Sample Preparation Guides

General Information

Occurrence – Thallium is the fifth Group IIIA element and has an atomic number of 81. The average abundances of Thallium are 0.07 ppm in Earth’s crust and <0.1 ppm in groundwaters.¹ The metal occurs in pyrites and trace amounts are found in Zn and Pb ores. It is toxic and is not considered to be essential for plants or animals.

Uses – Used in glass production and in commercial pest poisons. It should be noted that Tl has largely been phased out of pest control products, leaving it will few commercial uses. Thallium is a component in the electrodes of dissolved Oxygen meters and is still used in photocell production.²

Chemical Properties – Thallium is shiny but dulls to a blue-gray color as the oxide forms due to contact with air. Thallium exists in nature as a mixture of ²⁰⁵Tl (70.5%) and ²⁰³Tl (29.5%). It is most often found in the +1 oxidation state, unlike the other Group IIIA elements which typically occur in the +3 form.

Tl Chemistry as Practiced & Observed at IV

Depending on the application, Inorganic Ventures makes Thallium products from Thallium (I) nitrate, Thallium (III) oxide, or Thallium metal. The purity is typically found to be 99.999% using ICP-MS and ICP-OES. The trace metallic impurity data can be found in Section 5.0 of the Certificate of Analysis. Our stock offerings, MSTL-10PPM, MSTL-100PPM, and CGTL1 are preserved in 1% v/v HNO₃. CGTL10 is preserved in 5% v/v HNO₃.  

Sampling and Handling 

Stability – We have found that 2-100 ppb levels are stable for months in 1% v/v HNO₃ and H2SO₄. 1-10,000 ppm solutions are chemically stable for years in 2-5% HNO₃. All stability studies were performed in LDPE.

Thallium is stable with most metals and inorganic anions. Care should be taken if HCl will be used in the analysis. In these cases we recommend that the Tl be in its +3 oxidation state. The sulfite, thiocyanate, and oxalate are moderately soluble, the phosphate and arsenite are slightly soluble, and the sulfide is insoluble.

Contamination Risks – Thallium is not a common contaminant in labware or reagents. However, analysts should always take precautions against cross-contamination between samples containing Tl. For more information about common contamination concerns, please see Chapters 8, 9, and 10 of the Inorganic Ventures Trace Analysis Guide. 

The Metal, Oxides, Ores and Organic Matrices

Metal – Thallium metal is best dissolved in HNO₃, and this will primarily form the Tl⁺¹ ion.

Oxides – Thallous oxide, TlO₂, is readily soluble in water, but Thallic oxide, Tl₂O3, requires high levels of acid. For more information on acid digestions of inorganic samples, please see Chapter 11 of the Inorganic Ventures Trace Analysis Guide.

Ores - For ores, we recommend carbonate fusion in Pt crucibles., followed by HCl dissolution. For more information on sample preparation by fusion, please see Chapter 13 of the Inorganic Ventures Trace Analysis Guide.

Organic Matrices - For organic matrices, we recommend a digestion using sulfuric acid and peroxide or dry ashing following by HCl dissolution. For more information on ashing of inorganic samples, please see Chapter 14 of the Inorganic Ventures Trace Analysis Guide.

Testing Methods

Flame and Graphite Furnace Atomic Absorption, ICP-OES, and ICP-MS methods are typically recommended for Tl. Analysts should account for Tl⁺¹ and HCl stability issues. Use Tl⁺³ if preparing samples or standards in the presence of chloride. See the table below for common interferences: