 |
Perkin-Elmer Elan 6000 ICP-MS showing quadrapole chamber housing the mass detector system. |
Metals analysis is a focus of the Laboratory; the primary instrument used
is a Perkin Elmer Elan 6000 inductively couple {argon} plasma spectrometer
(ICP) equipped with a mass spectrometer (MS) detector system, described in
detail below. Atomic absorption spectrometry (AA) is also available for single-element
metal determinations using either a flame system (Perkin Elmer 5000) or a
graphite furnace (GFAA) insturment (Perkin Elmer 4100ZL) located at the Plant
Sciences Building on the UGA campus.
ICP-MS technology is capable of (essentially) simultaneous determination of up to 80 elements in a liquid sample in a single run of a few minutes. The mass-selective detector is extremely sensitive, particularly for heavier elements in the periodic table, giving very low (sub-ppb[parts per billion], down to ppt [parts per trillion]) detection limits. The detector system is also relatively immune to many of the chemical and spectroscopic interferences that plague optical emission ICP systems.
This periodic table indicates in color the elements that can be determined by ICP-MS, along with color-coded detection limit (DL) ranges; these DL's apply to optimum conditions, but can be approached through careful analysis (for routine analyses, values might be multiplied by 3-5x). It is clear that heavier trace elements have the lowest detection limits, and the lighter elements are correspondingly less sensitive, although all are essentially in the sub-ppb range. All 73 of the elements shown on the table may be determined on an individual sample using a special semi-quantitative element scan called "TotalQuant"; typically, however, only a suite of elements is of interest, and these elements can be custom selected for each sample set, and the instrument individually calibrated for each. We routinely run 10 metals of environmental interest (including EPA regulated metals), as well as a 20-element scan that includes a wider range of more exotic elements. The "major" cations (Ca, Mg, Na, K) can be added to either of the above scans. See the sample fee page for details on elements included and prices.
Mercury (Hg) analysis is also available using a dedicated Hg analyzer based on the cold vapor spectrometric method; the Perkin-Elmer FIMS 4000 system can perform ppt-level Hg analysis on water and digest/extract samples with minimal matrix interference. Hg speciation (methylated forms) methodology is under development using this equipment, and can be tailored to specific types of samples.
Nearly any liquid sample can be used for ICP-MS analysis, although total salt contents are typically diluted to < 2% prioir to aspiration; this may reduce DL's of some very high-salt samples via dilution. Organic solvents may be used, although we haven't tried this yet. Soils, rocks, and plant tissue may be extracted or digested in a variety of solutions to solubilize all or some part of the element(s) in the sample. Various sample preparation methods are discussed in the sample preparation section of this document.
If only one element in a sample is of interest, atomic absorption may be an alternative choice for analysis. Flame AA (FAA) is a well-established, low-cost method for ppm-level detection limits for a number of elements. Graphite furnace AA (GFAA) has ppb-level detection limits for many elements due to improved sample atomization; the PE 4100ZL unit has Zeeman background correction for improved signal stability at low concentrations. Sample type and preparation are similar to those for ICP analysis. Cost per sample is significantly lower than for ICP; for on-campus users interested in learning to use the Perkin-Elmer 5000 unit, special arrangement can be made. See the sample fee page for availability of elements and pricing.
Data quality is a prime emphasis at the lab, give the importance of accuracy in analysis in both research and regulatory arenas. A rigorous protocol of quality assurance/quality control (QA/QC) is followed for every sample batch run for metals analysis, including re-calibration and re-zeroing, replication, individual calibration of all elements in a sample run over the concentration range of interest, and use of check standards to ensure proper calibration. With larger sample batches, sample spikes and certified reference materials (NIST or equivalent) are run to confirm recovery of analyte elements. QA/QC information is provided with every sample set for you to evaluate detection limits, precision, and overall data quality.
