Quantitative determination of the veterinary drug monensin in horse feed samples by square wave voltammetry (SWV) and direct infusion electrospray ionization tandem mass spectrometry (DI–ESI–MS/MS)

Abstract This paper presents for the first time the determination of monensin monosodium salt ( MnzNa ) by means of square wave voltammetry (SWV), cyclic voltammetry (CV), and, in parallel, direct infusion electrospray ionization tandem mass spectrometry (DI–ESI–MS/MS). The influence of various factors, such as pH, buffer composition, and SWV parameters on current response was studied. The best SWV signal was obtained at about −1.50 V versus an Ag/AgCl/KCl reference electrode in Britton–Robinson (B–R) buffer. Under optimal conditions, the SWV response of the renewable silver amalgam film electrode Hg(Ag)FE was linear over two MnzNa concentration ranges, from 7.5 × 10 −8 to 5.0 × 10 −7  mol L −1 and from 5.0 × 10 −7 to 1.0 × 10 −5  mol L −1 . The limits of detection and quantification were 1.27 × 10 −8  mol L −1 and 4.23 × 10 −8  mol L −1 , respectively. The applicability of the developed SWV method was investigated in the determination of MnzNa in horse feed by the standard addition method. CV was applied to understand the electrode mechanism of MnzNa . Finally, direct infusion electrospray ionization tandem mass spectrometry (DI–ESI–MS/MS) was used to determine MnzNa in horse feed samples by the external calibration method. The detector response was linear in the concentration range of 1.1 × 10 −7 to 1.4 × 10 −6  mol L −1 . The obtained limits of detection and quantification were 3.4 × 10 −8  mol L −1 and 1.1 × 10 −7  mol L −1 , respectively. Statistical analysis of MnzNa determination results from SWV and DI–ESI–MS/MS did not reveal any significant differences between them.