Trace metal analysis of coal fly ash collected plain and on a quartz fibre filter

A simple, uniform procedure has been developed for microwave-based digestion of fly ash samples collected from the hoppers of an electrostatic precipitator (ESP), or collected from flue gases on a heat-resistant quartz fibre filter and for subsequent atomic absorption spectrometric analysis of trace metals (Be, Cd, Co, Cr, Cu, Mn, Ni, Pb, V and Zn). HNO(3), HCl, HF and mixtures have been tested as digestion acids. The combination of HNO(3) and HF has been found to be efficient for the digestion of fly ash samples with and without quartz fibre filter material. In spite of the complicated matrix, results with satisfactory accuracy and precision (relative standard deviation below 10% for most of the elements) have been obtained. In the case of analysis of fly ash together with a quartz fibre filter, the calibration curve has to be determined by standard addition to a blank solution containing a dissolved blank quartz fibre filter.     

A Sequential Extraction Method Measures the Toxic Metal Content in Fly Ash from a Municipal Solid Waste Incinerator

The purpose of this research was to develop an optimized pretreatment procedure for toxic metals (Pb, Cd, Zn and Cu) content in fly ash from a municipal waste incinerator. In addition, modified sequential extraction procedures were used to characterize the chemical composition of the fly ash samples. The sequential extraction resolved the fly ash elements into the following chemical forms: soluble, exchangeable, carbonate, oxide, organic, and silicate compounds. Certified reference city waste incineration ash (BCR.176) was used as target ash samples. A H₂O₂+HNO₃+HF mixed acid digestion solution with a low temperature evaporation procedure was selected as optimal for the fly ash digestion. The digested solution was analyzed by inductively coupled plasma mass spectrometry (ICP‐MS), which effectively determined the concentrations of the toxic metal elements in BCR.176. Except for Cd, the recovery of Pb, Zn, and Cu under H₂O₂+HNO₃+HF digestion and their sequential extraction procedures were higher than 95%. The relative standard deviations (RSD) for recoveries of the four elements were within 10%. Furthermore, the sequential extraction procedure's results provided information on the potential mobility of the studied elements. Most of the Cd was bound to water‐soluble and carbonate material in the fly ash samples. Most of the Pb, Zn, and Cu was released to carbonates and bound to organic matter in the fly ash samples.     

Determination of trace elements in fly ash samples by FAAS after applying different digestion procedure

The fly ash samples obtained from Kangal Power Plant were prepared for FAAS analysis by a new approach. The trace elements of the fly ash samples were leached with appropriate solvents under suitable conditions. The leaching method is known as an effective technique for substances dissolving very hard and refractory materials. The leaching effects of solvents and their mixtures were investigated on fly ash samples that are used largely in analysis of soil and sediment samples.The fly ashes mainly consist of glassy aluminosilicates. The major components of the samples are SiO₂, Al₂O₃, CaO and Fe₂O₃. Therefore, decomposition of the silicate lattice of the fly ash is required for liberation of trace elements. The dissolution process can be completed by using a mineral acid such as concentrated HCl. This technique has an advantage that the fly ash can be dissolved without any oxidation at room temperature.Maximum element recoveries were obtained by the procedure of 37% HCl leaching after the samples were treated with 2.0 ml of concentrated HF. It was also observed that maximum mass loss occurred in this procedure. The effect of the four leaching reagents, which are HCl, HNO₃, HClO₄ and HNO₃ + HClO_4, were investigated on fly ash samples that were treated with concentrated HF. An optimum leaching method was determined based on the confidence of analytical results and element recovery rates.     

Ultrasonic dissolution for ICP-MS determination of trace elements in lightly loaded airborne PM filters

A simple single-step ultrasonic dissolution procedure for low mass (<1?mg) particulate matter (PM) filter samples using HNO₃–HF acid solution is proposed for multi-element determination using ICP-MS. The PM-loaded PTFE filter samples are inserted directly into disposable centrifuge tubes for acid extraction using ultrasonic digestion (UD). Potential interferences owing to contamination and element loss are minimized. Key factors influencing element recoveries are investigated, including digestion solution composition, acid concentration, temperature, and matrix interferences. Optimized conditions for UD include an acid mixture consisting of 4.0?mL HNO₃ and 0.1?mL HF with ultrasonication proceeding at 90°C for one hour, followed by 10-fold dilution. Recoveries of 80–120% are achieved for almost all of the 20 elements tested (Be, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Ag, Cd, Sb, Ba, Pb and U) in four standard reference materials with contrasting matrices: NIST 1648 (urban PM), NIST 2584 (indoor dust), NIST 2710 (soil), and NIST 1633b (coal fly ash). The exception is Cr in NIST 1648 for which recovery is low (30%) using this method. Element concentrations obtained for PM-loaded filter samples using the proposed UD?+?ICP-MS method agree with results obtained using energy dispersive X-ray fluorescence (paired t-test p?>?0.2; 95% CI).     

Comparative study of different digestion procedures using supplementary analytical methods for multielement-screening of more than 50 elements in sediments of the river Elbe

The suitability of four different digestion procedures, i.e. i.) an aqua regia digestion according to DIN 38 414-S7, ii.) a pressure digestion using HNO₃/HF in PTFE-vessels, iii.) a HNO₃/HF + HCl-pressure digestion in PTFE-vessels and iv.) a HNO₃/HF + HCl-pressure digestion using microwave induction, has been evaluated with regard to the quantitative determination of about 50 elements in environmental samples. Three sediments of the river Elbe and two standard reference materials (MESS-1 and NIST 1645) have been employed. The analytical results from the dissolved samples, obtained using inductively coupled plasma mass- and optical emission spectrometry as well as total reflection X-ray fluorescence spectrometry, have been compared with those obtained by instrumental neutron activation analysis. Only digestion procedures using HNO₃/HF with a subsequent evaporation to dryness and dissolution in HCl have led to appropriate results for a wide range of elements (more than 50 elements in total). Because of its low contamination risk and its time saving, the microwave digestion is preferred. For this digestion procedure the accordance among the different instrumental methods used is high (better than 15% deviation) in general. A few elements (16) could be determined quantitatively only by a single method.     

Multielement characterization of soil samples with ICP-MS for environmental studies

The recovery of trace elements of ecotoxic importance has been studied on certified soil and sediment reference samples after pressurized digestions with HNO₃, HNO₃+HF and HNO₃+HCl+HF mixtures, respectively. The acid digests have been analyzed by ICP-MS. The results indicate that digestion with nitric acid alone is satisfactory for the recovery of As, Cd, Co, Cu and Zn. Cr and Pb showed lower recoveries with HNO₃ alone but addition of HF improved their extraction. With appropriate corrections, ICP-MS can be used for the routine analysis of soils and sediments. These digestion procedures, evaluated based on reference samples, have been used for the trace element characterization of soil samples from the German Environmental Specimen Bank.     

A rapid ultrasound-assisted thiourea extraction method for the determination of inorganic and methyl mercury in biological and environmental samples by CVAAS

A rapid ultrasound-assisted extraction procedure for the determination of total mercury, inorganic and methyl mercury (MM) in various environmental matrices (animal tissues, samples of plant origin and coal fly ash) has been developed. The mercury contents were estimated by cold vapour atomic absorption spectrometry (CVAAS). Inorganic mercury (IM) was determined using SnCl₂ as reducing agent whereas total mercury was determined after oxidation of methyl mercury through UV irradiation. Operational parameters such as extractant composition (HNO₃ and thiourea), sonication time and sonication amplitude found to be different for different matrices and were optimized using IAEA-350 (Fish homogenate), IM and MM loaded moss and NIST-1633b (Coal fly ash) to get quantitative extraction of total mercury. The method was further validated through the analysis of additional certified reference materials (RM): NRCC-DORM2 (Dogfish muscle), NRCC-DOLT1 (Dogfish liver) and IAEA-336 (Lichen). Quantitative recovery of total Hg was achieved using mixtures of 5% HNO₃ and 0.02% thiourea, 10% HNO₃ and 0.02% thiourea, 20% HNO₃ and 0.2% thiourea for fish tissues, plant matrices and coal fly ash samples, respectively. The results obtained were in close agreement with certified values with an overall precision in the range of 5-15%. The proposed ultrasound-assisted extraction procedure significantly reduces the time required for sample treatment for the extraction of Hg species. The extracted mercury species are very stable even after 24 h of sonication. Closed microwave digestion was also used for comparison purposes. The proposed method was applied for the determination of Hg in field samples of lichens, mosses, coal fly ash and coal samples     

Comparative study of bulk and partial digestion methods for airborne PM10-bound elements in a high mineral dust urban site in Constantine,Algeria

When high mineral loads in atmospheric particulate matter (PM) are present, particular attention should be paid to the selection of appropriate acidic digestion protocols for wet chemical analysis. We report on a comparative study of elemental recovery yields from five different pre-analytical acid digestion procedures for mineral-rich urban background PM₁₀ samples collected in the city of Constantine (Northeastern Algeria). Five reference materials (NIST 1633b, UPM 1648, NAT-7, SO-2 and SO-4) were also digested according to the same protocols. The selected acidic digestion/extraction procedures are widely used for PM chemical analysis and comprise P1 (HNO₃/HF/HCl), P2 (HCl/HNO₃), P3 (HCl/H₂O₂/HNO₃), P4 (HNO₃/HF/HClO₄) and P5 (HNO₃/H₂O₂); the latter assisted with microwave digestion. Elemental recovery yields were compared for major and trace elements typically determined in PM for source apportionment analysis and the results evidenced large differences. For most elements, the bulk extraction procedures (requiring the use of HF) allowed a full elemental recovery, particularly for elements that are associated with aluminium silicate species and oxides that are resistant to mild acid attack. In contrast, in the extraction protocols without HF low recovery yields were obtained for elements such as Al, Ti, Zr, Sc and other aluminium silicate-related elements in PM₁₀ samples with high mineral dust load. We highlight that the European standard digestion method EN-14902:2005 should be applied specifically for the metals for which this method was developed, but caution should be taken when the analysis of other elements in PM is required, especially in urban areas where road and vehicle wear dust is likely to be a major component of ambient PM. When using wet chemistry analysis for PM source apportionment studies, we strongly recommend HF bulk dissolution of samples to ensure the reliability of the geochemical information when coupled with an appropriate analytical tool.     

Influence of digestion methods on the determination of total Al in food samples by ICP-ES

Summary To determine total Al in a variety of food and total diet samples using ICP-ES, HF pre-treatment, prior to wet digestion (HNO₃/HClO₄) seems to be necessary. Compared with results obtained after HF pre-treatment, the determination of Al using pressure microwave digestion with HNO₃ or HNO₃/HClO₄ digestion recovered only between 25–50% Al for dried spinach and flour and 40–75% for total diet samples, respectively. In most cases the addition of 0.25 ml HF (40%) per gram dry mass resulted in maximum Al yield. The results are in acceptable agreement with those obtained by neutron activation analysis (NAA).     

Determination of total chromium in terrestrial and marine samples by electrothermal atomic absorption spectrometry after pressure digestion

A comparison between two commonly used sample digestion procedures was performed for the determination of total chromium in biological matrices. Ten reference materials (terrestrial and marine matrices) have been digested in HNO₃, HNO₃ + HClO₄ and HNO₃ + HF, respectively, under pressure in quartz vessels of a high pressure asher (HPA) or in PTFE bombs with external heating. Much lower chromium values than expected were obtained in most of the reference materials by using quartz vessels with nitric acid because of adsorption of chromium at quartz surfaces. Determinations after sample digestion in PTFE vessels with external heating showed expected results, except in some reference materials which precipitated more silica. An improvement of the results was observed by using a mixture of nitric acid and perchloric acid, but only the combination of nitric acid and a small amount of HF provided the desired results in all the reference materials studied. Received: 29 January 1997 / Revised: 20 May 1997 / Accepted: 22 May 1997     

Determination of total chromium in terrestrial and marine samples by electrothermal atomic absorption spectrometry after pressure digestion

A comparison between two commonly used sample digestion procedures was performed for the determination of total chromium in biological matrices. Ten reference materials (terrestrial and marine matrices) have been digested in HNO₃, HNO₃ + HClO₄ and HNO₃ + HF, respectively, under pressure in quartz vessels of a high pressure asher (HPA) or in PTFE bombs with external heating. Much lower chromium values than expected were obtained in most of the reference materials by using quartz vessels with nitric acid because of adsorption of chromium at quartz surfaces. Determinations after sample digestion in PTFE vessels with external heating showed expected results, except in some reference materials which precipitated more silica. An improvement of the results was observed by using a mixture of nitric acid and perchloric acid, but only the combination of nitric acid and a small amount of HF provided the desired results in all the reference materials studied. Received: 29 January 1997 / Revised: 20 May 1997 / Accepted: 22 May 1997     

The Determination of Co in Plant Materials by Radiochemical Neutron Activation Analysis

The influence of irradiation conditions on the results of Co determination in plant samples by radiochemical neutron activation analysis (RNAA), after the conventional and microwave assisted wet digestion, has been investigated. Nine CRMs of botanical origin were examined. The study has demonstrated that the effectiveness of mineralization depended significantly on the kind of sample and the irradiation conditions. When analyzed CRMs were subjected to long-term irradiation in a high neutron flux, the mineralization using the microwave technique was necessary to obtain the correct results of Co determination in some of the plant samples. It has been proved that microwave digestion in a mixture of HNO₃+H₂O₂+HF should be a standard method of wet ashing, independent on matrix and irradiation conditions.     

Ultrasound-assisted extraction of gold and silver from environmental samples using different extractants followed by electrothermal-atomic absorption spectrometry

Ultrasound-assisted extraction combined with electrothermal-atomic absorption spectrometry has been applied to the determination of silver and gold at μg g^{− 1} levels in different environmental samples such as soil, sediment, fly ash and industrial sludge. Two different extraction systems have been tried, i.e. acid mixtures (HCl, HF, and HNO₃) and thiourea in diluted H₂SO₄ medium. In both cases, an efficient cup-horn sonoreactor was used as ultrasonic device to accelerate the extraction process. This ultrasonic processor allows the use of any extractant including HF and simultaneous treatment of up to six samples. Recovery ranged from 81% to 107% for silver, and from 91% to 105% for gold. Optimal acid mixtures were 25% v/v HNO₃ + 25% v/v HF for Ag and 25% v/v HNO₃ + 25% v/v HCl for Au. The thiourea method required 0.6% m/v thiourea + 2% v/v H₂SO₄. The latter method was considered advantageous since efficient Au and Ag extractions were obtained in a short time, and moreover, wastes generated were less harmful to the environment. Limits of detection for Ag and Au were 0.012 and 0.050 μg g^{− 1}, respectively. Repeatability expressed as relative standard deviation ranged from 2 to 10% for both metals. Both extraction methods were applied to the determination of Au and Ag in sediments and soils located at different sampling points from Galicia (Spain).     

Application of ICP-AES to the determination of rare earth elements in phosphate samples

Summary ICP-AES has been used for the determination of rare earth elements (REE) in samples of phosphorite deposits collected from the Western Desert, Egypt. Complete dissolution of the samples was achieved by using acid digestion with HF/HNO₃/HCl in a PTFE closed vessel and subsequent treatment with HClO₄, with the same procedure but with fuming HCl replacing HClO₄ and with HNO₃ and fuming HCl in a quartz vessel and subsequent treatment with HF/HClO₄/HNO₃. Analysis lines for La, Ce, Pr, Nd, Sm, Gd, Dy and Y were selected after study of the spectral interferences for the sample types concerned. Results revealed that the average total content of the REE, which could be directly determined in the present samples, varies between 1.08 and 1.53 mg/g, whereas individual element concentrations range from 40 to 300 g/g. Analysis results obtained with the different dissolution techniques were found to be in good agreement. On leave from the National Research Centre, Physics Department — Spectroscopy Laboratory, Cairo, Egypt     

Simultaneous Determination of 11 Elements in Fly Ash by Inductively Coupled Plasma Orthogonal Acceleration Time-of-Flight Mass Spectrometry After Closed-Vessel Microwave-Assisted Extraction with Ammonium Fluoride

A method for simultaneous multi-element analysis of fly ash samples by inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry (oaTOF-ICP-MS) after closed-vessel microwave extraction with ammonium fluoride was introduced here. Corrosive and/or toxic acids like HF, HCl or HClO₄, as well as HNO₃, which are commonly used during sample preparation of the fly ash samples, are avoided in this method. The spectral effects due to the formation of different Cl, Na, K, Ca, Mg-containing polyatomic species interfering with the determination of a number of elements like As, Se or Ni during the oaTOF-ICP-MS analysis are negligible. Under the optimum experimental extraction conditions evaluated using a fractional factorial design (10 mg of the sample extracted with 5 mL of 140 g/L NH₄F for 10 min at 200°C), analysis of the resulting supernatant with Rh as an internal standard enabled precise and accurate simultaneous determination of 11 elements (Li, Be, Ni, As, Se, Rb, Sb, Cs, W, Tl and U) at trace and ultratrace levels. The accuracy was assessed by analysing two certified reference materials, namely Fine Fly Ash CTA-FFA-1 and Constituent Elements in Coal Fly Ash Standard Reference Material® 1633b. The precision of the reported method was better than 10%.     

Assessment of three digestion procedures for Zn contents in Pakistani soil by flame atomic absorption spectrometry

Evaluation of three different digestion procedures for accurate determination of elemental concentration in soils was undertaken. The digestion procedures, two leaching and a total dissolution processes were compared for twenty-one soil samples. The soil standard reference materials (SRMs), IAEA Soil-5 and IAEA Soil-7 were analysed for quality control purposes. Zinc (Zn) was analysed using flame atomic absorption spectrometry (FAAS). Precise analysis was accomplished in the SRM and soil samples, which was better than 4.7% for leaching and total dissolution procedure. Compared with the elemental concentration in soil samples, HF–HClO₄ procedure achieved greater accuracy, where as HNO₃–H₂O₂ and HNO₃–H₂SO₄–HCl procedures were comparable with slight variation in a few samples.     

Analytical evaluation of a cup-horn sonoreactor used for ultrasound-assisted extraction of trace metals from troublesome matrices

In this work, a sample preparation method based on ultrasound-assisted extraction of trace metals from a variety of biological and environmental matrices using a cup-horn sonoreactor is described. Diluted acids (HNO₃, HCl and HF) and oxidants (H₂O₂) were tried for extraction, the extracts being directly analyzed by electrothermal-atomic absorption spectrometry. The cup-horn sonoreactor combines the advantages of probe and bath sonicators, allowing a variety of conditions to be used for metal extraction from troublesome matrices. This system facilitates the use of HF to destroy the silicate lattice, application of simultaneous treatments of up to six samples and short treatment times. Quantitative metal recoveries are achieved from different matrices (animal and vegetal tissues, soil, sediment, fly ash, sewage sludge) under a set of extraction conditions ranging from the use of 3 min sonication time and 3% volume/volume HNO₃ for some animal tissues to 40 min sonication time along with 5% volume/volume HNO₃ + 20% volume/volume HF for sediment. Vegetal matter required the use of 5% volume/volume HNO₃ + 5% volume/volume HF for extraction of some elements.     

Characterization and determination of 28 elements in fly ashes collected in a thermal power plant in Argentina using different instrumental techniques

Different techniques were selected for comprehensive characterization of seven samples of fly ashes collected from the electrostatic precipitator of the San Nicolás thermal power plant (Buenos Aires, Argentina). Particle size was measured using laser based particle size analyzer. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the mineral phase present in the matrix consisting basically of aluminosilicates and large amounts of amorphous material. The predominant crystalline phases were mullite and quartz. Major and minors elements (Al, Ca, Cl, Fe, K, Mg, Na, S, Si and Ti) were detected by energy dispersive X-ray analysis (EDAX). Trace elements (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, V and Zn) content was quantified by inductively coupled plasma optical emission spectrometry (ICP OES). Different acid mixtures and digestion procedures were compared for subsequent ICP OES measurements of the dissolved samples. The digestion procedures used were: i) a mixture of FH + HNO₃ + HClO₄ (open system digestion); ii) a mixture of FH + HNO₃ (MW-assisted digestion); iii) a mixture of HF and aqua regia (MW-assisted digestion). Instrumental neutron activation analysis (INAA) was employed for the determination of As, Ba, Co, Cr, Ce, Cs, Eu, Fe, Gd, Hf, La, Lu, Rb, Sb, Sc, Sm, Ta, Tb, Th, U and Yb. The validation of the procedure was performed by the analysis of two certified materials namely, i) NIST 1633b, coal fly ash and ii) GBW07105, rock. Mean elements content spanned from 41870 μg g^− 1 for Fe to 1.14 μg g^− 1 for Lu. The study showed that Fe (41870 μg g^− 1) ? V (1137 μg g^− 1) > Ni (269 μg g^− 1) > Mn (169 μg g^− 1) are the main components. An enrichment, with respect to crustal average, in many elements was observed especially for As, V and Sb that deserve particular interest from the environmental and human health point of view.     

Comparison of microwave digestion procedures for the determination of some elements in asphaltite ash using ICP-AES

A microwave digestion procedure for asphaltite ash was developed in an attempt to facilitate routine analysis and obtain reproducible conditions or comparable results. The conditions of the most effective procedure for 0.1 g asphaltite ash samples are 1 ml of HNO3 + 3 ml of HCl + 1 ml of HF + 1 ml of deionized water as acid mixture and 15 min for digestion time. The digestion was accomplished in five stages applying continuously 90% to 20% of the microwave power and 20 to 100 psi of the pressure for 10 min of total time. Concentrations of selected elements, Cr, Co, Fe, Mn, Ni and Zn were measured using inductively coupled plasma-atomic emission spectroscopy. The proposed method of digestion provided precise results with relative standard deviations generally less than 3% for investigated elements. Results for fly ash as standard reference material was in good agreement with certified values.     

Determination of metal concentrations in lichen samples by inductively coupled plasma atomic emission spectroscopy technique after applying different digestion procedures

Three digestion procedures have been tested on lichen samples for application in the determination of major, minor and trace elements (Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V and Zn) in lichen samples collected in Aegean Region of Turkey by inductively coupled plasma atomic emission spectrometer (ICP-AES). The acid mixture of concentrated HNO₃, H₂O₂ and HF were used. The instrument was optimized using lichen matrix considering RF power, nebulizer pressure, auxiliary flow rate and pump rate. The accuracy of the overall analyses was first estimated by analysis of two certified reference materials. Good agreement between measured and reference values were found for almost all elements. As the second way of determining the accuracy, results obtained from independent analytical techniques (ICP-AES and instrumental neutron activation analysis (INAA)) were compared for all elements by analyzing real samples. Correlation coefficients of two techniques for the elements ranged between 0.70 (Mg) and 0.96 (Fe). Among the three digestion systems, namely microwave, open vessel and acid bomb, microwave digestion system gave the best recovery results. The method detection limit (MDL) was computed using reagent blanks of microwave digestion system since it provides cleaner sample preparation. Detection limit is adequate for all elements to determine the elements in lichen samples. The precision was assessed from the replicate analyses of reagent blanks of microwave digestion system and was found to be less than 1.5% relative standard deviation (R.S.D.).