Trade-off between Pore-Throat Structure and Mineral Composition in Modulating the Stability of Soil Organic Carbon.

The preservation of soil organic carbon (OC) is an effective way to decelerate the emission of CO2 emission. However, the coregulation of pore structure and mineral composition in OC stabilization remains elusive. We employed the in situ nondestructive oxidation of OC by low-temperature ashing (LTA) combined with near edge X-ray absorption fine structure (NEXAFS), high-resolution microtomography (µ-CT), field emission electron probe microanalysis (FE-EPMA) with C-free embedding, and novel Cosine similarity measurement to investigate the C retention in different aggregate fractions of contrasting soils. Pore structure and minerals contributed equally (ca. 50%) to OC accumulation in macroaggregates, while chemical protection played a leading role in C retention with 53.4%-59.2% of residual C associated with minerals in microaggregates. Phyllosilicates were discovered to be more prominent than Fe (hydr)oxides in C stabilization. The proportion of phyllosilicates-associated C (52.0%-61.9%) was higher than that bound with Fe (hydr)oxides (45.6%-55.3%) in all aggregate fractions tested. This study disentangled quantitatively for the first time a trade-off between physical and chemical protection of OC varying with aggregate size and the different contributions of minerals to OC preservation. Incorporating pore structure and mineral composition into C modeling would optimize the C models and improve the soil C content prediction.

Automated infrared ashing with palladium nitrate as an ashing aid for the determination of selenium in plant foods by inductively coupled plasma mass spectrometry.

Based on the automatic light wave ashing instrument, palladium nitrate was used as an ashing aid for the first time to collect selenium in the process of food ashing pre-treatment, and a method for the determination of selenium in food by ashing method was established with inductively coupled plasma mass spectrometry. At the same time, the effects of magnesium nitrate, rhodium nitrate, and nickel nitrate as ashing aids on selenium collection were investigated using certified plant standard materials. The capture of selenium by magnesium nitrate, rhodium nitrate, and nickel nitrate as ashing aids did not exceed 50%. Using palladium nitrate as an ashing aid, six food standard materials were measured, with selenium recovery rates ranging from 97 to 106%. A complete analysis cycle can be completed within an hour. The method detection limit of selenium was 0.021 µg g-1, and the relative standard deviation of five measurements was less than 7%. The experimental results show that palladium nitrate is an excellent ashing aid for capturing selenium, and it is far superior to the other three aids. In addition, the mechanism of palladium nitrate as an ashing aid for capturing selenium was discussed.

Dry torrefaction and continuous thermochemical conversion for upgrading agroforestry waste into eco-friendly energy carriers: Current progress and future prospect.

Agroforestry Waste (AW) is seen as a carbon neutral resource. However, the poor quality of AW reduced its potential application value. Even more unfortunately, chlorine in AW led to the formation of organic pollutants such as dioxins under higher temperatures. Alkali and alkaline earth metals (AAEMs) in ash may deepen the reaction degree. Co-pretreatment of dry torrefaction and de-ashing followed by thermochemical conversion is a promising technology, which can improve raw material quality, inhibit the release of organic pollutants and transform AW into eco-friendly energy carriers. In order to better understand the process, theoretical basis such as the structural characteristics, thermal properties and separation methods of structural components of AW are described in detail. In addition, dry torrefaction related reactors, process parameters, kinetic analysis models as well as the evaluation methods of torrefaction degree and environmental impact are systematically reviewed. The problem of ash accumulation caused by dry torrefaction can be well solved by de-ashing pretreatment. This paper provides a comprehensive discussion on the role of the two- and three-stage conversion technologies around dry torrefacion, de-ashing pretreatment and thermochemical conversion in products quality enhancement. Finally, the existing technical challenges, including suppression of gaseous pollutant release, harmless treatment and reuse of torrefaction liquid product (TPL) and reduction of torrefaction operating costs, are summarized and evaluated. The future research directions, such as vitrification of the reused TPL (after de-ashing or acid catalysis) and integration of oxidative torrefaction with thermochemical conversion technologies, are proposed.

Determination of Minerals in Soft and Hard Cheese Varieties by ICP-OES: A Comparison of Digestion Methods.

For sample preparation prior to mineral analysis, microwave digestion (~2 h) is quicker and requires lower acid volume as compared to dry (6-8 h) and wet digestion (4-5 h). However, microwave digestion had not yet been compared systematically with dry and wet digestion for different cheese matrices. In this work, the three digestion methods were compared for measuring major (Ca, K, Mg, Na and P) and trace minerals (Cu, Fe, Mn and Zn) in cheese samples using inductively coupled plasma optical emission spectrometry (ICP-OES). The study involved nine different cheese samples with moisture content varying from 32 to 81% and a standard reference material (skim milk powder). For the standard reference material, the relative standard deviation was lowest for microwave digestion (0.2-3.7%) followed by dry (0.2-6.7%) and wet digestion (0.4-7.6%). Overall, for major minerals in cheese, strong correlation was observed between the microwave and the dry and wet digestion methods (R2 = 0.971-0.999), and Bland-Altman plots showed best method agreement (lowest bias), indicating the comparability of all three digestion methods. A lower correlation coefficient, higher limits of agreement and higher bias of minor minerals indicate possibilities of measurement error.

Sample Preparation and Analytical Techniques in the Determination of Trace Elements in Food: A Review.

Every human being needs around 20 essential elements to maintain proper physiological processes. However, trace elements are classified as beneficial, essential, or toxic for living organisms. Some trace elements are considered essential elements for the human body in adequate quantities (dietary reference intakes, DRIs), while others have undetermined biological functions and are considered undesirable substances or contaminants. Pollution with trace elements is becoming a great concern since they can affect biological functions or accumulate in organs, causing adverse effects and illnesses such as cancer. These pollutants are being discarded in our soils, waters, and the food supply chain due to several anthropogenic factors. This review mainly aims to provide a clear overview of the commonly used methods and techniques in the trace element analysis of food from sample preparations, namely, ashing techniques, separation/extraction methods, and analytical techniques. Ashing is the first step in trace element analysis. Dry ashing or wet digestion using strong acids at high pressure in closed vessels are used to eliminate the organic matter. Separation and pre-concentration of elements is usually needed before proceeding with the analytical techniques to eliminate the interferences and ameliorate the detection limits.

Influence of Additive N2 on O2 Plasma Ashing Process in Inductively Coupled Plasma.

One of the cleaning processes in semiconductor fabrication is the ashing process using oxygen plasma, which has been normally used N2 gas as additive gas to increase the ashing rate, and it is known that the ashing rate is strongly related to the concentration of oxygen radicals measured OES. However, by performing a comprehensive experiment of the O2 plasma ashing process in various N2/O2 mixing ratios and RF powers, our investigation revealed that the tendency of the density measured using only OES did not exactly match the ashing rate. This problematic issue can be solved by considering the plasma parameter, such as electron density. This study can suggest a method inferring the exact maximum condition of the ashing rate based on the plasma diagnostics such as OES, Langmuir probe, and cutoff probe, which might be useful for the next-generation plasma process.

Chemical status of zinc in plant phytoliths: Impact of burning and (paleo)environmental implications.

Phytoliths are microscopic structures made of amorphous opal (opal-A), an amorphous hydrated silica, dispersed within plant tissues and persisting after the decay of the plant. Silicon is known to alleviate metal toxicity in plants, but the role of phytoliths in metal sequestration and detoxification is unclear. Dry ashing, the most common protocol for phytolith extraction, was previously shown to lead to sequestration of metals by the phytoliths; however, the mechanisms of this process remained elusive. The purpose of this study was to evaluate whether the association between metals and phytoliths results from dry ashing or pre-exists in plant tissues. Thus, we compared phytoliths extracted by dry ashing at 700 °C and plant leaves before and after dry ashing. A combination of ICP-MS, XRD, SEM-EDX and Zn-K-edge EXAFS spectroscopy was used to assess elemental concentrations, morphology and crystallography of silica, and chemical status of Zn. Results demonstrated a phase transition from amorphous opal (opal-A) to opal-CT and α-cristobalite, and the sequestration of metal in phytoliths during dry ashing. For Zn, Mn and Pb, a linear relationship was found between the concentration in phytoliths and in leaves. In the phytoliths, Zn was sequestered in silica in tetrahedral configuration. We hypothesize that this association results form a solid-state reaction during ashing, involving a redistribution of Zn from the organic material to the silica, possibly promoted by the release of structural water from amorphous opal throughout the heating procedure. This study improves our understanding of the impact of high temperature treatments on plant biomass and phytoliths. It suggests that Zn toxicity alleviation in plants by silicon does not rely on its sequestration by phytoliths. In natural settings, wild fire events and biomass burning may lead to metal sequestration in low-soluble form, which should be considered in modeling of biogeochemical cycles and in paleoenvironmental studies.

Design and Fabrication of Millimeter-Wave Frequency-Tunable Metamaterial Absorber Using MEMS Cantilever Actuators.

In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced MEMS cantilever array having initial out-of-plane deflections, and the cantilevers were electrostatically actuated to generate a capacitance change. The dimensional parameters of the absorber were determined via impedance matching using a full electromagnetic simulation. The designed absorber was fabricated on a glass wafer with surface micromachining processes using a photoresist sacrificial layer and the oxygen-plasma-ashing process to release the cantilevers. The performance of the fabricated absorber was experimentally validated using a waveguide measurement setup. The absorption frequency shifted down according to the applied DC (direct current) bias voltage from 28 GHz in the initial off state to 25.5 GHz in the pull-down state with the applied voltage of 15 V. The measured reflection coefficients at those frequencies were -5.68 dB and -33.60 dB, corresponding to the peak absorptivity rates of 72.9 and 99.9%, respectively.

Pyrolysis of High-Ash Natural Microalgae from Water Blooms: Effects of Acid Pretreatment.

Natural microalgae (NA, cyanobacteria) collected from Taihu Lake (Jiangsu, China) were used for biofuel production through pyrolysis. The microalgae were de-ashed via pretreatment with deionized water and hydrochloric acid, and the samples obtained were noted as 0 M, 0.1 M, 1 M, 2 M, 4 M, 6 M, 8 M, respectively, according to the concentration of hydrochloric acid used in the pretreatment. Pyrolysis experiments were carried out at 500 °C for 2 h. The products were examined by various techniques to identify the influence of the ash on the pyrolysis behavior. The results showed that the ash inhibited the thermal transformation of microalgae. The 2 mol/L hydrochloric acid performed the best in removing ash and the liquid yield increased from 34.4% (NA) to 40.5% (2 M). Metal-oxides (mainly CaO, MgO, Al2O3) in ash promoted the reaction of hexadecanoic acid and NH3 to produce more hexadecanamide, which was further dehydrated to hexadecanenitrile. After acid pretreatment, significant improvement in the selectivity of hexadecanoic acid was observed, ranging from 22.4% (NA) to 58.8% (4 M). The hydrocarbon compounds in the liquid product increased from 12.90% (NA) to 26.67% (2 M). Furthermore, the acid pretreatment enhanced the content of C9-C16 compounds and the HHV values of bio-oil. For natural microalgae, the de-ashing pretreatment before pyrolysis was essential for improving the biocrude yield and quality, as well as the biomass conversion efficiency.

Evaluation of plasma cleaning as an approach for the preparation of soil minerals for forensic comparison by photon and electron microscopy.

Although organic material is often used for forensic analysis, a substantial portion of the data gathered for determination of common origin of forensic soil samples is the inorganic, mineralogical composition of the sample, which may be obscured by the presence of soil organic material (SOM). Traditionally, SOM is removed by acidic, alkaline, or peroxide digest, or by combustion, but these techniques risk the damage to or destruction of target minerals of interest. Low-temperature plasma ashing, on the other hand, removes organic materials by exposing them to plasma ions with high-kinetic energy, converting organics to easily removed volatile products (CO, CO2 , H2 O, or methane) while avoiding the thermal alterations caused by heat combustion. This study exposed grains of known mineral types to 20 min of a low-pressure O2 plasma generated by a 10 MHz frequency generator. Powder x-ray diffraction was chosen as an independent method to evaluate the minerals for chemical or structural changes caused by this ashing process. Side-by-side comparison of before and after diffractograms revealed minimal, if any, variation in the detected 2θ and subsequently calculated d-spacing: differences in d values were found to generally be less than 1%, and most were within Hanawalt Search Index uncertainties by no less than a full order of magnitude. Peak intensity changes were similarly minimal. This study strongly suggests that low-temperature plasma ashing can be used for the isolation of inorganic soil material fraction for forensic soil analysis with little or no concern for potential alteration of the mineral grains.

Content of toxic metals and As in marine and freshwater fish species available for sale in EU supermarkets and health risk associated with its consumption.

BACKGROUND: The present study investigated Pb, Cd and As concentrations in canned tuna, tuna steak, rainbow trout, smoked mackerel, and Baltic and Atlantic cod, as well as Atlantic salmon. The aim was to spot check the quality of the most commonly purchased types of fish that are available for sale in most common supermarket chains throughout the Poland, as well as to determine potentially less contaminated sources of fish available for retail. A dry ashing digestion protocol followed by inductively coupled plasma mass spectrometry analysis was employed to achieve a better recover of heavy metals and As from fish muscle tissues. RESULTS: The cumulative concentration of metals and As in fish muscle tissue decreases in order: farmed Atlantic salmon > mackerel > Baltic cod > rainbow trout > canned tuna fish > Atlantic cod > yellowfin tuna steak. It was found that canned tuna from Central and Eastern Pacific Ocean were more contaminated than tuna from East and West Indian Ocean, Baltic cod was significantly more contaminated than cod from North-East Atlantic. Smoked mackerel from North-East Pacific Ocean is three times more contaminated than mackerel from Northern North Sea. All fish, except for yellowfin tuna steak, should not be intended for retail because they exceed maximum levels for Cd and Pb. CONCLUSION: Consuming only one serving (140 g) of Baltic cod exposes one to 51% of the daily acceptable Cd intake, while the same portion of canned tuna and smoked mackerel from the Pacific Ocean deliver 69% and 72% of this element respectively. The most cadmium is consumed with smoked mackerel from the North Sea, comprising as much as 162% of the daily acceptable dosage . © 2020 Society of Chemical Industry.

Determination of Metals in Tree Rings by ICP-MS Using Ash from a Direct Mercury Analyzer.

Elemental profiles in cores of tree trunks (bole wood) have been used for environmental monitoring and reconstruction of metal pollution history. Mercury (Hg) is a global pollutant that can be accurately measured in tree rings in a simple and pragmatic fashion using a direct mercury analyzer (DMA) that is based on thermal decomposition, amalgamation, and atomic absorption spectrophotometry. In this feasibility study, we demonstrate that the ash remaining after the DMA analyses can be used to quantify a wide range of other non-volatile elements (Ba, Be, Co, Cr, Cu, Fe, Ga, Mg, Mn, Ni, Pb, Sr, Th, and U) in that same sample of wood by inductively coupled plasma mass spectrometry (ICP-MS) after microwave-assisted acid digestion. Other elements (Ag, Cd, Cs, Rb, Tl, and V) exhibited poor recoveries, possibly due to losses during sample preparation. We assessed the accuracy with reference materials, spikes, and by comparison with EPA Method 3052 (Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices). For the first group of elements (deemed suitable for the method), recoveries ranged between 80% and 120% and the relative standard deviation was generally < 15%, indicating acceptable precision. We applied the method to five species of trees: eastern red cedar (Juniperus virginiana), loblolly pine (Pinus taeda), shortleaf pine (Pinus echinata), white oak (Quercus alba), and tulip poplar (Liriodendron tulipifera) from Holly Springs National Forest in north Mississippi, USA. Mercury concentrations (ng/g ± SE) were highest in the cedar (1.8 ± 0.3; n = 5), followed by loblolly pine (1.6 ± 0.3, n = 3), shortleaf pine (1.2 ± 0.2; n = 3), oak (1.1 ± 0.2; n = 5), and poplar (0.5 ± 0.1; n = 5). Concentrations of other elements were generally Fe > Mg > Ba ≈ Sr ≈ Mn > Cr ≈ Cu > Ni ≈ Rb > Co > Ga ≈ Ag, with the other elements generally below the method detection limit (MDL). Overall, we showed that the DMA can be used to not only determine total Hg in segments of tree core, but can serve as the ashing step in the preparation of wood for ICP-MS analysis, thus allowing the determination of non-volatile elements along with Hg in the very same sample.

Impacts of agricultural land use change on soil aggregate stability and physical protection of organic C.

Soil aggregate stability and soil organic carbon (SOC) physical sequestration is essential to regulation of anthropogenic climate change. However, relative knowledge remains elusive. The total SOC stock, aggregate stability, capacity of physically protected C, structure of macroaggregates and Al/Fe oxides under rice-wheat rotation (RW), rice-vegetable rotation (RV) and afforested land (AL) were analysed. We chose 1-2 mm macroaggregates for low-temperature ashing (LTA) treatment to mimic natural oxidation to assess the capacity of physically protected C. Using scanning electron microscopy, the N adsorption method, and energy dispersive spectroscopy, we explored the internal structure of macroaggregates under different land use types. All land use types could physically protect over 50% of SOC. AL showed the strongest capacity of C sequestration, followed by RW, which preserved 67.1% and 59.6% of SOC, respectively. After 5 h of LTA treatment, the amount of SOC removed from the macropores in cropland (RW and RV) was higher than that in AL. In micropores with further oxidation, AL and RW both lost only 5% of SOC. Fe oxides were more correlated with C dynamics than Al oxides. Free Fe oxides were associated with the easily oxidised organic matter. Soil aggregate stability significantly correlated with Al/Fe oxides (p < 0.05). The RW and AL had a greater soil aggregate stability than the RV owing to the relatively higher content of Al/Fe oxides. In conclusion, the conversion of RW to RV reduced the mechanical stability of soil aggregates and the capacity of C physical sequestration, while the conversion of RW to AL increased these two properties. Land use change affected C physical sequestration mainly via changes in surface area, pore development and the content of Fe oxides in macroaggregates.

Integration Method of Microchannel and Vertical Micromesh Structure for Three-Dimensional Cell Culture Using Inclined Exposure and Inclined Oxygen Ashing.

Culturing cellular tissues inside a microchannel using an artificial three-dimensional (3D) microstructure is normally conducted to elucidate and reproduce a biological function. The thick photoresist SU-8, which has a microscale resolution and high aspect ratio, is widely used for the fabrication of microchannels and scaffolds having 3D structures for cell culture. However, it is difficult to accurately fabricate a mesh structure with a pore size that is smaller than the cells that has an overall height greater than 50 µm because of the deterioration of the verticality of exposure light and the diffusion of acid, which accelerates the crosslinking reaction in the SU-8 layer. In this study, we propose a method of integrating a vertical porous membrane into a microchannel. The resolution of the vertical porous membrane becomes more accurate through inclined oxygen ashing, without degrading the robustness. Because a single mask pattern is required for the proposed method, assembly error is not generated using the assembly-free process. The fabricated vertical porous membrane in the microchannel contained micropores that were smaller than the cells and sufficiently robust for a microfluidic system. HepG2 cells were attached three-dimensionally on the fabricated vertical porous membrane to demonstrate 3D cell culture.

Determining phytolith-occluded organic carbon sequestration using an upgraded optimized extraction method: indicating for a missing carbon pool.

Phytolith-occluded organic carbon (PhytOC) is considered one of the most promising terrestrial carbon (C) sinks. Different methods are used for phytolith extraction from wet-ashing techniques and the subsequent determination of PhytOC content from soil. This is in order to optimize the wet-ashing techniques and to improve estimation accuracy of C sequestration potential of phytoliths from soil. Results show that the organic matter removal and carbonate removal protocol, applying sonication, has a significant effect on phytolith extraction. Namely, the sequential removal of first organic matter and then carbonates applied to such methods could eliminate greater than 17.14, 46.68, and 26.17% extraneous material compared to other methods. Moreover, phytoliths extracted using methods that apply sonication eliminated 7.49, 42.70, and 17.57% more extraneous material than methods that did not. Additionally, the procedure associated with the second oxidation step significantly influenced the determination of PhytOC content, that is, 29.34, 33.75, 26.41, and 64.64% of excess organic C were oxidized during this step. The upgraded optimal method we recommend for phytolith extraction in association with wet-ashing techniques and the subsequent determination of PhytOC content is therefore to first apply sonication, then the second oxidation step, and finally the removal of organic matter. Using this optimal upgraded method, we estimated the C sequestration potential of phytoliths from the soil of slash pine in China at 0.51 Mt. C. Furthermore, using this upgraded optimal method increased the precision of the carbon sequestration potential of phytoliths from soil by up to 63.83%.

Development of a rapid and accurate method for the determination of sodium in vacuum gas oils (VGOs) by ICP-OES.

Sodium in vacuum gas oils (VGOs), even at trace levels, produces corrosion by-products in the refinery pipelines and it is a significant catalyst poison, especially for those from atmospheric or vacuum distillation units, thus its concentration in middle-distillate petroleum products needs to be controlled. In addition, sodium contamination was an issue in this study, as sodium might be present even in the dust floating in the air. The use of an ultrapure sodium-free water and the disposal of a clean and dust-free room were the key to be successful on the development of this method. Different sample preparation methods were studied as sample preparation optimisation was an important step in this study. Dry ashing by different processes, wet acid digestion with different acid mixtures, wet acid microwave-assisted digestion, and dilution with a proper solvent were tried to find the appropriate sample preparation method. An accurate and precise method for the determination of sodium in vacuum gas oils (VGOs) by ICP-OES at trace levels has been developed by ashing the sample with a new piece of equipment designed and created by the Instituto de Tecnología Cerámica (ITC), that permits to calcine the sample in one hour and avoids analyte losses or analyte contamination. The quantification limit achieved by the whole sodium determination method is lower than 1 mg kg-1, which allows it to be used as control method in the petrochemical industry.

Simultaneous determination of arsenic, cadmium and lead in plant foods by ICP-MS combined with automated focused infrared ashing and cold trap.

A fully automated focused infrared lightwave ashing sample preparation system was proposed and applied to the pretreatment of volatile arsenic, cadmium and lead in plant foods prior to inductively coupled plasma mass spectrometry (ICP-MS) determination. All the steps of ashing pretreatment were automatically accomplished within forty minutes. Gold-plated infrared quartz tubes produced focused infrared to supply a rapid heating. Ozone was used to accelerate sample carbonization. A cool trap was used to capture volatile arsenic, cadmium and lead. Three certified plant food reference materials were determined. The recoveries of the three elements were between 90% and 107%. Five real plant foods were analyzed by the proposed method and microwave digestion. The results showed no significant difference.

Mild Salt-Sensitive Hypertension in Genetically Determined Low Nephron Number is Associated with Chloride but Not Sodium Retention.

BACKGROUND/AIMS: One potential pathomechanism how low nephron number leads to hypertension in later life is altered salt handling. We therefore evaluated changes in electrolyte and water content in wildtype (wt) and GDNF+/- mice with a 30% reduction of nephron number. METHODS: 32 GDNF+/- and 36 wt mice were fed with low salt (LSD, 0.03%, normal drinking water) or high salt (HSD, 4%, 0.9% drinking water) diet for 4 weeks. Blood pressure was continuously measured by telemetry in a subgroup. At the end of the experiment and after standardized ashing processes electrolyte- and water contents of the skin and the total body were determined. RESULTS: We found higher blood pressure in high salt treated GDNF+/-compared to wt mice. Of interest, we could not confirm an increase in total-body sodium as predicted by prevailing explanations, but found increased total body and skin chloride that interestingly correlated with relative kidney weight. CONCLUSION: We hereby firstly report significant total body and skin chloride retention in salt sensitive hypertension of GDNF+/-mice with genetically determined lower nephron number. Thus, in contrast to the prevailing opinion our data argue for the involvement of non-volume related mechanisms.

An approach to determining nickel, vanadium and other metal concentrations in crude oil.

The ability to accurately determine the metal content of crude oils is necessary for reasons ranging from the need to identify the source of the oils (Ni and V) to removing components that might inhibit catalysis during refining or impact negatively on the environment during hydrocarbon combustion. Here we show that ashing followed by chemical oxidation and acid digestion, coupled with ICP-MS analysis, provides an accurate method for determining the concentration of metals in crude oil. Nickel and vanadium concentrations were measured in certified Ni and V oil standards and in various light, intermediate and heavy crude oils after application of a single vessel ashing-chemical oxidation-acid digestion sample preparation and storing technique. Prior to the ashing, chemical oxidation and acid digestion, an aliquot of the crude oil was placed in a 10 ml Pyrex™ culture tube and capped with quartz wool. The capped culture tubes were then subjected to thermal combustion, followed by chemical oxidation and leaching. The leachates and the aqueous standards were diluted and analyzed for their Ni and V contents using inductively coupled plasma mass spectrometry (ICP-MS). The measured concentrations of Ni in oil standards, reported to contain 1, 100, and 1000 mg kg-1 Ni (±2% error), were 1.1 ± 0.01, 99.8 ± 1.46, and 1025 ± 24 mg kg-1 respectively. The corresponding concentrations of V in these standards, reported to contain 2, 100, and 1000 mg kg-1 V, were measured to be 1.93 ± 0.06, 104 ± 1.3, and 1027 ± 7.5 mg kg-1, respectively. Crude oil samples, A, B, C, D and E, that varied significantly in their composition, and ranged from light to heavy, were determined to contain 5.59 ± 0.32, 4.05 ± 0.03, 6.22 ± 0.22, 33.8 ± 0.7 and 41.6 ± 3.5 mg kg-1 Ni, respectively. Their V contents were determined to be 11.98 ± 0.1, 12.2 ± 0.1, 16.5 ± 0.4, 34.7 ± 0.4, and 104 ± 8.9 mg kg-1, respectively. The results were thus repeatable on average to 4.1% and 2.75% for Ni and V, respectively; the repeatability was worst (∼8.5%) for crude oil E, a heavy (viscous) oil with a very high asphaltene content (27.2%). This modified single vessel ashing-digestion technique (combustion, chemical oxidation, acid leaching and storing) minimizes contamination and significantly reduces the loss of ash. Our results are repeatable, comparable to, and in some cases superior to those of other methods. The method is applicable to a wide range of crude oil compositions, is very accessible and robust, easy to use, and does not require costly equipment in preparing the samples for analysis by ICP-MS.

Fully automated focused infrared microashing combined with use of ICP-based instruments for rapid analysis of multiple elements in biological samples.

A fully automated focused infrared microashing sample preparation system was proposed for preparation of biological samples with high organic matter content for the determination of multiple elements combined with inductively coupled plasma optical emission spectroscopy and inductively coupled plasma mass spectrometry. The whole ashing procedure, including sample transfer, carbonization and oxidation of the sample, dissolution of ash, constant volume control, and homogenization of the solution, was automatically controlled. Gold-plated infrared tubes were used to produce and focus infrared radiation to heat the sample. Ozone was used to accelerate the carbonization of samples at a lower temperature to avoid the production of large amounts of empyreumatic oil. In addition, the self-designed double-layer tube serves as a site for ashing and carbonization of the sample and as a container for dissolving ash, as well as for holding the solution. This is the only container in the entire system to reduce the risk of pollution. Eight biological certified reference materials were used as examples to evaluate the performance of the proposed device. A sample ashing pretreatment cycle, from solid sample to liquid solution, took only 40 min and simultaneously treated 12 samples. Except for individual results, the relative errors between the certified values and recorded values for 38 micro and trace elements, including Ca, Mg, Na, P, Li, Be, Sc, Ti, V, Mn, Co, Ni, Cu, Zn, Rb, Sr, Y, Mo, Ag, Cs, Ba, Tl, Th, U, and rare earth elements, were typically less than 30%. The relative standard deviations for five determinations were typically less than 15%. Graphical abstract Automated dry ashing sample preparation system. ICP inductively coupled plasma.