Determination of Methyl p-Hydroxy-benzoate, the Metabolite of the Candidate Vaginal Contraceptive Drug 4߰-Carbomethoxyphenyl 4-Guanidinobenzoate Mesylate, in Rabbit Plasma: Application of a rapid and sensitive liquid chromatography-tandem mass spectrometry method

Abstract

Arapid,sensitiveand selectivel iquid chromatography-tandem mass spectrometry (LC-MS/MS)m ethod wasdeveloped fort he determination of methyl p-hydroxybenzoate(CAS 99-76-3),the metaboliteo fthe candidatevaginalcontraceptived rug4¢ -carbomethoxyphenyl 4-guanidinobenzoatemesylate(4 ¢ -CMGB) in rabbitplasma.The samplesw erep repared byliquid-liquid extractionwith ethylacetateafters piking withthe internalstandard,ethylp -hydroxybenzoate (PHBA-Et). Chromatographicseparation wasachieved on aC 18 column (4.6mm  150mm,5 l m) withamobile phase compositionofm ethanol-water(55:45, v/v)d elivered at1.0ml/min. LC-MS/MS analysisw ascarried out on aL C-triplequadrupole mass spectrometerusing atmosphericpressurechemicali onization (APCI)and negativem ultiple reaction monitoring (MRM). Ionsmonitored were m/z 151 fi 92forPHBA-Meand m/z 165 fi 92forPHBA-Etw ithargon ata pressureo f0.8 Pa and collision energyof 32 eVforcollision-induced dissociation (CID). The assaywaslinearoverthe range of 2.0-100 ng/ml forPHBA-Me. The average recovery was103.9 %. The established method hasbeen applied in a pharmacokineticstudyof 4 ¢ -CMGB gel in rabbit.