Region 8
Serving Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming and 27 Tribal Nations
Region 8 Laboratory Metals Chemistry
National Information
Regional Information
The six states of Region 8 (CO, MT, ND, SD, UT, WY) have many active and abandoned hard rock mines, smelters and tailings piles. Because of the potential for metals leaching into snowmelt and rainwater thereby impacting groundwater and surface streams and lakes, a large proportion of the Laboratory's work involves testing for metals in soils, sediments, biota or tailings.
Nutritionally, metallic elements are crucial in many metabolic processes. Yet, too much of certain metals in food, water, air or soil can be detrimental to the organism. Thus EPA and other organizations and agencies have set concentration limits for these commonly occurring elements in drinking water, ambient streams, waste water, hazardous wastes disposal, and growing soils.
Normally to test these various matrices for toxic metals, a preparation step (e.g. digestion) is required to release the metals from their bonded state to available ions in solution. Reduction or containment of metals releases, is the ultimate goal of monitoring metals by the Regional Laboratory's metals section. Broad-based watershed studies provide assessment of the current status for large areas; site specific analysis can reveal the potential contamination and risk from a superfund site, hazardous waste spill or permit discharge.
Instruments used by the Region 8 Laboratory
Currently, the only atomic absorption (AA) spectrometer utilized (other than for mercury) has the graphite furnace (GF) atomizer. This instrumentation, a SIMAA 6000 model, permits the detection of trace metals in the sub ug/L (parts per billion) range in waters or digest solutions. The principles of atomic absorption permit nearly spectral-free analysis but can be subject to myriad chemical interference. The design of the instrumentation and delayed platform technique circumvent nearly all common chemical interferences. Presently, the laboratory has the capability for single or simultaneous (up to 4 elements) GFAA analyses. This technique is more costly and time consuming compared to inductively coupled plasma(ICP) simultaneous analyses. The main advantages of GFAA are the very low reporting limits and requirement for low volumes of sample (< 1ml). Elements commonly requested for GFAA analysis are cadmium, lead, antimony, thallium, arsenic, selenium, and silver.
Emission Spectrometry
The most common instrumentation utilizing this technique is the ICP spectrometer. The lab currently possesses four such instruments allowing either sequential, simultaneous, or radial-viewed or axial-viewed determination of both major and trace metals. The strong points in ICP analysis are the ability to test 20-40 elements simultaneously (analyst selectable) in a reasonable time and low range of 1-100 ug/L. Due to the ICP's very hot plasma (6000-8000 degree Celsius), very few chemical interferences are possible. The spectral output, caused by excited atoms or ions, is very rich however with many lines for each elements; some lines may overlap the analyte lines of interest thereby creating a spectral interference. Also sample introduction via a cross-flow nebulizer and spray chamber, that sorts droplet sizes, can be subjected to transport interference (e.g. viscosity, surface tension, high salt content). Line choices, background correction, spectral overlap corrections, autosampler pumping and internal standards can circumvent most of these spectral and transport interferences. Similar to the other techniques being discussed, sample introduction, calibration, spectral gathering, quantification, QC critiquing, and instrument control is automated and under control of a PC.
Mass Spectrometry
When ions created in an ICP plasma are siphoned off into a vacuumed mass spectrometer (MS) and separated according to mass/charge ratio, this composite analytical technique is termed ICP-MS. The advantages of using the lab's Elan 6000 model ICP-MS is very low detection levels for most metals (.01-.1 ug/L) with few chemical and spectral interferences. However, samples with high dissolved salts and acid content do provide an opportunity for transport or mass overlaps interference. As such, the techniques works best on cleaner waters or low acid solutions after dilutions are performed. Similar to ICP, the working linear range covers 4-6 decades and can apply to minor or major elements when certain masses are detuned. Automated multi-element techniques tend to reduce per element costs in samples. Oftentimes, ICP-MS reporting limits are limited by the cleanliness of glassware, air, bottles or reagents coming into contact with the samples. One other capability of ICP-MS is the ability to determine isotopic ratios of elements in the samples.
Cold Vapor Atomic Absorption
This special technique of AA is utilized solely for determining mercury in samples; there is no atomizer but instead an elongated round cell is substituted, that conducts the mercury vapor cloud through the light beam. The degree of absorption of the light beam by the mercury atoms is utilized to quantify mercury in the digested sample. Digestion of a sample, even in clear waters, is necessary since mercury bonds are strong and usually in the wrong oxidation state. Mercury is one of the more toxic metals and especially detrimental to the neurological system. The method, although labor intensive and relatively slow, is quite sensitive; reporting limits are typically .1-1.0 ug/L. Collectors and analysts must be aware that the holding time (sample stability) is only 28 days; all other metals, except Cr6+ speciation, have a holding time of 180 days.
X-Ray Fluorescence
The laboratory has an in-house capability for non-destructive analysis of soils, sediments, and tailings for metals having atomic number >20. Typical reporting levels for these heavy metals are in the low-mid parts per million (PPM) range, dry weight. After minimal sample preparation (sieving, drying, grinding), a quick scan for multiple elements can be performed by energy dispersive X-ray fluorescence (usually under five minutes). This capability is handy for site assessment of hazardous waste projects or remediation with low costs and fast turnaround time. The lab's Spectrace 6000 XRF is potentially transportable to a site but not hand portable. Typical elements requested are cadmium, lead, arsenic, and zinc. Spectral and chemical interference are minimal. The calibration techniques, fundamental parameters, requires that calibration standards have similar but not exact matrix type to samples; also standards should be well characterized.