SOME COMMENTS ON THE DETERMINATION OF MICROCYSTIN TOXINS IN WATERS BYHIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

This paper describes some of the problems that may arise during the an alysis of microcystin toxins and nodularin using the method described by Lawton, Edwards and Codd (Analyst, 1994, 119, 1525), Difficulty may be caused by the appearance of additional peaks in the HPLC chromatog rams as a result of leaching of material from the C-18 trifunctional ( C-18t) solid-phase extraction cartridges, and co elution of other orga nic compounds in the water makes it difficult to identify toxins using their characteristic UV spectra, expecially at low toxin concentratio ns. Samples containing chlorine must be treated with sodium thiosulfat e since the presence of chlorine results in low toxin recoveries, espe cially of nodularin, The published method specifies the use of sodium sulfite and acidification with trifluoroacetic acid for the removal of chlorine, but application of this procedure has been shown to produce inconsistent toxin recoveries, and zero percentage recoveries were re corded in 71% of the analyses performed with treated waters having a m icrocystin LR concentration of 0.4 mu g l(-1), The use of microcystin LR as an 'internal standard' to adjust the recovery of other microcyst in toxins is at best qualitative.