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The best way to keep W in solution is with HF.

We are using your Tungsten (W) standard and are having trouble keeping the Tungsten in solution. We would prefer not to use HF due to safety concerns. We use a matrix of 2% HNO3 and dilute your standard to 0.1, 1, 5, and 10ppm for standards. We calibrate W separately due to stability issues. Usually if we make the standards fresh daily, everything runs fine. We are having trouble with LCSs and matrix spikes that have gone through a 3050 digestion. We have tried with and without HCl in the final 3050 step. Adding HCl made the LCS lower than without using it. Can you give me any tips or tricks to stabilize W without using HF?


The best way to keep W in solution is with HF. However, HF is hazardous, attacks glass and many analysts would prefer to avoid having to work with it. If you do not want to use HF, then there are the following options:

  1. Dilute into HCl. Although not as effective as HF, the use of HCl is better than nitric acid.
  2. If HCl is not an option, then increase the concnetration of nitric acid from 2% to 10%. The higher nitric acid oconcentration will slow down the hydrolysis of the W. This may also require lowering the W concentration but try the levels referenced in your email first.
  3. If the nitric acid must remain at 2%, then lower the concentration of the W. I would suggest a maximum concentration of 1 ppm W for a 2% nitric acid solution.
  4. If all of the above are not acceptable then keep the W separate and make dilutions into dilute (5% wt./volume) triethanol amine (TEA)/ water solutions. Make certain that the pH is 8 or greater and, if not, increase the concentration of the TEA. The W will be stable at the concentrations you require, no HF is needed and the HF already present (or any added as part of a sample preparation) is rendered non-corrosive i.e. it will not attack glass introduction systems, analysts, or equipment when the pH is 8 or greater and TEA is present.

Please feel free to call us with any questions and thank you for using the Inorganic Ventures products.

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. Feel free to contact us to verify whether these suggestions apply to your unique circumstances.