OHSU

Preparing Sample Submissions

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General Guidelines

Our ICP-MS sample introduction system requires liquids or fully dissolved solids. Additionally, all samples are diluted into either an acidic (1% nitric acid) or basic/organic (4% ammonium hydroxide, triton, n-butanol, EDTA) matrix. These final dilutions are carried out with trace-metal grade compounds and are typically performed by our lab.

A few things to remember when submitting samples:

  • Please label all samples and blanks.
  • Please include a full list of the samples and attach it to the sample submission form.
  • We do not need a large sample. For solids we generally prefer 100-500 mg, but we can easily work with less; as long as you can weigh it accurately, we can measure it. For liquids/solutions submitted, the necessary amount is concentration dependent and determined by the sensitivity of the instrument for the element to be measured. That said, for a typical biological sample the same rule holds as for solids: if you can determine the accurate sample volume submitted we can probably determine the elemental concentration!
  • Solid samples must be digested before measurement. We offer this service for a small fee (see Pricing). If you feel strongly about doing this digestion step yourself (which we do not recommend), please look at the protocol below. This protocol is sufficient to digest many types of samples. We suggest that you talk with us before starting your own sample digestions. Some samples may require a more complicated digestion to obtain a homogenous solution.
  • If you prepare your own samples (solid or dissolved) you will also need to submit a blank sample that was prepared identically.


Pre-treatment of glass and plasticware

Doubly deionized (DDI) water should be used whenever diluting samples or rinsing labware. If this is not available, please include a sample of the water used.
Metal contamination is a potential hazard when measuring samples at very high precisions, so metal tools should be avoided when preparing samples, while non-metal labware should be pre-treated with trace metals grade concentrated nitric acid to leach out contaminants. For plastic storage vessels, it is sufficient to fill the vessels with 1% nitric acid for at least 24 hours, before rinsing them with DDI water and using them for sample storage. Clean glassware should be soaked in 10% nitric acid for several days and then stored in 2.5% nitric acid.

Erlenmeyer double boilers for sample digestion, with sample tubes on the right
Erlenmeyer double boilers for sample digestion, with sample tubes on the right

Digestion setup

For each sample, we advise using two 15 mL plastic conical tubes (one for storing the sample prior to digestion and one for storing the digested sample), a borosilicate test tube, and a 25 mL glass Erlenmeyer flask. In a fume hood, add 20 mL DDI water to the Erlenmeyer and rest the borosilicate tube inside; place the setup on a hot plate to form a double boiler, as shown above.


Generic liquid and solid samples

Measure the volume or weight of the sample as precisely as possible before adding the sample to a borosilicate test tube; immediately add one volume of concentrated nitric acid (1 mL for samples ranging from 50-150 mg; 0.5 mL for samples under 50 mg). For each set of prepared samples, a blank must be made by treating a volume of concentrated nitric acid as the other samples have been treated. Once samples and the blank have been prepared, set the hot plate to 90-95 °C. Incubate 2-3 hours; water should begin to evaporate from the Erlenmeyer flasks but the nitric acid should not boil, although it will become yellow.  Remove samples from heat and let cool. Once cool, add 1 volume (same as previous addition of nitric acid) of Trace Metals Grade hydrogen peroxide. Decant entire sample mixture into a dry, pre-rinsed acid-treated 15 mL conical tube. Carefully rinse test tube twice with 1% nitric acid and decant into conical tube, bringing the total volume up to 6 mL.

 

Additional advice

If you would like more advice on how to handle, process, and transport your samples, please Contact Us for assistance at no charge.