LC-MS/MS determination of the isomeric neurotoxins BMAA (beta-N-methylamino-L-alanine) and DAB (2,4-diaminobutyric acid) in cyanobacteria and seeds of Cycas revoluta and Lathyrus latifolius.

Since diverse taxa of cyanobacteria has been linked to biosynthesis of BMAA, a controversy has arisen about the detection of neurotoxic amino acids in cyanobacteria. In this context, a novel LC-MS/MS method was developed for the unambiguous determination of beta-N-methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB) in cyanobacteria and selected plant seeds. Both neurotoxic and non-proteinogenic amino acids were analyzed without derivatization considering the total concentration of the free and protein-bound form. The investigation of overall 62 cyanobacterial samples of worldwide origin by application of this method revealed the absence of BMAA, whereas seeds of Cycas revoluta contained 6.96 microg g(-1) of free BMAA. In contrast, the isomer DAB was confirmed in 16 cyanobacterial samples in concentrations of 0.07-0.83 microg g(-1),whereof one sample is distributed as nutritional supplement. In addition, seeds of Lathyrus latifolius contained 4.21 microg g(-1) of free DAB. Limits of detection were for BMAA<1.0 microg g(-1) in the cyanobacterial matrix and<0.14 microg g(-1) in angiosperm seeds. DAB exhibits higher sensitivities of <0.06 microg g(-1) in cyanobacteria and <0.008 microg g(-1) in angiosperm seeds. The highly specific analysis method with increased detection sensitivity eliminates the disadvantages of derivatization-based methods to be discussed.