الفهرس 
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Abstract
This study holds significant value for laboratories engaged in the analysis of veterinary drug residues. It can assist such laboratories in reducing the time required for preparing stock solutions, streamlining sample preparation processes, and minimizing expenses associated with acquiring high-quality reference standard materials and solvents.
The study suggested that reference standard materials for veterinary drugs may still be usable beyond their manufacturer’s expiry dates, provided that thorough comparisons are conducted. The research has shown that reference materials from various classes of veterinary drugs exhibited excellent stability even after their expiry dates. However, additional studies are required to assess the stability of reference materials in other drug families. The majority of the results from the 12-month stability experiments of veterinary drug stock solutions were consistent with previous studies, except for those that exceeded the employed tolerance limits. Long-term stability data, covering periods of 30 to 36 months, were obtained for 17 veterinary drug stock solutions.
The choice of solvent plays a crucial role in determining the stability of stock solutions of veterinary drug compounds. The use of a basic mixture of methanol/water (8:2) contributed to the stability of oxolinic acid for a period of 12 months, whereas methanol alone resulted in poor stability for penicillins. Further experiments will be conducted to investigate the stabilization of penicillin V in solvent mixtures that do not contain methanol.
In the evaluation of stability results, a limited tolerance limit of ±10% was employed, following the guidelines outlined in the European Commission document SANTE/11813/2017. It’s worth noting that other literature has utilized broader tolerance limits of 29%. Consequently, testing laboratories have the flexibility to apply these findings according to their specific criteria for stability assessment, taking into consideration the uncertainties and variations in analyte responses observed in their LC-MS/MS systems.
The UPLC-MS/MS method for analyzing veterinary drug residues in liver involved the optimization of various parameters. The method utilized a Kinetex C18 column and a mobile phase consisting of methanol and acetic acid. Efficient extraction of veterinary drug residues from liver samples was achieved using acetonitrile with McIlvaine buffer, UltraTrax, and shaking with two steel balls. A subsequent clean-up step with C18 dispersive Solid-Phase extraction was performed, followed by analysis using UPLC-MS/MS.
The method was rigorously validated in accordance with the guidelines outlined in the Analytical Procedures and Methods Validation for Drugs and Biologics issued by the FDA. Across all tested compounds, the method demonstrated robust performance, with relative standard deviations (RSD) consistently below 12%. Additionally, the recoveries for most of the tested compounds fell within the range of 81% to 118%, with the exception of dimetridazole (62%) and malachite green (36%).