Khris B. Olsen

Measurement of ultratrace levels of chromium by adsorptive–catalytic stripping voltammetry in the presence of cupferron

An ultrasensitive adsorptive–catalytic stripping (voltammetric and potentiometric) procedure for determining trace levels of chromium in the presence of cupferron is described. The method offers higher sensitivity than previous adsorptive stripping schemes for chromium. Optimum experimental conditions were found to be a 1 × 10–3 mol l–1 piperazine-N,N′-bis(ethanesulfonic acid)(PIPES) solution (pH 7.0) containing 1 × 10–4mol l–1 cupferron and a preconcentration potential of –0.82 V. A preconcentration time of 1 min results in a detection limit of 1.0 ng l–1. The relative standard deviation at 100 ng l–1 is 2.4%(n= 20, for 20 s preconcentration). The stripping potentiometric scheme allows convenient measurements of chromium in the presence of dissolved oxygen. The identical stripping response for chromium(III) and chromium(VI) solutions makes the method applicable to the measurement of the total chromium content. The simultaneous determination of chromium and uranium is illustrated. The merits of the proposed procedure are demonstrated by the analysis of soil and groundwater samples.

Detection of organomercury, selenium and arsenic compounds by a capillary column gas chromatography-microwave plasma detector system

Abstract Low-pressure and atmospheric-pressure microwave-induced helium plasma detectors were interfaced with a capillary column gas chromatograph. A number of dialkyl mercury, diaryl mercury and monoalkyl mercury chlorides have been separated on both systems. The capillary column is well suited for the separation of organomercury compounds, but the selection of the appropriate scavenge gas is critical to achieve good peak shapes for these mercury compounds. The atmospheric pressure system exhibited better sensitivity and selectivity for organomercury compounds than the low-pressure system. In addition to the organomercury compounds, satisfactory separation has been achieved for trimethyl, triethyl and triphenylarsine on the gas chromatograph lowpressure microwave plasma detector system. Preliminary work using the atmospheric-pressure system for arsenic and selenium line selection is also presented.

FIELD SCREENING OF CHROMIUM, CADMIUM, ZINC, COPPER, AND LEAD IN SEDIMENTS BY STRIPPING ANALYSIS

Stripping analysis (SA) was successfully employed for field verification of metals contaminants in soils and sediments at hazardous waste sites. Microwave digestion procedures were tailored to meet the needs of field activities and electrochemical measurements. An adsorptive stripping voltammetric (AdSV) scheme was used for monitoring total chromium and for chromium speciation, while conventional anodic stripping voltammetry (ASV) and potentiometric stripping analysis (PSA) were used for measuring cadmium, zinc, copper, and lead. The results demonstrate that SA is capable of on-site identification of contaminated layers in soils and sediments. Concentration values measured by SA correlated well with those obtained by U.S. Environmental Protection Agency (EPA)-approved atomic or mass spectroscopy methods. The remarkable sensitivity, portability, low-power need, and low cost of SA make it an attractive choice for on-site analysis of selected metals during site characterization and remediation activities. 12 refs., 6 figs., 2 tabs.

A low-pressure Beenakker-type microwave-induced helium plasma source as a simultaneous multi-element gas chromatographic detector

Abstract A low-pressure version of a Beenakker-type microwave-induced helium plasma optical emission spectroscopy detector for gas chromatographic effluents is described. The plasma is sustained in a 1.3-rum i.d. quartz tube and is viewed axially through a quartz window. Operating characteristics of the source were studied for power levels of 15–115 W, for carrier-gas flows of 20–1000 mi min−1, and for pressures of 2–700 torr. A gas chromatographic system involving a fused-silica capillary column is used as the sample introduction system for compounds containing carbon, hydrogen, nitrogen, sulfur, and chlorine. Elemental response factors and the precision of elemental response ratios were studied. The use of this detector in evaluating empirical formulae is also discussed. Empirical formulae for a number of hydrocarbons and sulfur-containing aliphatic and heterocyclic compounds are presented, together with a discussion of the factors that affect accuracy and precision. It is concluded that this type of detector combines some of the best fearutes of the atmospheric-pressure Beenakker and the Evenson-type sources.

Flow probe for in situ electrochemical monitoring of trace chromium

A submersible electrochemical probe for in situ monitoring of trace chromium is described. The new flow probe relies on the coupling of an ultrasensitive adsorptive–catalytic stripping voltammetric procedure with a submersible operation. Such in situ monitoring involves a continuous delivery of an internal (ligand–catalyst, DTPA–NO3–) reagent solution, a microdialysis collection of the target chromium ion, transport of the Cr–DTPA complex and nitrate-ion catalyst to the working-electrode compartment and adsorptive–catalytic stripping detection of the complex. The optimization of various parameters resulted in a detection limit of 0.10 µg l–1 (with 10 min accumulation), good precision and stability (RSD 6% for n=80 at 25 µg l–1 chromium) and a rapid response to sudden changes in the chromium level. A stable response was obtained for both Cr(VI) and Cr(III) species. The attractive performance of the submersible probe holds great promise for environmental and industrial monitoring.

Field experience with ambient-level flame-photometric sulphur detectors☆

Carbon dioxide exhaled by the operators produces increased levels of this gas inside the trailers used for housing monitoring equipment for use in the field. These levels can be high enough to produce serious calibration errors in flame photometric detectors used for measuring ambient concentrations of gaseous sulphur products. Quantitative measurement of the carbon dioxide interference in the sulphur emission is reported, as well as a method of estimating the extent of quenching agent pollution.

Detection of thiophenes in the offgas condensate of an oil shale retort by a GC-microwave induced helium plasma detector

SummaryA series of alkylthiophenes and dimethyl disulfide were tentatively identified in an oil shale retort gas condensate from a 6-kg bench-scale retort using gas chromatography with a microwave-induced helium plasma detector (GC-MIP). The sulfur species were present in concentrations ranging from 1.5 to 10.7 mol ppm in the undiluted offgas. The GC-MIP technique was successful in selectively detecting the sulfur components in the complex mixture. Quantitation was simplified relative to GC with flame-photometric detection because of the absence of quenching or other interference problems at the concentrations studied. Attempts to determine stoichiometry of the sulfur components by comparison of carbon, hydrogen, and sulfur ratios with those of standards were unsuccessful because of the complexity of the carbon and hydrogen chromatograms.

Measurement of Helium-3/Helium-4 Ratios in Soil Gas at the 618-11 Burial Ground

Seventy soil gas-sampling points were installed around the perimeter of the 618-11 Burial Ground, approximately 400 feet downgradient of well 699-13-3A, and in four transects downgradient of the burial ground to a maximum distance of 3,100 feet. Soil gas samples were collected and analyzed for helium-3/helium-4 ratios from these 70 points. Helium-3/helium-4 ratios determined from the soil gas sampling points showed significant enrichments, relative to ambient air helium-3 concentrations. The highest concentrations were located along the northern perimeter of the burial ground. Helium-3/helium-4 ratios (normalized to the abundances in ambient air) ranged from 1.0 to 62 around the burial ground. The helium-3/helium-4 ratios from the 4 transect downgradient of the burial ground ranged from 0.988 to 1.68. The helium-3/helium-4 ratios from around the burial ground suggest there is a vadose zone source of tritium along the north side of the burial ground.

Noble gas migration experiment to support the detection of underground nuclear explosions

A Noble Gas Migration Experiment injected 127Xe, 37Ar, and sulfur hexafluoride into a former underground nuclear explosion shot cavity. These tracer gases were allowed to migrate from the cavity to near-surface and surface sampling locations and were detected in soil gas samples collected using various on-site inspection sampling approaches. Based on this experiment we came to the following conclusions: (1) SF6 was enriched in all of the samples relative to both 37Ar and 127Xe. (2) There were no significant differences in the 127Xe to 37Ar ratio in the samples relative to the ratio injected into the cavity. (3) The migratory behavior of the chemical and radiotracers did not fit typical diffusion modeling scenarios.

Measurement of Fukushima aerosol debris in Sequim and Richland, WA and Ketchikan, AK

Aerosol collections were initiated at several locations by Pacific Northwest National Laboratory (PNNL) shortly after the Great East Japan earthquake of May 2011. Aerosol samples were transferred to laboratory high-resolution gamma spectrometers for analysis. Similar to treaty monitoring stations operating across the Northern hemisphere, iodine and other isotopes which could be volatilized at high temperature were detected. Though these locations are not far apart, they have significant variations with respect to water, mountain-range placement, and local topography. Variation in computed source terms will be shown to bound the variability of this approach to source estimation.