In this paper, the polaro raphjc reduction of 2-IHA and its Mo(VI)-2-IHA complex by differential pulse polarographic and by cathodlc strip ing voltammetry are shown. Very low detection limits have been achieved using cathodic stripping volLmmetry to determine this method.
EXPERIMENTAL ApparatusA Metrohm Herisau E-506 polarecord assembl was used with a Metrohm Stand 663 VA as workinThe dropping time was mechanicall maintained at 7s. An Ag/AgCI reference electrode was used and t k auxilia electrode was a glassy-carion rod wire.#e optimum experimental va ues were as follows : temperature = 25 * 0.1"C. pulse amplitude = -50 mV, scan rate potential = 6 mV s-. I .
ReagentsGeneral procedure DPP an cathodic strippin voltammet studies. 10 pl of 0.5 M HC104, 4 ml of 0.5 M NaClO and 1 ml of 5 . 7~1 0 -~M 2-IHA were acfded to16 myof distilled and deionized water in the polarogra hic ce?l (pH 3.0 and 0.1 M ionic strength were the optimum conditions). Prior to each investigation the solufon was purged with oxygen-free nitrogen for 10 min before addition of the required amount of metal and the reagent to the cell and purging for further 2 minutes.Urine treatment. Conc. HNO3 (200pl) and conc. HC104 (200pl are added to a 1 ml sample of urine. The solution is shaken and heated to dryness. Then 1 ml of distilkd and d ionized water is added and this solution is transferred into a polarographic cell, containing 1 m! of,5.7xlO-S M 2-IHA solution, 10,pl of 0.5 M HClO4 and 4 .ml of 0.5 M NaClO~,solution and distilled and deionized water up to 20 ml. The dissolved air is removed with nitro en for 10 minutes.The solution is svirred for3 minutes with an accumulation potential of + 0.2 V. When the stirrer is turned off, the potential is linearb shifted towards more ne ative values, using the differential pulse modula on lo solution. The graph of peak current versus molybdenum concentration is linear between 70-4 Mand 3xIg9 M under these conditions.
RESULTS AND DISCUSSION DPP studiesInfluence of pH. The influence of pH in the polarographic reduction behavior of the complex Mo(Vl)-2-IHA was studied in the interval between pH 0.90 and 3.60 using different buffers (Britton-Robinson) and perchloric acid. In this interval of pH two very well defined and very sensitive waves appeared. The two waves (I and II) disappear at pH > 3.60.The pH study was carried out with a 2-IHA concentration of 4x10-5 M and a concentration of 5x10-6 M Mo(Vl). The optimum condition was found to be pH 3.00 (perchloric acid), and under these conditions the peak potentials were -0.19 V (peak I) and -1 ,I6 V (peak II) (versus Ag/AgCI reference electrode) (Figure 1). Nuture of the electrode process. In order to understand the characteristics of the electrode process, studies on the influence of temperature and on the metal concentration were carried out.The effect of the temperature was investigated in the interval from 16°C to 40°C with a thermostatized cell. Temperature coefficients up 5% C-1 were obtained, high enough to require all polarograms to be run DPCV) with a p...
