Sample Preparation Guides

General Information

Occurrence – Tellurium is a rare metalloid named after the Roman goddess of the earth, Tellus. It has a very low abundance in the earth’s crust of only about 1 ppb. It can be found by itself in nature but is more often present in compounds with other elements such as silver (Ag) and gold (Au). The most common of these compounds are sylvanite (AgAuTe₄), calaverite (AuTe₂) and krennerite (AuTe₂).¹

Chemical Properties – Tellurium is atomic number 52, found in Group 16, Period 5 on the Periodic Table with a molecular weight of 127.60 amu, possible oxidation states of +6, +5, +4, +2, -1 and -2, and a coordination number of 6. Its most common oxidation states are the +4 and +6. IV standards contain Te⁺⁴. It has multiple stable isotopes including ¹²⁰Te (0.09%), ¹²²Te (2.55%), ¹²³Te (0.89%), ¹²⁴Te (4.74%), ¹²⁵Te (7.07%), ¹²⁶Te (18.84%), ¹²⁸Te (31.74%), and ¹³⁰Te (34.08%). Tellurium has a relatively high ionization energy, making it one of the more difficult elements to reliably detect at very low levels and/or in complex sample matrices via ICP-OES.

Uses – Tellurium’s primary industrial uses include as a semiconductor, in alloys to improve the strength, machinability, and/or resistance to corrosion of other metals, as a coloring agent, and in blasting caps (used to detonate explosives).¹

Tellurium Chemistry as Practiced & Observed at IV

Inorganic Ventures uses high purity (≥ 99.98%) tellurium metal as the starting material for our tellurium standards, but we have tellurium standards available in three different matrices: HNO₃ (as H₂TeO₃), HNO₃ + HF (as [TeF₆]^2-), and HCl (as [TeCl₆]^2-).

Sampling and Handling

Stability – Tellurium is stable in dilute or concentrated HCl, HF, H₃PO₄, H₂SO₄, and HNO₃ if the concentration is below 1000 ppm.  If concentrations >1000 ppm are needed, an additional stabilizing ligand such as chloride or fluoride will need to be used in conjunction with HNO₃. Te is also stable if it is in solution alone with an alkali hydroxide matrix.

Contamination Risks – Tellurium does not pose a major contamination risk as it has very low abundance in nature. Areas of contamination would be from human activities such as mining and smelting or run off from manufacturing facilities that use Te in their products. Environmental samples often must be pre-concentrated prior to analysis to be able to analyze Te in the samples.

Potential Loss During Sample Preparation – If an ashing technique is used, an ashing aid such as MgO and nitrate together must be used to avoid loss of tellurium.²

The Metal, Alloys, Oxides and Organic Matrices

Metal and Alloys – soluble in solutions of alkali hydroxides, a 1:2 mixture of H₂O and HNO₃ for smaller sample sizes, and either a 2:1 mixture of HNO₃ and HF or a 1:1:1 mixture of H₂O, H₂SO₄, HNO₃.

Oxides – TeO₂ is soluble in HCl and the alkali hydroxides. TeO₃ is soluble in hot concentrated solutions of the alkali hydroxides.

Minerals/Alloys – soluble in acid digestions with HNO₃ or HNO₃ / HF.

Organic Matrices – Vegetable Matter - dry ash 100 g of the well-ground and mixed vegetation into a concentrated solution of 25 g of magnesium nitrate and magnesium oxide. Dry, ignite and muffle until the ash is a uniform gray color.

Testing methods

Tellurium can be analyzed using ICP-OES and ICP-MS techniques, but ICP-MS is more commonly used due to the low abundance and high ionization energy of Te requiring a higher sensitivity technique able to achieve lower detection limits. Another common analytical technique for Te analysis is graphite furnace atomic absorption (GF-AA). However, a hydride generation system can help to enhance transport efficiency, and therefore signal intensities for Te, allowing ICP-OES to be a viable option for trace Te analysis as well. On ICP-MS the lower abundance and mass number isotopes, 120, 122, 123, and 124 all suffer from isobaric interferences from either Sn or Sb. 125, 126, and 128 have a polyatomic oxide interference from ¹⁰⁹Ag¹⁶O, ¹¹⁰Pd¹⁶O, ¹¹⁰Cd¹⁶O, ¹¹¹Cd¹⁶O, ¹¹²Cd¹⁶O and ¹¹²Sn¹⁶O. The 130 isotope has an isobaric Ba interference, as well as oxide interferences from Cd and Sn. Mo, Zr, Nb, Sr, Y, and Rb can also cause interferences on Te isotopes on ICP-MS if chloride is present (chloride polyatomics). Using a collision cell gas or KED (kinetic energy dispersion) mode will help to reduce these interferences.

Recommendations for some of the preferred wavelengths (ICP-OES) and masses (ICP-MS) to use for a tellurium analysis are given below. Detection limits capabilities can be improved by adding a hydride generation system.

References

1. National Center for Biotechnology Information (2024). PubChem Element Summary for AtomicNumber 52, Tellurium. Retrieved September 6, 2024 from https://pubchem.ncbi.nlm.nih.gov/element/Tellurium.
2. Bock, R. (1979). A Handbook of Decomposition Methods in Analytical Chemistry. Weinheim/Bergstr: Verlag Chemie GmbH.