Dartmouth Trace Element Analysis Core: Lab methods

Transcription

1 Dartmouth Trace Element Analysis Core: Lab methods General All prices are based on analysis of up to 14 elements of interest to the investigator. More analytes can be included in the run after discussion with TEA Lab staff. Typically we do not analyse for major elements (Na, mg, Ca, K,) but these can be included after discussion with TEA Lab staff. Similarly we do not analyse samples with ppm levels of trace elements, unless they are diluted substantially before analysis. Mercury can be included as an analyte in a regular analytical run, however, low level Hg analysis usually requires cold vapor generation which is run separately to the other elements and requires an additional analysis charge. Instrumental Analysis is performed on an Agilent 8800 (ICP-QQQ) or 7700x. Samples requiring the most sensitive analysis and lowest detection limits are analysed on the 8800 ICP-MS. For the 8800, Se and As are analysed in O 2 reaction mode with mass shifting to m/z 91 and 94 respectively, all other analytes are analysed in an identical manner to the 7700x. For the 7700x, all analytes except Hg, Pb U, and Se are analysed in collision mode with Heat a flow rate (usually ml/min) optimized to minimize background at m/z 75. Hg, Pb and U are analysed in normal (no gas) mode for maximum sensitivity. Pb data is the sum of Pb206, 207 and 208. Selenium and cadmium are analysed in reaction mode with H 2 as the reactive gas at a flow rate of 6 ml/min. An internal standard solution containing Sc, Ge, Y, In, Rh, Te, Bi in 1% HNO 3 and 4% butan-1-ol is T-ed into the sample stream prior to nebulization. The addition of butanol increases sensitivity for As and Se and normailizes carbon content for sample sets were dissolved C may be variable and otherwise cause sample specific signal enhancement or suppression. The instrument is tuned in all analysis modes daily to meet or exceed the manufacturer s specifications. Details of the calibration and laboratory QC are contained in the QC document. Specific Analyses Trace metals in water Water samples should be filtered and acidified (0.5% optima HNO 3 or equivalent). Samples should be stored in clean plastic (LDPE, PP, Teflon, PETG) bottles or metal free centrifuge tubes (e.g VWR series). A minimum of 10mls 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.

2 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% HNO 3prior to analysis using the methods outlined above. Whole blood samples are thawed, vortexed then acid digested with 9:1 HNO3:HCl. The TEA core utilizes 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 HNO 3 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 70C for 2 hrs. The tubes are allowed to cool and 0.05 ml of H 2O 2 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 H 2O 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 above. Trace Elements in Nails (and hair) Washing of toenails Any 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 (nail polish, dirt etc.) without extracting metals from inside the nails. 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 HNO 3 (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 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

3 are removed from the microwave and 200 µls of H 2O 2 added to each tube. The tubes are again lightly capped and put through a second heating cycle. After cooling, 9.5 mls of DI water is added to each tube and the final digestion weight is recorded. The digested toenails are analysed by ICP-MS following the procedures described above. Trace Elements in soils and sediments Soil and sediment 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 HNO 3 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 fillets 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 mls of optima HNO 3 is added and the vessel is capped and placed in the digestion rack. The 40 place rack can accommodate 34 samples with 2 blanks, 2 SRMS and 2 duplicates for QC purposes. The lab has a range of certified quality control materials suitable for biological and environmental sample types. 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 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 analysed as described above in the trace metals in solution section. Arsenic speciation in solutions Arsenic speciation in solutions is conducted by ion chromatography coupled to ICP-MS. We employ an Agilent LC 1260 interfaced with our Agilent 8800x ICP-MS. For well water/drinking water etc. we anlyse for As(III) and As(V) using a Hamilton PRP100X column with a 40 mm phosphate eluant at a flow rate of 1.5 ml/min. For urine samples we utilize the same column and eluent but also include arsenobetaine, arsenocholine, monomethyl arsenic acid, and dimethylarsenic acid. In general a 4 point calibration is conducted during each run and second source calibration checks are performed every ten samples.

4 Sample injection volume for standards and samples is 100 µl. Data is processed in MassHunter using the chromatography optional software. For urine analysis, certified urine samples from NIST and NIES are run with each sample batch. More in depth descriptions of our As speciation methods are published in: Jackson, BP Fast Ion Chromatography-ICP-QQQ for arsenic speciation. Journal of Analytical Atomic Spectroscopy. DOI: /C5JA00049A Taylor, V.F., Jackson, B.P, Siegfried, M. Francesconi, K., Kirshtein, J. Voytek, M Multiple Arsenic speciation and cycling in food chains from mid-atlantic hydrothermal vents. Environmental Chemistry, 9(2): Jackson, B.P, Taylor, V.F., Punshon, T. Cottingham, K.L. (2012) Arsenic concentration and speciation in infant formulas and first foods. Pure and Applied Chemistry 84: General Mercury speciation in waters, soils and biological tissues We now use the automated methylhg system MERX-M (Brooks Rand, Seattle, WA) interfaced with our ICP-MS instruments. The MERX consists of an autosampler, a purge and trap unit and a packed gas chromatography unit, and uses EPA method 1630 where ethylation with NaBH 4 converts methylhg and inorganic Hg to the volatile ethylated derivatives. These volatile species are then purged with an inert gas (ultra pure N 2) and trapped on Tenax traps. The Tenax traps are then thermally desorbed and the ethylated Hg species are carried in a Ar/Xe gas stream onto a packed gas chromatography column heated isothermally at 36 C. The effluent flow from the column is directed to an ICP-MS, which serves as an element specific detector to generate chromatograms for 199 Hg, 201 Hg, and 202 Hg. We use isotope dilution for quantification so all samples are spiked prior to analysis with an appropriate amount of enriched 199 Hg 2+ and CH Hg +. Water samples are poured into pre-weighed 40 ml glass autosampler tubes and the weight of sample recorded. An appropriate amount of enriched isotope spike for each Hg species is then added to the sample and the weight of each spike is recorded. The sample is buffered with a citrate buffer (300 µl of 2M buffer) and the ethylating reagent (40 µl of 1% NaBH 4) is added. The samples are then run directly on the MERX-ICP-MS system. Low level inorganic Hg determination ( < 1 ppt) is presently not reliably measured by this technique in our laboratory because of analytical blank issues. No such issues are present for methylhg which can be measured accurately to low pg/l concentrations. Biological tissues are extracted in a 25% KOH/methanol solution. Approximately 50 mg sample is weighted into an amber glass vial and the enriched spikes are added and their weights recorded. Three ml of 25% KOH/methanol extractant is added and the sample is shaken overnight. A 50 µl aliquot of the extracted sample solution is then added to the 40 ml MERX autosampler vial and 40 ml DI is added to fill the vial. The vial is then buffered and ethylated and analysed as described above for water analysis.

5 Soil and Sediment samples are analyzed separately for methylhg and total Hg. Due to the very large ratio of inorganic Hg to methyl Hg in soils and sediments, the species have to be separated and analyzed individually. For methylhg determination, 0.5 g of sediment is weighted into a PP tube, along with the single isotope methylhg spike. Five ml of 18%KBr and 5% H 2SO 4 and 1 ml of 1M CuSO 4 are added to each sample, then vials are capped and shaken for 1 hr. A 5 ml aliquot of CH 2Cl 2 is then added to each sample, and the samples are shaken for another hour. Samples are centrifuged at 3000 rpm for 15 min. then the CH 2Cl 2 fraction (containing methylhg) extracted with a pipette and transferred to another PP vial. Ten ml of DI water is added to each vial and the vial is placed in a warm water bath and bubbled with Ar until all of the CH 2Cl 2 has evaporated. Samples are then transferred to 40 ml amber glass vials buffered, ethylated and filled with DI water prior to analysis. More in depth descriptions of our Hg speciation methods are published in: Jackson, B., V Taylor, R.A. Baker, E. Miller Low level mercury speciation in freshwaters by isotope dilution GC-ICP-MS. Environ. Sci. Technol. 43, Taylor, V.F., B.P. Jackson, C.Y. Chen, Mercury speciation and total trace element determination of low-biomass biological samples. Anal. Bioanal. Chem. 392: Method Development We have experience in hyphenated techniques for speciation analysis and laser ablation ICP-MS for 2D mapping of biological or geological thin sections. Much of this work requires some tinkering to arrive at suitable analytical conditions, or requires extensive data processing after the analysis. We welcome enquiries for research in spatial distribution and/or metal speciation in biological and environmental samples. Quality Control The Trace Element Analysis Laboratory follows quality control procedures outlines in EPA SW 846 ( and EPA method 6020 ( These procedures are outlined below. Calibration. The ICP-MS is calibrated using NIST traceable single and multi-element standards containing the analytes of interest. Multi-point calibration curves (n 5) are constructed for each analyte with correlation coefficient criteria > The calibration is followed by an Initial Calibration Blank (IBC) and an Initial Calibration Verification (ICV). The ICV (which is also the solution for subsequent Continuing Calibration Verifications (CCV)) is made from a second source of single and multi-element

6 standards and contains all the analytes at concentrations at or below the mid-point calibration range. Acceptance criteria for the ICV and CCV are ± 10%. The CCV is run after every 10 samples. Laboratory Control Samples (LCS) and Standard Reference material (SRM) The TEA generally uses Standard Reference Materials (SRM) as LCS s. For solid samples the SRM is chosen to match the sample matrix (soil/sediment/animal tissue/plant tissue) as closely as possible. The LCS is taken through all sample preparation steps and handled in an equivalent manner to a sample. For aqueous samples the LCS is a Certified Water Sample such as SLRS 5 ( or similar. Acceptance criteria for LCS are ± 20% of the certified or accepted value. Duplicates and Spikes Unless sample is limiting, duplicate and spike analysis are performed on all sample batches. Duplicate solid samples are digested at a frequency of one duplicate per 20 samples. Analytical duplicates and spikes are performed at a frequency of one each per 20 samples. Recovery criteria for all analytes are 80%-120% of the spike amount.