Direct fluorimetric determination of dissolved aluminum in seawater at nanomolar levels

A highly sensitive method for the direct determination of dissolved aluminum in seawater at nM levels has been developed. This method is based on the formation of an aluminum complex with salicylaldehyde picolinoylhydrazone (SAPH), which shows a maximum blue–green fluorescence (λex=384 nm, λem=468 nm) at pH 5.4. The studied method has an average limit of detection of 9.8 nM (calculated in the concentration range of 3.7×10−8–9.3×10−7 and a precision of 1.85% at 1.66 × 10−7 M, and it has been successfully applied to the determination of dissolved aluminum in seawater in both synthetic and real samples by using an external calibration and/or the standard addition method. The tolerance limits of foreign ions have been also evaluated, before and after the addition of masking agents. Finally, the proposed method has been compared with a spectrophotometric method.