Determination of phenoxyacid herbicides and degradation products in surface water by LC-ESI-/MS/MS: Application to stormwater retention ponds in the City of Regina, Saskatchewan

This study explores development of a new liquid chromatography tandem mass spectrometry method to determine the phenoxyacid herbicides 2-methyl-4chlorophenoxyacetic acid, 2-(2-methyl-4-chlorophenoxy)propanoic acid, 4-(2-methyl-4-chlorophenoxy)butanoic acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propanoic acid, 4-(2,4-dichlorophenoxy)butanoic acid, 2-(2,4,5-trichlorophenoxy)propanoic acid, (3,6-dichloro-2-methoxy)benzoic acid and the nitrile herbicide 3,5-dibromo-4-hydroxybenzonitrile, along with their degradation products 4chloro-2-methylphenol, 2,4-dichlorophenol, 2,4,5-trichlorophenol and 3,5-dibromo-4-hydroxybenzoic acid in water samples. The samples were extracted from the water matrix using solid phase extraction and ultimately quantitated using liquid chromatography negative ion electrospray tandem mass spectrometry with selected reaction monitoring and a total instrument analysis time of 40 minutes. Chromatography is performed on a Zorbax Eclipse XDB-C18 (50 x 4.6 mm i.d., 1.8 mum) with a gradient elution using water:methanol with 2 mmol L-1 ammonium acetate mobile phase at a flow rate of 0.15 mL/min. Methanolic ammonia (1000 mmol L-1) is added post column at a flow rate of 0.05 mL/min to increase ionization of the degradation products in the mass spectrometric source. Limits of detection achieved were between 1 and 20 ng L-1 in 1 L of an extracted surface water sample. Calibration curves were linear with correlation coefficients better than 0.961.;Stormwater retention pond and creek samples were collected from May, 2007 to October, 2007 in Regina, Saskatchewan. Mecoprop and 2,4-dichlorophenoxyacetic acid were detected in 100% of samples with a range in concentrations of 36 to 3267 ng L-1 for 2,4-dichlorophenoxyacetic acid and 15 to 2403 ng L-1 for mecoprop. 2-Methyl-4chlorophenoxyacetic acid was detected in 71% of samples (range 11 to 379 ng L-1) and dichlorprop was detected in 14% of samples (range 47 to 1260 ng L-1 ). The degradation product of mecoprop and 2-methyl-4-chlorophenoxyacetic acid (4-chloro-2methylphenol) was detected in 13% of samples (range 22 to 101 ng L-1) and 2,4-dichlorophenol (degradation product of 2,4-dichlorophenoxyacetic acid and dichlorprop) was detected in 6% of samples (range 22 to 302 ng L-1). Ratios of the herbicide concentrations in water from the stormwater ponds were compared to formulations to identify potential local urban usage contributions.