Monitoring of cyanotoxins in water from hypersaline microalgae colonies by ultra high performance liquid chromatography with diode array and tandem mass spectrometry detection following salting-out liquid-liquid extraction

Abstract

In this study two different analytical approaches have been developed to determine the presence of sev-eral cyanotoxins in saline water samples from a continental salt marsh. A salting-out assisted liquid-liquidextraction (SALLE) has been used in combination with ultra-high performance liquid chromatography-tandem mass spectrometry and UV-diode array detection (UHPLC-MS/MS and UHPLC-DAD). The targetanalytes are eight microcystins named MC-RR, MC-YR, MC-LR, MC-WR, MC-LA, MC-LY, MC-LW, MC-LFand nodularin (NOD), covering a wide range of polarities. The separation was achieved using a ZorbaxEclipse Plus RRHD C18 column (50 × 2.1 mm, 1.8 m) in less than 7.5 and 5.5 min for UV and MS/MSdetection, respectively. The mobile phase used consisted of water (solvent A) and acetonitrile (MeCN)(solvent B), both containing 0.01% of formic acid for DAD and 0.4% of formic acid for MS/MS detection,at a flow rate of 0.4 mL min−1. The temperature of the column was set at 25◦C and 20 L of samplewere injected. The main parameters affecting the SALLE procedure were studied and the following opti-mum values were obtained: neutral pH, 2 mL of acetonitrile as extraction solvent and 1.2 g of ammoniumsulfate as salting-out agent for 4 mL of water sample. The validation protocols for both methods wereaccomplished with real water samples obtaining LODs ranging from 1.0 to 3.4 g L−1and 0.02 to 0.11 gL−1for DAD and MS/MS respectively. Although the SALLE-UHPLC-DAD methodology is easier and cheaperthan UHPLC-MS/MS significantly better detection limits were achieved with tandem mass spectrometryas well as allowing for unambiguous identification. Extraction recoveries were higher than 77.0% (exceptfor MC-RR and NOD which were 53.2% and 54.3, respectively) with satisfactory inter-day and intra-dayprecisions (RSD below 13.3%).