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Magnetic Multi-Walled Carbon Nanotubes Modified with Polythiophene as a Sorbent for Simultaneous Solid Phase Microextraction of Lead and Cadmium from Water and Food Samples

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Overview

This analytical-method paper applied a magnetic solid-phase microextraction method to water and food samples, including black tea, rice, infant dry formula milk, and cow milk. It is routeable as occurrence context because Table 4 reports unspiked sample concentrations for Pb and Cd.

Key numbers

Solid food values below are reported on a dry-weight basis (samples were dried at 110 °C before digestion per the methods section); cow milk values are on a fresh-liquid basis. Units are µg/g for solids (equivalent to mg/kg, or ppb × 1,000) and µg/L for liquid milk.

  • Table 4 reports black tea at Pb 5.62 ug/g dry weight (RSD 0.89%; equivalent to 5,620 ppb) and Cd 0.53 ug/g dry weight (RSD 1.88%; 530 ppb).
  • Rice was non-detect for Pb and had Cd 0.45 ug/g dry weight (RSD 2.20%; 450 ppb).
  • Two infant dry formula milk samples (n=2, different Iranian manufacturers) ranged Pb 1.35 to 3.86 ug/g dry weight (RSDs 2.07 to 2.22 percent) and Cd 0.02 to 0.03 ug/g dry weight (RSDs 3.30 to 3.57 percent); equivalent ranges 1,350 to 3,860 ppb Pb and 20 to 30 ppb Cd.
  • Cow milk: Pb 60.68 ug/L (RSD 2.47%) and Cd 2.55 ug/L (RSD 3.92%).
  • Method LODs were 0.54 ug/L for Pb and 0.03 ug/L for Cd; LOQs were 1.82 ug/L for Pb and 0.11 ug/L for Cd. Method RSDs at 50.0 ug/L Pb and 5.0 ug/L Cd (n=6) were 1.5 percent and 2.1 percent.
  • Enhancement factors were 197.6 for Pb and 195.5 for Cd; preconcentration factor 200; extraction recovery 98.8 percent for Pb and 97.7 percent for Cd.

Methods

The paper developed polythiophene-coated magnetic multi-walled carbon nanotubes (MMWCNT@PT) for magnetic solid-phase microextraction, followed by flame atomic absorption spectrometry on an Analytik Jena novAA 300 with hollow cathode lamps and an air-acetylene flame (Pb at 283.3 nm, Cd at 228.8 nm). Food samples were dried at 110 °C, ground, then digested with concentrated HNO3 plus 30% H2O2 with heating to dryness before redissolution and pH adjustment to 6.0 for extraction. Cross-validation was performed by graphite-furnace AAS (ETAAS) on the same samples; results agreed at the 95 percent confidence level.

Implications

The source supports method-application occurrence context for Pb and Cd in tea, rice, infant formula powder, and cow milk. Because it is primarily an analytical-method paper with small sample coverage, it should not be treated as a market survey.

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