Determination of atrazine, deethylatrazine and deisopropylatrazine in water and sediment by isotope dilution gas chromatography-mass spectrometry

Methods for the trace analyses of atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) in water and sediment have been developed by using stable-isotope dilution with gas chromatography-mass spectrometry detection. Water samples are spiked with known amounts of ¹³C₃-atrazine, ¹³C₃-DEA and ¹³C₃-DIA and submitted to solid-phase extraction with C₁₈ bonded silica. Pesticides are eluted from the solid phase with ethyl acetate. Sediment samples are spiked and equilibrated with a known amount of each labeled standard before supercritical fluid extraction (SFE) using a 4% (v/v) methanol-CO₂ mobile phase at 43°C and 10 MPa with off-line collection in methanol. A gas chromatograph coupled with a quadrupole mass spectrometer operated in the selected ion monitoring (SIM) mode was used to analyze the concentrated sample extracts. When compared to conventional liquid-liquid extraction methods, these methods decrease extraction time, labor, and solvent volume required. Quantification of the triazines by using isotope dilution compensates for differences in physical recovery for atrazine and its metabolites, especially when large ( > 100 ml) water volumes are extracted. Method detection limits for atrazine, DEA and DIA are 0.02, 0.02 and 0.10 μ g 1^-1, respectively, in water. In sediment, the method detection limits are 0.10, 0.20 and 0.50 ng g^-1 for atrazine, DEA and DIA, respectively. More than 4000 water and 800 sediment samples have been analyzed by these methods for more than two years. The average accuracy (bias) for atrazine-fortified water samples is +6.4% (n = 200) and the precision from duplicate analyses is ±6.0%. Precision of the SFE method for atrazine is ±11% at the 2 ng g^-1 level whereas accuracy is -3.2% (n = 8) for recovery of ¹³C₃-atrazine standard at the 5 ng g^-1 level.