A novel derivatization method for the determination of Fosfomycin in human plasma by liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection via phase transfer catalyzed derivatization.

An analytical method employing novel sample preparation and liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometric detection (LC-APCI/MS) was developed for the determination of fosfomycin in human plasma. Sample preparation involves derivatization through phase transfer catalysis (PTC) which offers multiple advantages due to the simultaneous extraction, preconcentration and derivatization of the analyte. Using a PT catalyst, fosfomycin was extracted from plasma in an organic phase and, then converted to a pentafluorobenzyl ester with the use of pentafluorobenzyl bromide (PFBBr) derivatization reagent. The method was fully optimized by taking into account both PTC and derivatization parameters. Several catalysts, in a wide range of concentrations, with different counter ions and polarities were tested along with different extraction solvents and pH values. Thereafter, the derivatization procedure was optimized by altering the amount of the derivatization reagent, the temperature of the reaction and finally, the derivatization duration. As internal standard (I.S.) ethylphosphonic acid was chosen and underwent the same pretreatment. The derivatives were separated on a pentafluorophenyl (PFP)-C18 analytical column, which provides unique selectivity, using an isocratic elution with acetonitrile-water (70-30, v/v). The method was validated according to US Food and Drug Administration (FDA) guidelines and can be used for a bioequivalence study of fosfomycin in human plasma. The correlation coefficient (r(2)) of the calibration curve of spiked plasma solutions in the range of 50-12000 ng/mL was found greater than 0.999 with a limit of quantitation (LOQ) equal to 50 ng/ml (for 500 µL plasma sample).

Hydrophilic interaction vs ion pair liquid chromatography for the determination of streptomycin and dihydrostreptomycin residues in milk based on mass spectrometric detection.

Streptomycin (STR) and dihydrostreptomycin (DHSTR) are two of the most common aminoglycoside antibiotics used in veterinary medicine. The physicochemical properties of both substances, make their determination challenging. In the present study the development of methods based on ion-pair chromatography (IPC) and on hydrophilic interaction chromatography (HILIC), for the determination of the above mentioned aminoglycosides in the range of 100-1000 µg L(-1) is described. The two methods were validated according to EU requirements for residues in food. The recoveries for the IPC method were 69.3% and 56.5% of STR and DHSTR, respectively, and for HILIC method 85.5% and 72.3%, respectively. The intra- and inter-day precision, studied at 100, 200 and 300 µg kg⁻¹ levels in milk samples, gave %RSD ≤ 13 for both methods. LOQs for the HILIC method were 14 µg kg⁻¹ for both analytes and for the IPC method were 109 and 31 µg kg⁻¹, for STR and DHSTR, respectively. The sensitivity of the HILIC method is 80 and 210 times greater than that of the ICP method, for STR and DHSTR, respectively.