title: Capillary electrophoresis absorption detection using fiber-loop ring-down spectroscopy.
abstract: The application of phase-shift, fiber-loop, ring-down spectroscopy (PS-FLRDS) as an on-line detector for capillary electrophoresis (CE) of biomolecules is demonstrated. CE was conducted using a custom-designed capillary/fiber interface coupled to an absorption detector, which is based on the ring-down of an optical signal in a closed fiber waveguide loop. The ring-down times were obtained by measuring the phase difference between intensity modulated light entering and exiting the fiber loop. The incorporation of a microlens to enhance transmission through the sample gap led to an improvement of the sensitivity by up to 80% compared to the square-cut fiber and a reduction in the detection limit. The performance of the PS-FLRDS absorption technique as an online detector was characterized by flow injection through a capillary. Good repeatability and linear response were obtained, and the detection limit using the lensed fiber/capillary interface system was determined to be alpha(min) = 1.6 cm(-1) for an absorption path of approximately 30 microm. PS-FLRDS coupled to CE was also applied to the analysis of human serum albumin (HSA) by using a NIR dye as a noncovalent label. The excess free dye and the dye/protein complex were resolved. The labeling coefficient was determined to be approximately 6, and good repeatability of peak areas (RSD = 8.7%) was obtained for the analysis of HSA. Furthermore, an excellent linear response (R2 > 0.99) was obtained between the peak areas and concentrations of HSA. The detection limit of labeled HSA was determined to be 1.67 microM.
authors.affiliation: Department of Chemistry, Queen's University, Kingston, Ontario, Canada.
authors.forename: Runkai
authors.initials: R
authors.lastname: Li
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Loock
authors.forename: Richard D
authors.initials: RD
authors.lastname: Oleschuk
mesh_terms: D019075:Electrophoresis, Capillary / Q000379:methods*; D006801:Humans; D012680:Sensitivity and Specificity; D012709:Serum Albumin / Q000032:analysis; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D012709:Serum Albumin