Available online at www.sciencedirect.com Talanta 74 (2008) 1400–1407 Indirect fluorescent determination of selected nitro-aromatic and pharmaceutical compounds via UV-photolysis of 2-phenylbenzimidazole-5-sulfonate Wei Zhang, Christopher R. Wilson, Neil D. Danielson ∗ Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, United States Received 28 January 2006; received in revised form 18 September 2007; accepted 19 September 2007 Available online 29 September 2007 Abstract An indirect fluorescence (FL) detection method via the reactivity of UV-photolyzed 2-phenylbenzimidazole-5-sulfonate (PBSA) has been developed for non-fluorescent aromatic compounds. At high pH with UV photolysis, PBSA in the excited state is known to be quenched by reaction with oxygen species and analyte compounds that are reactive toward these oxygen species produced during photolysis can lessen the loss of PBSA FL. After off-line photolysis of PBSA in the presence of various nitro-aromatic test compounds, the increase in PBSA FL is clearly evident. A flow injection (FI) instrument using a PBSA mobile phase propelled through a Teflon coil wrapped around a Hg lamp is optimized and modified for use for liquid chromatography (LC). For the on-line FI determination of the non-fluorescent nitro-aromatic compounds such as 4- nitroaniline, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, and -nitronaphthalene, a positive linear response for PBSA FL from about 0.5 to 15 M and detection limits generally between 0.2 and 1 M (4–20 pmol) are found. Linear responses and detection limits of selected pharmaceutical compounds such as the antibacterial nitrofurantoin, antihistamines chlorpheniramine and brompheniramine, and other compounds were similar. In general, detection limits using UV detection at about 214 nm were not as good in the 1–2 M range but linearity extended up to 100 M. The amino acid phenylalanine and small peptides containing this aromatic amino acid were also determined using this method. Application of this detection method for the liquid chromatography determination of 4-nitroaniline, 2-nitrophenol, nitrofurantoin, and salicylate is shown. © 2007 Elsevier B.V. All rights reserved. Keywords: Indirect fluorescence detection; 2-Phenylbenzimidazole-5-sulfonate; Nitro-aromatic compounds; Antihistamines; Amino acids 1. Introduction For reproducibility and selectivity, aromatic compounds are often determined by flow injection (FI) or liquid chromatography (LC) with fluorescence (FL) detection. For those non-fluorescent or weakly fluorescent aromatic compounds, e.g. nitro or halogen functional group-substituted aromatics, chemical derivatization that introduces fluorophores to those molecules is generally required for FL detection [1–3]. Off-line derivatization pro- cedures for nitro-aromatics accommodate reaction versatility, but sometimes extreme conditions, e.g. long reaction times and time-consuming sample purification and preconcentration procedures are required [4–6]. Therefore, some on-line deriva- tization techniques have been published for FL detection of ∗ Corresponding author. E-mail address: danielnd@muohio.edu (N.D. Danielson). non-fluorescent compounds such as aminoglycoside antibiotics [7] and polyamines [8] using a Cu 2+ –tryptophan ligand displace- ment reaction. After LC separation, weakly fluorescent phenols were oxidized electrochemically on-line to dimers and higher oligomers before fluorescent detection [9]. Nitro-substituted polynuclear aromatic hydrocarbons can be determined by FL detection method via post-column reduction of the NO 2 group to NH 2 using either a catalyst column packed with alumina par- ticles coated with Pt or Pd metal [10] or an electrochemical cell [11]. Lifetime and fouling of the column or electrode could be problematic. Photochemical derivatization, applied to pharmaceuticals such as methotrexate [12], chloramphenicol [13], sulfamet- hazine [14], and efavirenz [15] as well as agricultural products such as pesticides [16,17], pyrethoids [18], and benzoylureas [19], can lead to the formation of strongly fluorescent photoprod- ucts. The FL response of dansyl derivatives of chlorophenols can be enhanced by several orders of magnitude after photo- 0039-9140/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2007.09.016