Ml Of Nitric Acid Research Articles

Comparison of New Ultrasonic Digestion Approaches for Plant Matrices in the Analysis of Trace Metals by Inductively Coupled Plasma–Optical Emission Spectroscopy Analysis: Contrast with USEPA Method 3050B

ABSTRACTAn ultrasonic method using two approaches, A and B, along with a reference Environmental Protection Agency (EPA) Method 3050B [i.e., a mixture of 30 mL of nitric acid–hydrochloric acid–hydrogen peroxide–water (HNO3-HCl-H2O2-H2O)] were contrasted for leaching of a plant matrix. The trace metals were arsenic, cadmium, cobalt, chromium, copper, mercury, manganese, nickel, lead, selenium, and zinc (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Se and Zn) and quantified by ICP-OES followed by an investigation into residue formation and the impact of digestion time. Approach B was the most accurate and precise with percent recoveries ranging between 99 and 120%, whereas ultrasonic approach A and the USEPA method 3050B gave similar results with poor accuracies and precisions. In the optimization of the digestion time using approach B, the total metal recovery was fairly the same over a period of 120 min except for Cr and Cu, which showed slight variations.

Levels of essential and non-essential metals in linseed (<i>Linum usitatissimum</i>) cultivated in Ethiopia

The levels of essential and non-essential metals were determined in linseed (Linum usitatissimum) samples collected in November 2011 from five different sites (Bale, East Gojam, Shoa, South Wello and Tigray) in Ethiopia where its cultivation is common. A 0.5 g dried powdered linseed was digested with 2 mL of nitric acid (HNO3), 1 mL of perchloric acid (HClO4) and 1 mL of hydrogen peroxide (H2O2) at 270 oC for 2:30 hours and the levels of metals determined by flame atomic absorption spectrometer. The accuracy of the optimized procedure was evaluated by analyzing the digest of the spiked samples with standard solution. Recoveries of the spiked samples varied from 91% to 109%. The levels (mg kg-1) of metals determined were in the ranges Na (242–614), K (6,494–6,755), Mg (2,679–3,118), Ca (540–744), Cr (13–30), Mn (17–28), Fe (198–242), Co (23–42), Ni (12–16), Cu (25–45), Zn (29–40), and Pb (12–32). Cd was below method detection limit. K and Fe were with the highest concentration from major and trace metals, respectively. Analysis of variance (ANOVA) at 95% confidence level indicated that there is significant difference in the levels of all metals between the five samples means except K and Ni. The results indicated that Ethiopian linseed is a good source of essential metals and free from the toxic metal Cd but not from Pb. KEY WORDS: Linseed, Linum usitatissimum, Essential metals, Non-essential metals, Ethiopia Bull. Chem. Soc. Ethiop. 2014, 28(3), 349-362.DOI: http://dx.doi.org/10.4314/bcse.v28i3.4

On-line flow injection solid phase extraction using imprinted polymeric nanobeads for the preconcentration and determination of mercury ions

• Presentation of a new analytical method for mercury separation. • Highly selective separation and fast determination of hazardous mercury ion. • Determination of Hg 2+ ion in water and hair samples with acceptable accuracy and precision. • On-line determination of mercury ion based on Hg-IIP NPs through FIA. This work reports a new analytical method for the preconcentration and determination of Hg 2+ ions based on flow injection technique coupled with a solid phase extraction process. Hg 2+ ion imprinted polymeric (IIP) nanomaterials were prepared by using the bulk polymerization procedure, and then applied as an efficient solid phase extractor for selective separation of Hg 2+ ions. The prepared sorbent was characterized using FT-IR spectroscopy, scanning electron microscopy (SEM), various thermal analysis methods, and Brunauer, Emmett, and Teller adsorption isotherm analysis (BET). According to the results, surface area, pore volume and average pore diameter of the prepared Hg-IIP were found to be 3.05 × 10 2 m 2 g −1 , 1.07 cm 3 g −1 and 15.33 nm, respectively. In the sorption studies, after preconcentration and loading of Hg 2+ ions on the IIP sorbent, its mercury content was eluted by suitable solution and then determined photometrically, by a designed on-line recording process coupled with a flow injection procedure. The influence of the mercury concentration, preconcentration and elution times, nature, volume, and concentration of the eluent, pH, and flow rate of the solution and eluent on the polymer affinity has been investigated. Bound Hg 2+ ions can be eluted with 5 mL of nitric acid 1.0 mol L −1 and then treated with diphenylthiocarbazone, finally quantified photometrically at 485 nm. The relative standard deviation and detection limit (3 σ ) of the method for eight replicates at optimum pH, were evaluated as 4.2% and 0.036 ng mL −1 , respectively. The IIP sorbent show an excellent selectivity for Hg 2+ ion over other metal ions and was successfully applied to the selective extraction and determination of Hg 2+ ion in water and human hair samples.

Analysis of metal contents in Portland Type V and MTA-based cements.

The aim of this study was to determine, by Atomic Absorption Spectrometry (AAS), the concentration levels of 11 metals in Type V gray and structural white PC, ProRoot MTA, and MTA Bio. Samples, containing one gram of each tested cement, were prepared and transferred to a 100 mL Teflon tube with a mixture of 7.0 mL of nitric acid and 21 mL of hydrochloric acid. After the reaction, the mixture was filtered and then volumed to 50 mL of distilled water. For each metal, specific patterns were determined from universal standards. Arsenic quantification was performed by hydride generator. The analysis was performed five times and the data were statistically analyzed at 5% level of significance. Only the cadmium presented concentration levels of values lower than the quantification limit of the device. The AAS analysis showed increased levels of calcium, nickel, and zinc in structural white PC. Type V PC presented the greatest concentration levels of arsenic, chromium, copper, iron, lead, and manganese (P < 0.05). Bismuth was found in all cements, and the lowest concentration levels were observed in Portland cements, while the highest were observed in ProRoot MTA. Both PC and MTA-based cements showed evidence of metals inclusion.

Determination of Bromine in Plastics by ICP-MS Using Microwave Digestion

A microwave digestion method for the determination of bromine in polyethylene (BCR 680 and 681) and peach leaves (SRM1547) by inductively coupled plasma mass spectrometry (ICP/MS) has been investigated. In the microwave digestion system, a sample of 0.1–0.3 g was weighed and 7 mL of nitric acid and 1 mL of hydrogen peroxide were added in a quartz insert. The insert was used within the standard TFM vessel which 6 mL of 10% hydrogen peroxide was added. The accuracy of the digestion method was evaluated. The recovery and the standard deviation (n = 3) for the bromine tested was 109% and 9.4%. The results obtained by the present method were in good agreement with the certified values.

EXTRACTION AND SPECIATION OF CHROMIUM(VI) AND CHROMIUM(III) AS ION-ASSOCIATION COMPLEXES OF TETRAMETHYLAMMONIUM-CHROMATE

A specific, selective and simple method for speciation of chromium(VI) and chromium(III) has been developed. This method is based on the quantitative extraction of chromium(VI) and chromium(III) as an ion association of tetramethylammonium-chromate in methyl isobutyl ketone (MIBK), followed by back extraction and preconcentration with an acidic diphenylcarbazide (DPC) solution. Back extraction was applied to achieve further preconcentration by a final factor of 20. The chromium(VI)-DPC complex was determined by a UV-Visible spectrophotometer. The optimum conditions of this method are as follows, optimum wavelength at 545 nm, MIBK as organic solvent, 7.5 mL of nitric acid (65%) for each 100 mL sample, mole ratio of TMAC to Cr(VI) of 2x104:1, 5 min shaking time, mole ratio of DPC to chromium(VI) of 8:1, and immediate UV-Vis measurement after obtaining of back-extract. The calibration curve was linear in the concentration range 0.00-0.40 µg.mL-1 of chromium(VI) with a regression equation of Abs=0.0038+1.7427x, in which x was the chromium species concentration ( µg.mL-1). The correlation coefficient (r) for the curve was 0.9991 and the detection limit was found to be 0.946 µg.mL-1. The result of analysis and speciation of chromium in water samples from a river near a leather processing plant in Yogyakarta area showed that the total content of chromium was in the range of 0.04 - 0.05 µg.mL-1 consisting of 0.03 - 0.04 µg.mL-1 of chromium(VI) and 0.002 - 0.01 µg.mL-1 of chromium(III). This result indicates that the concentration of chromium in the river is still below the safety limit. Keywords: extraction, speciation, chromium, preconcentration, ion-association, tetramethylammonium

Identification of a Novel Selenium-containing Compound, Selenoneine, as the Predominant Chemical Form of Organic Selenium in the Blood of Bluefin Tuna

A novel selenium-containing compound having a selenium atom in the imidazole ring, 2-selenyl-N(alpha),N(alpha),N(alpha)-trimethyl-L-histidine, 3-(2-hydroseleno-1H-imidazol-5-yl)-2-(trimethylammonio)propanoate, was identified from the blood and other tissues of the bluefin tuna, Thunnus orientalis. The selenium-containing compound was purified from the tuna blood in several chromatographic steps. High resolution mass spectrometry and nuclear magnetic resonance spectroscopy showed that the exact mass of the [M+H](+) ion of the compound was 533.0562 and the molecular formula was C(18)H(29)N(6)O(4)Se(2). Its gross structure was assigned as the oxidized dimeric form of an ergothioneine selenium analog in which the sulfur of ergothioneine is replaced by selenium. Therefore, we named this novel selenium-containing compound "selenoneine." By speciation analysis of organic selenium compounds using liquid chromatography inductively coupled plasma mass spectrometry, selenoneine was found widely distributed in various tissues of the tuna, with the highest concentration in blood; mackerel blood contained similar levels. Selenoneine was measurable at 2-4 orders of magnitude lower concentration in a limited set of tissues from squid, tilapia, pig, and chicken. Quantitatively, selenoneine is the predominant form of organic selenium in tuna tissues.

Application of ZnO Nanoparticles EM Wave Detector Prepared by Sol-Gel and Self-Combustion Techniques

Zinc oxide (ZnO) has found many important applications such as optoelectronic devices, sensors and varistors. The challenging part however is synthesizing ZnO nanoparticles and its utilisation as EM detectors. Sol-gel and self-combustion techniques were chosen in this study due to the ability to produce single phase and nano-size samples. The starting mixture consists of 10 grams of zinc (II) nitrate, Zn(NO3)2.6H2O salt which was dissolved in 50 mL of nitric acid, HNO3.The solution was stirred at 250 rpm continuously for 1 day. The mixture was then gradually heated for every 15 minutes until it combusted at 110oC for the self-combustion technique. For the sol-gel technique, the dissolved mixture was heated at 40oC, 50oC, 60oC and 70oC until the gelatine was formed. After the drying process, the as-prepared samples were annealed at 100oC and 200 oC for 1 hour for each technique. Characterizations were performed by using X-Ray Diffraction (XRD), Raman Spectra and Scanning Electron Microscopy (SEM).The XRD analysis showed a major peak of [101] plane at 2Ө for the self-combustion technique and the sol-gel technique. Raman results for the samples prepared via sol-gel and self-combustion techniques had shown the major peak of ZnO that is located at the Raman shifts of 437.67 cm-1. Using the Scherrer equation, single crystal nano particle of ZnO was successfully obtained in the range of 38.49 nm to 50.70 nm for the sample prepared via the sol gel technique. By the self-combustion technique, the average dimension of the as-prepared sample is in the range of 34-49 nm. Further heat treatment resulted in a major change of the Raman shift corresponding to the single phase ZnO nano particles. The best samples were used as electromagnetic (EM) detectors. The EM detectors are polymer based composite which were prepared using a casting technique.

Determination of Total Chromium in the Marine Sediment Certified Reference Material by Inductively Coupled Plasma Optical Emission Spectrometry after Pressurized Acid Decomposition

(1) The marine sediment (NMIJ CRM 7302a) was directly decomposed with a mixture of 1 mL of hydrofluoric acid, 1 mL of nitric acid and 8 mL of (1 + 1)sulfuric acid in a Teflon sealed vessel at 230°C for 16 h. The total chromium was determined. (2) An indirect acid method after the decomposition of organic materials by H2SO4-HNO3 was compared to a direct acid decomposition method (1). The analytical results of the total-chromium (t-Cr) by methods (1) and (2) coincided with the certified value of the NMIJ CRM 7302a. The direct method of (1) was recommended for a pre-treatment of a marine sediment sample. On the other hand, an electron probe micro-analyzer (EPMA) was applied to an element analysis of the trace precipitation in a direct acid decomposition process in a Teflon-sealed vessel. The white trace precipitation was a crystal of AlF, and the black trace precipitation was carbon. Trace chromium was not detected by the precipitations. How to obtain accurate data from the pre-treatments was discussed regarding the data of this method and other data : that is EPA 3050B, ISO 11466, EPA 3052B, or NAA found from the Union Internationale des Laboratories Indepentants, Inter-Laboratoriy Practice report. The importance of deciding the assigned value was discussed for a statistical evaluation of the data of participants in a proficiency testing. The certified reference materials (CRM) should be furnished by both the sheet decomposition methods of CRM in addition to methods (sheet) for accurate quantitative analyses of the analytes in the CRM.

Ultrasound-Assisted Pseudodigestion for Toxic Metals Determination in Fish Muscles Followed by Electrothermal Atomic Absorption Spectrophotometry: Multivariate Strategy

A simple and efficient procedure for the determination of arsenic (As), cadmium (Cd), and lead (Pb) in the edible parts of freshwater fish by ultrasonic-assisted acid pseudodigestion (USD) was developed. A Plackett-Burman experimental design was used as a multivariate strategy for the evaluation of the effects of several variables at once. Five variables--sonication time, sample mass of muscle tissue, temperature of the ultrasonic bath, mL of nitric acid, and mL of a mixture of acid and oxidant--were regarded as factors. From these studies, certain variables showed up as significant, and they were optimized by a 23+star central composite design, which involved 16 experiments. Optimum values of the variables were selected for the development of USD to determine the contents of As, Cd, and Pb in fish muscles used as pollution bioindicators from Lake Manchar (Sindh, Pakistan). The determination of the 3 toxic metals under study was performed by electrothermal atomic absorption spectrometry. The accuracy of the optimized procedure was evaluated by analysis of certified reference materials BCR 185R bovine liver and by comparison with conventional wet acid digestion methodology. The result obtained by the optimized method showed good agreement with the certified values and sufficiently high recovery. No significant differences were observed for P = 0.05. Relative standard deviation values (average of 10 separate determinations) were 1.21, 5.52, and 5.32% for As, Cd, and Pb, respectively.

Determination of Cd and Pb in biological reference materials by electrothermal atomic absorption spectrometry: A comparison of three ultrasonic-based sample treatment procedures

Three different ultrasonic-based sample treatment approaches, the automated ultrasonic slurry sampling, the ultrasonic assisted acid solid–liquid extraction (ASLE) and the enzymatic probe sonication (EPS) were compared and discussed for the determination of Cd and Pb by ET–AAS in biological reference materials. The sample mass chosen to perform the analysis was 10 mg and the liquid volume was 1 ml of nitric acid 1 M. The best results were obtained with the slurry procedure with which it was possible accurate and precise determination of the Cd and Pb content in four of the five reference materials studied. Optimum performance (total metal extraction) of ASLE assisted by ultrasound for Cd was only achieved in two of the four materials assessed whereas total Pb recovery was only possible in three of the five samples. Total extraction with the enzymatic probe sonication was only obtained for Cd in oyster tissue. Neither ASLE nor EPS were able to extract Cd or Pb from spruce needles. Pb concentration obtained after EPS was found to be highly dependent from sample centrifugation speed and time.

Purification of multi-walled carbon nanotubes through microwave heating of nitric acid in a closed vessel

We demonstrate that microwave-assisted heating in 5 mL of nitric acid eliminates impurities, such as amorphous carbon, carbon nanoparticles, and metals, from multi-walled carbon nanotubes (MWNTs). Heating the closed reaction vessel under microwave irradiation at 160 °C for 30 min is a very effective means of purifying the MWNTs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm that these reaction conditions are beneficial for removing the impurities and ensuring that the MWNTs remain intact. In contrast, a purification temperature of 180 °C provides too strongly oxidizing conditions that destroy the MWNTs. The ratio of the G and D bands in the Raman spectra also confirms that a temperature of 160 °C is optimal. The defect peak that we observed in the differential thermogravimetry (DTG) analysis of the raw material was not present after microwave purification. The presence of metal impurities in the MWNTs can be reduced significantly when using this method.

Low-blank isotope ratio measurement of small samples of lithium using multiple-collector ICPMS

A new method is presented for separation of lithium from silicate rocks and high precision MC-ICPMS analysis. A relatively small (3.57 meq) resin volume is able to separate lithium from all silicate rocks in a single step using only 16 ml of nitric acid mixed with methanol. Some advantages of the method are high sample throughput, low blanks and elution parameters that are insensitive to lithology. Elution schemes are presented for a range of igneous rocks and minerals. δ 7Li values for standards from the U.S. Geological Survey (USGS) for BCR-1, BHVO-2 and AGV-2 are 2.4‰, 4.6‰ and 7.9‰, respectively. Reference materials from the Geological Survey of Japan (GSJ) JB-2 and JR-2 give δ 7Li values of 4.7‰ and 3.8‰, respectively. The data for most reference rocks reproduce to within better than 0.5‰. This column method can also be used for the direct separation of high-field-strength elements (Ti, Zr, Hf, Nb, Ta) from silicate rocks.

Evaluation of closed-vessel microwave digestion method for the determination of trace impurities in polymer-based photoresist by inductively coupled plasma mass spectrometry

A closed microwave digestion method followed by inductively coupled plasma spectrometric (ICP-MS) analysis was evaluated for the determination of trace impurities in photoresist. To optimize the digestion procedure, several digestion parameters such as acid, heating temperature and heating time were evaluated. Besides, the digestion efficiency of used photoresist material and the recovery of analyte elements obtained by the use of gravimetric method and ICP-MS measurement, individually, were also compared to clarify the completeness of digestion. According to our experiments, the gravimetric method was found to be not so relevant to the completeness of digestion, because the remaining sample matrix could cause suppression effect in the subsequent ICP-MS measurement. In view of minimizing blank value and working time, a simple single-step heating program was proposed to mineralize 0.25 ml of photoresist material with 5 ml of nitric acid at 180 °C for 10 min. Based on the comparative study of the analytical results obtained by instrumental neutron activation analysis (INAA) and proposed method, the reliability of proposed method for the determination of trace metallic impurities in photoresist material has been confirmed.

A simple optimized microwave digestion method for multielement monitoring in mussel samples

With the aim of obtaining a set of common decomposition conditions allowing the determination of several metals in mussel tissue (Hg by cold vapour atomic absorption spectrometry; Cu and Zn by flame atomic absorption spectrometry; and Cd, PbCr, Ni, As and Ag by electrothermal atomic absorption spectrometry), a factorial experiment was carried out using as factors the sample weight, digestion time and acid addition. It was found that the optimal conditions were 0.5 g of freeze-dried and triturated samples with 6 ml of nitric acid and subjected to microwave heating for 20 min at 180 psi. This pre-treatment, using only one step and one oxidative reagent, was suitable to determine the nine metals studied with no subsequent handling of the digest. It was possible to carry out the determination of atomic absorption using calibrations with aqueous standards and matrix modifiers for cadmium, lead, chromium, arsenic and silver. The accuracy of the procedure was checked using oyster tissue (SRM 1566b) and mussel tissue (CRM 278R) certified reference materials. The method is now used routinely to monitor these metals in wild and cultivated mussels, and found to be good.

Determination of total and labile fraction of metals in seawater using solid phase extraction and inductively coupled plasma atomic emission spectrometry (ICP-AES)

A rapid and simple method is described for the preconcentration and discrimination between the organic fraction and the labile fraction of the metals Mn, Cd, Cu, Z, V, Ni, Pb, and Fe from seawater using 8-hydroxyquinoline, which forms neutral complexes with these metals, followed by adsorption on C18 chemically bonded silica gel. The sample flow rate through the C18 column was about 4 ml min−1. The metal ions adsorbed on the C18 column were stripped using 10 ml of nitric acid (2M) and the volume of seawater sample was about 500 ml (preconcentration factor, ∼50). Trace metal ions and the major elements (Ca, Na, Mg, K) were analysed in the samples using inductively coupled plasma atomic emission spectrometry (ICP-AES). The results of fractionation showed that Cd, Pb, Mn and V were mainly in the labile fraction, while the other studied metals were partially present in the organic fraction. Also the results showed excellent reproducibility, and the accuracy of the method was demonstrated by measurement of total metal concentrations from runs of certified reference materials, SLEW-3, CASS-3, NASS–3, which have different ionic strengths.

Preconcentration of Cr(III), Co(II), Cu(II), Fe(III) and Pb(II) as calmagite chelates on cellulose nitrate membrane filter prior to their flame atomic absorption spectrometric determinations

A method for the preconcentration and determination of Cr(III), Co(II), Cu(II), Fe(III) and Pb(II) ions by atomic absorption spectrometry has been described. The method was based the collection of metal–calmagite complexes on a soluble cellulose nitrate membrane filter. The detection of the solution was obtained by flame atomic absorption spectrometry (FAAS) after completely dissolving the membrane with 0.5 ml of nitric acid at 80 °C. The metal ions were recovered quantitatively at pH 8. Various factors which affect the collection and determination of metal ions such as, type and size of the membrane filter, solvent for dissolution of the species retained on the filter were investigated. The detection limits were varying 0.06 μg l −1 for Cu to 2.5 μg l −1 for Cr. An application of the proposed method for analyte ions in mineral and tap water samples was also described with satisfactory results (recoveries >95%, relative standard deviations <10%).

Development and evaluation of an analytical procedure for the determination of antimony in plant materials by hydride generation atomic absorption spectrometry

A procedure for the reliable trace determination of Sb in plant samples based on hydride generation atomic absorption spectrometry (HG-AAS) was developed. Prior to HG-AAS, aliquots (200–400 mg) of dry samples were mineralized with 3 ml of nitric acid, 0.5 ml of sulfuric acid, 0.5 ml of hydrofluoric acid and 0.3 ml of perchloric acid in open digestion vessels made of glassy carbon in a heating block. The accuracy and precision of the developed method was evaluated by the use of six certified plant reference materials. Experimental results for Sb in these reference materials (CRM 281 Rye Grass, BCR, Brussels, Belgium; GBW 07604 Poplar Leaves, GBW 07602 Bush Branches and Leaves and GBW 07605 Tea, Institute of Geophysical and Geochemical Exploration, Langfang, China; and SRM 1515 Apple Leaves and SRM 1575 Pine Needles, NIST, Gaithersburg, MD, USA) agreed well with the certified or indicative values. The detection limit (3ς) in digestion solutions of plant samples was 0.01 µg l–1, the quantification limit of the entire procedure for a reliable determination of Sb was 70 pg Sb g–1 dry powder. The reproducibility of repetitive measurements of digestion solutions was 3.4% at 0.5 µg Sb l–1 and 2.0% at 1 µg Sb l–1. To demonstrate the suitability of the developed method, Sb was determined in leaves of elder bushes (153 ± 5 ng g–1), poplar leaves (75 ± 4 ng g–1) and beech leaves from two different locations (79 ± 3 and 100 ± 3 ng g–1), pine shoots (71 ± 4 ng g–1) and spruce shoots from two sites (141 ± 6 and 29 ± 1 ng g–1). The quantification of Sb from fresh and freeze-dried spruce shoots and beech leaves revealed that the drying process has no distinct influence on the concentration of Sb in the investigated plant materials.

Determination of arsenic in arsenic compounds and marine biological tissues using low volume microwave digestion and electrothermal atomic absorption spectrometry

Determination of arsenic in arsenic compounds and marine biological tissues using low volume microwave digestion and electrothermal atomic absorption spectrometry

Determination of lead concentration and lead isotope ratios in calcium supplements by inductively coupled plasma mass spectrometry after high pressure, high temperature digestion

The presence of lead as a contaminant in calcium supplements has aroused considerable public health interest in recent years. In this investigation lead and lead isotope ratios were determined by ICP-MS in ten brands of calcium supplements after high pressure/temperature digestion. Calcium supplements (200 to 250 mg) were digested in 2 mL of nitric acid at 230 °C and at a pressure of 1770 psi (1.2 × 104 kPa). Lead concentrations were determined by matrix-matched lead standards prepared in a high-purity calcium carbonate matrix. Good recoveries of lead and calcium were obtained for certified animal bone reference material. High levels of Pb (8 to 28 μg Pb per g of calcium) were found in calcium supplements that contain dolomite or bone meal. Chelated and refined calcium supplements had lower Pb levels (0.8 to 0.9 μg Pb/g Ca). Application of lead isotope ratios to distinguish the origin of calcium sources was also explored.