title: A voltammetric sensor for the simultaneous determination of L-cysteine and tryptophan using a p-aminophenol-multiwall carbon nanotube paste electrode.
abstract: Two amino acids, L-cysteine and tryptophan, could be simultaneously determined in an aqueous solution (pH 6.0) using a carbon nanotube paste electrode (CNPE) modified with p-aminophenol as a mediator. The results indicate that the electrode is efficient in terms of its electrocatalytic activity for the oxidation of L-cysteine, leading to an overpotential reduced by more than 550 mV. Using differential pulse voltammetry, we could measure L-cysteine and tryptophan in one mixture independently from each other by a potential difference of about 600 mV. Electrochemical techniques are used to determine the diffusion coefficients, kinetic parameters such as electron transfer coefficient, and the rates of electro-oxidation of L-cysteine at the surface of the p-aminophenol-modified CNPE. The peak current is found to depend linearly on L-cysteine and tryptophan concentrations within the ranges of 0.5 - 100 µmol L(-1) L-cysteine and 10.0 - 300 µmol L(-1) tryptophan. The detection limits for L-cysteine and tryptophan are found to be 0.3 and 5.7 µmol L(-1), respectively. The proposed method is also used for the determination of L-cysteine and tryptophan in urine, river water, blood plasma, and serum samples using standard addition methods.
authors.affiliation: Department of Chemistry, Isfahan University of Technology, Isfahan, Iran. Ensafi@cc.iut.ac.ir
authors.forename: Ali A
authors.initials: AA
authors.lastname: Ensafi
authors.forename: Samira
authors.initials: S
authors.lastname: Dadkhah-Tehrani
authors.forename: Hassan
authors.initials: H
authors.lastname: Karimi-Maleh
mesh_terms: D000627:Aminophenols / Q000737:chemistry*; D003545:Cysteine / Q000032:analysis* / Q000097:blood / Q000737:chemistry / Q000652:urine; D004563:Electrochemistry; D004566:Electrodes; D006801:Humans; D037742:Nanotubes, Carbon / Q000737:chemistry*; D009824:Ointments; D015203:Reproducibility of Results; D045483:Rivers / Q000737:chemistry; D013997:Time Factors; D014364:Tryptophan / Q000032:analysis* / Q000097:blood / Q000737:chemistry / Q000652:urine; D014867:Water / Q000737:chemistry
chemical_list: D000627:Aminophenols; D037742:Nanotubes, Carbon; D009824:Ointments; D014867:Water; D014364:Tryptophan; D003545:Cysteine; C026729:4-aminophenol