Cysteine.HCl only
Leonardo, I just skipped the L-Cysteine.HCl since is contaminated with Hg 😏. I adjusted the pH to 2.3 with HCl/NH3.
It will work. Just read the specs of your column, should tell the pH range. Prepare and dilute your samples with the same mobile phase. Hg is very sticky and cysteine complexes both Hg and gold to avoid memory effects (with increased background and detection limits), lost by binding to glassware plasticware, etc