DIODE LASER-BASED CONCENTRATION GRADIENT DETECTOR FOR CAPILLARY ISOTACHOPHORESIS

A diode laser-based, universal concentration gradient detector was app lied to capillary isotachophoresis (CITP). The inexpensive CITP instru ment also included a 30 cm long, 300 mum i.d. capillary, a 5 cm focal length lens and a photodiode light beam position sensor. Factors affec ting the sensitivity and performance of the detector, i.e., separation conditions, spatial resolution of the detector, and the concentration of leading electrolyte, were discussed theoretically and experimental ly. The diode laser-based concentration gradient detector appears to b e one of the best detectors for CITP due to its high resolution, deriv ative nature, and low cost. The experimental detection limit reached 4 x 10(-6) M for small cations, which was near the theoretical value. T he detection limit can be further reduced by at least one order of mag nitude if a longer capillary is used. The CITP-concentration gradient detector instrument has high efficiency, and was applied to detect imp urities in antidepressant drugs.