Simultaneous determination of tyrosine and levodopa in human plasma using enzyme-induced excitation-emission-kinetic third-order calibration method

• Third-order calibration method for quantifying tyrosine and levodopa.
• Oxidation reactions of analytes using polyphenol oxidase as a catalyst.
• Monitoring kinetic evolutions of excitation–emission matrix fluorescence.
• Exploiting the second-order advantage and expanding a high-order advantage.

This paper presented a method for the simultaneous determination of two target analytes, tyrosine (Tyr) and levodopa (Lev), in human plasma matrices using enzyme-induced excitation-emission-kinetic third-order calibration method based on the alternating quadrilinear decomposition (AQLD) algorithm. The work skillfully exploited the oxidation reactions of Tyr and Lev using polyphenol oxidase as a catalyst. A four-way data array was constructed by the kinetic evolutions of excitation–emission matrix fluorescence for a group of samples, and followed by the four-way data decomposition. The proposed method could be applied in plasma sample analyses with satisfactory results. The actual concentration of Tyr in human plasma was identified as 8.80 ± 0.54 μg mL− 1, but Lev was not found in the presented sample. Using high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) as reference method, the F-test and t-test suggested that there were no significant differences between these two methods. The satisfactory results indicated that this third-order calibration method has the potential to give accurate quantitative analyses, particularly in complex systems containing unknown spectral interferents and existing serious collinearity problems.