Solid sampling analysis by flame atomic absorption spectrometry for lead determination in seawater samples after pre-concentration using cocrystallized alizarin red - naphthalene

A device for direct solid analysis by flame atomic absorption spectrometry (DSA-FAAS) with prior solid phase extraction procedure is proposed for the determination of lead in water samples. A buffer solution (NH4Cl-NH3, pH 8.1) and alizarin red - naphthalene solid phase were added for Pb sorption. After, samples (up to 200 mL) were filtered and the naphthalene matrix was dried, ground to particle size < 80 µm and then maintained into a desiccator up to the Pb determination by DSA-FAAS. Test samples (from 0.1 to 2 mg) were weighed into small polyethylene vials. Vials were connected to a homemade device for solid introduction directly into a conventional air + acetylene flame. Test samples were carried as a dry aerosol to a T-quartz cell specially designed for DSA-FAAS. The T-quartz cell was positioned above the burner and below the optical path of the instrument. In the flame, the generated atomic vapor produced a transient signal that was totally integrated in 2 s. The effect of operating conditions on the analytical signal was evaluated. Background signals were always low (wavelength=217.0 nm) and no memory effects were observed. A characteristic mass of 1.1 ng for Pb was found. Calibration was performed using different masses of solid alizarin red-naphthalene spiked with Pb reference solution. Results were considered satisfactory, for concentration ranging from 30 and 50 µg L-1, regarding to both accuracy (recoveries from 94 to 103%) and precision (relative standard deviation less than 5%, n=6). The stability of lead in the solid phase (naphthalene + alizarin red) was evaluated up to 45 days and the results showed that the solid material could be stored during this period. The proposed device used for solid introduction into the flame atomizer may be easily fitted to conventional atomic absorption spectrometers.