Weak Cation-exchange Extraction Research Articles

Confirmation of gentamicin and neomycin in milk by weak cation-exchange extraction and electrospray ionization/ion trap tandem mass spectrometry.

A new procedure for the confirmation of two aminoglycoside antibiotics in milk was developed and validated. This work is among the early applications of ion trap mass spectrometry for regulatory methodology, and it incorporates a novel weak cation-exchange extraction. The procedure was validated for the confirmation of both gentamicin and neomycin at 30 ng ml(-1) and above. Milk is first treated with acid and centrifuged. The supernate, excluding the fat layer, is buffered with sodium citrate to neutral pH. The extract is applied to a weak cation-exchange solid-phase extraction column. Aminoglycosides are eluted with acidified methanol. Following separation by ion-pair liquid chromatography, analytes are ionized with an electrospray interface. Protonated molecular ions are selectively stored in an ion trap mass spectrometer, then collisionally dissociated to yield unique product ion spectra. Confirmation is based on matching spectral responses between samples and comparison standards consisting of a bona fide standard spiked into control extracts. Method performance was demonstrated with replicate samples of control milk, fortified milk, and milk containing incurred residues of each compound.

Sensitive determination of ambenonium chloride in serum from patients with myasthenia gravis using ion-exchange resin extraction and reversed-phase ion-pair chromatography.

An effective and selective procedure for the extraction of ambenonium chloride (AMBC) from serum using a weak cation-exchange extraction cartridge has been developed. The solid-phase extraction procedure permitted the extraction of AMBC from serum without adhesion to materials such as the containers. A 200-microliter volume of the eluate could be directly injected on to a reversed-phase ion-pair high-performance liquid chromatographic column. The recovery was in the range 97-100%. The limit of detection for AMBC was 0.5 ng/ml in serum (signal-to-noise ratio = 3). The method was used to determine the serum concentration of AMBC in patients with myasthenia gravis. The method would be useful for monitoring AMBC in serum in order to study its pharmacokinetic behaviour in patients under oral administration therapy.