Determination of ionophore coccidiostats in feedingstuffs by liquid chromatography-tandem mass spectrometry Part I. Application to targeted feed.

A new and fit to purpose multi-analyte method for the determination of six coccidiostats (monensin A, salinomycin, narasin composed of its principal component narasin A and its minor component narasin I, lasalocid, semduramicin and maduramicin) in poultry and cattle compound feed by liquid chromatography tandem mass spectrometry (LC-MS/MS) has been developed and in-house validated. The concentration level of the target analytes at which the validation experiments have been carried out varied between 1 and 9 mg kg(-1). The method developed involved a simple extraction of the coccidiostats from the feed samples followed by a clean-up by solid-phase extraction prior to chromatographic analysis. The analytes were quantified either by matrix-matched standards or by the standard addition technique, obtaining the following performance profile of the method for the various analyte/matrix combinations. When quantifying against matrix-matched standards, the concentration independent intermediate precision expressed in terms of relative percentage standard deviation varied between 4 and 10% and the relative percentage recovery rates ranged from 86 to 120%, depending on the target analyte and matrix. When using the standard addition technique, the corresponding values for the intermediate precision varied between 2 and 8% and the relative percentage recovery rate ranged from 73 to 115%. The limit of detection (LOD) and limit of quantification (LOQ) were different for the various analyte/matrix combinations but were in all cases below 0.014 and 0.046 mg kg(-1), respectively. Based on the obtained method performance characteristics, the method is considered suitable for the determination of ionophore coccidiostats in target feed. The main field of application of the validated method is to enforce European legislation regarding the authorisation of coccidiostats, focusing on the measurement at the authorised levels and at low level in feed during the withdrawal period at which the coccidiostats must not be added to the feed. Overall, the method proposed appears to be appropriate as a confirmatory method for the monitoring of these six ionophore coccidiostats and can therefore be considered as complementary to the official HPLC-UV methods.