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Sample
Types and Preparation
At the Lab, both liquid and solid samples may be submitted for analysis; liquids such a stream or pore waters, soil or tissue extracts, or digestates can be directly analyzed on most instruments. Sample volumes required are typically low--10 mL is sufficient for most analyses, although if available, 100 + mL samples are prefered. Very small volumes (< 1 mL) can be accomodated for many analyses--check with us first for details. If submitted samples contain appreciable suspended solids, they must be filtered or digested prior to analyses (see sample fee page for costs of these services). For some analyses (i.e., CNS analysis), solid samples can be analyzed directly; for most others, however, solids must be digested or extracted to a liquid form. A wide range of solid sample preparation techniques are used for various types of samples and analytes, and the Lab can accomodate most of those in common use. For most analyses, 5 or 10 g of material is sufficient; characterization work such as particle size and mineralogy requires at least 100 g of material.
Most solid samples need to be
dried (in order to correct for moisture content) and ground (to help subsampling)
before most analysis, and this adds some cost (see price
list ); you can prep many samples prior to submission to save this
cost. Extraction
and Preparation Methods
Inorganic analysis (metals): For soils, sediments, rocks and plant tissue, a boiling nitric acid digest is often used to extract metals (EPA method 3050A). This involves digestion of the sample in conc. nitric acid on a hot plate, followed by hydrogen peroxide to further oxidize organics and solubilize metals. This works well for highly organic samples (e.g., plant tissue), but less well for soils and rock material. The Lab has available a microwave digestion system which can be used for more resistant materials, which improves digestion efficiency. For analyses requiring Si, Al, and/or more complete digestion of silicious materials, an HF (hydrofluoric acid) digest is available, using either pressurized Teflon bombs at 160 C, or using microwave digestion. Essentially total dissolution of the sample is affected with HF-based methods. Custom types of extractions are available for specific applications; weak acid extracts or complexing agents can be used to extract a variety of inorganic contaminants or nutrient elements from samples. Call for details. Organic analysis: Organic compounds are traditionally extracted from solids using solvent extraction combined with heating (Soxhlet refluxing) or using ultrasonic energy to enhance partitioning of the compound into the solvent phase. For volatile and semi-volatile compounds, direct vaporization using purge-and-trap methodology is also an option, and has many advantages for many compounds compared to solvent- based methods. Both ultrasonic extraction and purge-and-trap are available at the Lab; call to discuss which method is best suited for the compound(s) of interest. Soil characterization: For identification of mineral components in soils, it is often of most interest to focus on the colloid (<2 micron) fraction rather than the whole soil; X-ray diffraction and surface area analysis are much more informative on a 2 micron sample than on whole soils. We can separate the colloid fraction prior to analysis, or discuss with you the advantages of different approaches. How
to Submit Samples
You can visit us anytime at the Lab, and bring your samples for drop-off; for directions, see map . You can also mail samples to us (our address) , although please contact us to be sure to get shipping instructions and a price quote for your samples before you ship. |