Trisodium citrate dihydrate

The captan standard was purchased from Dr. Ehrenstorfer (Augsburg, Germany). All reagents were of sufficiently high purity for GC analysis. Acetonitrile, acetone, and petroleum ether were purchased from Honeywell Specialty Chemicals Seelze GmbH (Seelze, Germany). Anhydrous magnesium sulphate, sodium chloride, and tri-sodium citrate dihydrate were from Chempur (Piekary Slaskie, Poland). Sodium citrate dibasic sesquihydrate was purchased from Sigma-Aldrich (Steinheim, Germany). As for the sorbents, PSA was purchased from Supelco (Bellefonte, PA, USA), Al₂O₃, ZrO₂, SiO₂ were from POCH (Gliwice, Poland) and Florisil^® was from Sigma-Aldrich (St. Louis, MO, USA).

The acetonitrile, acetone, and sodium chloride were provided by Honeywell (Charlotte, NC, USA). Petroleum ether, magnesium sulfate anhydrous, sodium sulfate anhydrous, trisodium citrate dihydrate (Na₃C₆H₅O₇·2H₂O), were from Chempur (Piekary Śląskie, Poland), and disodium hydrogen citrate sesquihydrate (Na₂HC₆H₅O₇·1.5H₂O) was purchased from Sigma-Aldrich (Burlington, MA, USA). A primary secondary amine (PSA, a polymerically bonded ethylenediamine-N-propyl phase that contains both primary and secondary amines, 50 µm particle size, 70 Å pore size), internal standard triphenyl phosphate (TPP, molecular formula: C₁₈H₁₅O₄P, molecular weight: 326.3 g/mol, CAS No: 115–86-6), and fluopyram were from Supelco (Bellefonte, PE, USA), and tebuconazole was supplied by Instytut Przemysłu Organicznego (Warsaw, Poland). The purity of all standards was above 98%. Fungicide standards at the concentration of 1000 µg/mL were prepared in acetone and stored at − 17 °C. Working solutions were prepared by dissolving appropriate amounts of the standard solution in Petroleum ether and stored at 4 °C.

Chitosan powder (99.9%) of low molecular weight (50–190 kDa) was purchased from NANOSHEL and used as received. A detailed study of the physico-chemical properties of the used chitosan was reported elsewhere [34 (link)]. Acetic acid (>99.7%), trisodium citrate dihydrate (>99.0%), CuSO₄ × 5H₂O (>99.0%), H₂SO₄ (98.0%), and AgNO₃ (>99.0%) were purchased from Chempur and used without further purification. All solutions were prepared using deionized water with a resistivity higher than 18 MΩ cm (Polwater).