CAS 52-90-4 appears in our catalog under these names: L-CysteineAcetylcysteine EP Impurity B, L-Cysteine, Acetylcysteine EP Impurity B, L-Cysteine, >95% (HPLC), L-Cysteine/ 99.58% (existing batch purity). Offered by: Chemat Brand, TRC, Mikromol, TargetMol, GLPBio. Available pack sizes: on request, 10g, 10mg, 2,5g, 100mg, 1g, 500mg, 250g.