Leveraging multi-mode microextraction and liquid chromatography stationary phases for quantitative analysis of neurotoxin β-N-methylamino-L-alanine and other non-proteinogenic amino acids

Effective quantitative analysis of BMAA (β-N-methylamino-L-alanine) and its isomers without the need for derivatization has always been an analytical challenge due to their poor retention and separation on various liquid chromatography stationary phases. Previous studies that utilized conventional hydrophilic interaction chromatography (HILIC) demonstrate false negatives compared to reverse-phase workflows with derivatization. This work evaluates the chromatographic behavior of BMAA and its isomers, in their underivatized forms, on selected stationary phases, in particular fluorophenyl-based columns, to attain effective retention and separation. Detection and quantification were achieved with an ion-trap mass spectrometer. Extraction and preconcentration were achieved via solid phase microextraction (SPME) by assessing the effectiveness of multiple extraction phases, including hydrophilic-lipophilic balanced (HLB) and mixed-mode (MM). A MM extraction phase consisting of C₈ and benzene sulfonic acid moieties provided ideal extraction performance for BMAA and its isomers (2,4-diaminobutyric acid, DABA; N-(2-aminoethyl) glycine, AEG). Chromatographic separation was achieved within 8 min on a fluorophenyl stationary phase, ensuring high throughput without derivatization, and showing exceptional improvement from conventional HILIC methods. Limits of quantification in water for BMAA and AEG were 2.5 µg L⁻¹ and DABA was 5 µg L⁻¹, with linear dynamic ranges from 2.5 µg L⁻¹ - 200 µg L⁻¹ for BMAA and AEG and 5 µg L⁻¹ - 200 µg L⁻¹ for DABA.