Electrokinetic chromatography of twelve monomethylbenz[a]anthracene isomers using a polymerized anionic surfactant A method for the separation of twelve monomethyl-substituted benz[a]anthracene isomers using poly-(sodium undecylenic sulfate) (poly-SUS) surfactant by means of electrokinetic capillary chromatography (EKC) is described. Several parameters such as concentration of acetonitrile (ACN), pH, as well as applied voltage were studied to optimize the EKC separation. ACN at a concentration of 35% v/v, 12.5 mM phosphate- borate buffer, 30 kV with 0.5% w/v poly-SUS at a pH of 9.5 provided a resolution of a mixture of nine out of twelve methylbenz[a]anthracene (MBA) isomers in 50 min. The results of this study suggest that molecular length of MBA rather than length-to-breath ratio plays an important role in the elution order of some isomers. Keywords: Electrokinetic chromatography / Polymerized surfactant / Methylbenz[a]anthracene isomers / Carcinogenic compounds EL 3218 Cevdet Akbay 1 Isiah M. Warner 1 Shahab A. Shamsi 2 1 Department of Chemistry, Louisiana State University, Baton Rouge, LA, USA 2 Department of Chemistry, Georgia State University, Atlanta, GA, USA 1 Introduction Recently, polycyclic aromatic hydrocarbons (PAH) have evoked considerable attention [1±5]. PAHs and their alkylated derivatives are well known as serious environ- mental contaminants and some are believed to contribute to the incidence of cancer in living organisms [6, 7]. Methyl-substituted PAHs such as monomethylbenz[a]an- thracenes (MBA) are among the most biologically active alkylated aromatic compounds found in the environment [8, 9]. There are 12 possible positional isomers of MBAs (see Fig. 1), whose carcinogenicity depends mostly on the position of the methyl group on the benz[a]anthracene molecule. For example, 7-MBA has been found to be the most carcinogenic compound, followed by 6-, 8-, and 12- MBA, which have almost equal carcinogenic activity. The 9- and 11-MBA are the next most carcinogenic com- pounds; however, 1-, 2-, 3-, 4- and 5-MBA have low carcinogenicity [8, 10±12]. Different methods using gas chromatography (GC) on conventional nonpolar phases, and high-performance liquid chromatography (HPLC) have been published on the separation and identification of MBAs [13±16]. Several liquid-crystalline alkene compounds based on the biphenylcarboxylate ester were evaluated as sta- tionary phases for separation of MBAs in capillary GC, although some isomers were not resolved [13]. Garrigues and his co-workers [14] have studied the extracts of rock and air particulate matter by high-resolution Shpol©skii spectrometry (HRS). This technique allows identification of isomers of MBA based on the sharpening of the fluorescence emission spectra at low temperature in n- alkane polycrystalline frozen solution. However, before HRS analysis, isomers of MBA need to be isolated by use of a highly selective reversed-phase HPLC column. Wise et al. [15, 16] observed a linear relationship between the calculated length-to-breadth ratios (L/B) of PAHs, (includ- ing many mono- and dimethylated PAHs) and their reversed-phase LC retention. In general, they found an increase in HPLC retention with an increasing L/B of PAHs. Capillary electrophoresis (CE) of nonionic analytes cannot be performed in a free solution due to the lack of electric charges on the analytes. This problem can be overcome by employing a charged additive that forms micelles Correspondence: Professor I. M. Warner, Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA E-mail: isiah.warner@chemgate.chem.lsu.edu Fax: +504-388-3971 Abbreviations: ACN, acetonitrile; BGE, background electrolyte; EKC, electrokinetic chromatography; L/B, length-to-breath ratio; MBA, monomethylbenz[a]anthracene; PAH, polycyclic aromatic hydrocarbon; poly-SUS, poly-(sodium undecylenic sulfate)  WILEY-VCH Verlag GmbH, 69451 Weinheim, 1999 0173-0835/99/0101-0145 $17.50+.50/0 Electrophoresis 1999, 20, 145±151 145 CE and CEC Figure 1. The chemical structure of MBA employed in this study. The numbers show the position of substituted methyl- groups on the benz[a]anthracene molecule.