Sensitivity enhancement by on-line preconcentration and in-capillary derivatization for the electrophoretic determination of amino acids

• Published in: Electrophoresis 2001-12, Vol.22 (20), p.4355-4361
• Main Authors: Latorre, Rosa M., Saurina, Javier, Hernández-Cassou, Santiago
• Format: Article
• Language: English
• Subjects: Amino acid analysis; Amino Acids - analysis; Buffers; Capillary electrophoresis; Electrophoresis, Capillary - methods; In-capillary derivatization; Large-volume stacking; On-line preconcentration; Sensitivity and Specificity
• ISSN: 0173-0835; 1522-2683
• DOI: 10.1002/1522-2683(200112)22:20<4355::AID-ELPS4355>3.0.CO;2-T

This study describes an application of on‐line preconcentration by large‐volume stacking in combination with in‐capillary derivatization for enhancing spectrophotometric detection sensitivity in capillary electrophoresis. The method is illustrated by an example dealing with the determination of amino acids with 1,2‐naphthoquinone‐4‐sulfonate as a labelling agent. Samples are dissolved in water in order to create a stacking process based on differences in the conductivity between this medium and a concentrated running buffer. The in‐capillary derivatization is accomplished following a sandwich procedure in which the sample is inserted between two segments of reagent. Amino acid derivatives are obtained and separated in a fused‐silica capillary with a sodium borate electrolyte buffer using 2‐propanol as an organic modifier. The method is applied to the analysis of amino acids in pharmaceutical and feed samples. A good concordance between the predicted values and those obtained with the standard method is observed, with overall quantification error below 5%. The proposed procedure allows the detection limits sensitivity to be enhanced in 1000‐fold with respect to conventional precapillary derivatization.