EPA's Region 6 Office
Serving: Arkansas, Louisiana, New Mexico, Oklahoma, Texas, and 66 Tribal Nations
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The Inorganic Laboratory Team analyzes environmental samples for trace metals, mercury, and RCRA characteristics. The samples analyzed may include drinking water, waste treatment water, solid wastes, surface and ambient waters, and sediment/soils. These tests support all programs i.e. air, water RCRA, Superfund, and criminal investigation.
Inorganic Extraction Laboratory
The extraction laboratory is designed to prepare water and solid samples for analysis by Inductively Coupled Plasma (ICP), Graphite Furnace Atomic Absorption (GFAA), mercury, cyanide, and RCRA characteristics. The samples are subjected to a variety of digestion techniques. ICP and GFAA samples for water are routinely prepared by adding Nitric and Hydrochloric acids or Nitric acid and Hydrogen Peroxide to a 100 ml aliquot then heating the sample on a hot plate until a reduction in volume allows acids to become concentrated. The heat and acids allow the metals within the samples to change to a state which can be detected by the instrumentation and quantified. A similar procedure is accomplished when soil or sludge samples are prepared using one gram of sample material. These procedures are simple and require only beakers, watch glasses, hot plates, and fume hoods. Final steps before analysis require filtration of the samples to remove any solid particles from the solution before analysis and volumetric flasks to bring the samples to a final volume of 100 ml.
Digestion of samples to be analyzed for mercury uses reagents such as sulfuric acid, concentrated nitric acid, potassium permanganate, and potassium persulfate which are added to a 100 ml water sample which is then incubated in a hot water bath at 95 degree Celsius for 2 hours. Soil samples use 0.2 grams of sample material and aqua regia in addition to potassium permanganate and incubation for 30 minutes in a hot water bath. Hydroxylamine reagent is added to all samples prior to giving the samples to the analyst. Other preparation techniques used on a non-routine basis may include microwave digestion, chelation pre-concentration, or direct analysis.
The Houston Laboratory has two mercury analyzers, both use cold vapor atomic absorption technology. The instruments are designed to measure the mercury vapor produced form the prepared samples upon the addition of stannous chloride reagent by the analyst. These instruments are similarly calibrated with known standard materials to establish a concentration curve. Sample concentration is calculated against this curve. The two systems differ in their detection limit capabilities. One instrument has a detection limit around 200 ug/liter and the other can detect 25-30 ug/liter mercury.
Acid Wash Room
All laboratory glassware used in the preparation, filtration, dilution or storage of metals samples must first undergo a thorough cleaning. The acid wash laboratory is in an isolated room containing tubs of strong acids under a special acid fume hood. The glassware is first collected from all areas of use. It is then washed with soap and water. Once clean, the glassware is soaked in the various tubs of acids for several days, triple rinsed with tap acid-metal-free deionized water. The glassware is then air dried and stored in covered containers for use.
Inductively Coupled Plasma Laboratory (ICP)
The ICP laboratory contains one ICP-atomic emission spectrometer. The multichannelled instrument simultaneously measure up to twenty six (26) trace metals at once. The instrument introduces the digested sample into a spray chamber and into the very high temperature argon plasma. The emissions generated from the metals contained in the sample are optically focused onto photomultiplier tubes and intensities measured. The instrument is calibrated using mixed element standards. The emissions from standards and samples are ratioed to arrive at a sample concentration. The ICP will measure in the range of mg/liter to log ug/liter concentrations.
Graphite Furnace Atomic Absorption Laboratory (GFAA):
The GFAA instruments are single element analytical systems capable of very low detection limits, i.e. less than or equal to 1 ug/liter. Both systems operate by introducing a small amount of digested sample into a graphite tube. The tube is gradually heated and the elements in the sample are placed in a ground state condition at approximately 2700 degrees Celsius. The instrument measures by absorption; the presence of the element of interest and quantitates against an established calibration curve. Both instruments have automated sample introduction systems and are computer controlled. Typical elements measured by this method include arsenic, selenium, thallium, and lead.