Larger Sample Mass Research Articles

Some factors affecting supercooling and the equilibrium freezing point in soil–water systems

For six monomineral, homoionic clayey soils, the temperature of spontaneous nucleation T sn and the equilibrium freezing point T f were determined by use of the Differential Scanning Calorimetry (DSC) technique. The temperature of spontaneous nucleation T sn was determined on the cooling run, as the initial temperature of the observed exothermic peak. The temperature of equilibrium freezing (or melting) T f was interpreted as the initial temperature of the last non-zero thermal impulse in the diagram of real thermal impulses distribution q ( T ) obtained on warming. The supercooling Ψ was calculated as the difference between T f and T sn . The obtained results testify the strong dependency of the equilibrium freezing point T f on the water content w . It has been proved that T f can be expressed as a power function of the water content w and the plasticity limit w P , with an asymptote at w equal to the unfreezable water content w nf . In contrary, a scatter of results was observed for T sn and Ψ , which could be related to the effect of factors other than the water content. The best fitted model expresses the temperature of non-equilibrium freezing T sn as a function of the water content w , the plastic limit w P and an extensive parameter of the sample, i.e. its mass m , the effect of which proved fully statistically significant. The results give evidence of the strong effect of both soil plasticity and the sample mass on the temperature of spontaneous nucleation and the supercooling. By use of auxiliary empirical function, relating the unfreezable water content w nf to the plastic limit w P , it was possible to calculate such a mass m Ψ = 0 of a soil sample, for which the supercooling equals zero. At high water contents the predicted supercooling tends to zero for very large sample masses, from about 10 5 kg in a practically uncohesive soil ( w P = 1%) to 10 8 kg in an extremely cohesive soil ( w P = 100%).

Comparison of direct sampling and emulsion analysis using a filter furnace for the determination of lead in crude oil by graphite furnace atomic absorption spectrometry

The determination of trace elements in crude oil is difficult due to the complex nature of the sample and the various different chemical forms in which the metals can occur. The advantage of graphite furnace atomic absorption spectrometry is that only a minimum of sample pretreatment is required. In this work two techniques have been compared to establish a fast and reliable method for lead determination in crude oil. In the first one the crude oil samples were weighed directly onto solid sampling (SS) platforms and introduced into the graphite tube for analysis. In the second one the samples were prepared as oil-in-water emulsions and analyzed in a filter furnace (FF). Twenty μL of a mixture of 0.5 mg L − 1 Pd + 0.3 mg L − 1 Mg + Triton X-100 has been used as the modifier, and calibration against aqueous solutions has been used for both methods. The sensitivity obtained with the FF was more than a factor of two better than that with SS; however, as a larger sample mass could be introduced in the latter case, so that the limits of detection for both techniques were 0.004 mg kg − 1 . Seven crude oil samples were analyzed using the two procedures, and all results were in agreement at a 95% confidence level using a paired Student's t-test. For validation purposes, three crude oil samples have been mineralized using an open-vessel acid digestion, and the results were in agreement with those found with direct sampling and with emulsion sampling using FF according to ANOVA test. Both methods are simple, fast and reliable, being appropriated for routine analysis; however, the direct method using SS technology should be preferred because of its simplicity, speed and commercial availability.

Chemical-looping combustion of methane with CaSO 4 oxygen carrier in a fixed bed reactor

Chemical-looping combustion is a promising technology for the combustion of gas or solid fuel with efficient use of energy and inherent separation of CO 2. Chemical-looping combustion of methane with calcium sulfate as a novel oxygen carrier was conducted in a laboratory scale fixed bed reactor. The effects of reaction temperature, gas flow rate, sample mass, and particle size on reduction reactions were investigated and an optimum operating condition was determined. The results show that this novel oxygen carrier has a high reduction reactivity and stability in a long-time reduction/oxidation test. The conversions of CH 4 increased with a higher temperature, smaller gas flow rate, larger sample mass and smaller particle size. The suitable reaction temperature seems to be around 950 °C. Low temperatures lead to a low CH 4 conversion, but a significant SO 2 formation was observed at a higher temperature. The release of SO 2, CO, H 2 via a series of side reactions, carbon deposition and agglomeration were also discussed. The formation of SO 2, CO, H 2, and carbon can be avoided by optimization of the operating conditions.

Thermal Decomposition Study of Isolated Lignin Using Temperature Modulated TGA

Temperature modulated TGA (MTGA) was utilized to study the kinetics of lignin pyrolysis. Three industrial lignin preparations were investigated: softwood kraft lignin, hardwood kraft lignin, and Alcell lignin. Unlike conventional TGA, MTGA provides apparent activation energy (E a ) distribution curve using a single experimental run in a relatively short experimental time. Under Hi-Res conditions using a dynamic heating rate, the activation energies were higher than those determined using a constant heating rate. Likewise, small sample masses provided higher activation energies than those run with large sample mass. These effects can be eliminated by using a relatively large sample mass, > 10 mg. In this study, we discuss the effect of MTGA conditions on calculating E a distribution curves for lignin pyrolysis.

Speciation/fractionation of nickel in airborne particulate matter: Improvements in the Zatka sequential leaching procedure

Modifications are reported to the sequential leaching analytical method for nickel speciation/fractionation specified by Zatka so that larger sample masses can be analyzed. Improvements have been made in the completeness of the sulfide/metallic separation during the peroxide-citrate leach step by use of a larger volume of leachant, a longer leach duration and an orbital shaker. Minimal extraction of metallic nickel in this prolonged sulfidic nickel extraction has been confirmed. An increase in the number of samples analyzed simultaneously using these modifications has resulted in substantial productivity improvements and concomitant lower costs. It is critical for practitioners of sequential leaching techniques to recognize potential limitations and to use professional judgment when interpreting results. For example, results obtained may not be biologically relevant in assessing health risks; the acts of sampling and storage may result in changes in fractionation with time; surface coatings/films may alter the ability of a leachant to react with the target compound; and leaching behaviours may be different for samples differing only in particle size distributions.

Evaluation of Bulk Sediment Sampling Criteria for Gravel-Bed Rivers

Abstract Many research and management applications in river science require accurate estimates of one or more percentiles from the grain-size distribution of subsurface bed material. These include the estimation of bedload fluxes using most common formulae, the evaluation of bed material as a source of fine sediment, and the characterization of streambed substrates for spawning success. The standard criteria for collecting subsurface fluvial samples demand large sample masses, which are difficult to obtain in many field situations. Consequently the criteria may be ignored or, where the criteria are followed, substantial time and effort is expended to collect relatively few samples. Grain-size information may therefore be of a low quality, and restricted sampling may leave important spatial and temporal patterns of variation undetected. This study uses a coupled field and laboratory approach to evaluate existing bulk-sampling recommendations for a set of sediment mixtures that are representative of natural gravel beds. Based on an analysis of bias and precision of a suite of grain size percentiles, matrix-supported sediments tend to be characterized more easily than framework-supported sediments for a given range in grain size. Percentiles from bimodal distributions are more difficult to estimate accurately over the full range compared to unimodal distributions, especially near the bimodality gap. In general, most percentiles from most mixtures achieve negligible levels of bias and good precision with sample masses that are substantially less than those currently recommended. In the absence of a fuller understanding of the relations between sampling performance and sediment characteristics it would be imprudent to abandon these criteria. However, where a project requires a large number of samples, a sampling experiment or incremental field sample could prove to be a cost-effective tool for reducing overall effort by establishing specific criteria for the sediments under examination.

Evaluation of a technique for determining Re and PGEs in geological samples by ICP-MS coupled with a modified Carius tube digestion

In the determination of Re and platinum group elements in geological samples, various techniques have been employed for digesting samples, including Carius tube, high-pressure asher (HPA-S), alkali fusion and nickel sulfide fire assay. The normal Carius tube technique is able to digest relatively small amount of sample and has a possible safety problem caused by a high internal pressure. This paper reports a modified Carius tube method which utilizes a sealed stainless steel high-pressure autoclave filled with water to prevent explosion of the tube. During heating, the external and internal pressures of the Carius tube increase simultaneously, such that the possible explosion of Carius tube can be avoided. Consequently, this technique allows a higher temperature (up to 330°C), a greater volume of aqua regia (up to 2/3 of the total volume of the Carius tube) and thus larger sample mass (12 g) relative to the normal Carius tube technique. Fairly good agreement were obtained for PGE poor mafic rocks (IPGE < 0.03 ng/g). The efficiency to dissolve ultramafic rocks and chromites at different temperatures was investigated. We demonstrate that this technique is more effective than normal Carius tube technique for ultramafic rocks and chromites containing refractory minerals and the detection limits and precision can be improved for PGE poor mafic samples. The total procedural blanks are lower than 0.003 ng for Os, 0.03 ng for Re, Ir, Ru and Rh and 0.4 ng for Pd and Pt.

Laser ablation-inductively coupled plasma-dynamic reaction cell-mass spectrometry (LA-ICP-DRC-MS) for the determination of Pt, Pd and Rh in Pb buttons obtained by fire assay of platiniferous ores

As a result of the low concentration in which the platinum group metals (PGMs) Pt, Pd and Rh occur in platiniferous ores and their heterogeneous distribution over the matrix, their determination is usually preceded by analyte pre-concentration and separation of the analyte from the matrix. The Pb fire assay technique is an elegant method for this purpose, whereby the elements of interest are collected from a relatively large sample mass in a Pb button. It was the aim of this work to evaluate the capabilities of laser ablation-ICP-mass spectrometry (LA-ICP-MS) for the analysis of such Pb buttons. Matrix-matched standards were produced by spiking lead ingots with an aqueous standard solution and subsequent re-melting of these ingots to obtain homogeneous solid standards with known PGM concentrations. These standards permitted quantitative results to be obtained. In standard (vented) mode, the determination of Rh by ICP-MS was hindered by spectral overlap of the 103Rh+ signal with that of 206Pb2+. Cool plasma conditions permitted reduction of the Pb2+ signal intensity, but since analyte signal intensities decreased as well, the improvement in the limit of detection (LOD) for Rh was insufficient to make this approach fit-for-purpose. Use of NH3 as a reaction gas (at a flow rate of 0.2 Ar-equivalent mL min−1) in a dynamic reaction cell (DRC) resulted in electron transfer to Pb2+, while Rh+ showed no reactivity towards this gas. The use of chemical resolution to overcome the Rh+/Pb2+ overlap did not interfere with the determination of the other PGMs of interest. LODs achievable with this approach were <100 ng g−1 for Pt, Pd and Rh. The capability of this approach was evaluated by analysing Pb buttons produced from actual flotation concentrate samples from platiniferous ores, originating from the Merensky reef and the UG-2 reef, both located in the South-African Bushveld Igneous Complex. The accuracy attainable using LA-ICP-DRC-MS was estimated by comparison of the results thus obtained with those calculated for the lead buttons based on NiS fire assay and subsequent ICP-OES analysis of the same flotation concentrate samples. No significant differences could be established and in the majority of cases, the deviation between the LA-ICP-DRC-MS result and the corresponding reference value was <10%. The precision was typically ∼10% relative standard deviation (RSD) for Pt and Rh. For Pd, however, the precision was observed to be worse (typically ∼15% RSD), probably as a result of a more heterogeneous distribution over the Pb matrix.

Multinomial distributions applied to random sampling of particulate materials

When sampling a batch consisting of particulate material, the distribution of a sample estimator can be characterized using knowledge about the sample drawing process. With Bernoulli sampling, the number of particles in the sample is binomially distributed. Because this is rarely realized in practice, we propose a sampling design in which the possible samples have a nearly equal mass. Expected values and variances of the sample estimator are calculated. It is shown that the sample estimator becomes identical to the Horvitz–Thompson estimator in the case of a large batch‐to‐sample mass ratio and a large sample mass. Simulations and experiments were performed to test the theory. Simulations confirm that the round‐off error due to the discrete nature of particles is negligible for large sample sizes. Sampling experiments were carried out with a mixture of PolyPropylene (PP) and PolyTetraFluorEthylene (PTFE) spheres suspended in a viscous medium. The measured and theoretical variations are in good agreement.

Reduction of tungsten oxides with carbon. Part 2. Tube furnace experiments

Further information on the kinetics and mechanism of the reduction of WO 3 with carbon (in the form of graphite and of lamp black), complementing the results obtained in Part 1 using isothermal thermogravimetry in the temperature range 935–1100°C, was obtained using larger sample masses (up to 5 g) heated isothermally in flowing argon in a tube furnace (935–1060°C). The amounts of CO and CO 2 in the evolved gas were determined using infrared gas detectors. Results obtained supported the proposed two-stage reduction to W metal, via WO 2. The rate of reduction was influenced by the flow rate of argon, the CO CO 2 ratio in the product gases, the form of the carbon used, and the WO 3 carbon ratio. From kinetic data obtained from tube furnace experiments, an activation energy of 374 ± 2 kJ mol −1 was calculated for the diffusion-controlled first stage of the reduction with graphite. Lamp black was less reactive than graphite at the temperatures studied. Activation energies of 386 ± 9 kJ mol −1 and 465 kJ mol −1 were calculated from TG experiments for the reduction with graphite and lamp black, respectively. The gravimetric measurements from the tube furnace experiments were insufficient to analyse the kinetics of the second stage of reaction.

Accuracy and precision of heat capacity measurements using a heat flux differential scanning calorimeter

The accuracy and precision of a Setaram DSC 121 for the measurement of heat capacities of solids in the continuous mode was tested using sapphire and benzoic acid. The influence of the heating rate, mass of sample, and position of the crucible in the measuring tube on the obtained results is discussed. In the temperature range studied (320–440 K for sapphire and 320–370 K for benzoic acid) the accuracy and precision of the determination, based on the average results of three independent experiments, are better than 1% provided that adequate experimental conditions (large sample masses and low heating rates) and data handling procedures are used.

Thermal degradation of polymethacrylic ester containing bisphenol‐S

AbstractThermal degradation of polymethacrylic ester containing bisphenol‐S, poly(BPS‐M), was investigated under nitrogen and air atmosphere at various heating rates. Ozawa's method was used to calculate the kinetic parameters, activation energy, preexponential factor and reaction order. Thermodegradation of the polymer occurs in one or two stages in nitrogen and air, respectively. The temperature at the start of intense degradation (Tstart) and the temperature corresponding to a 50% mass loss (T50%) were found to be 300 and 402°C, respectively, at a heating rate of 10°C min−1 in nitrogen. Larger sample masses have a larger temperature interval (ΔT) and a greater mass loss (ΔW). The kinetic order of degradation is unity both in nitrogen and air. The direct pyrolysis mass spectrum of the polymer shows one degradation peak. The most important degradation process under inert atmosphere is the loss of carbon dioxide, phenol and sulphur dioxide. A possible mechanism for thermal decomposition of poly(BPS‐M) is proposed based on the product analyses.

Open-focused microwave-assisted digestion for the preparation of large mass organic samples

Microwave-assisted wet digestions of large sample masses (up to 10 g) of biological materials and hydrocarbon-based oil were successfully accomplished at atmospheric pressure using an open-focused system. The per cent. residual carbon contents (RCC) of the resulting solutions, trace element recovery and extent of contamination (magnitude of the blank) were used to characterize the performance of the methodology. A Prolabo Maxidigest M 401 unit, fitted with a modified reaction vessel, was used to solubilize samples of National Research Council of Canada (NRCC) certified reference materials TORT-1 and LUTS-1 (Lobster Hepatopancreas) as well as Conostan 75 base oil, using either HNO3 or a mixture of HNO3—H2SO4. Digestion efficiency increased with increased digestion time and sample mass (15% RCC with 0.25 g sample, 2% RCC with 8 g sample). The minimum spike recovery of added elements (As, Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, Se, Sr and Zn) was 94.5%(Sr) and averaged 99% in HNO3 and 97% in the mixed acid. Certified reference values for trace element content were achieved for TORT-1 and LUTS-1.

Procedure for the determination of 210Pb in phosphate ore, gypsum and phosphoric acid by radiochemical separation and gamma-ray spectrometry

A procedure is described for the determination of 210Pb in phosphate ore, gypsum and phosphoric acid by radiochemical separation and gamma-ray spectrometry of the 46.5 keV gamma ray of 210Pb. The procedure involves microwave dissolution, removal of interfering Fe by extraction with thiocyanate in isobutyl methyl ketone and extraction of Pb as the diethyldithiocarbamate (DDTC) complex into CHCl3. After evaporation of the CHCl3, the DDTC complex is decomposed and Pb is precipitated as PbCrO4. The chemical yield is determined gravimetrically and the precipitate is counted on a low-energy gamma-ray detector. Experiments proved the linearity between the 210Pb counting result for PbCrO4 masses in the range 15–100 mg. For materials with levels of approximately 500 Bq kg–1, 10 g of material are processed and the PbCrO4 preparate is counted for 24 h. Materials with a 210Pb content lower than 75 Bq kg–1 demand larger sample masses and/or longer counting times. The limit of determination is 75 Bq kg–1. A relative standard deviation of 2.5–5.0% at the 500 Bq kg–1 level for replicate 210Pb determinations in phosphate ore and gypsum was achieved. An inaccuracy of the method of less than 10% was derived from results for selected materials, that were also analysed by direct gamma-ray spectrometry.

Multielemental automated INAA system for gold ore samples

A methodological approach to the activation analysis of bulk samples up to 300 g mass on a reactor is proposed. As applied to the analysis of massive gold-bearing ore samples, the questions of representativity of the samples with inhomogeneous distribution of the component under examination, specific effects caused by gold particles as well as large sample dimensions and mass are studied and ways for taking into account their influence are suggested. An automated system of multielemental neutron activation analysis of large samples of gold-bearing ores has been developed. The system has found application in geological prospecting and the mining industry.

Effects of large sample loads on column lifetime in preparative-scale liquid chromatography

In preparative-scale liquid chromatography of proteins, the use of high sample concentration and large sample mass may result in irreversible adsorption to the support surface. This can change the stationary phase characteristics, reduce the capacity, shorten the column lifetime and diminish the economic viability of a particular separation method. Column recycling and regeneration can influence the throughput (mass purified per time unit) and selectivity, and affect the reproducibility. The effects of large sample loads on column lifetime and performance were evaluated for three strong anion-exchange columns: (1) a silica support with a quaternized polyethyleneimine (PEI) coating, (2) a polymeric support with an adsorbed PEI coating which also was quaternized, and (3) a polymeric support with a proprietary quaternary amine stationary phase. The column capacity for proteins was measured by frontal chromatography and monitored as a function of cycle number. The column lifetime was determined by examining chromatographic properties subsequent to the frontal chromatography. The change in protein binding capacity was then compared to the change in nitrate binding capacity. The column performance was evaluated under analytical conditions by measuring the change in resolution of standard protein mixtures.

Kinetic studies by thermogravimetry: the role of heat transfer of sample mass and of sample holder design on metal hydride kinetic results

Temperature measurements are carried out , in samples of different masses, according to the function of the material in which the sample holder is machined and as well as the function of its design. Under the same conditions of mass, temperature and hydrogen pressure, the temperature increase inside the sample is changed by a factor of 3 at a temperature of 21°C when the copper crucible is replaced by a plexiglass crucible. In addition , with a sample mass of 10 mg and with the sample holder which gives the best isothermal conditions , the exothermic hydride-formation kinetics are slower than with a less efficient holder or with a larger sample mass

Effects of experimental variables on purity determinations with differential scanning calorimetry

A description is given of the influence of calculation procedure, heating rate, sample mass, particle size and atmosphere on the determination of molar purity by means of melting point depression with differential scanning calorimetry. This determination is the most important pharmaceutical application of DSC. Nine substances, melting in the region 100–250°C were studied and factorial designs were used. A large sample mass leads to high purity values because of thermal insulation within the powder bed. Values even greater than 100 mole% were found. Since at high heating rates thermal and thermodynamic equilibrium cannot be attained, there must be an upper limit on heating rate in purity determinations; this appeared to be 0.05 K sec−1. However, sometimes heating rates below this value influence both the purity value and pure melting point, T0.The particle size of the sample also affected its purity value. The effects could be explained in terms of thermal lags, decomposition and evaporation during melting, or sublimation before melting. Decrease of particle size may either lead to low purity values, due to concurrent increase in structural disorder, or to increase in purity values, due to the formation of aggregates by electrostatic forces. It was concluded that if trituration of samples before subjecting them to DSC analysis causes aggregate formation, purity values which are too high may result.Very large particles give lower purity values because of thermal gradients in the sample.