Investigations into the HPLC separation of tetraalkylammonium cobalto-undecatungstometallates.

Abstract

Mutual separation between [N (C7H1S )4]6BCo (H20) W11 039 (AmCo+3B) and [N(C7H1s}4]6SiCo(H20}W11039 (AmCo+2Si) has been achieved for the first time. Reversed-phase C18 liquid chromatography, with 66.7/33.3 MeOH/petroleum ether phosphate buffer was used as the eluent. Several factors were found to affect the separation. First, the more polar the solvent, the less the retention time will be. Heteropoly compounds can be separated with a certain polarity of the mobile phase. This result appears to be related to the polarity of the solvents. Second, the oxidation number of the cobalt was found to affect the separation. The less the oxidation number of the peripheral hetero atom, the longer the retention will be. The retention time of AmCo+3B was 22.5 min; and the retention time of AmCo+2Si was 31. 5 min. As the "pH value" of the phosphate buffer of the 66.7/33.3 MeOH/petroleum ether mixture in the elute increases, the retention times of AmCo+2si and AmCo+3B decreases. Good chromatographic peaks were obtained when the "pH value" of the buffer was 4.5. Normal-phase silica liquid chromatography, with 100% methylene chloride, 80/20 CH2CI2/ACN and reversed-phase C18 liquid chromatography with CH2Cl2 also were found as possible systems to separate the AmCo+2Si and AmCo+3B samples. But these would require solvent program mode to finish the separation of the samples.