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[Accepted]
Published online May 7, 2024.
Analysis of Total Microcystins using LC-MS/MS: Assessment of Pretreatment Technique for MMPB(2-methyl-3-methoxy-4-phenylbutyric acid)
MINJEONG KIM  , JAEWON CHOI 
K-water, Daejeon, Korea
Correspondence:  JAEWON CHOI, Tel: 010-3046-3367, Fax: 0426294777, 
Email: choijw@kwater.or.kr
Received: 24 March 2024   • Accepted: 7 May 2024
Abstract
This study evaluates a novel approach for quantifying total microcystins (MCs) in surface water, addressing limitations associated with the LC-MS/MS method and the unavailability of standard materials for diverse MC variants. Traditionally, MC analysis employs LC-MS/MS globally, constrained by the scarcity of commercial algal toxin standards. The EPA's 2016 method 546, utilizing ELISA for MCs, does not fully address these issues. Our proposed method capitalizes on the chemical transformation of MCs into 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) through oxidation with potassium permanganate and sodium periodate. This transformation pivots on the consistent Adda structure in MCs, thus eliminating the need for variant-specific standards and enabling total MC quantification. Methodologically, the study perfected the sample preparation involving freeze-drying and a subsequent liquid-liquid extraction (LLE) process for salt removal. The oxidation process was optimized, and different quantitative methods using internal standards were evaluated for their efficacy in MMPB detection. An internal standard was also assessed for its stability and utility during oxidation.
Results
indicated that the MMPB method achieved a recovery rate of up to 50% and an analysis precision of 14%. Furthermore, quality assurance and quality control (QAQC) tests confirmed satisfactory calibration curve linearity and performance for spiked samples, albeit with lower quantification limits and recovery rates compared to individual MC analyses, attributed to the inherent sensitivity variances between MMPB and MCs and the complexity of the oxidation-centered pretreatment. In conclusion, while offering a viable alternative for total MC measurement in environmental samples, this MMPB-based method suggests potential improvements in standardization and sensitivity adjustments for broader application.
Key Words: cyanobacteria, total microcystins, microcystin, MMPB, LC-MS/MS
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