Selective quantitation of the neurotoxin BMAA by use of hydrophilic-interaction liquid chromatography–differential mobility spectrometry–tandem mass spectrometry (HILIC–DMS–MS/MS)

Abstract

The neurotoxin β-N-methylamino-L-alanine (BMAA) has been reported in cyanobacteria and shellfish, raising concerns about widespread human exposure. However, inconsistent results for BMAA analysis have led to controversy. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is the most appropriate method for analysis of BMAA, but the risk of interference from isomers, other sample components, and the electrospray background is still present. We have investigated differential mobility spectrometry (DMS) as an ion filter to improve selectivity in the hydrophilic interaction liquid chromatographic (HILIC)-MS/MS determination of BMAA. We obtained standards for two BMAA isomers not previously analyzed by HILIC-MS, β-amino-N-methylalanine and 3,4-diaminobutanoic acid, and the typically used 2,4-diaminobutanoic acid and N-(2-aminoethyl)glycine. DMS separation of BMAA from these isomers was achieved and optimized conditions were used to develop a sensitive and highly selective multidimensional HILIC-DMS-MS/MS method. This work revealed current technical limitations of DMS for trace quantitation, and practical solutions were implemented. Accurate control of low levels of DMS carrier gas modifier was essential, but required external metering. The linearity of our optimized method was excellent from 0.01 to 6 μmol L(-1). The instrumental LOD was 0.4 pg BMAA injected on-column and the estimated method LOD was 20 ng g(-1) dry weight for BMAA in sample matrix. The method was used to analyze cycad plant tissue, a cyanobacterial reference material, and mussel tissues, by use of isotope-dilution quantitation with deuterated BMAA. This confirmed the presence of BMAA and several of its isomers in cycad and mussel tissues, including commercially available mussel tissue reference materials certified for other biotoxins. Graphical Abstract Differential Mobility Spectrometry is used to increases the selectivity of BMAA analysis by HILIC-MS/MS.

The neurotoxin BMAA in aquatic systems : analysis, occurrence and effects

“…When using LC-MS/MS based methods, it is important to distinguish between BMAA and its structural isomers such as 2,4-diaminobutyric acid (2,4-DAB, mostly referred to as DAB), N-(2-aminoethyl) glycine (AEG), ß-amino-N-methylalanine (BAMA) and 3,4-diaminobutyric acid (3,4-DAB) [97,104]. Mostly, BMAA is chromatographically resolved from its structural isomers, but additional selectivity can be obtained by more advanced techniques such as differential mobility spectrometry [104].…”

“…Mostly, BMAA is chromatographically resolved from its structural isomers, but additional selectivity can be obtained by more advanced techniques such as differential mobility spectrometry [104]. Isotope dilution, e.g.…”

“…This work should be carried out with samples containing bound forms of BMAA, preferably matrix matched certified reference materials. Such materials are not available yet, but the recent finding of BMAA in commercially available mussel material [104] is promising. Until certified reference materials are available, samples that contain a relatively high concentration of bound BMAA, such as cycad seeds, can be used during method development and comparison.…”

“…Figure 8.2. Separation from isobaric compounds other than DAB and AEG is not described in this SOP, but see [104] for more information.…”

“…In LC-MS/MS analysis, BMAA should be properly separated from isobaric compounds such as α,γ-diaminobutyric acid (DAB), N-(2-aminoethyl) glycine (AEG) and β-amino-Nmethylalanine (BAMA) [97,104]. Furthermore, attention should be paid to the form in which BMAA can be present in natural samples: either free, bound in a fraction that precipitates with proteins or bound in a (0.1 M trichloroacetic acid, TCA) soluble fraction.…”