Determination of cobalt(II) in water by using adsorption on the surface of a quartz mass sensor as α-nitroso-β-naphthol complex

Abstract

Cobalt(II) reacts with α-nitroso-β-naphthol to form an insoluble complex in water. The precipitate adsorbed on a piezoelectric quartz crystal shifted the frequency. The frequency shifts were proportional to the amounts adsorbed. Acetic acid (10 mM) and α-nitroso-β-naphthol (1.5 mM) solutions were passed through the quartz mass sensor to get constant frequency (F₁). And then instead of the stream of the acetic acid solution, the cobalt(II) sample in 10 mM acetic acid solution was passed. After exactly 5 min, the stream was changed to the acetic acid solution to get a constant frequency (F₂). The frequency change resulting from the adsorption of cobalt(II) complex was calculated as the difference, F₁-F₂. The concentration range (260) μM of cobalt(II) could be determined from the calibration curve with good reproducibility. Cobalt(II) complex adhered could be removed from the sensor with acetic acid.