Talanta 72 (2007) 1404–1409 Optimization of phenolic compounds analysis by capillary electrophoresis Diana L.D. Lima, Armando C. Duarte, Valdemar I. Esteves ∗ CESAM—Department of Chemistry, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal Received 10 November 2006; received in revised form 17 January 2007; accepted 19 January 2007 Available online 30 January 2007 Abstract Operational parameters like migration time, temperature, voltage, composition of background electrolyte and content of organic modifier were optimized in CZE for the determination of lignin-like phenolic compounds. The applied background electrolyte buffer consisted of a Na 2 B 4 O 7 , KH 2 PO 4 aqueous solution, pH 9.15 using acetonitrile as organic modifier with UV-detection. Compounds, such as acetosyringone, acetovanillone, syringealdehyde, p-hydroxyacetophenone, vanillin, syringic acid, ferulic acid, p-hydroxybenzaldehyde, p-coumaric acid, vanillic acid and p-hydroxybenzoic acid were applied as reference compounds. The quality and quantity of different phenolic compounds obtained upon alkaline CuO oxidation of a commercial humic acid were determined with CZE using ethylvanillin as internal standard. The optimized CZE revealed has being an appropriate method since it is quick, sensitive and quantitative and does not require a time-consuming sample preparation. © 2007 Elsevier B.V. All rights reserved. Keywords: Capillary zone electrophoresis; Humic acids; Phenols; CuO oxidation 1. Introduction Humic substances (HS) are the most important natural sunlight-absorbing components in aquatic environments. The major proportion of carbon on earth’s surface is present as humic substances, resulting of the decomposition of organic materials which can be found as colloidal or dissolved matter as well as soils constituents. According to general adopted procedure, HS can be divided into three fractions based on water solubility: (a) humin, the fraction that is not water soluble at any pH; (b) humic acids (HA), the fraction that is not soluble under acidic conditions (pH bellow 2) but becomes soluble at higher pH; finally, fulvic acid (FA), the fraction that is soluble under all pH conditions. Analytical methods have been used in order to develop structural models that allow a better understanding of the envi- ronmental role and basic functions of HS. The structural models suggest a relative biologically resistant and highly substituted core of aromatic nature with the presence of heterocyclic struc- tures. The units are linked to each other by alkyl chains of ∗ Corresponding author. Tel.: +351 234401408. E-mail address: Valdemar@dq.ua.pt (V.I. Esteves). different lengths that are highly substituted with functional groups, such as carboxylic, aliphatic, aromatic, hydroxyl and amino groups [6,12–15]. Lignin is an abundant and stable phenolic macromolecule, hardly accessible to most organisms, found in vascular plants, with an important role on plants structure and essentially absent in all other living organisms. A large number of phenolic com- pounds presents in lignin are also present in humic substances. Lignin has been used as a fingerprint of terrestrial input for marine organic matter, namely humic substances. Analyses of phenolic compounds derived from humic sub- stances or lignin gives evidence of the presence of terrigenous vascular plant material in marine samples and provides infor- mation on the taxonomic source and diagenetic state of humic substances, making a unique tracer for vascular plant mat- ter, suitable even for the chemotaxonomic distinction between angiosperms, gymnosperms and non-woody vascular plants. Phenols in these substances are considered fingerprints of the organic matter of terrestrial samples [1,2,10,11]. Due to the complexity of the sample, identification and quantification of phenols lignin-derived from humic substances require a previous oxidative hydrolysis with CuO, followed by extraction with an organic solvent—ethyl ether [1,2]. 0039-9140/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2007.01.049