Cryogenic sample grinding for copper, lead and manganese determination in human teeth by slurry sampling GFAAS

Abstract

A simple method is proposed for copper, lead and manganese determination in deciduous teeth by graphite furnace atomic absorption spectrometry (GFAAS) using slurry sampling introduction and cryogenic sample preparation. Teeth samples were ground in a cryogenic mill in two steps: pre-cooling (5 min) and cryogenic grinding (2 min) in liquid nitrogen. After grinding, 90% of the sample particles were lower than 150 µm. The minimum mass necessary for slurry preparation as an indicator of sub-sample homogeneity was evaluated by weighting masses between 5 and 20 mg directly in autosampler cups, followed by addition of 1 mL of a solution containing 0.04% Triton^® X-100 and 0.2% v/v HNO₃. Samples (20 µL) were sonicated during 20 s, before delivering into a W–Rh coated platform. Detection limits based on integrated absorbance were 34.0 ng g⁻¹ Pb, 7.4 ng g⁻¹ Mn and 18.0 ng g⁻¹ Cu for 2% m/v slurries. W–Rh permanent modifier permitted calibration against aqueous standards. The Certified Reference Material (H-5 animal bone) from the International Agency of Atomic Energy (IAEA) was analyzed to determine lead for method validation. For copper, lead and manganese, 12 human teeth samples were analyzed using the proposed method with calibration against aqueous solution and using a comparative Pd/Mg method with the same digested samples, and standard addition calibration, with no statistical difference at 95% level on applying the t-test.