The pesticides standards of deltamethrin, penconazole, kresoxim-methyl, cyproxonazole, epoxiconazole and azoxystrobin were supplied by Sigma-Aldrich (Seelze, Germany). The stock solutions (1000 mg/L) were prepared by dissolving the standards in methanol HPLC grade (99.9%) purchased by Sintorgan (Buenos Aires, Argentina), and stored under freezing condition (-18°C ± 1°C) in dark bottles sealed with PTFE/silicone caps. The working standard solutions (50 mg/L) were prepared in acetonitrile (ACN) of high purity grade for residue analysis, provided by Merck (Darmstadt, Germany).
Deionized water obtained from an E-pure water purification system (Barnstead/Thermolyne, Bedford, MA, United States) was used for sample swelling in the extraction step.
For extraction and partitioning, sodium chloride and anhydrous sodium sulfate were purchased from Biopack (Buenos Aires, Argentina); sodium hydrogencitrate sesquihydrate and sodium citrate dihydrate were obtained from Sigma-Aldrich (Seelze, Germany). For clean-up using d-SPE, C18 and PSA bulk powder were obtained from Agilent Technologies (Santa Clara, United States).
Deionized water obtained from an E-pure water purification system (Barnstead/Thermolyne, Bedford, MA, United States) was used for sample swelling in the extraction step.
For extraction and partitioning, sodium chloride and anhydrous sodium sulfate were purchased from Biopack (Buenos Aires, Argentina); sodium hydrogencitrate sesquihydrate and sodium citrate dihydrate were obtained from Sigma-Aldrich (Seelze, Germany). For clean-up using d-SPE, C18 and PSA bulk powder were obtained from Agilent Technologies (Santa Clara, United States).