Performance of a New 235 nm UV-LED-Based On-Capillary Photometric Detector

In this work, for the first time, a sub-250 nm light-emitting diode (LED) is investigated as a light source for optical detection in chemical analysis. A 235 nm deep ultraviolet-light-emitting diode (UV-LED) is employed within an on-capillary photometric detector and applied in capillary ion-exchange chromatography (IEC) for the detection of common ultraviolet (UV)-absorbing anions (here, iodide, nitrate, and nitrite). This investigation focused on fundamental properties of UV-LEDs, in particular, emission spectra, radiometric power, effective heat dissipation with a passive heat sink, and energy conversion. The detection showed excellent linearity with stray light down to 0.6%, and an effective path length at 92% of the used capillary inner diameter. The analytical performance parameters were demonstrated by detection of chromatographic separation of iodide in simulated seawater, showing a limit of detection (LOD) of 1.30 μmol L^-1, a linear range of 7.9-3937 μmol L^-1, and reproducibility (with a relative standard deviation (RSD)) of 0.6% for peak height 0.7% for peak area. In addition, nitrite and nitrate were selected to study the potential of using deep UV-LEDs as the light source in photometric detection for even lower-wavelength-absorbing analytes (λ_max = 209 nm for nitrite and 200 nm for nitrate), showing reproducibility (RSD = 1.2% and 3.6% for peak height and 0.9% and 2.9% for peak area, respectively) and LOD = 7 and 26 μmol L^-1.