Samples Containing Titanium

Hydrolytic Stability and Preferred Matrices

• Ti is particularly prone to hydrolysis due to its small ionic radius of 0.64 Angstrom for Ti⁺⁴. The hydrolysis of Ti⁺⁴ to Ti(OH)₂⁺² is complete in 1M HClO₄; no values have been reported for the relevant formation constants. The titanyl ion (Ti(OH)₂⁺²) further hydrolyses to Ti(OH)₃⁺ and Ti(OH)₄ (aq).
• Ti begins to precipitate (as the Ti(OH)₄) from solution at a pH of between -0.3 (high conc. Ti) to 2.5 ( low conc. Ti). Chelating and complexing agents that successfully retard hydrolysis are EDTA, Fluoride, oxalate, tartrate, and Tiron.
• Titanium oxide, hydroxide, and phosphate are all insoluble in water and neutral to basic media.
• The TiF₆^-2 ion is stable in aqueous solution and has been characterized by NMR.
• The following table shows the improvements in the hydrolytic stability of Ti⁺⁴ with different complexing agents. The pH where precipitation of Ti(OH)₄ begins is shown for 0.1 M solutions of each complexing agent:

• Ti can be mixed with many of the elements at high concentrations (200 to 2000 µg/mL) with the exception of the Alkaline and Rare Earths. When Ti is in the presence of transition metals excess HF is needed. The transition metals and some non-metals will strip the fluoride from the Ti leaving open the possibility of hydrolysis. Moderate to low levels (≤ 100 µg/mL) can be mixed with all of the elements. Ti is more stable in relatively high (greater than 5% v/v) levels of acid.
• Stability: 2-100 ppb levels stable (alone or mixed with all other metals) as the Ti(F)₆^-2 for months in 1% HNO3 / LDPE container. 1-10,000 ppm single element solutions as the Ti(F)₆^-2 chemically stable for years in 2-5% HNO₃ / trace HF in an LDPE container.

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