Isotope-labelling derivatisation: a broadly applicable approach to quantitation of algal toxins by isotope dilution LC-MS/MS

摘要

Two methods were developed for the analysis of algal biotoxins in complex biological and environmental samples to demonstrate the concept of isotope-labelling derivatisation for quantitation. These methods are based on dansyl chloride derivatisation of samples and dansyl-d(6) chloride derivatisation of toxin standards. Derivatised sample and standard are then mixed to achieve isotope dilution calibration in liquid chromatography-tandem mass spectrometry analyses. Quantitation of the marine toxin domoic acid (DA) in mussel tissues and the freshwater toxins anatoxin-a (ATX) and homoanatoxin-a (hATX) in cyanobacteria is demonstrated. For DA, isotope-labelling was incorporated into existing dansylation methodology using inexpensive and commercially available reagents. For ATXs, a novel sample preparation procedure is presented that involves solid phase extraction on a mixed reverse phase/weak anion exchange column that facilitates simultaneous clean-up of the derivatised toxins and removal of excess dansylation reagent through covalent bonding. The challenge of achieving co-elution in LC between deuterated and non-deuterated dansylated toxins was addressed by modifying separation conditions from the usual reverse phase (RP) separation to hydrophilic interaction liquid chromatography in the case of DA and a shortened RP separation with high organic modifier content in the case of the ATXs. The new methods gave limits of detection between 10 and 60 mu g kg(-1) and allowed for precise, accurate and fast determination of toxins in spiked control samples and matrix reference materials. This work demonstrates that isotope-labelling derivatisation is broadly applicable to the field of algal toxin analysis where derivatisation is well established but isotopically-labelled standards are not available.