Development, validation and application to real samples of a liquid chromatography with tandem mass spectrometry method for the determination of tetracyclines in beeswax

Accurate determination of four tetracycline residues in chicken meat by isotope dilution-liquid chromatography/tandem mass spectrometry

An analytical method based on isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC‒MS/MS) was developed to accurately determine four representative tetracyclines (tetracycline, chlortetracycline, doxycycline, and oxytetracycline) in chicken meat. Tetracyclines are known to have a great tendency for epimerization and keto-enol tautomerism, which often provoke major challenges in their determination. Since this isomerization was found to be unavoidable during the whole chain of the current analysis, the total content (µg kg^‒1) of individual tetracycline was quantified as a sum of each parent compound and its respective isomeric forms. Using this approach in combination with IDMS analysis, more consistent, accurate, and reproducible measurement results for the four tetracyclines in chicken meat were acquired. LC-MS/MS conditions and sample preparation processes were comprehensively optimized to minimize the chelating effect of tetracyclines and possible co-extracted interferences. Details of the sample preparation scheme, LC‒MS/MS detection, calculation equation, and method validation are described in this article. The method provided very good accuracy (97.7-102.6%) for all analytes across the concentration range of 10-200 µg kg^‒1, with relative standard deviations for intra-day and inter-day precision of less than 4%. The limits of quantification were below 0.2 µg kg^‒1, demonstrating the high sensitivity of the method. Furthermore, the measurement uncertainty was generally below 5.5%. Hence, the established method exhibits high-order metrological quality with superior performance over various existing methodologies. Moreover, this method can provide references for general food testing laboratories close to and far below the established maximum residue limits (100 µg kg^‒1) for animal muscle tissues.

Preparation of restricted-access material precolumns by grafting δ-gluconolactone onto a hybrid silica monolithic column for on-line solid-phase extraction of tetracycline residues from milk

A restricted-access material-hybrid monolithic column was prepared based on single-component organosiloxane and dynamic grafting of δ-gluconolactone for on-line solid phase extraction of tetracycline antibiotic residues from milk. The hybrid monolithic column was prepared in a stainless-steel chromatographic column using methyltrimethoxysilane as the single precursor. δ-Gluconolactone was covalently coupled to aminopropyl derivatized hybrid monolithic column, which formed hydrophilic structures on the surface of the pore of the restricted-access material-hybrid monolithic column. The columns were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, nitrogen adsorption, contact angle analysis, dynamic adsorption, and chromatographic performance evaluation. The restricted-access material-hybrid monolithic column was applied to the on-line extraction of tetracycline residues from milk. An enrichment factor of 15.8 and a good sample clean-up effect were obtained under the optimized conditions. The recoveries of the three spiked milk samples were between 81.7 and 102.5% with relative standard deviations (n = 3) in the range of 2-5%. The limits of detection (S/N = 3) for target compounds were in the range of 3.80-9.03 μg/kg. The results show that the on-line extraction using the restricted-access material-hybrid monolithic column was powerful for food sample pretreatment with high selectivity and good clean-up effect.