Performance of a simple UV LED light source in the capillary electrophoresis of inorganic anions with indirect detection using a chromate background electrolyte

Abstract

Light emitting diodes (LEDs) are known to be excellent light sources for detectors in liquid chromatography and capillary electromigration separation techniques, but to date only LEDs emitting in the visible range have been used. In this work, a UV LED was investigated as a simple alternative light source to standard mercury or deuterium lamps for use in indirect photometric detection of inorganic anions using capillary electrophoresis with a chromate background electrolyte (BGE). The UV LED used had an emission maximum at 379.5 nm, a wavelength at which chromate absorbs strongly and exhibits a 47% higher molar absorptivity than at 254 nm when using a standard mercury light source. The noise, sensitivity and linearity of the LED detector were evaluated and all exhibited superior performance to the mercury light source (up to 70% decrease in noise, up to 26.2% increase in sensitivity, and over 100% increase in linear range). Using the LED detector with a simple chromate–diethanolamine background electrolyte, limits of detection for the common inorganic anions, Cl⁻, NO₃⁻, SO₄²⁻, F⁻ and PO₄³⁻ ranged from 3 to 14 μg L⁻¹, using electrostatic injection at −5 kV for 5 s.