Large volume injection for the direct analysis of ionophores and avermectins in surface water by liquid chromatography-electrospray ionization tandem mass spectrometry

A simple method for the direct determination of residues of ionophore antibiotics and avermectin antiparasitics in surface water is reported. Using a large volume injector, a mixture of methanol and surface water is injected into an analytical liquid chromatography (LC) column and subsequently screened for residues of these veterinary pharmaceuticals using electrospray ionization tandem mass spectrometry. On-line sample enrichment and chromatographic separation are achieved using a single, short (20 mm) octadecylsilane LC column. The method permits the detection of four ionophores and two avermectins in surface water samples at low ng L⁻¹ concentrations. Minimal matrix effects were observed for a variety of surface water samples which permitted the use of reagent-based standards for quantitation.     

Multi-Residue Analysis of Avermectins in Bovine Liver and Muscle by Liquid Chromatography–Fluorescence Detector

A simple multi-residue analysis method for the quantitative determination of eprinomectin, abamectin, doramectin and ivermectin in bovine tissues was developed. The tissue sample was extracted with acetonitrile, followed by clean-up on a C₁₈ solid phase extraction cartridge. The eluate was derivatised before being analyzed by HPLC coupled to a fluorescence detector. The method was validated using bovine liver and muscle fortified with the drugs at 0, 5, 10 and 50 ng g⁻¹. The mean recoveries of the four drugs were 70.31–87.11% in liver and 79.57–93.65% in muscle, with relative standard deviations below 17.84% in liver and 14.68% in muscle. The limits of detection were between 0.5 and 1.0 ng g⁻¹ and the limits of quantification were 1–2 ng g⁻¹ in bovine tissues for the four drugs.     

Trace analysis of endectocides in milk by high performance liquid chromatography with fluorescence detection

An analytical method has been developed for the simultaneous determination of the following endectocide drugs in milk: ivermectin, abamectin, doramectin, moxidectin, eprinomectin, emamectin and nemadectin. Samples were extracted with acetonitrile, purified with solid-phase extraction on a reversed phase C₈, derivatised with N-methylimidazole, trifluoroacetic anhydride and acetic acid to a stable fluorescent derivative, and were further analysed by gradient high performance liquid chromatography (HPLC) on an endcapped reversed phase Supelcosil LC-8-DB. The derivatisation step was mathematically optimised and the method was validated according to the requirements of Commission Decision 2002/657/EC, using fortified raw bovine milk. Mean recovery was between 78 and 98%. The repeatability (CV_r) and within-laboratory reproducibility (CV_W) ranged from 4.6 to 13.4% and from 6.6 to 14.5%, respectively. Decision limits (CCα) for analytes with MRL values, namely eprinomectin and moxidectin, were determined to be 24.8 and 50.6 μg kg⁻¹, respectively. CCα values for unauthorised endectocides ranged from 0.1 to 0.2 μg kg⁻¹. Due to high acceptability regarding the required criteria and applicability to ovine and caprine milk, giving similar results, this multi-analyte method has been successfully implemented in pharmacokinetic research studies as well as statutory residue monitoring in Slovenia.     

The derivatisation of avermectins and milbemycins in milk: new insights and improvement of the procedure

Derivatisation of the avermectines ivermectin (IVM), doramectin (DOR), abamectin (ABA) and eprinomectin (EPR), and the milbemycin moxidectin (MOX) to fluorescent derivatives is commonly used for quantitative analysis at relevant levels using high performance liquid chromatography (HPLC) with fluorescence detection. Problems associated with the differences in reactivity towards derivatisation (EPM) and limited stability of the derived products (IVM, DOR, ABA) may seriously hamper the applicability of the method and the reliability of the obtained results. A study was performed to obtain more insight in this derivatisation process from an organic chemistry point of view. This study demonstrated the occurrence of two main fluorescent derivatives: the trifluoroacetyl esters (flu-TFA) and the derivatives with a free hydroxy group at the glycosidic ring (flu-OH). Optimisation of the derivatisation conditions resulted in a fast and reproducible formation of the fluorescent derivatives for all analytes including EPM. The improved procedure involves the addition of 1-methylimidazole (MI), trifluoroacetic anhydride (TFAA), triethylamine (TEA) and trifluoroacetic acid (TFA) with a subsequent incubation for 30 min at 70 °C. With this procedure for IVM, DOR and ABA flu-TFA derivatives are obtained instead of flu-OH derivatives as generally described in literature. The derivatisation is reproducible in different milk samples and the derivatives proved to be stable for at least 80 h at room temperature. Using the optimised procedure a limit of detection (LoD) of 0.1 μg kg⁻¹ in milk was readily obtained.     

Determination of avermectins in commercial formulations using microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) was developed for quantitative analysis of avermectins, such as abamectin, doramectin and ivermectin, in commercial formulations, using the microemulsion buffer containing a 50 mM phosphate buffer at pH 2.5, 1.1% (v/v) n-octane as oil droplets, 180 mM sodium dodecylsulphate as surfactant, 890 mM 1-butanol as co-surfactant and 30% (v/v) ethanol as organic co-solvent. High accuracy and precision of the method were obtained. The contents of avermectins in commercial formulations determined by MEEKC were found to be insignificantly different with those determined by high performance liquid chromatography (HPLC). Therefore, MEEKC can be used an alternative method to HPLC for quantitative determination of avermectins.     

Synthesis of 4″-alkoxy avermectin derivatives using rhodium carbenoid-mediated O-H insertion reaction

4″-Alkoxy avermectin derivatives have been synthesized using O-H insertion reaction with ethyl diazoacetate in the presence of Rh₂(OAc)₄ as a catalyst.