Strata sax

Oxytetracycline (OXT), chlortetracycline (CTC), tetracycline (TC), doxycycline hyclate (DC), tiamulin fumarate (TIAM), tylosine tartrate (TYL), ciprofloxacin (CIP), enrofloxacin (ENR), lincomycin (LINCO), trimethoprim (TRIM), activated carbon, EDTA disodium salt and formic acid were obtained from Sigma Aldrich (St. Louis, MO, USA). HPLC-grade methanol, acetonitrile and octadecyl C₁₈ 40 µm Prep LC sorbent were purchased from Baker (Deventer, The Netherlands). Disodium hydrogen phosphate and sodium hydroxide were from Chempur (Piekary Śląskie, Poland), citric acid was from Acros Organic (Morris Plains, NJ, USA) and PSA Bonded Silica sorbent was from Supelco (Bellefonte, PA, USA). Purified water was prepared with a Milli-Q water system from Millipore (Billerica, MA, USA).
McIlvaine-Na₂EDTA buffer was prepared by dissolving 11.406 g Na₂EDTA in 115.65 mL 0.2 M phosphate buffer and 184.65 mL 0.1 M citric acid. The pH was adjusted to 4.0 by adding 0.1 M citric acid or 0.2 M phosphate buffer. Three SPE cartridges were tested; OASIS HLB (60 mg, 3 mL) from Waters (Milford, MA, USA) and Strata-SAX (strong anion exchanger, 500 mg, 12 mL) and Strata-X-CW (weak cation mixed mode, 300 mg, 3 mL) both from Phenomenex (Torrance, CA, USA). An SPE manifold (J.T. Baker, PA, USA) and a pump as a vacuum source were used.

All solvents used for sample preparation were of HPLC grade and purchased from Sigma-Aldrich (Schnelldorf, Germany). All solvents used for sample analysis, water (H₂O), methanol (MeOH), and acetonitrile (ACN), were of LCMS grade and purchased from Sigma-Aldrich. Formic acid (≥96%) was purchased from Thermo Fisher Scientific (Waltham, MA, USA). H₂O for SPE was purified on a Milli-Q system (Merck Millipore, Billerica, MA, USA). Iturin A2 (>95%) was purchased from Sigma-Aldrich and the stock solution (20 μg·mL⁻¹) was prepared in HPLC grade MeOH. Sodium bicarbonate (NaHCO₃), 98% ¹³C-labelled, was purchased from Sigma-Aldrich. Fluorescence derivatisation was achieved with AccQ-Fluor reagent WAT052880 (Waters; Milford, MA, USA). The mixture of fumonisin B₁ (49.9 μg·mL⁻¹) and fumonisin B₂ (50.6 μg·mL⁻¹) in H₂O/ACN (1:1, v/v) was purchased from Romer Labs (Tulln, Austria). External standards valinomycin and chloramphenicol were purchased from Sigma-Aldrich. Five different, 3 mL, 30 mg, SPE cartridges, Strata-X, Strata-SCX, Strata-WCX, Strata-SAX, Strata-MAX, were purchased from Phenomenex (Torrance, CA, USA). Three millilitre, 30 mg Oasis-HLB SPE cartridges were purchased from Waters.