Electrochemical Method For The Determination Of Total Amino Acids Based On The Proton-coupled Electron Transfer Of Hydroquinone And Tetramethyl-1,4-benzoquinone

In aprotic solvents,Br?nsted acids and bases work as proton donors and proton acceptors which can release or accept protons during the reduction of p-benzoquinone（BQ）and the oxidation of hydroquinone（QH₂）,suppressing a sharp p H change near the electrode surface ground.Low concentrations of proton donor or acceptor causes a new peak.The peak current value of the new peak is independent on the concentration of p-benzoquinone or hydroquinone but is only related to the concentration of proton donor or proton acceptor.Amino acids,as amphoteric substances,can act as both proton donors and proton acceptors.Therefore,we studied the effect of amino acids on the electrochemical behavior of tetramethyl-1,4-benzoquinone（TMBQ）and hydroquinone and established an electrochemical method for the determination of amino acid concentrations basing TMBQ and QH₂ on glassy carbon electrodes,respectively.In acetonitrile solvent,we analyzed the determination of glycine,valine,alanine,phenylalanine,and the total amount of amino acids,respectively.We observed that the addition of amino acids induced the generation of a new cathodic peak around the-0.30V potential in the cyclic voltammetry（CV）of tetramethyl-1,4-benzoquinone,originating from the release of protons from the carboxyl groups of amino acids.In differential pulse voltammetry（DPV）quantitative determination,the peak current value of the new peak caused by amino acid is linearly related to the amino acid concentration.They all have a linear range of 0.10～0.50 m M with a detection limit of 8.0μM.To study the practicability of the method,we used the standard recovery method to verify the method.The recovery rate of the total amount of amino acids was 94.1～110%.The low concentration of amino acid generated a new anode peak near the+0.56 V potential of the hydroquinone cyclic voltammetry curve which was caused by the amino group of the amino acid accepting a proton.And the peak current value of the new peak was independent of the hydroquinone concentration.Using differential pulse voltammetry,it was found that the peak current value of the new peak caused by the amino acid had a good linear relationship with the amino acid concentration,and the linear range was0.05～0.30 m M.The detection limit to 8.0μM.Similarly,we carried out the standard recovery method to detect the actual samples.The standard recovery rate of the total amount of amino acids was 104～109%.The experimental results show that our proposed method can be successfully applied to the determination of the total amount of amino acids in real samples.Both TMBQ and QH₂ can be used for the determination of the total amount of amino acids,and the two methods are used to determine the amino acid content.And the two methods determine the content of amino and carboxyl groups of amino acids respectively,which can effectively exclude basic and acidic substances interference and improve the accuracy of the measurement.The two methods are are applied to the determination of total amino acids in amino acid functional beverages.The detection of total amino acids is basically consistent with the product labeling.In addition,the method has the advantages of low cost,simple operation,fast detection,and no complicated preprocessing.The two methods we have established have practical application value.