Determination of 234U/238U isotope ratios in environmental waters by quadrupole ICP-MS after U stripping from alpha-spectrometry counting sources

The ²³⁴U/²³⁸U isotope ratio has been widely used as a tracer for geochemical processes in underground aquifers. Quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS) equipped with a high-efficiency nebulizer and a membrane desolvator was employed for the determination of ²³⁴U/²³⁸U isotope ratios in natural water samples. The instrumental limit of detection for ²³⁴U was at the low pg L⁻¹ level with very low sample consumption. Measurement precision (²³⁴U/²³⁸U) was 3–5% for bottled mineral water with elevated uranium concentration (>1 μg L⁻¹). For the analysis of groundwater samples from the Almonte-Marisma underground aquifer (Huelva, Spain), uranium was stripped from stainless steel planchets that had previously been used as radiometric counting sources for alpha-particle spectrometry. Potential spectral interferences from other metals introduced during the dissolution were investigated. Matrix-matched blank solutions were needed to subtract the background on ²³⁴U due to the formation of platinum argides, and to allow for mass bias correction and background correction. The Pt appears to be an impurity present in the stainless steel, either as a minor component by itself or after extraction from the anode and a subsequent uranium electrodeposition. The ²³⁴U/²³⁸U isotope ratio data were in very good agreement with those of alpha spectrometry, while precision was improved by a factor of up to 10 and counting time was reduced down to ~20 min (10 replicate measurements).     

Comparison of ICP-MS and SIMS techniques for determining uranium isotope ratios in individual particles

The determination of uranium isotope ratios in individual particles is of great importance for nuclear safeguards. In the present study, an analytical technique by inductively coupled plasma mass spectrometry (ICP-MS) with a desolvation sample introduction system was applied to isotope ratio analysis of individual uranium particles. In ICP-MS analysis of individual uranium particles with diameters ranging from 0.6 to 4.2 μm in a standard reference material (NBL CRM U050), the use of the desolvation system for sample introduction improved the precision of ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios. The performance of ICP-MS with desolvation was compared with that of a conventionally used method, i.e., secondary ion mass spectrometry (SIMS). The analysis of test swipe samples taken at nuclear facilities implied that the performance of ICP-MS with desolvation was superior to that of SIMS in a viewpoint of accuracy, because the problems of agglomeration of uranium particles and molecular ion interferences by other elements could be avoided. These results indicated that ICP-MS with desolvation has an enough ability to become an effective tool for nuclear safeguards.     

Application of Inductively Coupled Plasma Mass Spectrometry to the determination of uranium isotope ratios in individual particles for nuclear safeguards

The capability of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of uranium isotope ratios in individual particles was determined. For this purpose, we developed an experimental procedure including single particle transfer with a manipulator, chemical dissolution and isotope ratio analysis, and applied to the analysis of individual uranium particles in certified reference materials (NBL CRM U050 and U350). As the result, the ²³⁵U/²³⁸U isotope ratio for the particle with the diameter between 0.5 and 3.9 μm was successfully determined with the deviation from the certified ratio within 1.8%. The relative standard deviation (R.S.D.) of the ²³⁵U/²³⁸U isotope ratio was within 4.2%. Although the analysis of ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios gave the results with inferior precision, the R.S.D. within 20% was possible for the measurement of the particle with the diameter more than 2.1 μm. The developed procedure was successfully applied to the analysis of a simulated environmental sample prepared from a mixture of indoor dust (NIST SRM 2583) and uranium particles (NBL CRM U050, U350 and U950a). From the results, the proposed procedure was found to be an alternative analytical tool for nuclear safeguards.     

High-precision measurement of mercury isotope ratios in sediments using cold-vapor generation multi-collector inductively coupled plasma mass spectrometry

An on-line Hg reduction technique using stannous chloride as the reductant was applied for accurate and precise mercury isotope ratio determinations by multi-collector (MC)-ICP/MS. Special attention has been paid to ensure optimal conditions (such as acquisition time and mercury concentration) allowing precision measurements good enough to be able to significantly detect the anticipated small differences in Hg isotope ratios in nature. Typically, internal precision was better than 0.002% (1 RSE) on all Hg ratios investigated as long as approximately 20 ng of Hg was measured with a 10-min acquisition time. Introducing higher amounts of mercury (50 ng Hg) improved the internal precision to <0.001%. Instrumental mass bias was corrected using ²⁰⁵Tl/²⁰³Tl correction coupled to a standard-sample bracketing approach. The large number of data acquired allowed us to validate the consistency of our measurements over a one-year period. On average, the short-term uncertainty determined by repeated runs of NIST SRM 1641d Hg standard during a single day was <0.006% (1 RSD) for all isotope pairs investigated (²⁰²Hg/¹⁹⁸Hg, ²⁰²Hg/¹⁹⁹Hg, ²⁰²Hg/²⁰⁰Hg, and ²⁰²Hg/²⁰¹Hg). The precision fell to <0.01% if the long-term reproducibility, taken over 11 months (over 100 measurements), was considered. The extent of fractionation has been investigated in a series of sediments subject to various Hg sources from different locations worldwide. The ratio ²⁰²Hg/¹⁹⁸Hg expressed as δ values (per mil deviations relative to NIST SRM 1641d Hg standard solution) displayed differences from +0.74 to −4.00‰. The magnitude of the Hg fractionation per amu was constant within one type of sample and did not exceed 1.00‰. Considering all results (the reproducibility of Hg standard solutions, reference sediment samples, and the examination of natural samples), the analytical error of our δ values for the overall method was within ±0.28‰ (1 SD), which was an order of magnitude lower than the extent of fractionation (4.74‰) observed in sediments. This study confirmed that analytical techniques have reached a level of long-term precision and accuracy that is sufficiently sensitive to detect even small differences in Hg isotope ratios that occur within one type of samples (e.g., between different sediments) and so far have unequivocally shown that Hg isotope ratios in sediments vary within approximately 5‰.     

Measuring magnesium,calcium and potassium isotope ratios using ICP-QMS with an octopole collision cell in tracer studies of nutrient uptake and translocation in plants

The ability of a quadrupole-based ICP-MS with an octopole collision cell to obtain precise and accurate measurements of isotope ratios of magnesium, calcium and potassium was evaluated. Hydrogen and helium were used as collision/reaction gases for ICP-MS isotope ratio measurements of calcium and potassium in order to avoid isobaric interference with the analyte ions from (mainly) argon ions ⁴⁰Ar⁺ and argon hydride ions ⁴⁰Ar¹H⁺. Mass discrimination factors determined for the isotope ratios ²⁵Mg/²⁴Mg, ⁴⁰Ca/⁴⁴Ca and ³⁹K/⁴¹K under optimized experimental conditions varied between 0.044 and 0.075. The measurement precisions for ²⁵Mg/²⁴Mg, ⁴⁰Ca/⁴⁴Ca and ³⁹K/⁴¹K were found to be 0.09%, 0.43% and 1.4%, respectively. This analytical method that uses ICP-QMS with a collision cell to obtain isotope ratio measurements of magnesium, calcium and potassium was used in routine mode to characterize biological samples (nutrient solution and small amounts of digested plant samples). The mass spectrometric technique was employed to study the dynamics of nutrient uptake and translocation in barley plants at different root temperatures (10 °C and 20 °C) using enriched stable isotopes (²⁵Mg, ⁴⁴Ca and ⁴¹K) as tracers. For instance, the mass spectrometric results of tracer experiments demonstrated enhanced ²⁵Mg and ⁴⁴Ca uptake and translocation into shoots at a root temperature of 20 °C 24 h after isotope spiking. In contrast, results obtained from ⁴¹K tracer experiments showed the highest ⁴¹K contents in plants spiked at a root temperature of 10 °C.     

Accurate measurement of uranium isotope ratios in soil samples using thermal ionization mass spectrometry equipped with a warp energy filter

A chemical and mass-spectrometric procedure for uranium isotopic analysis using a thermal ionisation mass spectrometer equipped with a Wide Aperture Retardation Potential energy filter has been developed and applied to uranium isotopic measurements for various soil samples. Soil samples were digested using a microwave digestor. Uranium was isolated from soil samples by the chemical separation procedure based on the use of anion-exchange resin and UTEVA extraction chromatography column. The isotope ratios were measured for two certified reference materials by using a VG Sector 54-30 thermal ionisation mass spectrometer in dynamic mode with Faraday cup and Daly ion counting system. Replicates of standard reference materials showed excellent analytical agreement with established values supporting the reliability and accuracy of the method. Precision of the ²³⁵U/²³⁸U ratio was achieved by a correction factor of 0.22% amu as a function of ion-beam intensity with sample loads of around 250?ng of U. The resulting reproducibility for standards and soil samples was better than 0.2% at two standard deviations (SD). Uranium isotopic compositions have been determined in several reference soil samples such as Buffalo river sediment, NIST 2704, river sediment SRM 4350b and ocean sediment NIST-4357 and a Chernobyl soil sample. There was a significant deviation from the natural uranium in comparison with Chernobyl soil samples.     

Determination of niacin in infant formula and wheat flour by anion-exchange liquid chromatography with solid-phase extraction cleanup

Niacin content must be included on food labels of infant formula products and bakery products containing enriched flour. Liquid chromatographic (LC) determination of niacin in complex food matrixes is complicated by the presence of endogenous compounds that absorb at the commonly used wave-length of 260 nm. Also, the presence of particulate matter in the standard sulfuric acid extraction procedure results in reduced life of LC columns and precolumns. A simple, rapid, solid-phase extraction (SPE) procedure for separation and cleanup of niacin from a complex food matrix digest has been developed. By using a vacuum manifold with the SPE column system, multiple samples can be processed quickly and efficiently for LC analysis, compared with gravimetric column cleanup. Sulfuric acid sample digest is passed over an aromatic sulfonic acid cation-exchange (ArSCX-SPE) or a sulfonated Florisil SPE column. Niacin is eluted with 0.25M sodium acetate-acetic acid, pH 5.6 buffer in vacuo. LC chromatograms of the resulting eluate are free of interference from other components absorbing at 260 nm at the retention time of niacin. Validation of the method was obtained from agreement of analytical results on available reference materials. For both SPE methods, values for niacin in SRM 1846 Infant Formula (milk-based powder) were within uncertainty ranges of the certified value. Use of several calibration procedures (the LC computer program, a peak area response graphic standard curve, or the method of standard additions) with both SPE procedures resulted in niacin values for 3 RM-Wheat Flours (not certified for niacin) in agreement (90-105%) with their respective values reported in the literature. Several commercial wheat flours showed a broad 260 nm interference, resulting in high niacin values. Niacin recoveries from spiked soy-based liquid infant formulas ranged from 95-107% with the ArSCX-SPE column. Calibration curves of niacin were linear up to 400 micrograms/mL, with a detection limit of 0.2 microgram/mL.     

Measurement of labile Cu in soil using stable isotope dilution and isotope ratio analysis by ICP-MS

Isotope dilution is a useful technique to measure the labile metal pool, which is the amount of metal in soil in rapid equilibrium (<7 days) with the soil solution. This is normally performed by equilibrating soil with a metal isotope, and sampling the labile metal pool by using an extraction (E value), or by growing plants (L value). For Cu, this procedure is problematic for E values, and impossible for L values, due to the short half-life of the ⁶⁴Cu radioisotope (12.4 h), which makes access and handling very difficult. We therefore developed a technique using enriched ⁶⁵Cu stable isotope and measurement of ⁶³Cu/⁶⁵Cu ratios by quadrupole inductively coupled plasma mass spectrometry (ICP-MS) to measure labile pools of Cu in soils using E value techniques. Mass spectral interferences in detection of ⁶³Cu/⁶⁵Cu ratios in soil extracts were found to be minimal. Isotope ratios determined by quadrupole ICP-MS compared well to those determined by high-resolution (magnetic sector) ICP-MS. E values determined using the stable isotope technique compared well to those determined using the radioisotope for both uncontaminated and Cu-contaminated soils.     

Precise and accurate determination of lead isotope ratios in mining wastes by ICP-QMS as a tool to identify their source

A methodology for a precise and accurate determination of lead isotope ratios in mining wastes by inductively coupled plasma quadrupole-based mass spectrometry (ICP-QMS) has been developed. The study of instrumental bias factors led to the conclusion that internal correction to compensate mass discrimination is required as well as an interference equation correction when Hg is present. The proposed method has been applied to determine lead isotope ratios in several mining wastes, soils and sediments collected at three mining areas in Spain (Aran Valley, Cartagena and Osor).Statistical analysis highlights that ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb lead isotope ratios can be used as a fingerprint of mining waste origin which is related to the geological age of the lead ore.On the other hand, no statistically significant isotopic differences between original ore samples (galena) and processing wastes within a mining district were found, corroborating a unique lead source. Moreover, the lead isotopic composition of soil and sediment samples collected at the studied mining areas is close to that determined in the mining tailings from the same areas, suggesting that the unusual high content of lead in these samples is derived from mining activities rather than from other lead sources.     

Estimation of boron isotope ratios using high resolution continuum source atomic absorption spectrometry

In the production of ¹⁰B enriched steels, the production–recycling process needs to be closely monitored for inadvertent mix-up of materials with different B isotope levels. A quick and simple method for the estimation of boron isotope ratios in high alloyed steels using high resolution continuum source flame AAS (HR-CS-FAAS) was developed. On the 208.9 nm B line the wavelength of the peak absorption of ¹⁰B and ¹¹B differs by 2.5 pm. The wavelength of the peak absorption of boron was determined by fitting a Gauss function through spectra simultaneously recorded by HR-CS-FAAS. It was shown that a linear correlation between the wavelength of the peak absorption and the isotope ratio exists and that this correlation is independent of the total boron concentration. Internal spectroscopic standards were used to compensate for monochromator drift and monochromator resolution changes. Accuracy and precision of the analyzed samples were thereby increased by a factor of up to 1.3. Three steel reference materials and one boric acid CRM, each certified for the boron isotope ratio were used to validate the procedure.     

Evaluation and correction of isotope ratio inaccuracy on inductively coupled plasma time-of-flight mass spectrometry

Isotope ratio measurements are found to have systematic bias when using the analog detection mode on an inductively coupled plasma time-of-flight (TOF) mass spectrometer. This bias is dependent upon the value of the ratio, the intensity of the signal, and the gain of the electron multiplier tube. The error should not appear if ion counting is employed instead of analog detection, although analog detection with time-of-flight has other distinct advantages. The cause of this isotope ratio inaccuracy is rooted in disproportionate recording of the analog signal because of the need to filter out noise by blocking analog signals below a threshold voltage. This attenuates smaller signals to a greater degree than larger signals. This variable “detection efficiency” causes a larger systematic error in the isotopic ratio as the isotopic abundances become more disparate. Ratios close to unity are generally accurate within the precision of the measurement. The use of an increased gain on the detector leads to improved ratio accuracy, but at the cost of decreased detector lifetime. This research presents a method of analyzing solutions using natural, known isotopic ratios to produce an efficiency correction curve. The average error of several isotope ratios for a 500 ng/mL solution of various elements with ratios between 3.4 and 10 was found to be 6.5% without correction, 3.0% with increased detector gain, 1.1% with efficiency correction and 0.6% with both increased gain and efficiency correction.     

Determination of phthalate esters in Chinese spirits using isotope dilution gas chromatography with tandem mass spectrometry

Phthalate esters are additives used in polyvinylchloride and are found as contaminants in many food products. An isotope dilution mass spectrometry technique has been developed for accurate analysis of 16 phthalate esters in Chinese spirits by adopting the 16 corresponding isotope‐labeled phthalate esters. The ethanol in the spirit sample was first removed by heating with a water bath at 100°C with a stream of nitrogen, after which the residue was extracted with n‐hexane twice. The phthalates collected were identified and quantified by gas chromatography with tandem mass spectrometry in multiple reaction monitoring mode. The spiking recoveries of 16 analytes ranged from 94.3 to 105.3% with relative standard deviation values of <6.5%. The detection limits for 16 analytes were <10.0 ng/g. The expanded relative uncertainties were from 3.0 to 14%. A survey was performed on Chinese spirits from the market. Six of the nine analyzed samples were contaminated by phthalates. Di‐n‐butyl phthalate and di‐2‐ethylhexyl phthalate showed higher detection frequency and concentrations. This isotope dilution gas chromatography with tandem mass spectrometry method is simple, rapid, accurate, and highly sensitive, which qualifies as a candidate reference method for the determination of phthalates in spirits.     

Determination of carbamate pesticides using micro-solid-phase extraction combined with high-performance liquid chromatography

We describe a simple and sensitive porous polypropylene membrane-protected micro-solid-phase extraction (μ-SPE) approach for the sample preparation and determination of carbamate pesticides in soil samples by high-performance liquid chromatography. The μ-SPE device consisted of C₁₈ sorbent held within a porous polypropylene envelope. In order to achieve optimum performance, several extraction parameters were optimized. Under the most favorable conditions, the extraction efficiency of the μ-SPE was very high, with detection limits in the range of 0.01–0.40 ng g⁻¹. This is more than two orders of magnitude lower than the limits obtained by the United States Environmental Protection Agency Methods 8321A and 8318. A linear relationship was obtained for each analyte in the range of 2 and 200 ng g⁻¹. The relative standard deviation for the analysis of aged soil samples spiked at 5 ng g⁻¹ was ≤11%. The reproducibility of separate μ-SPE device used for experiments was satisfactory (relative standard deviations ranged from 4 to 11%), indicating that the method is reliable for routine environmental analysis.     

Determination of compound-specific Hg isotope ratios from transient signals using gas chromatography coupled to multicollector inductively coupled plasma mass spectrometry (MC-ICP/MS)

MeHg and inorganic Hg compounds were measured in aqueous media for isotope ratio analysis using aqueous phase derivatization, followed by purge-and-trap preconcentration. Compound-specific isotope ratio measurements were performed by gas chromatography interfaced to MC-ICP/MS. Several methods of calculating isotope ratios were evaluated for their precision and accuracy and compared with conventional continuous flow cold vapor measurements. An apparent fractionation of Hg isotopes was observed during the GC elution process for all isotope pairs, which necessitated integration of signals prior to the isotope ratio calculation. A newly developed average peak ratio method yielded the most accurate isotope ratio in relation to values obtained by a continuous flow technique and the best reproducibility. Compound-specific isotope ratios obtained after GC separation were statistically not different from ratios measured by continuous flow cold vapor measurements. Typical external uncertainties were 0.16‰ RSD (n = 8) for the ²⁰²Hg^/198Hg ratio of MeHg and 0.18‰ RSD for the same ratio in inorganic Hg using the optimized operating conditions. Using a newly developed reference standard addition method, the isotopic composition of inorganic Hg and MeHg synthesized from this inorganic Hg was measured in the same run, obtaining a value of δ ²⁰²Hg = −1.49 ± 0.47 (2SD; n = 10). For optimum performance a minimum mass of 2 ng per Hg species should be introduced onto the column.     

Determination of tin and titanium in soils, sediments and sludges using electrothermal atomic absorption spectrometry with slurry sample introduction

Fast-heating programmes for determining titanium and tin in soils, sediments and sludges using electrothermal atomic absorption spectrometry (ETAAS) with slurry sampling are developed. For titanium determination, suspensions are prepared by weighing 5-40 mg of sample and adding 25 ml of a solution containing 50% (v/v) concentrated hydrofluoric acid. For tin determination, suspensions are prepared by weighing up to 300 mg of sample and then adding 1 ml of a solution containing 25% (v/v) concentrated hydrofluoric acid. Palladium (30 μg) and ammonium dihydrogen phosphate (7% w/v) are used as matrix modifiers for titanium and tin, respectively. Prior mild heating in a microwave oven is recommended for titanium determination. Calibration is carried out using aqueous standards. The tin and titanium contents of a number of samples obtained by using the slurry approach agree with those obtained by means of a procedure based on the total dissolution of the samples using microwave oven digestion. The reliability of the procedures is also confirmed by analysing several certified reference materials.     

Internal correction of hafnium oxide spectral interferences and mass bias in the determination of platinum in environmental samples using isotope dilution analysis

A method has been developed for the accurate determination of platinum by isotope dilution analysis, using enriched ¹⁹⁴Pt, in environmental samples containing comparatively high levels of hafnium without any chemical separation. The method is based on the computation of the contribution of hafnium oxide as an independent factor in the observed isotope pattern of platinum in the spiked sample. Under these conditions, the ratio of molar fractions between natural abundance and isotopically enriched platinum was independent of the amount of hafnium present in the sample. Additionally, mass bias was corrected by an internal procedure in which the regression variance was minimised. This was possible as the mass bias factor for hafnium oxide was very close to that of platinum. The final procedure required the measurement of three platinum isotope ratios (192/194, 195/194 and 196/194) to calculate the concentration of platinum in the sample. The methodology has been validated using the reference material “BCR-723 road dust” and has been applied to different environmental matrices (road dust, air particles, bulk wet deposition and epiphytic lichens) collected in the Aspe Valley (Pyrenees Mountains). A full uncertainty budget, using Kragten’s spreadsheet method, showed that the total uncertainty was limited only by the uncertainty in the measured isotope ratios and not by the uncertainties of the isotopic composition of platinum and hafnium. Figure Simultaneous correction of hafnium oxide spectral interferences and mass bias in the determination of platinum in environmental samples using isotope dilution analysis Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Determination of seven trace elements in natural waters after separation by solvent extraction and anion-exchange chromatography

A method is described for the determination of cadmium, cobalt, copper, manganese, lead, uranium, and zinc in samples of natural waters. After acidification with hydrochloric acid the water sample is filtered and the diethyldithiocarbamates of the trace elements are isolated by extraction with acetone—chloroform (2:5) at pH 5. Following this preconcentration step the metal ions are adsorbed on a column of the strongly basic anion-exchange resin Dowex 1-X8 (chloride form) using as sorption solution a mixture (5:4:1, $\text{v}\text{v}$) of tetrahydrofuran, methyl glycol and 6 M hydrochloric acid. Successive elution is effected with 6 M hydrochloric acid (Co, Cu, Mn and Pb), 1 M hydrochloric acid (U) and 2 M nitric acid (Cd and Zn); the metal ions in the eluates are determined by atomic absorption spectrophotometry (except uranium, which is determined fluorimetrically). The procedure was used to determine the trace-metals in water and snow samples collected in Austria and to analyse a sample of sea water from the Adriatic Sea.     

Analysis of salicylate and benzophenone-type UV filters in soils and sediments by simultaneous extraction cleanup and gas chromatography-mass spectrometry

An analytical method for the determination of UV filters in soil and sediment has been developed and validated considering benzophenones (BP) and salicylates as target analytes. Soil and sediment samples were extracted with ethyl acetate-methanol (90:10, v/v) assisted with sonication, performing a simultaneous clean-up step. Quantification of these compounds was carried out by gas chromatography-mass spectrometry (GC-MS) after derivatization of the extracts with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). Recoveries from spiked soil samples ranged from 89.8% to 104.4% and they were between 88.4% and 105.3% for spiked sediment samples. The effect of the residence time and soil moisture content on the recovery of these compounds was also studied. The precision, expressed as relative standard deviation, was in all cases below 6.1% and the limits of detection (S/N=3) varied from 0.07 to 0.10 ng g(-1) and from 0.11 to 0.28 ng g(-1) for soils and sediments, respectively. The validated method was applied to the analysis of five benzophenone and two salicylate UV filters in soil and sediment samples collected in different areas of Spain.     

ICP-MS测定土壤中铅同位素比值及地域差异性比较

建立用HNO_3-H_2O_2-HF体系微波消解前处理样品,利用电感耦合等离子体质谱测定土壤中铅同住素比值的方法,探讨并优化了影响测试结果的两种干扰因素.该方法中~(207)Pb/~(206)Pb和~(208)Pb/~(206)Pb的短期测量稳定性RSD分别达到0.12%和0.13%,长期测量的偏差分别在0.002和0.01以内,样品测量的最佳范围是10～40μg/L.采用标样-样品交叉法测定了湖南、湖北、云南、贵州、河南、福建、辽宁7个省的48个地区土壤中的铅同位素比值,结合聚类分析和主成分分析比较了各省土壤中同位素分布的差异,初步探讨了利用~(207)Pb/~(206)Pb和~(208)Pb/~(206)Pb比较烟叶产区的可能性.     

Determination of elemental selenium and pyrite-selenium in sediments

A method is described for the selective determination of concentrations of elemental selenium and pyrite-selenium in sediments. A 1 M sodium sulfite solution is used to solubilize elemental selenium and a Cr(II) solution releases selenium in pyrite. The accuracy of the methods was evaluated by using various selenium compounds. The detection limits for the elemental and pyrite-selenium procedures are 0.001 and 0.025 μg Se per gram of sediment, respectively. The relative standard deviationis < 10% for elemental selenium and < 16% for pyrite-selenium. These and other procedures were used for selenium speciation in marine and freshwater sediments.