Tailoring hydrophilic N,N-dialkyl-N?-acylthioureas suitable for Pt(ii), Pd(ii) and Rh(iii) chloride pre-concentration from acid aqueous solutions, and their complex separation by reversed-phase HPLCBased on the presentation given at Dalton Discussion No. 5, 10?12th April 2003, Noordwijkerhout, The N