A novel, simple and rapid method for screening and quantification of selected algal toxins, which includes four microcystins and anatoxin-a, in ambient freshwaters was developed based on direct evaporation and analysis by ultra-performance liquid chromatography-tandem mass spectrometry. Optimization of mass spectrometric conditions was performed to maximize the sensitivity and selectivity of the targeted analytes. A validation of the methodology was conducted to account for matrix interferences, method detection limits (MDLs), linearity, accuracy and precision for the compounds of interest. Excellent MDLs were achieved for anatoxin-a (0.0745 ng/mL) and the selected microcystins (0.118-0.172 ng/mL). Good linear correlations were obtained for the range of calibration standards (0.500-100 ng/mL), with R2 values between 0.9908 and 0.9995. It was shown that this method has distinct advantages over solid phase extraction by eliminating the sample clean-up step, improving reproducibility, decreasing analysis time, minimizing waste generation and being more cost effective compared to other methods. Additionally, little sample handling was required, reducing the risk of cross contamination and analyte loss. This method was validated by testing a set of fresh water samples and detecting total microcystin-RR at trace level concentrations (0.208-0.210 ng/mL), which was well below the provisional guideline limit of 1 µg/L for microcystin-LR set by the World Health Organization.
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