EPA Region 6 Laboratory Inorganic Analysis Group
- About the Inorganic Analysis Group
- Inorganic Sample Preparation Laboratory
- Mercury Analysis
- Inductively Coupled Plasma Laboratory -Atomic Emission Spectrometer (ICP-AES) Laboratory
- Inductively Couple Plasma-Mass Spectrometry -(ICP/MS) Laboratory
- Ion Chromatography (IC)
- Total Organic Carbon (TOC)
About The Inorganic Analysis Group
The Inorganic Laboratory Group 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 program areas including, air, water, RCRA, Superfund, and criminal investigation.
The Inorganic Analysis Group is part of the Laboratory Analysis Branch under the direction of the Laboratory Analysis Branch Manager.
Inorganic Sample Preparation Laboratory
The sample preparation laboratory is designed to prepare water and solid samples for analysis by Inductively Coupled Plasma (ICP), Inductively Coupled Plasma/Mass Spectrometry (ICP/MS), mercury, Ion Chromatography (IC), Total Organic Carbon, and RCRA characteristics. The samples are subjected to a variety of digestion techniques sometimes including TCLP extraction prior to digestion. Other preparation techniques used on a non-routine basis may include microwave digestion, chelation pre-concentration, or direct analysis.
ICP and ICP-MS samples for water are routinely prepared by adding nitric and hydrochloric acids or nitric acid and hydrogen peroxide to a 50 ml aliquot then heating the sample in a hotblock 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 half a gram of sample material. These procedures require sample vessels, watch glasses, hot blocks, pipettes, 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 50 ml.
Digestion of samples to be analyzed for mercury uses reagents such as sulfuric acid, nitric acid, potassium permanganate, and potassium persulfate which are added to 5 ml or 25 ml water samples, depending on the analytical instrument, which are then incubated in a hot block at 95 degrees Celsius for 2 hours. Soil samples use 0.1 grams of sample material and aqua regia in addition to potassium permanganate and incubation for 30 minutes in a hot block. Hydroxylamine reagent is added to all samples prior to giving the samples to the analyst.
ICP and ICP-MS samples for water are routinely prepared by adding nitric and hydrochloric acids or nitric acid and hydrogen peroxide to a 50 ml aliquot then heating the sample in a hotblock 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 half a gram of sample material. These procedures require sample vessels, watch glasses, hot blocks, pipettes, 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 50 ml.
Digestion of samples to be analyzed for mercury uses reagents such as sulfuric acid, nitric acid, potassium permanganate, and potassium persulfate which are added to 5 ml or 25 ml water samples, depending on the analytical instrument, which are then incubated in a hot block at 95 degrees Celsius for 2 hours. Soil samples use 0.1 grams of sample material and aqua regia in addition to potassium permanganate and incubation for 30 minutes in a hot block. Hydroxylamine reagent is added to all samples prior to giving the samples to the analyst.
The Houston Laboratory has three mercury analyzers, two using cold vapor atomic absorption technology with detection limits at 2 ug/L and a direct mercury analyzer (DMA) that doesn’t require a separate sample preparation procedure. The cold vapor instruments are designed to measure the mercury vapor produced from the prepared samples upon the addition of stannous chloride reagent, and one of the instruments has the capability for automated digestion and analysis of the liquid matrix. These instruments are similarly calibrated with known standard materials to establish a concentration curve. Sample concentration is calculated against this curve.
Inductively Coupled Plasma Laboratory - Atomic Emission Spectrometer (ICP-AES) Laboratory
The ICP laboratory contains two ICP-atomic emission spectrometers (AES). The multichannelled instrument simultaneously measure up to twenty-six (26) trace metals at once using their characteristic spectral emission lines. 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-AES will measure in the range of mg/liter to low ug/liter concentrations.
Inductively Couple Plasma-Mass Spectrometry (ICP/MS) Laboratory
The ICP-MS laboratory has two ICP-MS instruments used for metals analysis. These instruments measure most of the elements in the periodic table which have naturally occurring isotopes. The ICP-MS technique offers the opportunity to achieve lower detection limits than the ICP-AES at the part per trillion (ppt) range. The digested samples in the liquid form are introduced into the instrument sample introduction system which consists of a nebulizer and spray chamber. The nebulizer converts the liquid sample into very small droplets. These small droplets are carried through the spray chamber into the injector and then into the plasma which is at a temperature of approximately 6000C. The plasma ionizes the elements present in the droplets. These ions then pass through the interface and the ion lens of the mass spectrometer (the main difference between ICP-AES and ICP-MS). After being focused by the ion lens, the ions are separated by their mass-to-charge ratio in the mass spectrometer and measured by the detector. Once the detector measures the ions, the computerized data system is used to convert the measured signal intensities into concentrations of each element and generate a report of the results.
The IC instrument is used to analyze seven anions in both drinking and potable water. Ion chromatography measures concentrations of ionic species by separating them, based on their interaction with the resin inside the column. The columns temperate, length, and resin all play a significant part in separating the ionic species depending on the species size and type.
TOC is calculated based off the measurement of Total Carbon and Inorganic Carbon (TOC=TC-IC). The Houston Laboratory uses the combustion method, where a sample is heated to 680°C in the presence of oxygen which oxidizes all the carbon to form carbon dioxide. The carbon dioxide is pushed into the infrared cell and is selectively (total carbon and total inorganic carbon) detected.
The determination of total carbon in the water sample is oxidized to produce carbon dioxide, which is then measured by the detection system. Carbon Dioxide, which is released from the oxidized sample, is detected by an infrared detector. Inorganic carbon in the water is injected into a reaction chamber where it is acidified. Under these acidic conditions, all inorganic carbon is converted to Carbon Dioxide, which is transferred to the detector and measured. Under these conditions organic carbon is not oxidized, and only inorganic carbon is measured