Electrospray ionization and collision-induced dissociation of antibiotic polyether ionophores

Abstract

A series of polyether ionophores (lasalocid, monensin-A, narasin-A and salinomycin) was investigated by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). A fast short-column liquid chromatographic (LC) method, using a ternary gradient sequence, was developed to separate the ionophores in less than 4 minutes. Several mobile phase parameters such as pH and solvent additives were investigated, and their impact on both chromatographic and mass spectrometric behavior was studied. The ionophores readily formed stable complexes with various metal cations present as impurities in the solvents. Therefore, a method was developed to convert the ionophores into only sodium adduct species prior to ESI analysis. This procedure maximized both sensitivity and specificity in the subsequent MS/MS step. Low energy collision-induced dissociation (CID) of the sodium adduct ions resulted in a number of structure-diagnostic product ions for all ionophores. The proposed interpretation of these fragment ions is presented in this work. Additionally, the fragmentation of a series of monovalent carboxylic alkali-metal ion complexes of lasalocid was investigated under CID conditions. A comparison of the CID spectra revealed a decreasing degree of fragmentation in the order [M + H]+ approximately [M + NH4]+ > [M + Li]+ > [M-H + 2Li]+ > [M + Na]+ >> [M + Cs]+. To demonstrate the analytical potential of the LC/MS/MS method, its application to the determination of salinomycin in catfood samples was investigated. Salinomycin was recovered from catfood by a microwave solvent extraction procedure, and subsequently analyzed using LC/MS/MS of the sodium adduct ions.

First solid state alkaline-earth complexes of monensic acid A (MonH): crystal structure of [M(Mon)2(H2O)2] (M = Mg, Ca), spectral properties and cytotoxicity against aerobic Gram-positive bacteria

“…It should be mentioned that FAB-MS spectra of monensin complexes contain peaks of [MonH?Na] ? due to sodium traces from the matrix used (3-nitrobenzylalcohol), an observation that is in accordance with the high affinity of monensin to bind sodium ions and with data reported previously (Chamberlin and Agtarap 1970;Volmer and Lock 1998).…”

Structural study of spirolide marine toxins by mass spectrometry

“…The fate of this fragment is fivefold. There can be subsequent loss of one or two water molecules, leading to m/z 426 and 408, as often observed for polyether compounds [28,37,38,39]. It is important to mention that only two H 2 O losses are seen from this intermediate as opposed to three H 2 O-losses for the MH + ion, since there has been one water molecule lost in the fragmentation reaction.…”

“…3). Multiple water losses, characteristic of several polyether compounds [28,37,38,39], are observed, as well as a cluster of ions in the region of m/z 444, also related by several water losses. The base fragment is represented as a cyclic imine with stabilizing conjugation at m/z 164 (Fig.…”

Simultaneous determination of human and veterinary antibiotics in various environmental matrices by rapid resolution liquid chromatography–electrospray ionization tandem mass spectrometry

“…␤-Lactams include penicillin and cephalosporins sub-classes, and the ␤-lactam ring is easily cleaved in acidic and basic media [24]. Ionophore polyethers (IPs) consist of a carboxylic polyether backbone and can form pseudo-macrocyclic complexes with cations [25]. The physicochemical properties of the target compounds are summarized in Table S1 (Supporting information).…”