ИСТИНА

In this work for the first time an LED in the spectral range under 250 nm is investigated as a light source for optical detection in chemical analysis. A 235 nm deep UV-light-emitting diode (deep UV-LED) is demonstrated in on-capillary photometric detection in capillary ion-exchange chromatography (IEC) for detection of common 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 effective pathlength at 92% of the used capillary inner diameter. The analytical performance parameters were demonstrated by detection of chromatographic separation of iodide in artificial seawater, showing limit of detection (LOD) of 1.30 µM, linear range 7.9 to 3937 µmol L-1, and reproducibility as relative standard deviation (RSD) of peak height 0.6%, and peak area 0.7%. In addition, nitrite and nitrate were selected to study the potential of using deep UV-LEDs as light source in photometric detection for even lower wavelength absorbing analytes, showing reproducibility as RSD of peak height 1.2% and 3.6%, and peak area 0.9% and 2.9% respectively, and limit of detection 7 and 26 µmol L 1. The LOD values compare favourably with literature values given the short detection pathlength used here (100 µm capillary ID) and the spectral overlap between the analytes’ absorption bands and the LED emission. The potential of deep UV-LEDs in optical detection for robust low cost portable devices depends on future advances for higher optical power and energy conversion LEDs.