Gold nanorods of different aspect ratios are prepared using the growth‐directing surfactant, cetyltrimethylammonium bromide (CTAB), which forms a bilayer on the gold nanorod surface. Toxicological ...assays of CTAB‐capped nanorod solutions with human colon carcinoma cells (HT‐29) reveal that the apparent cytotoxicity is caused by free CTAB in solution. Overcoating the nanorods with polymers substantially reduces cytotoxicity. The number of nanorods taken up per cell, for the different surface coatings, is quantitated by inductively coupled plasma mass spectrometry on washed cells; the number of nanorods per cell varies from 50 to 2300, depending on the surface chemistry. Serum proteins from the biological media, most likely bovine serum albumin, adsorb to gold nanorods, leading to all nanorod samples bearing the same effective charge, regardless of the initial nanorod surface charge. The results suggest that physiochemical surface properties of nanomaterials change substantially after coming into contact with biological media. Such changes should be taken into consideration when examining the biological properties or environmental impact of nanoparticles.
Gold nanorods with different surface charges are prepared using a wet‐chemical method combined with layer‐by‐layer polyelectrolyte coating approaches (see image, scale bar = 100 nm). Toxicity studies using a human colon carcinoma cell line indicate similar toxicity profiles for both positively and negatively coated gold nanorods. Serum proteins from cell growth media adsorb onto nanorods, regardless of initial nanorod surface charge.
Rationale
Signal detection for uranium–lead (U–Pb) dating of zircon is typically performed via ion counters. Here, we develop a preliminary understanding of the strengths and limitations of ...faraday‐cup‐based detection.
Methods
A suite of zircon reference materials and the NIST‐610 glass were sampled using laser ablation followed by U–Pb isotope ratio measurement on a Neoma multicollector‐inductively coupled plasma‐mass spectrometer.
Results
We were able to produce geologically accurate 207Pb/206Pb, 206Pb/238U, and 207Pb/235U ratios for the NIST‐610 glass and the zircon standards, with ages ranging from ~2.5 Ga to ~337 Ma (TanBrown A, Oracle, 91550, Mud Tank, Temora, and Plešovice). Two of the younger zircon standards examined (94‐35, ~55.6 Ma, and Fish Canyon, 28.6 Ma) yielded accurate 206Pb/238U but not 207Pb/235U or 207Pb/206Pb ratios, whereas the youngest zircon standard (Penglai, ~4.4 Ma) failed for all three ratios of interest. The accuracy and precision of the all‐faraday method are directly tied to signal intensity, with reliable data capable of being produced even when both isotopes in a ratio have signals below ~0.001 V (equivalent to ~62 500 cps on an ion counter).
Conclusion
The all‐faraday cup multicollection method provides sufficient sensitivity to obtain geologically meaningful U–Pb data, with possible advantages being that laser pit depth‐dependent changes in the observed interelemental fractionation behavior may be easier to correct using a static collector configuration compared to when the ion beam is swept across a single detector while also removing the need for an interdetector‐type calibration. Further work is needed to refine the all‐faraday cup method (e.g., application of background subtraction and common Pb corrections, outlier removal, and interelement as well as down‐hole fractionation corrections), but our initial results demonstrate that the faraday detector method has sufficient sensitivity to warrant further study.
The analysis of environmental swipe samples for ultra-trace uranium (U) and plutonium (Pu) determinations is essential in the nuclear safeguards community. While mass spectrometry techniques for U ...and Pu detection continually improve, established separation methods are seldom reevaluated. Currently, actinide separations within the forensics community predominantly employ either Eichrom TEVA® or UTEVA® resins. The direct optimization of U and Pu separations utilizing both resins has not been widely reported. Here, several methods were explored with goals of increasing analyte recovery, acquiring cleaner blanks, and improving the separation efficiency of ultra-trace levels of U and Pu from environmental swipe samples. The optimized separation methodology of U and Pu was examined using certified reference materials and archived environmental swipe samples.
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•Greater than 98% recovery of U and Pu from TEVA and UTEVA cartridges.•Lower U and Pu process blank levels.•Improved separation of ultra-trace (fg-ng) U and Pu from environmental swipe samples.•Faster separation times with reduced reagent usa.
The analysis of impurities in a uranium ore concentrate (UOC) could provide information regarding the source, production history, and potential intended use of the UOC. This study involves the ...analysis of UOC samples for phosphorus and sulfur. Concentrations were determined by triple quadrupole inductively coupled plasma – mass spectrometry and compared with results from a pyrohydrolysis method as well as previously reported results. The sulfur and phosphorus concentrations, determined by the mass spectrometer, were used to explore possible trends in a series of UOC material, and the uncertainties were calculated using GUM workbench software. The triple quadrupole inductively coupled plasma – mass spectrometer method allows for the removal of interferences in the analysis of species.
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•A recent triple quadrupole ICP–MS method for determination of P and S in UOCs.•Ability to measure range of UOC material rapidly without reducing data quality.•Concentration of P and S were similar to traditional methods and/or referenced data.
The ability to directly measure uranium isotope ratios on environmental swipes has been achieved through a solution-based microextraction process and represents a significant advancement toward the ...development of a rapid method to analyze international nuclear safeguard samples. Here, a microextraction probe is lowered and sealed onto the swipe surface, and analytes within the sampling site (∼8 mm2) are dissolved and extracted into a flowing solvent of 2% nitric acid (HNO3). The mobilized species are subsequently directed into an inductively coupled plasma-mass spectrometer (ICP-MS) for accurate and precise isotope ratio determination. This work highlights the novelty of the sampling mechanism, particularly with the direct coupling of the microextraction probe to the ICP-MS and measurement of uranium isotope ratios. The preliminary method detection limit for the microextraction-ICP-MS method, utilizing a quadrupole-based MS, was determined to be ∼50 pg of 238U. Additionally, precise and accurate isotope ratio measurements were achieved on uranium reference materials for both the major (235U/238U) and minor (234U/238U and 236U/238U) ratios. While the present work is focused on directly measuring uranium isotopic systems on swipe surfaces for nuclear safeguards and verification applications, the benefits would extend across many applications in which direct solid sampling is sought for elemental and isotopic analysis.
Direct isotope ratio analysis of solid uranium particulates on cotton swipes was achieved using a solution-based microextraction technique, coupled to a quadrupole inductively coupled plasma - mass ...spectrometer (ICP-MS). This microextraction-ICP-MS methodology provides rapid isotopic analysis which could be applicable to nuclear safeguards measurements. Particulates of uranyl nitrate hexahydrate (UO2(NO3)2·6H2O) and uranyl fluoride (UO2F2) ranging from 6 μm to 40 μm in length were transferred to cotton swipes with a particle manipulator. The microextraction probe then delivers a 5% nitric acid (HNO3) solvent onto the swipe surface to extract the uranium species. The extracted sample is then delivered to the ICP-MS for isotopic determination. The majority of uranium signal (∼99% and ∼94% for UO2(NO3)2·6H2O and UO2F2, respectively) was detected in the first 15 s extraction, while subsequent extractions on the same location had low or no U signal, suggesting near complete removal of the solid uranium compounds from the swipe surface. Ten samples (for each of the uranium compounds), were analyzed for their isotopic composition. For UO2(NO3)2·6H2O, the determined isotope ratios resulted in a % relative difference (% RD) from the referenced isotope ratios of 0.97, 1.0, and 7.3% for 234U/238U, 235U/238U, and 236U/238U, respectively. The % RD of the UO2F2 isotope ratios were 1.9 and 0.60% for 234U/238U and 235U/238U, respectively. The preliminary limits of detection were determined to be 0.002, 0.4, and 60 pg for 234U, 235U and 238U, respectively This work demonstrates that microextraction ICP-MS is a rapid and sensitive method that could directly determine uranium isotope ratios of UO2(NO3)2·6H2O and UO2F2 particulates on cotton swipes.
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•Novel method for direct sampling of particulates on cotton swipe by microextraction-ICP-MS.•Femtogram detection limits achieved for minor uranium isotopes.•Determination of uranyl nitrate and uranyl fluoride particulates on swipes.
A laboratory study of uranium uptake from seawater has been conducted using batch and flow-through recycling experiments. Uranium adsorption from seawater, using amidoxime-based polymeric adsorbents, ...has been described by transport and kinetic models under the assumption of transport-limited or reaction-limited process for batch adsorption experiments. Mathematical models based on liquid film mass transfer, diffusion, or reaction kinetics have been evaluated in terms of the Sherwood number and the Thiele modulus to provide insight into the limiting mechanism. The value of the Sherwood number suggests that the external mass-transfer resistance is much smaller than the intraparticle diffusion resistance. The Thiele modulus was estimated on the basis of the rate constants from independent batch tests analyzed by a reaction kinetic model, and its value suggests that the uranium binding is the rate-limiting step compared to diffusion. The uranium uptake in batch experiments reached 4 mg U/g adsorbent over a period of nine weeks, which is much higher than the uranium uptake by a leading previously developed adsorbent tested at conditions similar to those in this study. The maximum uranium uptake in the flow-through recycling experiments was approximately 3.3 mg U/g adsorbent over a period of six weeks.
A fully automated method for the separation of low-concentration uranium from plutonium in environmental swipe samples has been developed. The offline chromatography system features renewable 1 mL ...Eichrom TEVA and UTEVA column generation from bulk resin slurry. Discrete fractions of the separated actinides are delivered into user defined vials for future analysis. Clean room background levels were achieved outside of a cleanroom environment with this method. Purification of uranium and plutonium from various sample matrixes and at various concentrations was successful. Major and minor isotope ratios for both elements were measured via multiple collector inductively coupled plasma mass spectrometry and were in good agreement with certified reference values. Validation of the separation method was conducted on archived environmental samples and agreed with values previously reported using standard column chemistry.
Uranyl fluoride (UO2F2) particles (<20 μm) were subjected to first-of-its-kind analysis via simultaneous laser-induced breakdown spectroscopy (LIBS) and laser ablation multi-collector inductively ...coupled plasma–mass spectrometry (LA–MC–ICP–MS). Briefly, a nanosecond pulsed high-energy laser was focused onto the sample (particle) surface. In a single laser pulse, the UO2F2 particle was excited/ionized within the microplasma volume, and the emission of light was collected via fiber optics such that emission spectroscopy could be employed for the detection of uranium (U) and fluorine (F). The ablated particle was simultaneously transported into the MC–ICP–MS for high precision isotopic (i.e., 234U, 235U, and 238U) analysis. This method, LIBS/LA–MC–ICP–MS was optimized and employed to rapidly measure 80+ UO2F2 particles, which were subjected to different calcination processes, which results in varying degrees of F loss from the individual particles. In measuring the particles, the average F/U ratios for the populations treated at 100 and 500 °C were 2.78 ± 1.28 and 1.01 ± 0.50, respectively, confirming loss of F through the calcination process. The average 235U/238U on the particle populations for the 100 and 500 °C were 0.007262 (22) and 0.007231 (23), which was determined to be <0.2% from the expected value. The 234U/238U ratios on the same particles were 0.000053 (11) and 0.000050 (10) for the 100 and 500 °C, respectively, <10% from the expected value. Notably, each population was analyzed in under 5 min, demonstrating the truly rapid analysis technique presented here.
The work described herein assesses the ability to characterize gold nanoparticles (Au NPs) of 50 and 100 nm, as well as 60 nm silver shelled gold core nanospheres (Au/Ag NPs), for their mass, ...respective size, and isotopic composition in an automated and unattended fashion. Here, an innovative autosampler was employed to mix and transport the blanks, standards, and samples into a high-efficiency single particle (SP) introduction system for subsequent analysis by inductively coupled plasma-time of flight-mass spectrometry (ICP-TOF-MS). Optimized NP transport efficiency into the ICP-TOF-MS was determined to be >80%. This combination, SP-ICP-TOF-MS, allowed for high-throughput sample analysis. Specifically, 50 total samples (including blanks/standards) were analyzed over 8 h, to provide an accurate characterization of the NPs. This methodology was implemented over the course of 5 days to assess its long-term reproducibility. Impressively, the in-run and day-to-day variation of sample transport is assessed to be 3.54 and 9.52% relative standard deviation (%RSD), respectively. The determination of Au NP size and concentration was of <5% relative difference from the certified values over these time periods. Isotopic characterization of the
Ag/
Ag particles (
= 132,630) over the course of the measurements was determined to be 1.0788 ± 0.0030 with high accuracy (0.23% relative difference) when compared to the multi-collector-ICP-MS determination.
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