Mass spectrometric investigation of gallium and zirconium complexes with octaethylporphyrin and tetraphenylporphyrin.

Gallium and zirconium octaethylporphyrin (OEP) and tetraphenylporphyrin (TPP) were examined by electrospray ionization (ESI) mass spectrometry. All systems were prepared in dichloromethane with addition of a stabilizing lipophilic anionic agent, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB). In the solutions examined both monomeric and dimeric metalloporphyrins were observed. In the gallium-OEP mass spectrum the ion registered at m/z 601 was attributed to monomeric Ga(OEP) and that at m/z 1219 to the dimeric form, Ga(OEP)OH. Peaks appearing in the ESI mass spectra of zirconium systems were substantially less intense, probably owing to the relatively low stability of complexes of this metal caused by its different geometry preferences. The most abundant monomeric zirconium-OEP complexes were [Zr(OEP)OH] (m/z 639) and Zr(OEP)Cl (m/z 657), and dimeric Zr(OEP)OH (m/z 639). Analogous species were observed in the Zr(TPP) system: monomeric [Zr(OEP)OH] (m/z 719) and Zr(TPP)Cl (m/z 737) and dimeric Zr(TPP)OH (m/z 719). In both cases series of other dimers, e.g. Zr(OEP)O(2)H (m/z 1277), Zr(OEP)OHCl (m/z 1313), Zr(TPP)(2)O(2)H, (m/z 1437), Zr(TPP)OHOH (m/z 1455) and Zr(TPP)OHCl (m/z 1473), appeared. The results obtained confirmed the hypothesis concerning the formation of dimeric metalloporphyrins in solutions containing stabilizing lipophilic anions. It also allowed us to explain the super-Nernstian slopes of the calibration curves towards primary anions of ion-selective electrodes with membranes containing the examined metalloporphyrins.