Analysis of Non-Aromatic Organic Acids in Beer by CE and Direct Detection Mode with Diode Array Detection Guillaume L. Erny 1,& , Joao E. A. Rodrigues 2 , Ana M. Gil 2 , Anto ´nio S. Barros 3 , Valdemar I. Esteves 1 1 CESAM, Department of Chemistry, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal; E-Mail: gl_erny@yahoo.fr 2 CICECO, Department of Chemistry, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal 3 QOPNAA, Department of Chemistry, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal Received: 17 April 2009 / Revised: 30 July 2009 / Accepted: 23 September 2009 Online publication: 18 October 2009 Abstract A method for the analysis of the main non-aromatic organic acids in beer using capillary electrophoresis is presented. In this work, malic, citric, succinic, pyruvic, acetic and lactic acids are separated using a sodium hydrogen phosphate background electrolyte with direct detection mode with a diode array detector. The separation exhibits lower sensitivity than equivalent methods with indirect detection mode, however, the risk of co-migration with unknown compounds in beer matrixes is significantly reduced. This is due to (i) a higher efficiency (250,000–400,000 theoretical plates), (ii) a higher selectivity than any equivalent method using an indirect detection mode, and (iii) the possibility to monitor other wave- lengths in parallel (260 nm for example) to check for possible co-migration with phenolic or benzoic acids. This was critical when working with beer samples as an unknown compound absorbing at 200 and 260 nm was detected in the neighbourhood of malic, citric and succinic acids. Such co-migration will not have been detected using single wavelength detection below 200 nm or indirect detection mode. Keywords Capillary electrophoresis Diode array detection Organic acids in beer Polybrene Introduction Beer is an alcoholic beverage obtained through fermentation of starches. It is widely consumed and its production dates back from antiquity. Beer contains CO 2 , ethanol, several inorganic salts and about 800 organic compounds [1]. It is acidic, with a pH ranging from 3 to 6 depending on the type of beer, and this acidity is due to the carbonic and or- ganic acids present in beer. Organic acids are essentially metabolic intermediates or by-products excreted by brewer’s yeast. More than 150 different organic acids have been identified in beer, including fatty acids, di- and tricarboxy acids, keto and aldo acids, aromatic acids, phenolic acids and polyheterocy- clic acids [1]. Despite the low total con- centration in organic acids (between 220 and 500 ppm), these compounds are essential for pH stability and taste of beer. As such, there is a growing need for the industrial brewer to monitor the concentration of organic acids and, thus, help control taste and quality. Capillary zone electrophoresis is now an accepted analytical separation tech- nique that is particularly suitable for the analysis of organic acids, as they are easily ionisable. Indeed, numerous re- ports and reviews deal with the separa- tion of organic acids in foods and beverages [2, 3] including beer [4–6]. In the case of non-aromatic organic acids, the analysis is complicated by the poor absorption of UV radiation at the usual working wavelength [7] of light detec- tors. When light detection is the only choice, the separation is usually per- formed using an indirect detection mode. However, indirect detection will not only detect any analytes present in the 2009, 70, 1737–1742 DOI: 10.1365/s10337-009-1377-4 0009-5893/09/12 Ó 2009 Vieweg+Teubner | GWV Fachverlage GmbH Full Short Communication Chromatographia 2009, 70, December (No. 11/12) 1737