An off-on-off fluorescence probe based on a pyrazole derivative for Al 3+ and Fe 3+ detection

A new fluorescence probe ( E )- N ′-(2,3-dihydroxybenzylidene)-1-(pyridin-2-yl)-5-(thiophen-2-yl)-1 H -pyrazol-3-carbohydrazide (L) was designed and synthesized, which could be applied as an off-on-off sensor for the successive detection of Al 3+ and Fe 3+ . The detection limits of L towards Al 3+ and Fe 3+ were determined to be 1.10 × 10 −8 M and 4.45 × 10 −8 M, respectively. The 1 : 2 binding stoichiometry of L to Al 3+ and Fe 3+ was established from Job plot analysis, 1 H NMR spectroscopy and mass spectrometry titration. Application experiments proved that L had excellent ability to monitor Al 3+ and Fe 3+ in tap water, and the sensing process could be performed on test paper as well.