ANALYSIS OF TETRACYCLINE, OXYTETRACYCLINE AND CHLORTETRACYCLINE IN PLASMA EXTRACTS BY ELECTROSPRAY TANDEM MASS-SPECTROMETRY AND BY LIQUID-CHROMATOGRAPHY

Pure standards of tetracyclines (tetracycline, oxytetracycline and chl ortetracycline) have been analyzed on a triple quadrupole mass spectro meter with Atmospheric Pressure Chemical Ionization (PSCI) and Electro spray Ionization (ESI). ESI appeared to be considerably more sensitive than APCI. Collisional. activation of the MH+ ions gave fragment ions at m/z values equal to MH+ - 35 which corresponds to loss of both H2O and NH3. The collisionally induced loss of 35 from MH+ was used in de veloping a mass spectrometric method based on loop injection and selec ted reaction monitoring (SRM) as the final analytical step, The method was tested on extracts from fortified plasma and the measurements fro m the MS-MS analysis were compared with results from High Performance Liquid Chromatogaphy (HPLC) analysis of the same samples, The fortifie d plasma (from pig) samples were purified by chelate affinity chromato graphy (amberlite XAD columns), After filtration and evaporation of th e solvent the redissolved residues were analyzed by HPLC and by MS-MS with ESI. The HPLC eluates (gradient of 0.01 M aqueous oxalic acid and CH3CN) were monitored at 356 and 369 nm, The signal to noise ratio in the analyses of extracts from plasma fortified to 20 ppb suggests a d etection limit for the MS-MS method below 10 ppb of tetracylines in pl asma.