Sodium hydrogenocitrate sesquihydrate

The pesticide standards used for the optimization and subsequent validation were provided by LGC (Teddington, United Kingdom) and Sigma-Aldrich (Steinheim, Germany) and were stored at 30 °C. A standard-mix solution was prepared using individual stock solutions. Individual stock solutions (800–1000 mg L⁻¹) were prepared from each standard in water and methanol and stored in the dark at 30 °C in amber glass vials. Acetonitrile and methanol (LC-MS quality) were obtained from Fluka Analytical (Steinheim, Germany). LC-MS grade water from Fisher Chemical (Fair Lawn, NJ, USA) was used. Formic acid was purchased from Sigma Aldrich (Steinheim, Germany). The salts employed in the extraction method (anhydrous magnesium sulfate, sodium chloride, sodium hydrogenocitrate sesquihydrate, and sodium citrate tribasic dihydrate) were supplied by Sigma-Aldrich (Steinheim, Germany).

The standards of pesticides included in the multiresidue method of study were provided by LGC (Teddington, UK) and Dr. Ehrenstorfer (Augsburg, Germany). The analytical standards were stored at −30°C. The standard-mix solution was prepared using individual stock solutions. Individual stock solutions (800–1000 mg/L) were prepared from each standard and stored in the dark at −30°C in amber glass vials.
Carbon dioxide (CO₂) 5.3 quality was supplied by Abello Linde (Madrid, Spain); LC-MS quality methanol used for mobile phase preparation was obtained from Fluka Analytical (Steinheim, Germany). LC-MS grade water from Fisher Chemical (Fair Lawn, NJ, USA) was used. The additives ammonium formate and formic acid were purchased from Sigma Aldrich (Steinheim, Germany). The salts employed in the QuEChERS extraction (anhydrous magnesium sulphate, sodium chloride, sodium hydrogenocitrate sesquihydrate, and sodium citrate tribasic dihydrate) were supplied by Sigma-Aldrich (Steinheim, Germany) except for PSA that was obtained from Supelco (Bellefonte, PA, USA).