Abstract: A high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) method was developed for the simultaneous determination of arsenite As(III),arsenate As(V),monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in dog plasma.The plasma samples were treated with methanol and the supernatant was evaporated to dryness under reduced pressureThe residue was reconstituted with mobile phase and the supernatant obtained after centrifugation was injected for the HPLC-HG-AFS analysis.The separation of the arsenicals was performed on a Hamilton PRP-X 100 anion-exchange column (250 mm×4.1 mm,10 μm) with isocratic elution by 15 mmol/L monopotassium phosphate solution (adjusted to pH 5.9 with KOH solution).The separation of the four arsenic species was achieved within 15 min.The method was applied to the arsenic speciation study in beagle dogs after single oral administration of realgar (equivalent to 11 mg As/kg) alone or Niuhuang Jiedu Pian (equivalent to 28 mg As/kg),respectively.DMA was found to be the predominant species in the dog plasma after dosing,with As(V) appeared as the quickly eliminating one.No traces of MMA or As(III) were detected at any sampling time.The main pharmacokinetic parameters found for DMA after oral administration of realgar and Niuhuang Jiedu Pian were as follows:c_max (14.7±4.2) and (57.0±32.0) ng/mL,t_max (2.4±0.5) and (2.5±0.5) h,AUC_0-36 h (151±13) and (636±418) ng ·h/mL,t_1/2(16.2±7.9) and (9.4±2.2) h,respectively.The influence of compounding in Niuhuang Jiedu Pian on the pharmacokinetics of arsenics was shown with significantly increased transformation of DMA and its faster elimination rate,suggesting the pharmacokinetic behavior of the arsenic was influenced by the compatibility effects of other ingredients in the compound preparation of Niuhuang Jiedu Pian.