Determination of trace elements in food samples by ICP-AES after preconcentration with p-toluenesulfonylamide immobilized on silica gel and nanometer SiO2

p-Toluenesulfonylamide was immobilized on silica gel and on nm-sized silicium dioxide (SiO2). Their adsorption efficiency toward metal ions was investigated by the batch equilibrium technique. Although silica gel and nm-SiO2 have the same composition (silicon and oxygen), the difference in their sizes and surface structures results in distinct chemical activity and selectivity. At pH 4, the adsorption capacity of modified silica gel adsorbent was found to be 4.9, 5.0, 33.2, and 12.6 mg g(-1) for Cr(III), Cu(II), Pb(II) and Zn(II), respectively. However, the adsorption capacity of nm-SiO2 adsorbent toward Cr(III) was 26.7mg g(-1) under ultrasonic dispersing. The potential application of p-toluenesulfonylamide-modified silica gel for simultaneous preconcentration of trace chromium, copper, lead and zinc from two standard reference materials and two food samples was performed with satisfactory results.