MPS (C3H7O3S2Na) 3-mercapto-1-propane sulfonic acid, sodium salt CAS No: 17636-10-1 Appearance: White powder Assay: â?¥90% Application: As brightener in acidic Copper baths to improve the deposition of copper coatings for decorative and functional purposes. The use of MPS together with polyethers and non-ionic surfactants results in brilliant and ductile coatings. An additional combination with polymeric amines, dyestuffs and other thio compounds is possible as well.