Fusing process for Titanium Oxides

Advice By Paul Gaines, Ph.D

Q: First, thank you for providing the wonderful resources on your website. Second, I was reviewing your Sample Preparation Guide regarding the fusing process for Titanium Oxides. I am wondering if you could clarify a few points or maybe offer some advice regarding for our case.

We are trying to measure the Ti level in vulcanized rubber samples, with the source being TiO2. We currently possess an MP-AES instrument which is not compatible with HF, so we are looking into the fusion techniques with pyrosulfate. We plan to ash the rubber sample at 850-900C so that should put the Ti in the brookite form. We then plan to fuse the residue with pyrosulfate prior to digestion and analysis on the MP-AES. I have two questions regarding these steps.

  1. When fusing the samples with potassium pyrosulfate, I see the ashing guide recommends 500C, but for how long do you recommend? We possess a fluxer so the heating and agitation is automated.
  2. The guide indicates that the fuseate is soluble in acids such as 30% sulfuric. For the MP-AES, we would prefer to be in dilute nitric acid or dilute aqua regia. Do you think the fuseate would be soluble in concentrated nitric or concentrated 1:3 nitric + HCL? Also, do you think the material will be stable once diluted to 2% nitric or dilute 1:3 nitric + HCL (~ 1% nitric & 1.6% HCL), which are the typical run conditions?
A: The time required for pyrosulfate fusions is typically ~20 minutes. The fuseate will be soluble in HNO3 and/or HCl, but Ti stability could vary. Concentrated HNO3 alone might work, but since your working solutions can contain HCl adding it sooner rather than later in the process would only help. As a rough guide, we stabilize 10,000 ppm solutions of Ti in 40-50% (v/v) HCl, and would recommend at least 20-30% HCl for 1000 ppm Ti. The stability at lower levels will be a function of Ti concentration, matrix, and time. If you require stability for only ~1 day, then the working matrix of ~ 1% nitric & 1.6% HCl would probably be suitable for less than 1-10 ppm of Ti. Long term stability in only HNO3 matrices would be a concern. Regardless of the approach, you can test Ti stability after the fusion by conducting a spike recovery study and comparing different acid matrices to determine which approach provides the appropriate stability over the required time frame.

Serving you in chemistry,
Paul R. Gaines, Ph.D.
CEO of Inorganic Ventures & Fellow Chemist

DISCLAIMER: Advice offered by the chemists at Inorganic Ventures is intended for the individual posing the question.