Véréna Poinsot 1 Audrey Rodat 1, 2 Pierre Gavard 1 Bernard Feurer 2 Franc ¸ ois Couderc 1 1 Université Paul Sabatier, IMRCP, France 2 Picometrics, Toulouse, France Received July 5, 2007 Revised September 22, 2007 Accepted September 22, 2007 Review Recent advances in amino acid analysis by CE This paper describes a number of articles that have been published on amino acid (AA) analysis using CE during the period from June 2005 to May 2007. This review article follows the format of the previous articles of Smith (Electrophoresis 1999, 20, 3078–3083), Prata et al. (Electrophoresis 2001, 22, 4129–4138), and Poinsot et al. (Electrophoresis 2003, 24, 4047–4062 and Electrophoresis 2006, 27, 176–194). Several new developments in AA analysis with CE are reported describing the use of laser-emitting diodes for LIF, MS, and chips. In addition, we describe articles concerning clinical studies and neuroclinical applications. Keywords: Amino acids/ Capillary electrophoresis DOI 10.1002/elps.200700482 Electrophoresis 2008, 29, 207–223 207 1 Introduction The analysis of amino acids (AAs) is a research area in which a large number of studies continue to be reported. A major reason for these studies is because AAs are frequently found in biological media and analysts are required to detect trace levels in exceedingly small samples. New analyses that are more sensitive, more selective, or simpler to perform con- tinue to be required for clinical and neurochemical analyses. In addition, chirality of AAs is frequently used in the devel- opment of new analytical methods and instrumentation. In this new review, which follows the previous four reviews on this topic [1–4], we will summarize the variety of works on this topic that have been published from June 2005 to May 2007. Table 1 summarizes some experimental data. 2 New CE methods 2.1 CE-MS The interfacing of CE with MS using ESI is a popular tech- nique which requires the use of a sheath liquid because of the small flow rate of EOF. When a sheath liquid is employed, it becomes difficult to obtain high-sensitivity assays of small molecules such as AAs due to the presence of ions in the sheath liquid. In addition, it should be noted that ESI requires the use of volatile buffers. Nanomolar concentrations of AAs can be detected with transient ITP stacking with CE/ESI-MS. In a recent study, the AAs were diluted in ammonium acetate buffer and a formic acid solution was used as the BGE; the experimental data and computer simulations were examined as a multi- plexed approach for studying the selective nutrient uptake behavior of Escherichia coli within a complex broth medium. The migration behavior of charged metabolites was modeled (role of absolute mobility and pk a ) to support MS characteri- zation. The computer simulations using “Simul 5.0” helps de novo identification of unknown nutrients (Table 1) [5]. A porous tip at the end of the capillary was formed by removing 25–40 mm of the polyimide coating of the capillary and etching this section by a 49% HF solution. The electrical connection to the capillary outlet was achieved by simply inserting the capillary outlet containing the porous tip into the existing ESI needle (metal sheath) and filling the needle with the BGE. To test the utility of this tip, the analysis of AAs was performed using an AA standard containing 17 different AAs. A formic acid/18-crown-6-tetracarboxylic acid (18-C-6-TCA) solution was used as a complexation reagent to enhance the sensitivity of AAs detection. It was noted that the complex increases the apparent masses of the AAs (Table 1). Figure 1 shows the base peak chromatogram of the 17-AA standard using the 120 cm long porous tip capillary. The results obtained using the porous tip were very similar to results using other conventional interface designs. The etching process reduces the wall thickness of the etched sec- tion and results in a stable electrospray at approximately 1.5 kV, thereby simplifying the CE to ESI-MS interface. The role of the etching process is to reduce outer diameter of the tip and to make the capillary porous. These two processes are done in a single step, and if the capillary is blocked or damaged, a small section of the tip can be readily etched off Correspondence: Professor Franc ¸ ois Couderc, Université Paul Sabatier, Laboratoire des IMRCP, UMR5623, F-31062 Toulouse Cedex 9, France E-mail: couderc@chimie.ups-tlse.fr Fax: 133-05-61558155 Abbreviations: 5CFbCSE, 5-carboxyfluorescein-bis(5-carboxy- methoxy-2-nitrobenzyl)ether-b-alanine-carboxamide-succinimi- dyl ester; AA, amino acid; â-ME, b-mercaptoethanol; ClCD, con- tactless conductivity detection; FMOC, 9-fluorenylmethyloxycar- bonyl chloride; FQ, 3-(2-furoyl)quinoline-2-carboxaldehyde; GABA, g-aminobutyric acid; LED, light-emitting diode; MH, methylhistidine; NBD-F, 4-fluoro-7-nitro-2,1,3-benzoxadiazole; NDA, naphthalene-2,3-dialdehyde; OPA, o-phthalaldehyde; STDC, sodium taurodeoxycholate  2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.electrophoresis-journal.com