Rapid method for the simultaneous determination of six ionophores in feed by liquid chromatography/mass spectrometry.

This study discusses the development of a simple and sensitive method for detecting and quantifying six different ionophores in animal feed using liquid chromatography/mass spectrometry. The method offers good recovery rates and could help improve quality control in the feed industry.

Objective of the Study

• The research focused on developing a reliable, sensitive, and straightforward liquid chromatography/mass spectrometry (LC/MS) method for determining six different ionophores – lasalocid, monensin, laidlomycin, maduramycin, salinomycin, and narasin – in animal feed.

Method and Procedure

• Extraction of the ionophores was achieved by shaking 1 g of the feed with 4 mL of a methanol-water solution (9 + 1, v/v) for 45 minutes. After centrifugation, the diluted extracts were analyzed without any cleanup.
• The analysis was performed using a Betasil C18 column (150 x 4.6 mm id, 5 pm particle size) on an LC/MS system.
• To improve the sensitivity of the method and the efficiency of the ionization of the compounds, the LC/MS system was operated in the atmospheric pressure chemical ionization (APCI) mode. It is the first time this mode is used for ionophores analysis.
• The mobile phase of the liquid chromatography consisted of 50 mM ammonium acetate as solvent A and a mix of acetonitrile-methanol (7 + 3, v/v) as solvent B, used in a gradient run.

Results and Recovery Rates

• Excellent recovery rates between 81-120% were recorded for all compounds at fortification levels of 1-200 microg/g, with relative standard deviation (RSD) being less than or equal to 15%. Exceptions were maduramycin at 2 and 5 microg/g and salinomycin at 1 microg/g, where RSD was slightly higher.
• At a lower concentration of 0.5 microg/g, an 87-119% recovery was achieved, with RSD up to 20%.
• Specifically, lasalocid recovered at a higher rate of 133% in sow feed, while salinomycin’s recovery rate was lower at 79% in horse feed.
• When analysing proficiency test samples, the method showed a good agreement with the certified values, indicating its reliability and potential for practical use in the feed industry.

Conclusion and Implications

• This study enhances our capacity to detect and quantify six different ionophores in animal feed quickly and with high sensitivity.
• The method offers good recovery rates, making it a potentially powerful tool for quality control measures in the feed industry.