Strata x cw

HPLC-grade acetonitrile, methanol, and isopropanol were purchased from J.T. Baker (Deventer, The Netherlands). Ethylenediaminetetraacetic acid (EDTA), sodium chloride, and sodium hydroxide were from POCH (Gliwice, Poland), and potassium hydrogen phosphate (K₂HPO₄) was from Chempur (Piekary Śląskie, Poland). Ammonium acetate, heptafluorobutyric acid (HFBA), and trichloroacetic acid (TCA) were obtained from Sigma–Aldrich, (St. Louis, MO, USA). Formic acid was from Fluka (Charlotte, NC, USA). Syringe 0.22 µm hydrophilic polyvinylidene fluoride (PVDF) membrane filters were purchased from Restek (Bellefonte, PA, USA). Ultra-pure water was generated by a Millipore Milli-Q System (Millipore, Molsheim, France).
The analytical reference standards of DHSTR, GEN, KAN, NEO, PAR, STR, and SPC were purchased from Dr Ehrenstorfer (Augsburg, Germany), and AMI, APR, HYG, RIB, SIS, TOB from Sigma–Aldrich (St. Louis, MO, USA). Strata X (100 mg, 6 mL), Strata X-CW (100 mg, 6 mL), and Strata X-AW (100 mg, 6 mL) cartridges were from Phenomenex (Torrance, CA, USA). Oasis HLB (60 mg, 3 mL) cartridges were from Waters (Milford, MA, USA). All matrices were obtained from local supermarkets or were originating from the Polish official residue control program. Samples were analyzed to ensure the absence of aminoglycoside residues and kept frozen at −18 °C until use.

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.

Samples were made salt free by passing through polymeric cartridge Strata-X-CW (Cat No. 8B-S035-JEG, Phenomenex). The cartridge was first conditioned by adding 10-ml methanol followed by 10-ml distilled water. The flow-through was discarded, and then 10 ml of the sample was added to the cartridge. The flow-through from the cartridge was collected, tested for harvesting activity and then analyzed using HPLC and HR-LC–MS.