Use of dye aggregation phenomenon for spectrophotometric and SIA-LAV determination of bismuth(III) as a specific ion association complex between tetraiodobismuthate and Astra Phloxine

Abstract A simple, rapid, highly sensitive and selective non-extraction spectrophotometric and sequential injection analysis with lab-at-valve (SIA-LAV) methods for the determination of bismuth(III) have been developed based on the formation of a specific ion association complex (IA) between tetraiodobismuthate(III) anion and the polymethine dye Astra Phloxine (AP). The changes in the absorption spectra resulting from the formation of the IA are explained in the framework of the exciton theory by the aggregation of dye ions. The analytical wavelength was chosen in the region of an intense narrow bathochromically shifted band with maximum at 600 nm related to the band of the aggregated dye in a specific IA. It was shown that any cationic dye, including representatives of triphenylmethane, rhodamine and polymethine dyes, is capable of forming specific IAs. One of the most important prerequisites for the formation of a specific IA is its relatively low solubility. The UV-visible spectrum of the AP cation was calculated using the time-dependent density functional theory (TD-DFT). Superiority of the TD-DFT with the Franck-Condon approximation, which takes into account vibronic effects, was shown over the traditional non-vibrationally resolved TD-DFT calculations. The PBE1PBE functional is the most suitable in comparison with the used M06, CAM-B3LYP, WB97XD and M11 functionals. Carrying out the chemical reaction and mixing in an external mixing chamber allowed the mixing conditions to be adapted to the requirements necessary for the complete formation of the specific IA. Thus, the maximum possible sensitivity was achieved, which was about an order of magnitude higher than when using the classical SIA approach. Calibration ranges and detection limits (indicated in parentheses) for the developed spectrophotometric and SIA-LAV procedures were 0.04-0.5 (0.01) and 0.1-1.7 (0.03) µg L−1, respectively. The molar absorptivity and Sandell's sensitivity were found to be 6.6 × 104 mol−1 L cm−1 and 3.16 × 10−3 μg cm−2, respectively. The proposed methods were successfully applied for the determination of bismuth content in pharmaceutical compositions and alloys.