Hot Plate Digestion Research Articles

CCQM-K160: platinum group elements in automotive catalyst

Main textThe platinum group elements (PGEs) play an important role in reducing emissions from automotive vehicles through their use in catalytic convertors but also for catalysis in the pharmaceutical industry. The immense economic value of platinum (Pt), palladium (Pd) and rhodium (Rh) highlights the importance of highly accurate measurements. Therefore, there is a need for National Metrology Institutes (NMIs) and Designated Institutes (DIs) to demonstrate measurement capability in this space.A pilot comparison (CCQM-P63) for precious metals in automotive catalyst took place in 2006, but with a limited number of institutes participating. Furthermore, this study was performed over 17 years ago. Therefore, there was a need to maintain existing capability and demonstrate new capability in a key comparison, in order to claim calibration and measurement capability claims (CMCs). With the core capability matrix, this study falls into the "Difficult to dissolve metals/metal oxides" which will support CMC categories 8 (Metal and metal alloys), 9 (Advanced materials) and 14 (Other materials).Eleven NMIs and DIs participated in the Key Comparison CCQM-K160 Platinum Group Elements in Automotive Catalyst. Participants were requested to evaluate the mass fractions of Pt, Pd and Rh in mg/kg in an unused autocatalyst material (cordierite ceramic base). The Key Comparison Reference Values (KCRVs) and Degrees of Equivalence (DoEs) were calculated utilising the NIST Decision Tree for the measurands. The participants utilised a number of sample preparation and analytical methods including hot plate digestion, microwave digestion and sodium fusion, followed by either atomic absorption spectroscopy (AAS), inductively coupled plasma optical emission spectroscopy (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS) detection. Several calibration techniques were used, namely external calibration, standard addition, isotope dilution mass spectrometry (IDMS) and an exact matching procedure. Additionally, one participant employed instrumental neutron activation analysis (INAA) with k0 standardisation which is a direct solid analysis method. The majority of participants claimed traceability to NIST primary calibrants or their own CRMs. Furthermore, several matrix CRMs were included or spiked samples for quality control. All institutes were required to determine the dry mass fraction using the stipulated protocol.The NIST decision tree was implemented for the calculation of the KCRVs and DoEs. The participant results overall showed good agreement with the KCRV, despite the variety of dissolution procedures and measurement techniques for this highly complex matrix and challenging measurands. Successful participation in CCQM-K160 demonstrated measurement capabilities for the determination of mass fraction of Pt, Pd and Rh in the mg/kg range and will support broad scope CMC claims for a wide range of challenging matrices.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Total Phosphorous and Mineral Content Determination in Rock Phosphates using ICP-MS

ABSTRACT Phosphorous (P) is an essential element for plant growth and development, and its scarcity is a severe crop output constraint. Determination of total P in soil and fertilizers is very important in agriculture as the amount of P is related to crop production. Rock phosphate (RP) is an excellent natural source of P widely used for P fertilizer production. The objective of this study was to compare two different digestion methods, microwave digestion and hot plate digestion, and to evaluate the performance of two analytical techniques, inductively coupled plasma mass spectroscopy (ICP-MS) and colorimetry (UV-VIS), for measuring total P in imported RP samples. The validation of microwave digestion followed by analysis in ICP-MS was performed. Phosphorus has detection and quantification limits of 1 mg L−1 and 5 mg L−1 respectively through ICP-MS analysis. Average P recovery was found 92.12–96.53%. Precision in terms of intra-day (%RSDR = 2.76–5.98 evaluated using ICP-MS) and inter-day (%RSDr = 2.92–6.75) were found to be within the acceptable range (20%), indicating consistency of the proposed method to determine total-P over traditional UV-VIS method. The combination of microwave-assisted digestion and ICP-MS offers superior efficiency in determining both phosphorus (P) and heavy metals, including aluminum, iron, zinc, cadmium, strontium, manganese and chromium, in RP samples. Hence, this method is novel and rapid and is used for the quantification of total P in different RP samples for quality control.

Lead Exposure of Four Biologically Important Common Branded and Non-branded Spices: Relative Analysis and Health Implication.

Technological advances and socioeconomic development of Bangladesh are leading to the best choice between branded and non-branded powdered spices. But toxic metal issues can be another factor to elect them. So lead (Pb) exposure and its consequence on the human body for these two categories of four common spices have been ascertained here. A validated laboratory method using hot plate digestion and flame atomic absorption spectrometry (FAAS) has been used for that. The obtained mean concentration of Pb in branded and non-branded spice powders followed the decreasing order of turmeric > coriander > red chili > cumin powder and turmeric > red chili > cumin > coriander powder, respectively, where, in any analysis mode, the non-branded items are potentially ahead of Pb exposure. The market-based mean concentration between these two categories was not a significant difference (t-test). Approximately 90% of the spice samples have shown within the maximum allowable limit by Bangladesh Standard. The sum of estimated daily intake indicated that most of the city market (67%) for non-branded items and some branded (33%) samples have crossed the maximum tolerable daily intake (> 0.21mg/kg). So, the human health risk assumption for the inhabitant of studied areas suggests there is no significant level of risk for them due to the consumption of spices regarding non-carcinogenic risk factor (THQ and total THQ) and carcinogenic risk factor (CR). But the development of a quality control process for loose spice powders as well as toxic metal screening from raw materials to finish products urgently needed and continuous monitoring with identifying the source of toxic metal is highly recommended.

Simultaneous Determination of Insoluble Fluoride‐Forming and High Field‐Strength Element Abundances in Rock Samples by ICP‐QMS through Isotope Dilution‐Internal Standardisation

A new method for precise measurement of the mass fractions of insoluble fluoride‐forming elements (IFFEs) and high field‐strength elements (HFSEs) in rock samples by ICP‐QMS was developed. Unlike previous methods, in which the two elemental groups are measured separately using two solutions prepared from distinct sample aliquots (i.e., separate methods), this technique prepares a solution by acid digestion from a single sample aliquot, then divides the solution into two fractions that are dedicated to the measurement of IFFEs and HFSEs. The incorporation of IFFEs/HFSEs into insoluble fluorides during HF digestion was overcome by adjusting the Ca‐Al‐Mg composition of the sample by Al addition before acid digestion. The acceptable composition was Ca/(Ca+Al) < 0.43 and Mg/(Mg+Al) < 0.40 with hot plate digestion, whereas the limited condition of Ca/(Ca+Al) < 0.40, Mg/(Mg+Al) < 0.40 and Al/(Mg+Ca) < 1.86 was required for digestion under high pressure and temperature. For samples with an unacceptable composition, the change in Ca‐Al‐Mg composition by Mg/Ca addition should be prohibited because the reaction of HF with the added solution before sample decomposition forms fluorides that coprecipitate HFSEs. The developed method yielded mass fractions consistent with data from the separate methods (± 5%) and achieved a repeatability of < 4% for most elements.

Efficiency of acid digestion procedures for geochemical analysis of tungsten mining wastes

There is an increasing global demand for tungsten, which is a critical element used in various industries. There are millions of tons of current and legacy mineral processing tungsten tailings worldwide that can potentially contaminate the environment and pose human health risks. These tailings could also become valuable resources if we thoroughly characterize their geochemical composition. In this study, an innovative method was developed to achieve the complete digestion of tungsten tailings. We tested three different digestion methods (hotplate digestion, bomb digestion and ColdBlock TM digestion) and compared the results. Additionally, an alkali fusion for major element analysis was applied and tested. The results showed that alkali fusion is the best method for major element analysis, while bomb digestion is best for tungsten and trace element analysis, although volatile chlorite loss was also observed. The hot plate digestion method was not recommended, owing to poor recovery of trace elements compared to the bomb digestion method. The quicker and safer ColdBlock TM digestion method can be used for bismuth, molybdenum, and several rare-earth element analyses, as indicated by their recovery being close to that from the bomb digestion method.

Development of a Single-Step Microwave-Assisted Digestion Method using Dilute Nitric Acid for Determination of Bismuth in Bismuth-containing Pharmaceuticals by Hydride Generation-Atomic Fluorescence Spectrometry

A single-step microwave assisted digestion (MWAD) procedure employing very dilute solutions of HNO3 was developed for the quantitative determination of bismuth in bismuth-containing pharmaceuticals by hydride generation-atomic fluorescence spectrometry (HG-AFS). Experimental parameters affecting MWAD process such as acid concentration (HNO3), digestion time and temperature were optimized to get quantitative recovery of bismuth. The studies indicated that the method is rapid (within 15 min) including cooling time and recovery > 98% was obtained using 10mL of 5% (v/v) HNO3 as digestion medium with ~0.1g of sample. The optimum microwave digestion parameters obtained were: temperature – 180oC, pressure – 25 bar and hold time - 10 min. A clear solution with negligible residue was obtained after microwave digestion. The digested sample solution was appropriately diluted with 2% (v/v) HCl for subsequent analysis by HG-AFS. The reproducibility, expressed as % RSD was lower than 2% for the allopathic medicine. Under optimal conditions, the limit of detection (LOD) for Bi was calculated to be 0.024mg/kg. The methodology was optimized using a bismuth-containing pharmaceutical – Pylobis, purchased from a local pharmacy. The optimized MWAD approach was further applied to few other bismuth-containing pharmaceutical products. The developed method has significant advantages when compared to the conventional hot-plate digestion methods reported for Bi-containing pharmaceuticals, employing large volumes of concentrated acids. These investigations revealed that the proposed MWAD method in combination with HG-AFS can be utilized for the rapid determination of Bi in pharmaceutical products on regular basis.

Determination of Cu, Zn, Ga, Ag, Cd, In, Sn and Tl in Geological Reference Materials and Chondrites by Isotope Dilution ICP‐MS

Mass fractions of Cu, Zn, Ga, Ag, Cd, In, Sn and Tl were determined via isotope dilution quadrupole ICP‐MS in twenty‐one geological reference materials (RMs) and the carbonaceous chondrites Orgueil (CI1), Murchison (CM2) and Allende (CV3). The RMs comprise basaltic/mafic (BCR‐2, BE‐N, BHVO‐1, BHVO‐2, BIR‐1, BRP‐1, JB‐2, OKUM, W‐2, WS‐E), intermediate/felsic (AGV‐2, G‐2, JA‐2, RGM‐1), ultramafic (DTS‐2b, MUH‐1, PCC‐1, UB‐N) and sedimentary (MAG‐1, OU‐6) rocks. Pressure digestion was applied for nonbasaltic samples to ensure effective sample digestion. For basaltic RMs, hot plate digestion was found to be sufficient for a quantitative recovery of the target elements. To minimise interferences and increase ion beam intensities during isotope ratio analyses by ICP‐MS, separation of the target elements was carried out from single sample aliquots using a novel anion exchange procedure. The intermediate precision (2s) estimated from two to four replicate analyses was usually < 4% and results are in agreement with literature data, where available. Especially for Ag and Tl, the intermediate precision was compromised, likely due to low ion beam intensities and, hence, higher background and blank contributions. For ultramafic RMs, nugget effects and incomplete digestion might compromise the intermediate precision. Results for the carbonaceous chondrites Orgueil (CI1), Murchison (CM2) and Allende (CV3) agree well with previously reported data.

Development of a Rapid and Simple Digestion Method of Freshwater Sediments for As, Cd, Cr, Cu, Pb, Fe, and Zn Determination by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES): An Evaluation of Dilute Nitric Acid

ABSTRACT In this study, a simple and rapid methodology based on the hot-plate digestion method using dilute nitric acid solution was used to extract trace metals (such as As, Cd, Cr, Cu, Pb, Fe, and Zn) from freshwater sediments. The concentrations of the elements were determined using inductively coupled plasma-optical emission spectrometry (ICP-OES). The factors (temperature, nitric acid concentration, and volume) affecting the digestion method were optimized using one-factor-at-a-time (OFAT) or univariate methodology, and the optimization process was carried out using freshwater sediment certified reference material (CRM015). The optimal conditions for temperature, nitric acid concentration, and time in the method were 180°C, 10 mL of 5 mol L−1 HNO3, and 45 min, respectively. Under optimum conditions, the limit of detection (LOD) ranged between 0.02 and 0.08 µg L−1 and the limit of quantification (LOQ) ranged from 0.07 and 0.27 µg L−1. In addition, the method detection limits (MDLs) and method quantification limits (MQLs) were 0.10–0.17 and 0.30−0.57 µg g−1, respectively. The overall accuracy of the method determined by recovery of the trace elements in the CRMs ranged from 98 to 111% with the precision ranging from 1.4 to 5.8%. The method was successfully applied for the determination of target metals from real freshwater sediment samples.

A Statistical Review of Alternative Zinc and Copper Extraction from Mineral Fertilizers and Industrial By-Products.

Rapid, accurate, and low-cost alternative analytical methods for micronutrient quantification in fertilizers are fundamental in QC. The purpose of this study was to evaluate whether zinc (Zn) and copper (Cu) content in mineral fertilizers and industrial by-products determined by the alternative methods USEPA 3051a, 10% HCl, and 10% H2SO4 are statistically equivalent to the standard method, consisting of hot-plate digestion using concentrated HCl. The commercially marketed Zn and Cu sources in Brazil consisted of oxides, carbonate, and sulfate fertilizers and by-products consisting of galvanizing ash, galvanizing sludge, brass ash, and brass or scrap slag. The contents of sources ranged from 15 to 82% and 10 to 45%, respectively, for Zn and Cu. The Zn and Cu contents refer to the variation of the elements found in the different sources evaluated with the concentrated HCl method as shown in Table 1. A protocol based on the following criteria was used for the statistical analysis assessment of the methods: F-test modified by Graybill, t-test for the mean error, and linear correlation coefficient analysis. In terms of equivalents, 10% HCl extraction was equivalent to the standard method for Zn, and the results of the USEPA 3051a and 10% HCl methods indicated that these methods were equivalents for Cu. Therefore, these methods can be considered viable alternatives to the standard method of determination for Cu and Zn in mineral fertilizers and industrial by-products in future research for their complete validation.

Extraction Methods for Quantifying Iron, Calcium and Magnesium in a Historic Brickwork Produced During the Spanish Colonial Period in the Philippines

This study demonstrates the feasibility of performing chemical analyses on heritage materials in the Philippines. Four extraction methods were evaluated based on the percentage of iron, calcium and magnesium in a clay brick sample obtained from an old Spanish colonial period church at Ilocos Norte. Aqua regia (1:3 HNO3:HCl, v/v) solvent was used to extract these elements by conventional hot plate digestion. The extraction methods are: digesting the sample directly with aqua regia (M1), sample pre-digested with NH4Cl and ethyl alcohol prior to the actual digestion (M2) and soaking the sample with aqua regia for 24 hours (M3) and 48 hours (M4) before digestion. Atomic absorption spectroscopy (AAS) was employed to quantify the concentration of the intended elements. The percentage composition of iron ranges from 4.193 to 4.418%, calcium from 0.123 to 0.203%, and magnesium from 2.346 to 2.458%, respectively. Energy-dispersive X-ray spectroscopy (EDX) analysis was done to support the data obtained from AAS. M1 was more effective in extracting calcium from the brick sample, while M2, M3 and M4 were useful for extracting iron and magnesium. Infrared spectroscopy (IR) provided a basic mineralogical composition of the sample, with peaks that were attributed to quartz, kaolinite, calcite, silicates and hematite.

Assessing Heavy Metals Pollution in the Agricultural Lands of Gaza Strip that Has Undergone Three Successive Wars

The intensive airstrikes on agricultural lands in the Gaza Strip create craters of 20 m diameter and 10 m depths. Samples from the craters are collected from fourteen different locations, were analyzed to assess the impact of war activities on soil pollution. Soil samples were analyzed for major heavy metals (Ni, Cr, Cu, Mn, Co and Pb) by using hotplate digestion and A Perkin-Elmer Analyst 600 GF-AAS analyzer, equipped with pyrolytically coated graphite tube with integrated platform Zeeman background and correction. The results showed that most of the soils had mean Ni concentration that was over four times higher than the control, Cr was five times, Cu was thirty one times higher, Mn was greatly higher than the control (114 times), Co was five times higher while Pb was twelve times higher than the control. Due to its texture, some samples from sandy soil origins had not significant higher metals concentration than the control. Ni, Cr, Cu, Mn, Co and Pb clearly contributed by the content of munitions of the airstrike. Soil pollution by Cu, Mn and Pb was more widespread than the other heavy metals, which was contributed mostly by munitions. The results also indicate that the concentration of specific heavy metals depends on the type of the explosives material and the soil texture. The current research highlighted the danger and risk of munitions on the agricultural lands. It is highly recommend for the relevant institutions to monitor and follow up research program to investigate the fate of the metals in soil, groundwater and food chain to protect the environment and health.

Gravimetric preparation and characterization of primary reference solutions of molybdenum and rhodium.

Gravimetrically prepared mono-elemental reference solutions having a well-known mass fraction of approximately 1g/kg (or a mass concentration of 1g/L) define the very basis of virtually all measurements in inorganic analysis. Serving as the starting materials of all standard/calibration solutions, they link virtually all measurements of inorganic analytes (regardless of the method applied) to the purity of the solid materials (high-purity metals or salts) they were prepared from. In case these solid materials are characterized comprehensively with respect to their purity, this link also establishes direct metrological traceability to The International System of Units (SI). This, in turn, ensures the comparability of all results on the highest level achievable. Several national metrology institutes (NMIs) and designated institutes (DIs) have been working for nearly two decades in close cooperation with commercial producers on making an increasing number of traceable reference solutions available. Besides the comprehensive characterization of the solid starting materials, dissolving them both loss-free and completely under strict gravimetric control is a challenging problem in the case of several elements like molybdenum and rhodium. Within the framework of the European Metrology Research Programme (EMRP), in the Joint Research Project (JRP) called SIB09 Primary standards for challenging elements, reference solutions of molybdenum and rhodium were prepared directly from the respective metals with a relative expanded uncertainty associated with the mass fraction of U rel(w) < 0.05%. To achieve this, a microwave-assisted digestion procedure for Rh and a hotplate digestion procedure for Mo were developed along with highly accurate and precise inductively coupled plasma optical emission spectrometry (ICP OES) and multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) methods required to assist with the preparation and as dissemination tools.

Nutrient and trace metal distribution in the Gulf of Astakos, Aetoloakarnania, Greece

The Gulf of Astakos is a very important embayment of the Ionian Sea, as it offers an ideal environment for extensive aquacultures with tourism, agriculture and commercial activities. In view of the need for sustainable development of the region, the state of the gulf's quality was assessed on the basis of determinations of nutrients (NO3 -, NO2 -, PO4 3-, SiO4 4-, and NH4 +) and trace metals (Cd, Cu, Fe, Pb, Ni and Zn) along with physicochemical parameters in the seawater. The samples were collected in three sampling cruises during February 2000, May 2000 and July 2000 from ten sampling stations. Nutrients were determined by standard colorimetric methods UV-Vis, using a Varian spectrophotometer. Dissolved metals were pre-concentrated using Chelex-100 resin. Particulate metals were digested following a hot plate digestion in teflon bombs. Metal concentrations were determined by Flame or Graphite Furnace Atomic Absorption techniques with a Varian spectrometer equipped with Zeeman background correction according to the concentration levels. Seasonal fluctuations were recorded in both nutrient and metal concentrations presenting proportional fluctuations with those of the marine euphotic zones. The reduction of concentrations can be attributed to the low rainfall seasonal height, the reduced flow of the streams and in the bioaccumulation and consumption from the phytoplankton cells that bloomed during spring and early summer.

A single procedure for the accurate and precise quantification of the rare earth elements, Sc, Y, Th and Pb in dust and peat for provenance tracing in climate and environmental studies

The geochemical provenancing of atmospheric dust deposited in terrestrial archives such as peat bogs using trace elements is central to the study of atmospheric deposition over the continents and at the heart of many climate and environmental studies. The use of a single digestion method on all sample types involved in such a study (dust archive and sources) minimizes the contribution of the total analytical error when comparing sample compositions and attributing a source to the deposited dust. To date, this factor is limiting progress in geographical areas where the compositional variations between the sources and within the archive are small. Here, seven microwave and hot plate digestion methods were tested on rock, soil and plant reference materials to establish a unique method optimizing precision and accuracy in all sample types. The best results were obtained with a hot plate closed-vessel digestion with 2ml HF and 0.5ml HNO3 for 0.1g of sample, which allowed the precise, accurate and low blank quantification of the trace elements La–Yb, Sc, Y, Th and Pb by ICP-MS. This method was tested in a climate study in central Asia and temporal changes in the dominant dust source were for the first time successfully linked to changes in atmospheric circulation patterns above this region.

Interlaboratory evaluation of trace element determination in workplace air filter samples by inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) is becoming more widely used for trace elemental analysis in the occupational hygiene field, and consequently new ICP-MS international standard procedures have been promulgated by ASTM International and ISO. However, there is a dearth of interlaboratory performance data for this analytical methodology. In an effort to fill this data void, an interlaboratory evaluation of ICP-MS for determining trace elements in workplace air samples was conducted, towards fulfillment of method validation requirements for international voluntary consensus standard test methods. The study was performed in accordance with applicable statistical procedures for investigating interlaboratory precision. The evaluation was carried out using certified 37-mm diameter mixed-cellulose ester (MCE) filters that were fortified with 21 elements of concern in occupational hygiene. Elements were spiked at levels ranging from 0.025 to 10 μg filter(-1), with three different filter loadings denoted "Low", "Medium" and "High". Participating laboratories were recruited from a pool of over fifty invitees; ultimately twenty laboratories from Europe, North America and Asia submitted results. Triplicates of each certified filter with elemental contents at three different levels, plus media blanks spiked with reagent, were conveyed to each volunteer laboratory. Each participant was also provided a copy of the test method which each participant was asked to follow; spiking levels were unknown to the participants. The laboratories were requested to prepare the filters by one of three sample preparation procedures, i.e., hotplate digestion, microwave digestion or hot block extraction, which were described in the test method. Participants were then asked to analyze aliquots of the prepared samples by ICP-MS, and to report their data in units of μg filter(-1). Most interlaboratory precision estimates were acceptable for medium- and high-level spikes (RSD <25%), but generally yielded greater uncertainties than were anticipated at the outset of the study.

A novel approach for determining total titanium from titanium dioxide nanoparticles suspended in water and biosolids by digestion with ammonium persulfate

Titanium dioxide (i.e. TiO 2) in nano-form is a constituent of many nanomaterials that are used in sunscreens, cosmetics, industrial products and in biomedical applications. Quantification of TiO 2 nanoparticles in various matrixes is a topic of great interest for researchers studying the potential health and environmental impacts of nanoparticles. However, analysis of TiO 2 as Ti 4+ is difficult because current digestion techniques require use of strong acids that may be a health and safety risk in the laboratory. To overcome this problem, we developed a new method to digest TiO 2 nanoparticles using ammonium persulfate as a fusing reagent. The digestion technique requires short times to completion and optimally requires only 1 g of fusing reagent. The fusion method showed >95% recovery of Ti 4+ from 6 μg mL −1 aqueous suspensions prepared from 10 μg mL −1 suspension of different forms of TiO 2, including anatase, rutile and mixed nanosized crystals, and amorphous particles. These recoveries were greater than open hot-plate digestion with a tri-acid solution and comparable to microwave digestion with a tri-acid solution. Cations and anions commonly found in natural waters showed no significant interferences when added to samples in amounts of 10 ng to 110 mg, which is a much broader range of these ions than expected in environmental samples. Using ICP-MS for analysis, the method detection limit (MDL) was determined to be 0.06 ng mL −1, and the limit of quantification (LOQ) was 0.20 ng mL −1. Analysis of samples of untreated and treated wastewater and biosolids collected from wastewater treatment plants yielded concentrations of TiO 2 of 1.8 and 1.6 ng mL −1 for the wastewater samples, respectively, and 317.4 ng mg −1 dry weights for the biosolids. The reactions between persulfate ions and TiO 2 were evaluated using stoichiometric methods and FTIR and XRD analysis. A formula for the fusing reaction is proposed that involves the formation of sulfate radicals.

Separation and Measurement of Pa, Th, and U Isotopes in Marine Sediments by Microwave-Assisted Digestion and Multiple Collector Inductively Coupled Plasma Mass Spectrometry

This manuscript describes a new protocol for determination of Pa/Th/U in marine sediments. It is based on microwave-assisted digestion and represents an important reduction of working time over conventional hot-plate digestion methods, and the use of HClO(4) is avoided. Although Th and U are completely dissolved with a first microwave step, around 40% of (231)Pa remains undissolved, and a short hot-plate step with reverse aqua regia is required to achieve total digestion and spike equilibration. Next, the method involves a separation of these elements and a further purification of the Pa fraction using Dowex AG1-X8 resin. Separation with Bio-Rad and Sigma-Aldrich resins was compared; although both perform similarly for Th and U, Pa yields are higher with Bio-Rad. Finally, samples are measured using a Nu instruments multiple collector inductively coupled plasma mass spectrometer (MC-ICPMS). Overall chemical yields range around 50% for Pa, 60% for Th, and 70% for U.

Comparative study of hotplate wet digestion methods for the determination of mercury in biosolids

The re-use of biosolids is becoming increasingly popular for land applications. However, biosolids may contain elevated levels of metals and metalloids (including mercury) relative to background environmental concentrations. Consequently, reliable mercury analysis is important to allow classification of biosolids and to determine appropriate options for beneficial uses.This paper reports on a comparative study of 12 hotplate wet digestion methods for their suitability for the determination of mercury in biosolids. The methods were applied to mercury biosolids samples from four localities of two different sewage treatment plants in the State of Victoria, Australia. Samples were also spiked with methylmercury chloride and mercury sulphide to evaluate the Hg recovery in each hotplate digestion method. Aqua regia (HCl:HNO3=3:1), reverse aqua regia (HCl:HNO3=1:3), nitric, hydrochloric, sulphuric acid and their combinations with or without hydrogen peroxide were studied as wet digestion solutions. The method providing the best mercury recoveries was optimized. Under optimal conditions the corresponding analytical procedure consisted of 1h pre-digestion of 0.4g biosolids sample with 10ml reverse aqua regia with temperature increasing to 110°C and 3h digestion at this temperature. In the last 10min of the digestion step, 2ml hydrogen peroxide were added to ensure complete decomposition of all mercury containing compounds. After filtering and dilution with deionised water (1:10), the concentration of mercury was determined by cold vapour atomic absorption spectrometry.It is expected, that the wet acid digestion method developed in this study will be also applicable to biosolids from other sewage treatment plants and to other types of solid mercury samples with elevated levels of organic matter.

Nitric acid dissolution of large mixed cellulose ester filters for beryllium determination

Defense program use of beryllium has resulted in the need for a wide variety of sampling methods to assess the potential for airborne beryllium particulates. One technique employed in field sampling uses large (8 × 10 in.) mixed cellulose ester (MCE) filters in high volume air samplers. Standard methods for the acid digestion and analysis of the large MCE filters cannot be utilized as the increase in filter mass leads to an uncontrolled exothermic reaction (open flames). As this compromises data quality and presents a significant safety hazard, we propose here an alternative method for digesting these large filters to ensure a solution compatible with ICP-AES (inductively coupled plasma-atomic emission spectroscopy) analysis. The method is a modification of well accepted hot plate digestion methods, which avoids the use of the most hazardous acids such as perchloric or hydrofluoric. While only beryllium was investigated, it is likely that other metals on filters could be digested by this method. Filter media were spiked with a variety of beryllium sources to test the digestion, including beryllium solution spikes, beryllium metal, beryllium oxide and beryllium in soil. Recovery of beryllium metal (103%), beryllium in soil (96%) and beryllium solution spikes (93%) were excellent.

Biosolids compost amendment for reducing soil lead hazards: a pilot study of Orgro® amendment and grass seeding in urban yards

In situ inactivation of soil Pb is an alternative to soil removal and replacement that has been demonstrated in recent years at industrial sites with hazardous soil Pb concentrations. Most children exposed to elevated soil Pb, however, reside in urban areas, and no government programs exist to remediate such soils unless an industrial source caused the contamination. Modern regulated biosolids composts have low Pb concentrations and low bioaccessible Pb fractions and can improve grass growth on urban soils. High Fe and P biosolids composts can reduce the bioavailability and bioaccessibility of soil Pb and can aid in establishing vegetation that would reduce soil transfer into homes. For these reasons, we conducted a field test of their use to reduce Pb bioaccessibility in urban soils in Baltimore, MD USA. We chose biosolids compost for its expected reduction in the bioaccessible Pb fraction of urban soils, ease of use by urban residents, and ability to beautify urban areas. Nine urban yards with mean soil Pb concentrations >800 mg Pb kg −1 were selected and sampled at several distances from the house foundation before soil treatment. The soils were rototilled to 20 cm depth to prepare the sites, and resampled. The yards were then amended with 6–8 cm depth of Orgro® biosolids compost (110–180 dry t/ha) rich in Fe and P, mixed well by rototilling, and resampled. Kentucky bluegrass ( Poa pratensis) was seeded and became well established. Soils were resampled 1 year later. At each sampling time, total soil Pb was measured using a modified U.S. EPA nitric acid hotplate digestion method (SW 846 Method 3050) and bioaccessible Pb fraction was measured using the Solubility/Bioaccesibility Research Consortium standard operating procedure with modifications, including the use of glycine-buffered HCl at pH 2.2. Samples of untreated soils were collected from each yard and mixed well to serve as controls for the Pb bioaccessibility of field treated soils over time independent of positional variance within yards. At 1-year post-treatment, grass cover was healthy and reductions in bioaccessible Pb concentrations compared to pre-tillage were 64% (from 1655 to 595 mg kg −1) and 67% (from 1381 to 453 mg kg −1) at the sampling lines closest to the houses. Little or no reduction in bioaccessible Pb concentration was observed at sampling lines more remote from the house that also had the lowest bioaccessible Pb concentrations at pre-tillage (620 and 436 mg kg −1, respectively). For the control soils, changes over time in total Pb and bioaccessible Pb concentrations and the bioaccessible Pb fraction were insignificant. This study confirms the viability of in situ remediation of soils in urban areas where children are at risk of high Pb exposure from lead in paint, dust and soil.