Collector Mass Research Articles

Natural variations detected in the isotopic composition of copper: possible applications to archaeology and geochemistry

Copper isotopic compositions have been measured both in natural copper minerals from supergene/oxidation zones and in some ancient metal artefacts using two different instruments. Measurements were first made using a low temperature thermal ionisation technique with a thermal ionisation mass spectrometer (TIMS); independent data was obtained using a commercial inductively coupled plasma (ICP) magnetic sector multiple collector mass spectrometer. Significant variations of isotopic composition were found in both types of material, suggesting that there may be considerable potential for copper isotope analyses in metal provenance studies, at the least as a supplement to lead isotope studies. For minerals, δ values ranging from −1.63 to +7.71 were obtained, whilst archaeological artefacts had δ values from +0.22 to +4.32. This study also made a preliminary examination which suggests that fractionation of the isotopic composition of copper does not occur during smelting and fire refining processes thought to have been used in ancient times.

Determination of total thallium in fresh water by electrothermal atomic absorption spectrometry after colloid precipitate flotation

Tl(I) and Tl(III) are preconcentrated simultaneously from aqueous solutions by colloid precipitate flotation using two collectors: hydrated iron(III) oxide (Fe2O3·xH2O) and iron(III) tetramethylenedithiocarbamate (Fe(TMDTC)3). After the coprecipitation step and the addition of foaming agents, Tl(I) and Tl(III) were separated from the water by a stream of air bubbles. Various factors affecting Tl(I) and Tl(III) recoveries during the separation from water, including the collector mass, the nature of the supporting electrolyte, pH, ζ potential of the collector particle surfaces, type of tenside, etc., were investigated. Within the optimal pH range (6–6.5), establishing by a recommended procedure, Tl(I) and Tl(III) were separated quantitatively (94.9–100.0%) with 30 mg Fe(III). Both Tl ions were simultaneously separated without any previous conversion of one type of Tl ion to the other. Total Tl determination was performed by electrothermal atomic absorption spectrometry by previous matrix modification of the concentrated samples. The determination limit of Tl by this method is 0.108 μg l−1.

Determination of silver in fresh water by atomic absorption spectrometry following flotation preconcentration by iron(III) collectors

Colloid precipitate flotation of silver from fresh water is applied for preconcentration and separation. Optimal conditions using hydrated iron(III) oxide and iron(III) tetramethylenedithiocarbamate as collectors were investigated. Various factors affecting the silver recovery, including collector mass, nature of the supporting electrolyte, pH of the working medium, electrokinetic potential of the collector particle surfaces, type of surfactant, induction time etc., were checked. Within the optimal pH range (5.5–6.5) silver was separated quantitatively (94.9– 100.0%) with 30 mg Fe(III) as collector. The content of silver was determined by electrothermal atomic absorption spectrometry and compared to that from inductively coupled plasma-atomic emission spectrometry. The detection limit of silver by the method described is 0.01 μg/L.

Hafnium isotopic studies of the Cameroon line and new HIMU paradoxes

We present the first detailed Pb, Nd, Sr and Hf isotopic study of a classic HIMU system. The Hf isotopic compositions of 18 representative basaltic lavas from the length of the Cameroon volcanic line have been determined using the new technique of inductively coupled plasma magnetic sector multiple collector mass spectrometry. The Hf isotopic compositions are found to be the same on average in continental, oceanic, and continental-oceanic boundary sectors. The three islands from the oceanic sector, Pagalu, São Tomé and Principe, display a large spread in Pb and Sr isotopic compositions but have Hf and Nd isotopic compositions that are both uniform and identical to the HIMU islands of Tubuai and St. Helena. The Hf and Nd isotopic compositions of HIMU centers appear to be a more reproducible and characteristic feature than Pb and Sr isotopic compositions. On this basis, basalts along the entire Cameroon line have a similar origin. The data imply that Pagalu, with its unradiogenic 206Pb/ 204Pb (∼ I9) has incorporated the same Hf and Nd as Principe, Bioko, Etinde, Mt. Cameroon, St. Helena and Tubuai, all with average 206Pb/ 204Pb > 20. These data are consistent with the conclusion that the increase in 206Pb/ 204Pb toward the COB is due to young fractionation in U/Pb within the upper mantle. Neither the Hf isotopic composition of Cameroon line basalts, nor that of HIMU basalts in general, can be explained by recycling and storage of subducted N-MORB. Storage of more enriched components is required. Furthermore, the uniformity in HfNd isotopic space is difficult to explain by any recycling models and is more consistent with the HIMU source representing a distinctive and potentially important reservoir with specific Lu/Hf, Sm/Nd and age.

96/06232 Passive solar, country-style

In the present paper a tri-dimensional non-linear dynamic thermohydraulic model of a parabolic trough collector was developed in the high-level acausal object-oriented language Modelica and coupled to a solar industrial process heat plant modeled in TRNSYS. The integration is performed in an innovative co-simulation environment based on the TLK interconnect software connector middleware. A discrete Monte Carlo ray-tracing model was developed in SolTrace to compute the solar radiation heterogeneous local concentration ratio in the parabolic trough collector absorber outer surface. The obtained results show that the efficiency predicted by the model agrees well with experimental data with a root mean square error of 1.2%. The dynamic performance was validated with experimental data from the Acurex solar field, located at the Plataforma Solar de Almeria, South-East Spain, and presents a good agreement. An optimization of the IST collector mass flow rate was performed based on the minimization of an energy loss cost function showing an optimal mass flow rate of 0.22 kg/s m2. A parametric analysis showed the influence on collector efficiency of several design properties, such as the absorber emittance and absorptance. Different parabolic trough solar field model structures were compared showing that, from a thermal point of view, the one-dimensional model performs close to the bi-dimensional. Co-simulations conducted on a reference industrial process heat scenario on a South European climate show an annual solar fraction of 67% for a solar plant consisting on a solar field of 1000 m2, with thermal energy storage, coupled to a continuous industrial thermal demand of 100 kW.

Precise Measurement of Isotope Ratios with a Double-Focusing Magnetic Sector ICP Mass Spectrometer

The potential of a commercially available double-focusing magnetic sector ICP mass spectrometer (Element, Finnigan MAT, Bremen, Germany) for precise isotope ratio measurement at the low-resolution setting (R = 300) was evaluated. Optimization of scanning conditions led to a relative standard deviation for a set of 10 consecutive 2 min measurements of ∼0.1% ((206)Pb(+)/(207)Pb(+)) at signal intensities of ∼200 000 counts/s (peak height). This compares favorably with the best values ever reported for quadrupole ICPMS and barely exceeds the theoretical value (counting statistics). Increasing the signal intensity to values ≥500 000 counts/s (peak height) resulted in a further reduction of the RSDs obtained (for both (25)Mg(+)/(26)Mg(+) and (206)Pb(+)/(207)Pb(+)) to typically 0.04%. These figures are remarkably better than those reported for commercially available quadrupole ICPMS systems. This improvement significantly reduces the difference between isotope ratio precision of ICPMS on one hand and those of thermal ionization mass spectrometry and plasma source multiple collector mass spectrometry on the other.

Precise determinations of the isotopic compositions and atomic weights of molybdenum, tellurium, tin and tungsten using ICP magnetic sector multiple collector mass spectrometry

Precise determinations of the isotopic compositions of molybdenum, tellurium, tin and tungsten were obtained utilizing an inductively coupled plasma (ICP) source magnetic sector mass spectrometer equipped with multiple collectors. The results of this study are comparable to those measured by conventional and negative thermal ionization mass spectrometry (TIMS and NTIMS) and the values recommended by the International Union of Pure and Applied Chemistry (IUPAC), but with improvement in precision by up to two orders of magnitude. The relative isotopic abundances and atomic weight for each element calculated from the data obtained in this study are also in excellent agreement with previously published values. The only disagreement between this study and IUPAC recommended values is for tellurium. However, with the exception of 130Te, the Te data are in good agreement with those reported in a recent study by De Laeter [1]. The results of this study demonstrate the capability of this new instrument to produce precise and reproducible isotopic data for elements that are difficult to ionize and measure with TIMS. Furthermore, the greater precision of isotopic measurements possible with the ICP source multiple collector magnet sector mass spectrometer greatly enhances the prospects for research on the distribution and isotopic compositions of these elements in terrestrial and meteoritic materials.

Recent developments in inductively coupled plasma magnetic sector multiple collector mass spectrometry

This paper describes advances in isotopic measurements that have been made with an inductively coupled plasma source magnetic sector multiple collector mass spectrometer and presents results of new experiments aimed at further evaluating the instrument's capability. It is shown using standard solutions that trace element ratios such as Rb/Sr can be measured precisely without isotope dilution by comparison with reference solutions of known composition. Similarly, using a new wide flight tube, Pb isotopic compositions and U/Pb ratios can be accurately measured simultaneously without isotope dilution. The effects of deliberately including changes in the running conditions (r.f. power) are shown to be significant for measuring trace element ratios but not for mass bias and interference-corrected isotopic compositions. Finally, it is demonstrated that precise and accurate isotopic compositions of elements as refractory as W can be determined relatively easily by solution nebulization and even by direct laser ablation of complex silicates. Spectral interferences in such experiments are negligible. These experiments serve to highlight the remarkable potential that this new field offers for hitherto difficult isotopic measurements in nuclear, earth, environmental and medical sciences. Isotopic measurements can be made that are reproducible at high precision through a range of running conditions, even in the presence of isobaric interferences. The ability to correct for mass discrimination accurately using a second element of similar mass, the very high sensitivity for elements that are otherwise difficult to ionize, the demonstrated capability for laser ablation work and the ability to measure through a wide mass range simultaneously give this instrument major advantages over other more traditional techniques of isotopic measurement.

In situ hafnium isotope ratio analysis of zircon by inductively coupled plasma multiple collector mass spectrometry

Hf isotopic data are reported for ten ∼0.01-mm 2 subareas of a zircon crystal separated from the ∼ 318-Ma diatreme of Elie Ness, Fife, Scotland. In situ analysis was achieved by ablation sampling with a Nd:YAG laser into an inductively-coupled plasma, with ions dispersed by a sector magnet and integrated in a 7-Faraday multicollector array. Despite large interferences from Yb (16% of mass 176) and Lu (0.4% of mass 176), 2 se precision of ± 0.00004–0.00014 was achieved on 176Hf/ 177Hf in each subarea, each representing the analysis of ∼10 ng of Hf. Overall reproducibility of ± 0.00005 (2 sd) was obtained between the ten subareas, only a factor of 2–3 worse than that achieved by conventional TIMS Hf analysis based on 1–3 μg HE Reproducibility of single-spot analyses is about a factor of 2 better than reported for ion microprobe studies of zircon Hf, with far less potential for inaccuracies caused by molecular isobaric interferences. The Elie Ness zircons are isotopically homogeneous in Hf, but the technique is expected to have great value for the understanding of multicomponent zircons from granitoids and sediments.

Recovery of precious metals using nickel sulfide fire assay collection: problems at nanogram per gram concentrations

The NiS fire assay is widely used for the separation and concentration of PGE and Au from geological materials. The effect of collector mass on the recovery of PGE and Au in a Pt ore grade (µg g–1) sample and a komatiite sample which contained <10 ng g–1 of PGE are reported. The PGE and Au recoveries were not a function of collector mass for the ore grade sample. The recovery of Ir, Os and Au from the komatiite sample did not significantly depend on the mass of the collector used but Ru, Rh, Pd, and Pt recoveries were reproducible and dependent upon the collector mass. From these recoveries, estimates of the partition coefficients (Kd) were calculated for the sulfide and silicate melt phases. The Kd values were also estimated from direct analysis of the two phases. The recoveries of the precious metals were not always independent of the collector-to-flux-ratio. Also, the Kd values were found to depend upon the PGE concentrations. The Kd values obtained for an ore-grade sample were 4 to 103-fold higher than those obtained for a sample which contained < 10 ng g–1 PGE concentrations. Thus, when determining PGE concentrations at low levels using NiS fire assay collection, significant biases may occur.

Solar cooling in Madrid: Available solar energy

This paper analyzes the behaviour of an absorption chiller lithium bromide installation fed by a field of flat-plate solar collectors and condensed by swimming pool water. A method of calculation in a variable regime is developed in terms of the obtained experimental results. Starting from the meteorological variables of a clear summer day and from the project data (collector normalization curve, collector and installation mass), the minimum solar radiation level necessary to initiate the process, I[sub min], and the instantaneous available solar energy, Q[sub u] + W[sub 1] is determined. The solar radiation threshold, I[sub min], necessary to obtain the process temperature, t[sub ave], in each instant, is obtained by adding to the corrected Klein radiation threshold, I[sub k,c], the heat capacity effects of the collector, HCE[sub CO], and of the installation, HCE[sub ins], as well as the losses of heat of the pipes to the surroundings, Q[sub 1]. The instantaneous available solar energy, available useful heat, in addition to the wind collector losses to the surroundings, Q[sub u] + W[sub 1], is the difference, in each instant, between the radiation, I[sub g1T], and the radiation threshold, I[sub min].The integration during the day of the instantaneous available solar energy allowsmore » us to calculate the daily available function, H[sub T]. The value of H[sub T], measured in the swimming-pool water condensation installation reached 6.92 MJ/(m[sup 2] day ). The calculated values of H[sub T] for a conventional installation condensed by tower water, or air, have been 6.35 and 0.56 MJ/(m[sup 2] day). respectively.« less

High-Precision Lead Isotope Ratio Measurement by Inductively Coupled Plasma Multiple Collector Mass Spectrometry

An inductively coupled plasma (ICP) ion source coupled to a magnetic sector mass analyser equipped with seven Faraday detectors has been used to measure the lead isotope ratios in solutions of Sanshiro Pond sediment collected at the University of Tokyo, airborne particulates collected at Shinjuku in Tokyo and Merck multielement standard product number 97279494. A thallium correction technique was utilised to allow a simultaneous correction for mass bias. This work followed an earlier interlaboratory comparison study of the above-mentioned solutions using ICP quadrupole mass spectrometry, and has demonstrated a considerable improvement in analytical precision. The following isotope ratio measurements were recorded. Pond sediment solution containing 82ng ml-1 lead: 206Pb/204Pb=17.762±0.014; 206Pb/ 207Pb=1.1424±0.0009; 208Pb/204Pb=37.678±0.034. Airborne particulate solution containing 45 ng ml-1 lead: 206Pb/ 204Pb=17.969±0.006; 206Pb/207Pb=1.1528±0.0003; 208Pb/204Pb=37.915±0.021. Merck multielement standard solution containing 100ng ml-1 lead: 206Pb/204Pb=19.255±0.015; 206Pb/207Pb=1.2238±0.0004; 208Pb/204Pb=38.476±0.021 (All errors are given as ±2 standard deviations).

Communication. Isotope ratio measurement by inductively coupled plasma multiple collector mass spectrometry incorporating a high efficiency nebulization system

Isotope ratio analysis by inductively coupled plasma multiple collector mass spectrometry has been performed utilizing a high efficiency desolvating nebulization system for sample introduction. The high accuracy and high precision analysis of uranium, lead and hafnium reference materials at a concentration of 50 ng ml–1 are reported. Use of the high efficiency device has increased sample transmission and hence increased ion-signal levels by a factor of ten compared with conventional nebulization. The analysis of each uranium and lead solution required 29 ng of sample while the analysis of each hafnium solution required 290 ng of sample. The accuracy and precision of the measurements are comparable with those obtained by thermal ionization mass spectrometry. Transmission calculations indicate an ion:atom ratio of 1:5500 for each of the three elements. This is superior to that observed with other plasma source mass spectrometers and in the case of hafnium, exceeds that achieved with thermal ionization mass spectrometers.

Exergy optimization of flow rates in flat-plate solar collectors

The optimal flat-plate collector mass flow rate is determined by maximizing the exergy (available energy) delivery of the collector as the objective function. Collector and storage dynamics are neglected. Although the case where the pumping power loss is ignored results in bang-bang control, the case where this loss is included in the exergy equation results, after some assumptions, in an optimal mass flow rate that is a function of collector parameters, inlet and ambient temperatures and solar heat gain. Daily performance of a typical flat-plate solar collector with optimum mass flow rate is compared with the performance of the same collector using the mass flow rate obtained by maximizing the difference between the collected thermal energy and the required pumping power.

Computer-assisted null point method for the mass spectrometric measurement of relative abundance of hydrogen isotopes.

A multiplying digital-to-analog converter (DAC) has been incorporated into the measuring circuit of a conventional double collector mass spectrometer. Inverse feedback of a portion of the signal from the mass-2 peak (H2+) is controlled by the microcomputer so as to exactly cancel the ion current signal of the mass-3 peak (HD+ + H3+). The control to obtain the null point was so successful that we can regard the digital number being sent to the DAC as the proportional value to the ion current ratio. The software simulation of gas exchange in the ionization chamber from the sample gas to the reference gas and vice versa brought about the reduction of the measurement time.

Precise lead isotope measurements by the double spike technique: A reconsideration

A reappraisal of the “Double Spike Method” for correction of the mass discrimination in lead isotope analysis is presented in view of the possible efficiency of this method, especially as related to the improved performance of the new multi-collector mass spectrometers. First, the effects of mass discrimination during lead isotope analysis, using the silica-gel phosphoric acid method, are discussed in order to verify the validity of the linear discrimination law. In this discussion, we give evidence of a slight bias of the isotopic composition of the SRM 981 NBS lead standard, commonly used for mass discrimination calibrations. A rigorous way to deal with the propagation of the within-run statistical errors on the precision of the double spike correction is then presented. This allows the optimization of the parameters of the method (spike isotopic composition and precision, spiking proportion) and the calculation of the respective error associated with each corrected isotopic ratio. The perturbation of the double spike correction due to analytical contamination, which has caused previous failure in the application of the method, is avoided by preparation of the mixture between the spike and the sample at the very end of the chemical separation procedure. Using a single collector mass spectrometer, examples of application on lead standards and on a set of samples suggest a possible improvement in the precision by a factor of 3 compared to the usual method of fractionation normalization and confirm the usefulness of the method with the new generation of mass spectrometers.

The performance of a thermosiphon solar domestic hot water system with hot water removal

INTRODUCTION Thermosiphon (natural circulation) solar domestic hot water systems were investigated, both experimentally and numerically, by Close[l], Gupta and Garg[2], Ong[3], and Young and Bergquam[4]. Close used a 1.6m 2 (17.3ft 2) collector and a 113.6L (30gal) storage tank, while Ong utilized a 1.4m 2 (15ft 2) collector and a 106L (28gal) storage tank. These systems do not represent practical size systems although they do maintain the ratio between the storage tank volume and collector area, in English units, at about 2 which is a design rule of thumb[5]. Larger systems can have higher mass flow rates which can lead to transition or turbulent flow throughout the system. These higher mass flow rates increase the mixing in the storage tank and can complicate numerical modeling efforts. In the investigation of Young and Bergquam, a practical size thermosiphon system was tested, e.g. a 3.47 m 2 (37.4 ft 2) collector and 250L (66gal) storage tank§ Numerical models were presented in [4] for the collector, storage tank, and the thermosiphon mass flow rate. The relatively low velocities typical of natural circulation systems make the measurement of collector mass flow rates difficult. Consequently, only a few investigators have attempted to measure the flow rate in these systems. Even a small flow restriction placed in the flow to measure the flow rate can drastically reduce the flow and change the hydrodynamic behavior of the system. Ong[3] measured the mass flow rate by timing the passage of a single dye streak. A laser doppler anemometer was used by Morrison and Ranatunga[6] to measure mass flow rates of a scaled down laboratory system (an electric heater for the collector and a 66.7L (17.6gal) storage tank were used). The velocity profile was measured across a transparent test section and the resulting velocity profile integrated to obtain the mass flow rate. In all cases the flow was laminar. Accuracies of 2 per cent were reported in [6]. Although a laser doppler anemometer does not introduce any restrictions in the flow field its expense and complexity limit its use. An energy balance on the storage tank was used in [4] to calculate collector mass flow rates. The technique was verified by comparison to measurements taken on a pumped system using a turbine flow meter.

Seasonal, latitudinal, and secular variations in the abundance and isotopic ratios of atmospheric carbon dioxide: 1. Results from land stations

Between March 1977 and February 1982, 517 samples of air were collected in 51 glass flasks at four stations in the northern hemisphere near the Pacific ocean and at the South Pole. First, the CO2concentration of each sample was determined by nondispersive infrared gas analysis, and then the 13C/12C and 18O/16O ratios of the cryogenic extracted CO2 were determined with a triple collector mass spectrometer. For each station the secular trend and seasonal variation in 13C/12C ratio have been established as a function of CO2 concentration. The seasonally adjusted 13C/12C ratio is found to have decreased at a rate of about 0.02‰ per ppm increase in the seasonally adjusted CO2 concentration and to vary with latitude as expected if CO2 is being released by fossil fuel combustion in the northern hemisphere and from ocean water near the equator. At the three northernmost stations (La Jolla, California, at 33°N and two Hawaiian stations near 19°N) the 13C/12C ratio of the CO2 added to and withdrawn from the atmosphere during one annual cycle is circa −29‰ with respect to standard PDB, as expected from the exchange of atmospheric CO2 with the carbon of terrestrial plants. Near the equator at Fanning Island (4°N) the similarly computed 13C/12C ratio is −21‰, while at the South Pole it is about −13‰. This suggests that the seasonal variation in the southern hemisphere and tropics is partially a result of oceanic CO2 exchange.

Mathematical Analysis of a Zn / NiOOH Cell

A mathematical model has been developed to predict the time dependent behavior of a cell. The model uses experimentally determined polarization expressions to describe the losses between the positive and the negative electrodes. The electronic losses in the plane of the electrode are simulated by a network of resistors. The potential distribution, the current distribution, the cell voltage, the power capability, and the energy of a cell can be predicted. The mathematical model provides an analytical tool to evaluate, for example, the trade‐offs between power capability and current collector mass, needed to design an electric vehicle battery.

Stable Isotope Fractionation During Benzene Synthesis for Radiocarbon Dating

13C isotope analyses of different stages of benzene synthesis have been made to study partial isotope fractionation. More than 60 analyses of carbonates, charcoal, carbon dioxide, and benzene were made in a double collector mass spectrometer. In the first stage of the synthesis (conversion to carbon dioxide) little or no fractionation was observed, beyond the analytical error of the method. Later stages of the process, show a greater and systematic fractionation. The experimental techniques are described.