Steffen Nielsen

High resolution inductively coupled plasma mass spectrometry for the trace determination of plutonium isotopes and isotope ratios in environmental samples

A high resolution inductively coupled plasma mass spectrometric (HR-ICP-MS) method for the determination of plutonium isotopes and the 240 Pu/ 239 Pu isotope ratio utilising ultrasonic nebulisation was developed. Total plutonium concentrations ( 239+240 Pu) measured in environmental samples by this HR-ICP-MS method were in good agreement with data obtained from α-spectrometry. Quantification was performed by both external calibration and isotope dilution and the best agreement was found by applying isotope dilution. Detection limits of 5, 1 and 1 fg ml –1 were found for 239 Pu, 240 Pu and 242 Pu, respectively. These represent total amounts of 50, 10 and 10 fg or 0.1, 0.08 and 0.002 mBq of the three isotopes in a 10 ml sample volume. The precision (RSD) on the measurement of the 240 Pu/ 239 Pu ratio in environmental samples was approximately 2%, which is close to the theoretical precision (Poisson statistics). The influence of dwell time, number of sweeps and sample uptake rate on the measurement precision of the 240 Pu/ 239 Pu isotope ratio was investigated and the parameters were optimised using a 2 3 experimental design (a central composite design followed by a ridge analysis). The accuracy of the isotope ratio measurement was evaluated by comparing results from this HR-ICP-MS method with results from high resolution α-spectrometry and spectral deconvolution. Good agreement was found between the two techniques.

Determination of ultra-trace amounts of arsenic(III) by flow-injection hydride generation atomic absorption spectrometry with on-line preconcentration by coprecipitation with lanthanum hydroxide or hafnium hydroxide.

A time-based flow-injection (FI) procedure for the determination of ultra-trace amounts of inorganic arsenic(III) is described, which combines hydride generation atomic absorption spectrometry (HG-AAS) with on-line preconcentration of the analyte by inorganic coprecipitation-dissolution in a filterless knotted Microline reactor. The sample and coprecipitating agent are mixed on-line and merged with an ammonium buffer solution, which promotes a controllable and quantitative collection of the generated hydroxide on the inner walls of the knotted reactor incorporated into the FI-HG-AAS system. Subsequently the precipitate is eluted with 1 mol 1(-1) hydrochloric acid, allowing ensuing determination of the analyte via hydride generation. The preconcentration of As(III) was tested by coprecipitation with two different inorganic coprecipitating agents namely La(III) and Hf(IV). It was shown that As(III) is more effectively collected by lanthanum hydroxide than by hafnium hydroxide, the sensitivity achieved by the former being approximately 25% better. With optimal experimental conditions and with a sample consumption of 6.7 ml per assay, an enrichment factor of 32 was obtained at a sample frequency of 33 samples h(-1). The limit of detection (3sigma) was 0.003 microg 1(-1) and the precision (relative standard deviation) was 1.0% (n = 11) at the 0.1 microg 1(-1) level.

Selective flow injection analysis of ultra-trace amounts of Cr(VI), preconcentration of it by solvent extraction, and determination by electrothermal atomic absorption spectrometry (ETAAS)

A rapid, robust, sensitive and selective time-based flow injection (FI) on-line solvent extraction system interfaced with electrothermal atomic absorption spectrometry (ETAAS) is described for analyzing ultra-trace amounts of Cr(VI). The sample is initially mixed on-line with isobutyl methyl ketone (IBMK). The Cr(VI) is complexed by reaction with ammonium pyrrolidine dithiocarbamate (APDC), and the non-charged Cr(VI)-PDC chelate formed is extracted into IBMK in a knotted reactor made from PTFE tubing. The organic extractant is separated from the aqueous phase by a gravity phase separator with a small conical cavity and delivered into a collector tube, from which 55 mul organic concentrate is subsequently introduced via an air flow into the graphite tube of the ETAAS instrument. The operations of the FI-system and the ETAAS detector are synchronously coupled. A significant advantage of the approach is that matrix constituents, such as high salt contents, effectively are eliminated. The extraction procedure was optimized by a simplex approach. A central composite design was subsequently employed to verify the estimated operational optimum. An 18-fold enhancement in sensitivity of Cr(VI) was achieved after preconcentration for 99 s at a sample flow rate of 5.5 ml min(-1), as compared to direct introduction of 55 mul of sample, yielding a detection limit (3sigma) of 3.3 ng l(-1). The sampling frequency was 24.2 samples h(-1). The proposed method was successfully evaluated by analyzing a NIST Cr(VI)-reference material, synthetic seawater and waste waters, and waste water samples from an incineration plant and a desulphurization plant, respectively.

Determination of As(III) and As(V) by Flow Injection-Hydride Generation-Atomic Absorption Spectrometry via On-line Reduction of As(V) by KI

Abstract A volume-based flow injection (FI) procedure is described for the determination and speciation of trace inorganic arsenic, As(III) and As(V), via hydride generation-atomic absorption spectrometry (HG-AAS) of As(III). The determination of total arsenic is obtained by on-line reduction of As(V) to As(III) by means of 0.50% ( w v ) ascorbic acid and 1.0% ( w v ) potassium iodide in 4 M HCl. The combined sample and reduction solution is initially heated by flowing through a knotted reactor immersed in a heated, thermostatted oil bath at 140 °C, and subsequently, for cooling the reaction medium, a knotted reactor immersed in a water bath at 10 °C. By using the very same volume-based FI-HG-AAS system without the heating and cooling reactors, and employing mild hydrochloric acid conditions, As(V) is not converted to arsine, thereby allowing the selective determination of As(III). The injected sample volume is 100 μl while the total sample consumption per assay is 1.33 ml, and the sampling frequency is 180 samples per hour. The detection limit (3σ) for the on-line reduction procedure was 37 ng 1 −1 and at the 5.0 μg l −1 , the relative standard deviation (RSD) was 1.1% ( n = 10) by calibrating with As(III) standards; by calibrating with As(V) standards the detection limit was 33 ng l −1 and the RSD was 1.3% ( n = 10). For the selective determination of As(III) the detection limit was 111 ng l −1 and the RSD was 0.7% ( n = 10) at 5.0 μg l −1 . Both procedures are most tolerant to potential interferents. Thus, without impairing the assay, interferents such as Cu, Co, Ni and Se could, at a As(V) level of 5 μg l −1 , be tolerated at a weight excess of 2000, 30000, 200 and 200 times, respectively. The assay of a certified drinking water sample by means of multiple standard addition (five levels; each three replicates) was 9.09 ± 0.05 μ l −1 (certified value 9.38 ± 0.71 μg l −1 ).

Determination of ultra-trace amounts of selenium(IV) by flow injection hydride generation atomic absorption spectrometry with on-line preconcentration by co-precipitation with lanthanum hydroxide. Part II. On-line addition of co-precipitating agent

A flow injection procedure for the determination of ultra-trace amounts of selenium(IV) is described, which combines hydride generation atomic absorption spectrometry (HGAAS) with on-line preconcentration of the analyte by co-precipitation–dissolution in a filterless knotted Microline reactor. Based on a previously published procedure that requires the off-line premixing of sample and co-precipitating agent, the present approach facilitates on-line addition of the co-precipitant to the time-based aspirated sample. The sample and the coprecipitating agent (lanthanum nitrate) are mixed on-line and merged with an ammonium buffer solution of pH 9.1, which promotes precipitation and quantitative collection on the inner walls of an incorporated knotted Microline reactor. The SeIV preconcentrated by coprecipitation with the generated lanthanum hydroxide precipitate is subsequently eluted with hydrochloric acid, allowing an ensuing determination via hydride generation. At different sample flow rates, i.e., 4.8, 6.4 and 8.8 ml min–1, enrichment factors of 30, 40 and 46, respectively, were obtained at a sampling frequency of 33 samples h–1. The detection limit (3s) was 0.005 µg l–1 at a sample flow rate of 6.4 ml min–1 and the precision (relative standard deviation) was 0.5%(n= 11) at the 0.1 µg l–1 level.

Flow injection and atomic absorption spectrometry—An effective and attractive analytical chemical combination

One of the advantages of the flow-injection (FI) concept is that it is compatible with virtually all detection techniques. Being a versatile vehicle for enhancing the performance of the individual detection devices, the most spectacular results have possibly been obtained in conjunction with atomic absorption spectrometry (AAS)—initially with flame-AAS (FAAS) procedures, later for hydride generation (HG) techniques, and most recently in combination with electrothermal AAS (ETAAS). The common denominator for all these procedures is the inherently precise and strictly reproducible timing that the sample is subjected to in FI from the point of injection and introduction to the point of detection, which in turn allows suitable on-line pretreatments to be effected. The present article will—via a number of selected examples—point to some of the potentials at hand, encompassing the use of FI as a suitable vehicle for reproducible sample presentation to the AAS instrument, as a means for facilitating conversion techniques for determination of anions, for allowing on-line preconcentration procedures via incorporated column reactors or via (co)precipitation, for exploiting kinetic discrimination schemes in hydride generation reactions, and for providing new and exciting possibilities in assays of ultralevels of metalions when utilized in combination with ETAAS.

Dilution Methods in Flow Injection Analysis. Evaluation of Different Approaches as Exemplified for the Determination of Nitrosyl in Concentrated Sulphuric Acid

Abstract Instigated by developing a flow injection procedure for assay of nitrosyl in concentrated sulphuric acid, different approaches for reliable and robust on-line dilution in FIA were evaluated. These comprised the application of mixing tees in conjunction with mixing coils (including knotted reactors) of different internal diameter, zone sampling, the use of a mixing chamber, micro-sampling, and sample injection by means of pseudo-hydrodynamic injection. The individual approaches are described in detail, their advantages and disadvantages being emphasized in regard to their practical applicability. For each approach the criteria stipulated were that the procedure should allow a dilution factor of approximately 100, yet without excessive zone spreading, so that it, on one hand, could effectively eliminate the pronounced Schlieren effect encountered when mixing concentrated sulphuric acid with an aqueous diluent, and, on the other hand, would permit the sample material to be appropriately conditioned ...

Approaches to mimic the metallic sheen in beetles

A range of different beetles exhibits brilliant colours and metallic sheen. One of the most spectacular species is the Plusiotis resplendens from Central America with gold metal appearance. The beetle shells are made from chitin and have a number of unique properties that apart from spectacular aesthetic effects include metal sheen from non-metal surfaces combined with electric and thermal insulation. The reflection mechanism has been studied by a number of authors and is well understood. Basically there are 2 different reflection principles. One is the multilayer reflector where alternating layers have high and low refractive index. The other is the Bouligand structure where birefringent chiral nanofibres are organised in spiral structures. The paper describes work done to explore different approaches to mimic these structures using polymer based materials and production methods that are suitable for more complex double curved geometry. One approach is to use alternating layers of 2 different polymers applied by dipping and another is applying cholesteric liquid crystals in paint. However, none of them can yet make the desired metal-looking free-form surfaces.