Selective fluorescence sensors for p-phenylenediamine using formyl boronate ester with an assistance of micelles

A selective fluorometric approach for detection of p-phenylenediamine (PPD) was fabricated using the alizarin-boronic acid adduct with an assistance of micelles. When Alizarin Red S (ARS) reacted with 4-formylphenylboronic acid (4-FPBA) and yielded the boronate ester adduct (ARS/4-FPBA), the fluorescence emission turned on. However, upon the addition of PPD, the fluorescence intensity of the ARS/4-FPBA adduct decreased as a linear function of PPD concentrations. Enhancements in sensitivity and selectivity of this fluorescence sensor were studied by incorporating the sensor molecule into the hydrophobic core of micelles. The results showed significant improvement in sensitivity and selectivity comparing to the sensor in the buffer solution. Parameters affecting the fluorescence quenching of boronate ester adducts by PPD such as solution pH, 4-FPBA concentration, types of surfactants and surfactant concentrations were investigated. The optimum conditions for the determination of PPD was 2.0 mM cetyltrimethylammonium bromide (CTAB) in 50 mM phosphate buffer solution pH 7.0. The fluorescence intensity of the ARS/4-FPBA adduct in the presence of CTAB was remarkably 11 times as high as that in the buffer solution. The linear working concentration range was found to be 0.03-0.40 mM and the calibration sensitivity was 48 times higher than that from the system containing only buffer solution. Moreover, PPD exhibited the highest calibration sensitivity among the studied primary amines, confirming that the proposed sensor provided high sensitivity and good selectivity for PPD. The proposed sensor was used to determine PPD in spiked water samples satisfactorily.