Speciation of CdTe quantum dots and Te(IV) following oxidative degradation induced by iodide and headspace single-drop microextraction combined with graphite furnace atomic absorption spectrometry

Highlights: • A novel method for speciation of CdTe QDs and Te(IV) at (ultra)trace level was developed. • In-situ generation of H₂Te and trapping by an Au-containing microdrop was performed. • CdTe QDs are non-reactive toward hydride generation. • Iodide induces oxidative degradation of CdTe to Te(IV) thus allowing hydridation • We perform application to environmental waters containing both kind of Te species. -- Abstract: A novel speciation method for tellurium present as CdTe quantum dots (CdTe QDs) and Te(IV) in natural waters combining hydride generation with headspace single drop microextraction (HS-SDME) and subsequent measurement by graphite furnace atomic absorption spectrometry has been developed. It was found that NaBH₄ is only able to generate H₂Te from Te(IV) and not from CdTe QDs. The presence of iodide at high concentration in the acidified sample causes the oxidation of CdTe to Te(IV), thus allowing the simultaneous hydride generation from both species. Furthermore, a gold-containing microdrop exposed to the headspace was found to be an efficient trapping agent for H₂Te. Specifically, Au(III) in the drop is reduced by the H₂ generated from NaBH₄ decomposition forming gold nanoparticles, on which surface H₂Te is trapped via catalytic decomposition. Experimental parameters influencing hydride generation, its transport to the headspace and trapping by the drop have been studied. Under optimal conditions, the proposed method yielded detection limits of 0.13 μg L⁻¹ and 0.03 μg L⁻¹ for Te(IV) and total Te [i.e., Te(IV) + CdTe QDs], respectively. Intra-day repeatability and inter-day reproducibility were lower than 4.2% (n = 3) and 9.5% for both measurements, respectively. The method was applied to the analysis of natural waters, namely superficial water, groundwater and lake water, obtaining good recoveries for both Te species.