Determination of BMAA and three alkaloid cyanotoxins in lake water using dansyl chloride derivatization and high-resolution mass spectrometry
A new analytical method was developed for the detection of alkaloid cyanotoxins in harmful algal blooms. The detection of the nonproteinogenic amino acid β-N-methylamino-l-alanine (BMAA) and two of its conformation isomers, 2,4-diaminobutyric acid (DAB) and N-(2-aminoethyl) glycine (AEG), as well as three alkaloid cyanotoxins, anatoxin-a (ANA-a), cylindrospermopsin (CYN), and saxitoxin (STX), is presented. The use of a chemical derivatization with dansyl chloride (DNS) allows easier separation with reversed phase liquid chromatography. Detection with high-resolution mass spectrometry (HRMS) with the Q-Exactive enables high selectivity with specific fragmentation as well as exact mass detection, reducing considerably the possibilities of isobaric interferences. Previous to analysis, a solid phase extraction (SPE) step is used for purification and preconcentration. After DNS derivatization, samples are submitted to ultra high-performance liquid chromatography coupled with heated electrospray ionisation and the Q-Exactive mass spectrometer (UHPLC-HESI-HRMS). With an internal calibration using isotopically-labeled DAB-D3, the method was validated with good linearity (R2 > 0.998), and method limits of detection and quantification (MLD and MLQ) for target compounds ranged from 0.007 to 0.01 μg L−1 and from 0.02 to 0.04 μg L−1, respectively. Accuracy and within-day/between-days variation coefficients were below 15 %. SPE recovery values ranged between 86 and 103 %, and matrix effects recovery values ranged between 75 and 96 %. The developed analytical method was successfully validated with 12 different lakes samples, and concentrations were found ranging between 0.009 and 0.3 μg L−1 except for STX which was not found in any sample.