It is proved experimentally that the relaxation and complex electrochemical oscillations could be induced by inserting external resistors in the electrochemical systems in which bistability could be found.FeH2SO4 system,in which the Fe electrode exhibited bistability within the potential range of 0.309 V～0.406V(vs.SCE),was chosen in our experiments.When the applied potential was 0.340 V and no external resistor was inserted,no oscillations could be observed.While the applied potential was kept at 0.340 V and an appropriate external resistor was connected in series to the electrochemical system,relaxation or complex oscillations appeared.Upon the external resistance increased,the amplitude of the oscillations decreased gradually.The inducement of electrochemical oscillations is helpful to understand the mechanism of the metals dissolution and passive,and to control the dynamic behavior of some electrochemical systems.
In HCl-NaOAc of pH 4.30 buffer medium,pioglitazone hydrochloride reacts with eosin Y to form an ion-association complex,and the colour of solutions change obviously at the maximum fading wavelength 516 nm.The fading colour intensity is also proportional to the concentration of pioglitazone hydrochloride,and a sensitive spectrophotometric method is developed for determination of pioglitazone hydrochloride.The concentration of pioglitazone hydrochloride in the range of 7.05×10-7 mol/L～2.48×10-5 mol/L obeys Beer’ law at the maximum fading wavelength 516 nm.The apparent molar absorptivity ε516 is 3.65×104 L·mol-1·cm-1,and the detection limit is 3.16×10-7 mol/L.The method has high sensitivity and fairly good selectivity,and was applied to the determination of pioglitazone hydrochloride in medicine samples and human serum and human urine with satisfactory results.
