Determination of chromium by differential pulse polarography

In this study a method development was aimed at classification of chromium through Differential Pulse Polarography. Therefore, polarograms of Cr(III) and Cr(VI) were received in various acidic and basic environments. . Accordingly, it was determined that the optimal electrolyte environment was pH=2,5 0,1 M HNO3 + KNO3 for the designation of Cr(III) and in this environment it had only one peak around -0.8 V. It was observed that in all acidic environments Cr(VI) had two reduction peaks around -0,3 V and -0,8 V, in the environment of pH=12,5 0,1 M NaOH+NaAc had one around -1,0 V, in the environment of pH=9,0-12,5 0,1 M K2CO3 had two reduction peaks varying between ?0,4 and - 0,2 V and ?0,8 and 1,0 V. It was decided that for the designation of Cr(VI) the optimal environment was the environments of NaOH ve K2CO3. It was determined that in the examples where Cr(III) and Cr(VI) coexist, the peak obtained at -0,8 V in an acidic environment was a total peak pertaining to Cr(III) resulting from the reduction of Cr(III) and Cr(VI). The effects of various cations that shall be able to make an attempt in these environments were researched. In the presence of ions such as Zn2+, Cu2+, Ni2+, Se4+, Cd2+, Pb2+,Ti4+ , a method was developed for the classification in the examples where Cr(III) ve Cr(VI) coexist. Accordingly, it was suggested that first of all, in the samples in the environment of pH=12,5 NaOH or pH=9,0-12,5 K2CO3 the concentration of Cr(VI) be determined, and then in the environment of pH=2,5 vii HNO3 + KNO3 the concentration of Cr(III) from the total peak at -0,8 V pertaining to Cr(III) and Cr(VI) at -0,8 V be calculated. The method developed was applied to synthetic samples and the examples of Gerede stream, Ankara tap water and Engil ve Erçiş streams flowing into Van Lake. In synthetic samples Cr(III) was found with a fault of ten percent, in the environment of Cr(VI), NaOH as eight percent, in the environment of K2CO3 at -0,4 V as four percent. In the examples of Ankara tap water, Engil ve Erçiş streams while Cr(III) and Cr(VI) can not be determined, only at ninety percent of confidence level of Gerede stream, 1,5 ± 0,7 M at 50th meter, 1,0 ± 0,4 M at 300th meter and at 2000 meters 0,6 ± 0,01 M Cr(III) was determined. Key Words : Chromium, determination, differantial pulse polarography