Our ICP-MS sample introduction system requires liquids or fully dissolved solids.
All samples analyzed 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). We do not recommend digesting your samples yourself, but if you feel strongly about this, please look at the protocol below. While the protocol is sufficient to digest many types of samples, we suggest that you talk with us before starting your digestions to ensure that they do not require a more complicated digestion to obtain a homogeneous solution.
- If you prepare your own samples (solid or dissolved) you will also need to submit a blank sample that was prepared identically.
- If shipping your samples please prepare all samples on dry ice.
Water and Tool Selection
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 at such high precisions, so to avoid accidental metal contamination avoid metal tools when collecting and preparing samples, non-metal tools should be pre-treated prior to use, procedure under “Pre-treatment” section below.
Pre-Treatment of Glass and Plasticware
- 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.
For Inorganic/Non-Biological samples
If necessary, and possible, clean the sample material to remove all external purities.
Accurately weigh on a precision balance (+/- 0.1 mg) or measure the material directly into 15 ml centrifuge tubes (metal free, VWR, catalog number 89049-170), prior to digestion.
For Biological Samples
For animal tissues – samples should be weighed on a precision balance (+/- 0.1 mg) and digested with concentrated HNO3 (trace metal grade, Fisher Scientific) in Sarstedt poly-propylene culture tubes (55.516 series). Ideally the sample weight should be between 50 -100 mg, but we can work with samples as small as 10 mg or as large as 200 mg.
For blood, adherent cultures, cells, or bacteria – samples should be rinsed twice with an isotonic solution prior to detaching. Ideally, we prefer to have at least 50µl of blood or 106 cells/bacteria per sample submitted. If your samples are in suspension, they should be spun down, resuspended with an isotonic solution, and then spun down again before digestion. These steps will remove most of the external trace element content. Cells should be harvested directly into 15 ml (metal free, VWR, catalog number 89049-170) and, after removing aliquots for cell count or protein determination, the cells should be spun down and as much medium removed as possible.
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 below.
Digest your sample with approximately 10x the volume (in ml) of the weight (in mg); for example, 10 mg of sample is digested with 10 µl of concentrated HNO3 (trace metal grade, Fisher Scientific). We tend to err on the low side, e.g. we would digest 150 mg with 1 ml of HNO3.
Loosely cap the tubes and heat the samples for 1-2 hours at 90°C either by using the digestion setup described above or by using a heating block. Upon cooling to room temperature add 1% HNO3 (prepared using DDI water and trace metal grade HNO3, Fisher) to each sample as to get a final volume of 2000 µl. We will perform any additional dilutions in the Core, if necessary.
Ideally the sample weight should be between 50 -100 mg before digestion, see table below for amount of concentrated HNO3 (trace metal grade, Fisher Scientific) amounts corresponding to the sample weight. If at all possible, don’t use more than 2 ml in the 8 ml Sarstedt tubes.
After the addition of the concentrated HNO3 tubes should be loosely capped and digested for 1 hour at 90°C, either by using the digestion setup described above or by using a heating block. After cooling, preferably overnight to complete digestion, add 30% H2O2 (Optima grade, Fisher Scientific) at a volume equal to that which was used of the concentrated HNO3 to each sample; for samples digested in 1 ml conc. HNO3, the total volume should be 3.9-4 ml. After the addition of H2O2 the samples will gas out for a few days, the tubes should only loosely be capped.
Once samples have degassed 1 ml of each sample is then further diluted (4x) with 3 ml of 1% HNO3 (prepared using DDI water and trace metal grade HNO3, Fisher) into a 15 ml centrifuge tube (metal free, VWR, catalog number 89049-170), they should no longer gas out and can be capped tightly and wrapped with parafilm and transferred to a sturdy plastic bag to send to us, we recommend wrapping the tubes, or tube trays with paper towels for absorption in case of a sample leak.
10-50 mg.....................500 µl
50-100 mg...................1 ml
100-200 mg.................2 ml
Blood, adherent cultures, cells, or bacteria
To each sample tube 50 µl of concentrated HNO3 (trace metal grade, Fisher Scientific) is added and tubes loosely capped before being heated for 2 hours at 90°C either by using the digestion setup described above or by using a heating block.
After digestion is complete you may choose to add 450 µl of 1% HNO3 (prepared using DDI water and trace metal grade HNO3, Fisher) or DDI water – not both, to the samples prior to shipping, or ship them to us without the addition of HNO3 or DDI water.
If you prepare your own samples (solid or dissolved) you will also need to submit a blank sample that was prepared identically alongside your samples.
If you choose for the Core to send you tubes, we will also prepare the NIST and solution standard and send them along with the empty tubes so that they can be prepared along side your samples. This is recommended as to reduce the number of variables lending a more accurate measurement.
If you use your own tubes, please send us 10 additional tubes, each containing 100 µl of concentrated HNO3 (trace metal grade, Fisher Scientific), and we will do the controls here.