Synthesis and characterization of functionalized silica with 3,6-ditia-1,8-octanediol for the preconcentration and determination of lead in milk employing multicommuted flow system coupled to FAAS

Novel functionalized silica, containing 3,6-dithia-1,8-octanediol (Si-DIO), was synthesized and characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) of ¹³C and ²⁹Si. The Si-DIO was used to pre-concentrate and determine the amount of Pb(II) in milk samples employing a multicommuted flow system coupled to flame atomic absorption spectrometry (FAAS). For the adsorption process, a pre-concentration minicolumn with 100 mg of Si-DIO, a solution of 0.005 mg L⁻¹ Pb(II) at pH 9.0 and HNO₃ as the eluent was used, obtaining an enrichment factor of 28 times with retention efficiency higher than 99%. The Pb(II) ion, using the multicommuted flow system coupled to FAAS, showed a linear response between 0.005 and 20.0 mg L⁻¹; a linear coefficient where r = 0.9939 and n = 7; a detection limit estimated at 0.001 mg L⁻¹ and a relative standard deviation of 3.8% (n = 50). Fifty pre-concentrations runs were tested in the minicolumn without significant variation in the analytical signal. The proposal system showed analytical applicability to determine Pb(II) ion in milk samples, presenting recovery of 90.7–102.5%.