Electrochemical response of nitrogen-doped multi-walled carbon nanotubes decorated with gold and iridium nanoparticles toward ferrocyanide/ferricyanide redox system

Novel composite films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold (AuNP) and iridium (IrNP) nanoparticles possessing diameters of 12.5 and 2.7 nm, respectively. The electrochemical responses of fabricated composite films, further denoted as N-MWCNTs/MNPs (M: Au and Ir), toward ferrocyanide/ferricyanide, [Fe(CN)₆]^3−/4− redox couple was probed by means of cyclic voltammetry and electrochemical impedance spectroscopy techniques. The findings demonstrate that both N-MWCNT/MNP composite films exhibit greater electrochemical response and sensitivity toward [Fe(CN)₆]^3−/4− compared to unmodified N-MWCNTs. The results verify that the N-MWCNT/MNP composite films are extremely promising for application in electrochemical sensing.

     

The determination of melamine in muscle tissue by liquid chromatography/tandem mass spectrometry

In early 2007 it was determined that the compound melamine, suspected of having been involved in the deaths of numerous pets, had been fed to hogs intended for human consumption. This report describes a method for the analysis of melamine in porcine muscle tissue using solid-phase extraction (SPE) and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). Melamine was extracted in 50% acetonitrile in water. Homogenates were centrifuged and supernatants were acidified and washed with methylene chloride. The aqueous extracts were cleaned up using mixed-mode C8/strong cation exchange SPE and then concentrated, fortified with a stable isotope-labeled analog of melamine, and analyzed by HPLC/MS/MS. Gradient HPLC separation was performed using an ether-linked phenyl column with ammonium acetate/acetic acid and acetonitrile as the mobile phase. Multiple reaction monitoring (MRM) mode of two precursor-product ion transitions for melamine and one for the internal standard was used. A five point calibration curve ranging from 50 to 2000 ng/mL of melamine in solvent was used to establish instrument response. The method was validated by analysis of seven replicate porcine muscle tissue samples fortified with 10 ng/g of melamine. The mean recovery for the seven replicates was 83% with 6.5% relative standard deviation and the calculated method detection limit was 1.7 ng/g.