Separation of Nitrito- and Nitropentamminecobalt (III) Chloride by High Performance Liquid Chromatography

Reversed phase high performance liquid chromatography, chosen because of its ability to collect many data points over a long period of time with minimal involvement, was used to separate pentaamminenitritocobalt(III) chloride and pentaamminenitrocobalt(III) chloride. Pentaamminenitritocobalt(III) chloride was prepared, made into a concentrated solution, divided into aliquots and allowed to isomerize to pentaamminenitrocobalt(III) chloride over a period of twelve to eighteen hours. An injection was made approximately every forty-five minutes. The samples were analyzed at three wavelengths, 254 nm, 460 nm and 490 nm. The absorbance was collected and was used to determine the kinetics of the reaction. The isomerization from the nitrito to the nitro complex is a first-order reaction. The concentration of the nitrito isomer plotted against the time yields a line with a negative slope. The average rate constant determined was 6.6 ± 0.1 × 10-5 s-1 which is in excellent agreement with previously reported data for this reaction