Highly sensitive wavelength-dependent nonaqueous capillary electrophoresis for simultaneous screening of various synthetic organic dyes

Abstract

A novel multi-wavelength nonaqueous capillary electrophoresis (MW-NACE) technique based on wavelength-dependent laser-induced fluorescence (LIF) detection was investigated for the simultaneous screening of various synthetic organic dyes. Multi-wavelength excitation light sources were utilized to excite different organic dyes [e.g., 543nm for crystal violet (CV), methyl violet B (MVB), methyl violet B base (MBB), rhodamine 6G (R6G), and rhodamine B base (RBB); 635nm for nile blue A (NBA) and methylene blue (MB)] simultaneously. Using a nonaqueous buffer system composed of 15mM sodium borate and 835mM acetic acid in 100% ethanol (pH=5.4), all dyes were analyzed within 15min with excellent resolution (R≥4.0) under an electric field of 500V/cm. Calibration curves showed excellent linearity with square of correlation coefficients (r2) greater than 0.9908 over wide dynamic ranges of 0.4–50μM for CV, 0.8–50μM for MVB, 1.5–50μM for MBB, 0.08–5nM for R6G, 0.06–10μM for MB, 0.02–10μM for NBA, and 0.13–10 pM for RBB. The detection limits (S/N=3) of 40fM to 0.5μM were 10–200,000 times lower than those of previous detection methods. While adjacent peaks were not well distinguished with baseline separation in a single capillary, the devised technique was faster and more sensitive than conventional aqueous and nonaqueous CE approaches, thereby enabling the quantitative analysis of various dyes based on wavelength-dependent fluorescence detection with different excitation wavelengths.