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

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., 543 nm for crystal violet (CV), methyl violet B (MVB), methyl violet B base (MBB), rhodamine 6G (R6G), and rhodamine B base (RBB); 635 nm for nile blue A (NBA) and methylene blue (MB)] simultaneously. Using a nonaqueous buffer system composed of 15 mM sodium borate and 835 mM acetic acid in 100% ethanol (pH=5.4), all dyes were analyzed within 15 min with excellent resolution (R≥4.0) under an electric field of 500 V/cm. Calibration curves showed excellent linearity with square of correlation coefficients (r(2)) greater than 0.9908 over wide dynamic ranges of 0.4-50 μM for CV, 0.8-50 μM for MVB, 1.5-50 μM for MBB, 0.08-5 nM for R6G, 0.06-10 μM for MB, 0.02-10 μM for NBA, and 0.13-10 pM for RBB. The detection limits (S/N=3) of 40 fM to 0.5 μM 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.