Method For Determination Of Tyrosine Research Articles

New voltammetric method for determination of tyrosine in foodstuffs using an oxygen-functionalized multi-walled carbon nanotubes modified acetylene black paste electrode

In this paper, acetylene black paste electrode (ABPE) was prepared and modified by oxygen-functionalized multi-walled carbon nanotubes (MWCNT-COOH). The fabricated MWCNT-COOH/ABPE was further used for the investigation on the electrochemical behavior of tyrosine by cyclic voltammetry and second-order derivative linear sweep voltammetry. In 0.1 M pH 2.6 phosphate buffer solution, a well-defined anodic peak appeared at 924 mV, which was attributed to the electrooxidation of tyrosine on the modified electrode. The electrochemical parameters of tyrosine on the modified electrode were calculated. Under the optimal conditions, the oxidation peak current of tyrosine varies linearly with its concentration in the range of 0.04−1.0 μ M, 1.0−60 μ M and 60−600 μ M, and the detection limit is 0.02 μM. The MWCNT-COOH/ABPE was applied to the determination of tyrosine in food with satisfactory results.

Development of a Candidate Reference Method for Determination of Tyrosine in Serum by Isotope Dilution Liquid Chromatography-Tandem Mass Spectrometry

An isotope dilution liquid chromatography/tandem mass spectrometry is proposed as a reference method to determine the level of tyrosine in human serum. The advantages of this method include simple sample preparation without derivatization, the selective detection of compounds of interest in complex matrices, and the use of an isotopically labeled analogue as an internal standard. Tyrosine and its isotopically labeled analogue were monitored at a transfer m/z of 182.1/136.2 and 188.1/142.2, corresponding to [M+H]+/[M+H-HCOOH]+ in a multiple reaction monitoring mode. The expanded uncertainty for the measurement of tyrosine in the serum was approximately 0.95% within a 95% confidence level. For the verification of this method, a standard reference material with a certified value was analyzed. The analyzed result was in good agreement with the certified value. The isotope dilution liquid chromatography/tandem mass spectrometry result of the human serum was also compared with results obtained from clinical laboratories, and showed inconsistent results. These inconsistent results suggest that standards certified by the proposed reference method are required in order to improve measurement reliability in clinical fields.

An Improved Method for the Determination of Tyrosine Residues in Proteins Using 1-Nitro-2-napthol

A simple and reliable method for the quantitative determination of free tyrosine and. tyrosine residues in proteins is described. The method involves alkali-denaturation of proteins in a boiling water bath, the color forming reaction between tyrosine and 1-nitroso-2-naphthol in 19 N H2SO4, and measurement of the absorhance at 520 m μ. The method is preferable because of its simplicity, high sensitivity, reproducibility and remarkable stability of the red color. The procedure has been shown to be accurate with a wide variety of enzyme proteins.