A robust method for speciation, separation and photometric characterization of all [PtCl6−nBrn]2− (n = 0–6) and [PtCl4−nBrn]2− (n = 0–4) complex anions by means of ion-pairing RP-HPLC coupled to ICP-MS/OES, validated by high resolution 195Pt NMR spectrosc

A robust reversed phase ion-pairing RP-HPLC method has been developed for the unambiguous speciation and quantification of all possible homoleptic and heteroleptic octahedral platinumIV [PtCl6−nBrn]2− (n = 0–6) as well as the corresponding platinumII [PtCl4−nBrn]2− (n = 0–4) complex anions using UV/Vis detection. High resolution 195Pt NMR in more concentrated solutions of these PtII/IV complexes (≥50 mM) served to validate the chromatographic peak assignments, particularly in the case of the possible stereoisomers of PtII/IV complex anions. By means of IP-RP-HPLC coupled to ICP-MS or ICP-OES it is possible to accurately determine the relative concentrations of all possible PtII/IV species in these solutions, which allows for the accurate determination of the photometric characteristics (λmax and ɛ) of all the species in this series, by recording of the UV/Vis absorption spectra of all eluted species, using photo-diode array, and quantification with ICP-MS or ICP-OES. With this method it is readily possible to separate and estimate the concentrations of the various stereoisomers which are present in these solutions at sub-millimolar concentrations, such as cis- and trans-[PtCl4Br2]2−, fac- and mer-[PtCl3Br3]2− and cis- and trans-[PtCl2Br4]2− for PtIV, and cis- and trans-[PtCl2Br2]2− in the case of PtII. All mixed halide PtII and PtIV species can be separated and quantified in a single IP-RP-HPLC experiment, using the newly obtained photometric molar absorptivities, ɛ, determined herein at given wavelengths.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Ion-pairing RP-HPLC separation of all homoleptic and heteroleptic [PtCl6−nBrn]2− (n = 0–6) and [PtCl4−nBrn]2− (n = 0–4). ► High resolution 195Pt NMR validation of chromatographic peak assignments, including stereo-isomers of PtII/IV complexes. ► IP-RP-HPLC coupled to ICP-MS/OES gives accurate concentrations of all PtII/IV species in aqueous acidic solutions. ► UV/Vis photometric properties (λmax and ɛ) of all [PtCl6−nBrn]2− and [PtCl4−nBrn]2− complexes determined for future use.