INDIRECT FLUORESCENCE DETECTION OF FREE CYANIDE AND RELATED-COMPOUNDS BY CAPILLARY ELECTROPHORESIS

A capillary electrophoretic method to detect CN- and some related compounds (CNO-, SCN-, and NO3-) using a prototype laser-based indirect fluorescence detector has been developed. This method avoids interferences from Cl-, SO42-, CO32-, HCO3-, and ClO- and allows the detection of CN- in less than 4 min and the detection of related compounds in less than 8 min with precise migration times (R.S.D. about 1%). The measured detection limits of CN- [5x10(-6) M with DR=90 (dynamic reserve)] are close to the expected theoretical value [TR(CN) = 0.44 (transfer ratio)]. For the related compounds, the measured detection limits ranged from 10(-5) to 2 x 10(-6) M, depending on noise conditions (DR greater than or equal to 300). The results showed that the chosen analytical conditions were appropriate acid the detection limits could be improved using techniques to further decrease the noise (probably due to mechanical vibrations). Peak-height precision was about 10% R.S.D. and log-log regressions had slopes lower than one. These results seem to be due to instabilities in the indirect signal. The analysis of a quasi-real sample has been achieved, allowing identification of the related compounds present in a CN-/SCN- sample oxidized with ClO- and determination of the CNO- formed in this alkaline oxidation.