Spectrofluorometric determination and chemical speciation of trace concentrations of tungsten species in water using the ion pairing reagent procaine hydrochloride

A highly selective and low cost extractive spectrofluorimetric method was developed for determination of trace concentrations of tungsten (VI) in water. The method was based upon solvent extraction of the developed ion associate [(PQH+)2·WO42−] of the fluorescent ion-pairing reagent [2-(diethylamino)ethyl 4 aminobenzoate] hydrochloride namely procaine hydrochloride, PQH+·Cl− and tungstate (WO42−) in aqueous solution of pH 6–7 followed by measuring the resulting fluorescence enhancement in n-hexane at λex/em = 270/320 nm. The fluorescence intensity of PQH+·Cl− increased linearly on increasing tungstate concentration in the range 25–250 μg L−1. The limits of detection (LOD) and quantification (LOQ) of tungsten (VI) were found 7.51 and 24.75 μg L−1, respectively. Chemical composition of the developed ion associate and the molar absorptivity at 270 nm were found to be [(PQH+)2·WO42−] and 2.7 × 104 L mol−1 cm−1, respectively. Other oxidation states (III, IV, V) of tungsten species could also be determined after oxidation with H2O2 in aqueous solution to tungsten (VI). The method was applied for analysis of tungsten in certified reference material (IAEA Soil-7) and wastewater samples. The results were compared successfully (>95%) with the data of inductively coupled plasma-mass spectrometry (ICP-MS).