Spectrophotometric and fluorimetric determination of tri- and di-organotin and -organolead compounds using dithizone and 3-hydroxyflavone

Abstract

For the spectrophotometric determination of organotins and organoleads using dithizone, a suitable buffer system has been devised with adequate buffering capacity at pH 9, containing EDTA to complex interfering inorganic metals and a high concentration of sodium perchlorate suitable for increasing the distribution of the lower organotins in favour of the solvent. Triorganotins and triorganometals form complexes with a ratio of dithizone to organometal of 1:1; with diorganotins and diorganoleads the corresponding ratio is 2:1. Whether in practice this theoretical ratio is achieved depends upon the distribution coefficient (chloroform:buffer) and the affinity constant of the organometal for dithizone. Under our experimental conditions the affinity constant of triethyltin for dithizone is 3 × 10⁵ l mol^–1.

Of a large series of tri-organotins and -organoleads, only trimethyltin and triphenyltin form fluorescent complexes with 3-hydroxyflavone (excitation 400 nm, emission 514 nm). All of the other organotins and organoleads form complexes with absorbance maxima at 385 nm. Dimethyltin, although not forming a fluorescent complex, interferes in the determination of trimethyltin by quenching its fluorescence. By the measurement of fluorescence emission at 514 nm and absorbance at 385 nm mixtures of dimethyltin and trimethyltin can be determined.