|Highly Sensitive and Selective Quantification of Microcystin Toxins in Drinking Water By UHPLC-MS/MS
|Dr Alan McKeown
|Advanced Chromatography Technologies Ltd
Abstract Information :
Cyanobacteria or blue-green algae are common throughout the world. Microcystins are cyclic heptapeptides produced by cyanobacteria and associated with human hepatotoxicity. Under certain nutrient rich and environmentally favourable conditions, freshwater cyanobacteria have the potential to rapidly accumulate and form blooms. Concentrations of microcystins in water containing blooms can be highly variable and must be known for safe water supplies. Due to the hepatotoxic nature, the World Health Organisation (WHO) has set a provisional limit of 1g / L for total Microcystin-LR as a marker for cyanobacteria toxin levels.
Initial spiked water samples allowed optimisation of chromatography for separation and MS conditions for low level detection. This approach offers reproducible analyte recoveries and rapid sample preparation times. The Bruker EVOQ Elite triple quadrupole detector was employed to monitor appropriate MRM transitions and analyte separation was provided by an ACE Excel 2 micron C18 column. Experiments included optimisation of the MS conditions and transitions for sensitivity and reproducibility across the concentration ranges explored.
A rapid UHPLC method providing satisfactory separation and elution of Microcystin-LR (MC-LR), Microcystin-RR (MC-RR) and Microcystin-YR (MC-YR) in under 3.5 minutes was developed using the Bruker Advance UHPLC with an ACE Excel 2 micron C18 UHPLC column. Signal response studies indicated an improvement in sensitivity of x128 fold and x194 fold for MC-LR and MC-YR respectively when detecting the transition products of the doubly charged ions which dominate the mass spectra under full scan conditions. All three mycrocystins share the common m/z 135 product ion. The method was found to be linear for MC-LR, MC-RR and MC-YR from 0.05ppb to 50ppb with regression coefficient values (R∧2) = 0.999, 0.999 and 0.997 respectively. Repeatability at the 0.05ppb concentration level for MC-LR, MC-RR and MC-YR was demonstrated with RSD values (n = 7) of 10%, 7.1% and 8.1% respectively.