Analysis of a retan agent used in the tanning process and its determination in tannery wastewater

The chemical structure and composition of a retan agent, CNSF (condensation product of naphthalenesulfonic acid (NSA) and formaldehyde), and related components contained in tannery wastewaters were analyzed by ion-pair liquid chromatography coupled to electrospray ionization mass spectrometry (IPC-HPLC/ESI-MS) in negative ion mode. This method allows high-resolution separation of polymers. CNSF contained linear NSA oligomers (n = 1-11) that were eluted in order of increasing degree of polymerization. The area under the peaks was correlated to the concentration. The theoretical correlation between retention time and the molecular mass of CNSF oligomers can be used to predict the actual distribution of molecular mass or degree of polymerization. The CNSF consisted of 34.3% monomers, 14.8% dimers, 15.3% trimers and 12.1% tetramers. Other oligomers (n = 5-11) accounted for the remaining 23.5%. Using solid-phase extraction techniques and HPLC/MS, sulfonated monomers, dimers, and trimers were detected in three tannery wastewaters (A-C). Monomers (NSA and naphthalenedisulfonic acid) were one of the major components and ranged from 1.2- (C) to 22.0% (B). Concentrations of 2-naphthalenesulfonic acid were 4.9 mg/L (A), 30.1 mg/L (B), and 0.6 mg/L (C). A high proportion of dimers (18.5%) and trimers (14.5%) were detected in wastewater C, as compared with A (6.4 and 0.7%) and B (3.92 and 0.2%). The method presented allows the analysis of aromatic sulfonates in syntan and tannery wastewater.