Stability of Tl(III) in the context of speciation analysis of thallium in plants

The paper presents both “good” and “bad” results obtained during speciation analysis of thallium in plant tissues of a hyperaccumulator of this metal. The object was white mustard – Sinapis alba L. In this plant there were found traces of trivalent thallium. The crucial point of this study (especially in the case of so unstable thallium form as Tl(III)) was to prove that the presence of Tl(III) was not caused by the procedure of sample preparation itself, and that the whole analytical method provides reliable results. Choice of the method for conservation of the initial speciation, extraction with the highest efficiency and proving the correctness of the obtained data were the most difficult parts of the presented study. It was found that: both freezing and drying cause significant changes in the speciation of thallium; quantitative analysis could be performed only with fresh tissues of mustard plants; only short-term storage of an extract from fresh plant tissues is possible; the methodology is not the source of thallium (III); only the presence of DTPA can greatly limit the reduction of TI(III) to TI(I) (up to 1–3%); the UV irradiation results in disintegration of TI(III)DTPA in the presence of plant matrix (reduction up to 90%). •In contact with plant matrix it is not possible to avoid the reduction of Tl(III).•The presence of DTPA limits the reduction of TI(III) to TI(I).•In the presence of plant extract UV irradiation causes disintegration of TI(III)DTPA.•Immediate use of fresh material is recommended for Tl speciation study.•Electrochemical methods are alternative to LC ICP MS (validation).