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Trace Element Research Laboratory (TERL)
Analytical Methods

Select one of the links below to display the method descriptions associated with TERL.

Method Code

Method Title

001

Digestion of Biological Tissue

002

Digestion of Soil and Sediment

003

Digestion of Water, Soil, Sediment, and Biological Tissue for Mercury Analysis

004

Digestion of Water Samples for "Total Recoverable" Metals (Other than Mercury)

005

Analysis of Trace Metals by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP)

006

Analysis of Trace Metals by Graphite Furnace Atomic Absorption Spectroscopy (GFAAS)

007

Analysis of Mercury by Cold-Vapor Atomic Absorption Spectroscopy (CVAAS)

008

Analysis of Trace Metals by Flame Atomic Absorption Spectroscopy (FAAS)

009

Analysis of Trace Metals by Atomic Fluorescence Spectroscopy (AFS)

010

Analysis of Trace Metals in Biological Tissue, Soils, and Sediments by Instrumental Neutron Activation Analysis (INAA)

011

Analysis of Grain Size Distribution in Soil and Sediment Samples (GS)

012

Analysis of Soils and Sediments for Total Organic Carbon (TOC)

013

Analysis of Acid-Volatile Sulfide in Soils and Sediments (AVS)

014

Moisture Content of Sediment, Soil, and Tissue Samples

015

Preparation and Analysis of Tissue and Sediment Samples for Methyl Mercury (MeHg)

016

Analysis of Trace Metals in Water Samples by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS)

017

Analysis of Inorganic Arsenic (As) in Tissue and Sediment Samples

018

Analysis of Inorganic Species and Organic Arsenic in Tissues and Sediment Samples

019

Preconcentration of Water Samples for Trace Element Analysis

020

Determination of Total Suspended Solids

021

Nitrogen

022

Digestion of Biological Tissue in Microwave Oven Under Pressure

023

Digestion of Biological Tissue in Microwave Oven Under Ambient Pressure

024

Determination of Mercury in Tissue and Sediment

025

Determination of Mercury in Water

026

Determination of Methyl Mercury in Water

027

Determination of Perchlorate in Water

028

Determination of Anions in Water by Wet Chemistry Procedures

029 Determination of carbon, nitrogen, and/or stable C and N isotopes by isotope ratio mass spectroscopy

 

 

 

 

 

 

Lab Name: Trace Element Research Laboratory       Method Code: 001 

Digestion of Biological Tissue

Liquid or solid biological tissue samples are wet digested with nitric acid and converted into acidic digest solutions for analysis by various atomic spectroscopy methods. When possible, tissue is freeze dried in order to minimize loss of analytes and to facilitate subsequent sample preparation steps, and then homogenized to a fine powder by ball-milling in plastic containers. Approximately 0.20 to 0.25 g of powdered tissue is weighed into a Teflon reaction vessel and 3 ml of HNO3 are added. The closed reaction vessel is heated in a 130 C oven until digestion is complete. Samples are then diluted to a final volume of 20 ml with quartz distilled water and stored in 1 oz. polyethylene bottles for later analysis by instrumental techniques.

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Lab Name: Trace Element Research Laboratory       Method Code: 002

Digestion of Soil and Sediment

Soil and sediment samples are wet digested with nitric and hydrochloric acids and converted into acidic digest solutions for analysis by various atomic spectroscopy methods. Wet sediment is homogenized in its container, and an aliquot is freeze dried and homogenized to a fine powder. Approximately 0.5 g of powdered sediment is weighed into a tall form beaker and 10 ml of Aqua Regia (1:4v:v HNO3:HCl) are added. The vessel is heated on a hot plate for 2 hrs., with swirling, repositioning, and rinsing of the beaker walls (if necessary) at 1 hr. Samples are then transferred into centrifuge tubes and diluted to a final volume of 30 ml with distilled deionized water. They are spun to settle particles and transferred to 1 oz polyethylene bottles for storage until analysis. The samples are then diluted as necessary and analyzed for trace metals by various TERL analytical methods.

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Lab Name: Trace Element Research Laboratory       Method Code: 003

Digestion of Water, Soil, Sediment, and Biological Tissue for Mercury Analysis

Before samples are analyzed by the CVAAS method in use in this laboratory, the mercury is converted to the Hg2+ form. Mercury is digested by a modified version of EPA method 245.5 and 245.6. Sediment and tissue samples can be analyzed either freeze dried or on a wet basis. Sediment samples are homogenized by mixing before subsampling, while tissue samples are homogenized in the original sample containers either after freeze drying or with a Tekmar Tissumizer and subsampled. Samples are digested with nitric acid, sulfuric acid, potassium permanganate, and potassium persulfate in polypropylene tubes in a water bath at 90-95 C. Before analysis, hydroxylamine hydrochloride is added to reduce excess permanganate and the samples are brought to volume with distilled-deionized water.

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Lab Name: Trace Element Research Laboratory       Method Code: 004

Digestion of Water Samples for
"Total Recoverable" Metals (Other than Mercury)

Water samples are digested for two hours at 85 degrees Centigrade in polyethylene containers with ultrapure nitric and hydrochloric acids. Acid strength, on a vol:vol basis, is 1% HCl and 0.5% HNO3. Sample aliquots for digestion are taken after vigorous shaking to assure suspension of solids that may have settled. The original sample must have had preservative added (usually HNO3) in order to ensure that metals do not adhere to the walls of the container.

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Lab Name: Trace Element Research Laboratory       Method Code: 005

Analysis of Trace Metals by
Inductively Coupled Plasma Optical Emission Spectroscopy (ICP)

Liquid samples are nebulized and the resulting aerosol is transported to the plasma torch. Element-specific atomic-line emission spectra are produced by a inductively coupled argon plasma. The spectra are dispersed by a grating spectrometer, and the intensities of the lines are monitored by photomultiplier tubes or solid state detectors. Samples are quantitated by comparison with external standards. One or more internal standards may be incorporated to compensate for physical effects resulting from viscosity and varying levels of total dissolved solids in the samples. Background correction is required and is measured adjacent to analyte lines on samples during analysis.

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Lab Name: Trace Element Research Laboratory       Method Code: 006

Analysis of Trace Metals by
Graphite Furnace Atomic Absorption Spectroscopy (GFAAS)

Liquid samples requiring lower detection limits than are available by ICP are Analyzed by GFAAS, in which electrical resistance heating evaporates solvent (water), removes interfering species, and finally atomizes the analyte into the light path of an atomic absorption spectrophotometer. The method is subject to numerous chemical and physical interferences, and requires the use of matrix modifiers to produce accurate and reliable data in real-world sediment, tissue, and water digest solutions.

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Lab Name: Trace Element Research Laboratory       Method Code: 007

Analysis of Mercury by
Cold-Vapor Atomic Absorption Spectroscopy (CVAAS)

In this procedure, divalent mercury (Hg++) in aqueous samples (digests of water, tissue or sediment samples) is reduced to the elemental state (Hgo) by a strong reducing agent (stannous chloride). Gaseous Hgo enters the sweep gas and is introduced into an atomic absorption cell, where light produced by a mercury vapor lamp is absorbed by the free Hg atoms. Mercury in the sample is determined by comparing light absorption of the sample with that of external calibration standards.

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Lab Name: Trace Element Research Laboratory       Method Code: 008

Analysis of Trace Metals by
Flame Atomic Absorption Spectroscopy (FAAS)

Flame atomic absorption spectrophotometry relies on a flame to provide the heat necessary to evaporate the solvent (water) and break molecular bonds in order to produce a cloud of free atoms in the path of an atomic absorption spectrophotometer. In general, the method is rapid, sensitive, and free from inter-element interferences. Prior to analysis, samples must be digested using a method that is appropriate for the matrix. Depending upon element, the fuel (acetylene) is burned with either air or nitrous oxide as the oxidant. Background correction is used to compensate for molecular absorption and light scattering by solids.

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Lab Name: Trace Element Research Laboratory       Method Code: 009

Analysis of Trace Metals by
Atomic Fluorescence Spectroscopy (AFS)

Aqueous samples (including sample digests) are analyzed for mercury and hydride-forming elements (antimony, arsenic, and selenium) by atomic fluorescence. Analytes are introduced to the gas phase by reaction with a strong reducing agent (e.g. stannous chloride for mercury and sodium borohydride for the other elements), and free atoms are bombarded with light of element-specific wavelengths. Light that is released via atomic fluorsecence is measured by a detector set at a right angle to the source. Because of the low background signal, AFS is extremely sensitive and is appropriate when other methods (e.g. GFAAS) lack the sensitivity to determine ambient concentrations. Spectral interferences are few, but the method is subject to chemical and matrix interferences that may impact the cold-vapor and hydride generation steps.

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Lab Name: Trace Element Research Laboratory       Method Code: 010

Analysis of Trace Metals in Biological Tissue, Soils, and Sediments by
Instrumental Neutron Activation Analysis (INAA)

Biological tissue, soil, and sediment samples are freeze dried, powdered, weighed into poly vials and exposed to thermal neutrons. Depending upon target analyte and level of background radiation from interfering nuclides, samples are allowed to cool for a period of time before counting on high-resolution gamma ray detectors. Concentrations are determined by comparison of counts with those of external calibration standards. This method avoids sample digestion problems that may occur with certain analytes and sample matrices.

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Lab Name: Trace Element Research Laboratory       Method Code: 011

Analysis of Grain Size Distribution in Soil and Sediment Samples (GS)

This method incorporates wet-sieving and the pipette method to separate soil and sediment samples into sand, silt, and clay size fractions. A 0.0625 mm sieve is used to collect the sand fraction, which is dried and weighed. Material passing the sieve is diluted to volume and at given times, small volumes of suspension are withdrawn, evaporated, and the residue weighed. Values are expressed as percent of the dry sample on a weight:weight basis.

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Lab Name: Trace Element Research Laboratory       Method Code: 012

Analysis of Soils and Sediments for Total Organic Carbon (TOC)

Total organic carbon concentrations are determined on freeze-dried (or oven-dried at 40 to 50 C) soil and sediment by combustion in an oxygen atmosphere. The carbon dioxide that is produced is swept out of the furnace's combustion chamber, passes through a series of filters, traps, and catalysts, and finally is measured by an infrared detector. Samples are quantitated by comparison of peak area with that of external calibration standards. Prior to analysis, inorganic carbon is removed by acidification. TOC is reported as percent of the dry sample on a weight:weight basis.

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Lab Name: Trace Element Research Laboratory       Method Code: 013

Analysis of Acid-Volatile Sulfide in Soils and Sediments (AVS)

Determination of the quantity of acid volatile sulfide is part of a technique that has been developed to predict the bioavailability of metals in sediment. This approach is based on the recognition that many metal sulfides are extremely insoluble, and that formation of solid-phase sulfides in anoxic sediments may control the availability of metals to organisms. AVS, defined as sulfides that are converted to H2S upon exposure to 1N HCl at room temperature for 1 hour, is determined by releasing sulfide from soil and sediment particles with HCl, trapping hydrogen sulfide gas in a base, and measuring it by colorimetry. It is critical that samples to be analyzed for AVS are collected without a headspace and subsampled under an inert atmosphere in order to prevent oxidation of AVS by atmospheric oxygen.

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Lab Name: Trace Element Research Laboratory       Method Code: 014

Moisture Content of Sediment, Soil, and Tissue Samples

Moisture content is determined by weight loss upon freeze-drying, and is expressed as weight percent of the original wet sample. Depending upon sample size, either the whole sample or a representative aliquot is frozen and then dried under vacuum until a constant weight is attained. Samples are prepared and dried using plastic materials, whenever possible, in order to minimize potential contamination artifacts that might impact subsequent trace element analysis.

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Lab Name: Trace Element Research Laboratory       Method Code: 015

Preparation and Analysis of Tissue and Sediment Samples for
Methyl Mercury (MeHg)

Methyl mercury and other alkyl mercury compounds are of concern because of their toxicities, and because they are commonly found in the environment. Bioaccumulation results in elevated concentrations in higher trophic levels, especially when lower trophic levels include fish. The procedure used to extract these compounds in the Trace Element Research Laboratory follows the method of Uthe et al. (JAOAC 55: 583-589, 1972), and measures the sum of all organo-mercury species extracted into the solvent. This determination is essentially equivalent to the GC method for analyzing MeHg in fish muscle tissue (where almost all of the organo mercury is present as MeHg). In other organs, such as kidneys, much of the organic mercury may be present as a form other than MeHg, and may not be measured by methods that employ detectors that are specific for halogenated compounds. Samples are analyzed either wet or after freeze-drying. Homogenized aliquots are extracted in to an organic solvent with potassium bromide and copper sulfate added to improve partitioning between phases. The organic phase is digested in combusted glass vials, using nitric and sulfuric acids and potassium permanganate, in order to convert all mercury species to ionic mercury and to remove traces of organic solvent that would otherwise impact the measurement. Analysis is based upon the cold vapor atomic absorption method, although cold vapor atomic fluorescence can be used when lower detection limits are required.

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Lab Name: Trace Element Research Laboratory       Method Code: 016

Analysis of Trace Metals in Water Samples by
Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS)

Concentrations of trace elements in water samples are determined with an atomic spectroscopy method that relies on ionization of sample constituents in a high temperature argon plasma and separation of positively-charged ions on the basis of their mass:charge ratios (m:z) by a quadrupole mass spectrometer. The method offers extremely low detection limits but is subject to interferences from atomic and molecular ions having values within 1 AMU of the target ions. Sample preconcentration and matrix elimination can sometimes eliminate these problems, along with those resulting from high total dissolved solids.

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Lab Name: Trace Element Research Laboratory       Method Code: 017

Analysis of Inorganic Arsenic (As) in Tissue and Sediment Samples

Inorganic As species [As(III) and As(V)] are extracted from homogenized samples using the method of Willie (Spectrochim. Acta Part B, 51:1781-1790; 1996) and analyzed by hydride-generation atomic fluorescence spectrometry (HGAFS). A single result is reported (inorgAs) since the analysis involves a reduction of As(V) to As(III) prior to hydride generation. Small sample sizes can be accommodated by modifying extraction and analysis solution volumes. Development of reference materials certified for metal species is not yet complete, so spiked samples provide the best estimates of accuracy at this time.

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Lab Name: Trace Element Research Laboratory       Method Code: 018

Analysis of Inorganic Species and Organic Arsenic in
Tissues and Sediment Samples

Inorganic As species [As(III) and As(V)] are extracted from freeze- dried tissue with methanol-water and from freeze-dried sediment with 0.3 M phosphoric acid. An anion exchange resin is used to separate As(III) from As(V), and the inorganic species are analyzed by hydride generation atomic fluorescence spectroscopy. Organic As is calculated as the difference in total As and the sum of the inorganic forms [As(III) + As(V)].

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Lab Name: Trace Element Research Laboratory       Method Code: 019

Preconcentration of Water Samples for Trace Element Analysis

Water samples with severe matrix interferences and/or requiring detection limits below instrument DL's can be preconcentrated by one of several methods. Ideally, this separates analytes from matrix components while increasing analyte concentrations in solution. Prior to preconcentration, samples are digested with nitric acid and uV irridation. Depending upon analyte requirements, digested samples are preconcentrated by ion exchange, reductive coprecipitation, iron hydroxide precipitation, or chelation/solvent extraction. Resulting solutions are generally analyzed by either GFAAS, ICP, or ICP-MS.

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Lab Name: Trace Element Research Laboratory       Method Code: 020

Determination of Total Suspended Solids

Total suspended solids (TSS) in water samples is determined gravimetrically. Samples are vacuum-filtered through preweighed 0.45 micrometer pore size membrane filters, salts are rinsed from the filters with reagent water, and filters are reweighed after drying. TSS is reported in ppm (mg/liter).

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Lab Name: Trace Element Research Laboratory       Method Code: 021

Nitrogen

Analysis of nitrogen in tissue, soil, and sediment samples. Nitrogen (N) is determined colorimetrically after digestion of freeze dried samples. Results are reported in parts per million (ppm) on a dry weight basis.

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Lab Name: Trace Element Research Laboratory       Method Code: 022

Digestion of Biological Tissue in Microwave Oven Under Pressure

Liquid or solid biological tissue samples are wet digested with nitric acid and hydrogen peroxide and then converted into acidic digest solutions for analysis by various atomic spectroscopy methods. When possible, tissue is freeze dried in order to minimize loss of analytes and to facilitate subsequent sample preparation steps, and then homogenized to a fine powder by ball-milling in plastic containers. Approximately 0.20 to 0.25 g of powdered tissue is weighed into a Teflon reaction vessel and HNO3 (3 ml) is added. The closed reaction vessel is heated in a microwave oven at 160 psi and approximately 180 degrees C until digestion is complete. H2O2 (2 ml) is added to the sample and it is heated gently at ambient pressure to digest residual lipids. The samples is then diluted to a final volume of 20 ml with deionized water and stored in a 30 ml polyethylene bottle for later analysis by instrumental techniques.

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Lab Name: Trace Element Research Laboratory       Method Code: 023

Digestion of Biological Tissue in Microwave Oven Under Ambient Pressure

Liquid or solid biological tissue samples are wet digested with nitric acid and hydrogen peroxide and then converted into acidic digest solutions for analysis by various atomic spectroscopy methods. When possible, tissue is freeze dried in order to minimize loss of analytes and to facilitate subsequent sample preparation steps, and then homogenized to a fine powder by ball-milling in plastic containers. Approximately 0.2 g of powdered tissue is weighed into a polypropylene tube and HNO3 (2 ml) is added. The tube is capped with a vented lid and allowed to stand overnight to solubilize the sample. The sample is heated in a microwave oven at 100 degrees C for 20 minutes and then allowed to cool. H2O2 (0.25 ml) is added and after standing again overnight the sample is heated at 100 degrees C for 1 hour. Digest volume is determined gravimetrically and the sample is diluted as necessary with deionized water for analysis by instrumental techniques.

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Lab Name: Trace Element Research Laboratory       Method Code: 024

Determination of Mercury in Tissue and Sediment

Determination of mercury in tissue and sediment samples by decomposition, trapping, and atomic absorption. Total mercury is determined in wet or dry samples by combustion in a stream of oxygen, trapping on a gold column, release by electrothermal heating, and analysis by atomic absorption. Mercury is reported in ppm on either a wet or dry weight basis.

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Lab Name: Trace Element Research Laboratory       Method Code: 025

Determination of Mercury in Water

Determination of mercury in water by purging, trapping, and atomic fluorescence. Total mercury is determined in water by oxidation with BrCl followed by reduction of Hg (II) to Hg(0) with SnCl2. Hg(0)g is purged from the aqueous sample with argon and trapped on a gold column. The trapped Hg is released by heating and then analyzed by atomic fluorescence.

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Lab Name: Trace Element Research Laboratory       Method Code: 026

Determination of Methyl Mercury in Water

Determination of methyl mercury in water by distillation, ethylation, trapping, gas chromatography, and atomic fluorescence. Methyl mercury in water is distilled to separate it from interfering species and then ethylated with sodium tetraethyl borate. Methyl ethyl mercury is trapped on a Tenax column and then separated on an isothermal GC column. Following pyrolysis of the separated species, Hg is detected by atomic fluorescence.

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Lab Name: Trace Element Research Laboratory       Method Code: 027

Determination of Perchlorate in Water

The perchlorate anion is determined in water by ion chromatography. Perchlorate is separated and measured, using a system comprised of an ion chromatographic pump, sample injection valve, guard column, analytical column, suppressor device, and conductivity detector.

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Lab Name: Trace Element Research Laboratory       Method Code: 028

Determination of Anions in Water by Wet Chemistry Procedures

Anions are determined by classical wet chemistry procedures. Chloride ion is measured by titrating the sample with a standardized silver nitrate solution. Bicarbonate is determined by electrochemical titration to a pH of 4.5. Sulfate is determined turbidimetrically following formation of a barium sulfate precipitate. Back to the Top Back to the Top Arrow


Lab Name: Trace Element Research Laboratory       Method Code: 029

Determination of carbon, nitrogen, and/or stable C and N isotopes by isotope ratio mass spectroscopy

Stable istopes of C and N, as well as C and N content, are determined by isotope ratio mass spectroscopy. Samples are combusted under oxygen, converting C to CO2 gas and N to N2 gas. Ratios of the CO2 and N2 species are determined on a multicollector isotope ratio mass spectrometer. Values are reported as "delta 13C" and "delta 15N", in "per mil" (parts per thousand", relative to the PDB standard for C and air for N. Inorganic species can be removed by vapor acidification prior to analysis in order to measure only organic species.

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