Sample preparation: liquids and solids

Trace metals in Water: Water samples should be filtered and acidified (add 0.5% optima HNO3 or equivalent). Samples should be stored in clean plastic (LDPE, PP, Teflon, PETG) bottles or metal-free centrifuge tubes (e.g VWR 89049 series). A minimum volume of 10 ml of sample should be supplied. SEAWATER samples or BIOLOGICAL buffer samples CANNOT be run undiluted because of high total dissolved salts; please INFORM US if your samples have high TDS.

Trace Metals in Urine, Serum or Blood: Samples should be collected in acid-cleaned or otherwise certified metal-free containers. Consult TEA staff for details on sample collection and preservation for these matrices. Urine and serum/plasma samples are homogenized before sub-sampling and then diluted 10X in 1% HNO3 prior to analysis using the methods outlined above. Whole blood samples are thawed, vortexed then acid-digested with 9:1 HNO3:HCl. The TEA core uses urine and blood reference materials form NIST and NIES (Japanese reference materials) and participates in the Quebec Multi-element External Quality Assessment Scheme for biological samples.

Trace Elements in Cells: Washed cells are usually supplied as a centrifuged pellet in 1.5 ml Eppendorf tubes. These tubes are weighed and 0.1 ml of Optima HNO3 is added to each tube. The cells are left to react with the acid cold for a minimum of four hours. The tubes are then placed in a laboratory oven at 70˚C for 2 hrs. The tubes are allowed to cool and 0.05 ml of H2O2 is added to each tube and the tubes are again left to react cold then placed in an oven at 70˚C. After cooling 0.85 ml of DI H2O is added to each tube and the tube is capped, shaken and the contents are then decanted into a pre-weighed and labeled 7ml vial. The initial tube is then rinsed with a further 2 X 1 ml aliquots of DI water which are decanted into the 7ml vial. The final weight of the 7 ml vial is recorded. The initial 1.5 ml tube is allowed to dry then weighed to get the initial empty weight. The digested sample is then analysed by ICP-MS according to the standard procedures described below

Trace Elements in Nails and Hair

Washing of toenails: Visible dirt is removed from the nails, and they are transferred to a 7ml polyethylene vial. 2 ml of acetone is added and the vessel placed in an ultrasonic bath for 20 min, following a wash with 2 ml 1% solution of Triton X-100 in an ultrasonic bath for 20 minutes, after which the toenail sample is washed 5 times with deionized water and dried in a clean dry box. This washing procedure removes all external contamination (including nail polish and dirt) without extracting metals from inside the nail. When the toenails are completely dry, the 7ml vial is capped and the samples stored for microwave digestion.

Microwave digestion: The cleaned nail sample is weighted into a pre-weighed 15 ml polypropylene centrifuge tube (VWR trace metal clean) and 0.5 ml Optima HNO3 (Fisher Scientific) is added. Weights are recorded on a 4 or 5 place balance to 0.1 mg. The low pressure microwave digestion rack accommodates 120 15 ml tubes. Of these 120 places, 105 will be samples, six will be blanks, six will be certified reference materials and three will be fortified (spiked) blanks. The tubes are placed in the digestion rack, lightly capped and allowed to ‘pre-digest’ for 2-3 hrs. The digestion rack is then placed in a CEM MARS6 system and heated to 105°C with a 10 minute ‘time to temperature’ and a 15 minute hold time. After cooling, the samples are removed from the microwave and 200 μls of H2O2 added to each tube. The tubes are again lightly capped and put through a second heating cycle. After cooling, 9.5 ml of DI water is added to each tube and the final digestion weight is recorded. The digested toenails are analyzed by ICP-MS following the procedures described above.

Trace Elements in Soils and Sediments: Samples should be supplied dried and homogenized. The TEA lab does not perform total digestions of these matrices (i.e. no HF or fusion techniques are performed). Soils are digested using a combination of HNO3 and HCl (Optima grades) at 9:1 (other ratios of acids can be used) in an open vessel digestion. Approximately 0.25 g sample is weighed into a pre-weighed 50ml centrifuge tube and 5 ml of acid mix is added to the tube. The sample is left to react with the acids at room temperature for a minimum of 1 hr. Samples are lightly capped and placed in a 40 place digestion rack and placed in a Mars 6 digestion unit. The samples are heated at 110 C for 1 hr. After cooling 45 ml DI water is added to each sample vessel and the final weight is recorded.

Trace Elements in Biological tissues (fish muscle, plant tissues etc): For biological samples we use a MARS6 system (CEM, Mathews, NC) . Approximately 100 mg is weighed into a digestion vessel, smaller sample masses can be submitted if necessary. Two ml of Optima HNO3 is added and the vessel is capped and placed in the digestion rack. The 40-place rack can accommodate 34 samples, 2 blanks, 2 SRMs and 2 duplicates for quality control. The lab has a range of certified quality control materials suitable for biological and environmental samples. The vessels are heated to 180°C in 10 minutes and held at that temperature for a further 10 minutes. After the samples have cooled they are brought up to approximately 15 ml volume with DI water. Sample masses and final digestate volume can be scaled up or down depending on the situation. Digested samples are usually diluted a further 10- 100 times with DI prior to analysis. Lesser dilutions and/or method of standard additions can be used if there are significant matrix effects during the analysis. Once in solution, the samples are analyzed as described above in the trace metals in solution section.

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