Dry Ashing Technique Research Articles

Effects of rice-straw derived phytoliths on the surface charge properties of paddy soils

Straw of rice (Oryza sativa), a high Si-accumulating plant, is typically composed of amorphous silica bodies (namely phytoliths) that are deposited within the plant tissues. Recycling of rice straw is a traditional agricultural practice that introduces phytoliths into soil in many paddy regions. While the role of phytoliths as a carrier for nutrients, e.g., K, P, or terminal sink of Si, has been reported, it remains unclear to what extent phytolith can carry charges and act as a charge-interchange constituent in soils. Therefore, it was hypothesized that soil phytoliths can be involved in charge-related interactions e.g., pH buffering, multivalent cation exchange, polymerization, colloid stability or reactive transports. Based on a polyelectrolyte titration technique, our study evaluated surface charge (SC) dynamics of straw-derived phytoliths and paddy soils in the Mekong river and Red river deltas to characterize the possible contribution of phytoliths to soil SC properties. Phytoliths were extracted by both dry and wet ashing techniques and the SC of the obtained phytoliths were measured in the pH range from 3.5 to 8.0. The SC was detected to vary from slightly positive at low pH to –78.5 mmolc kg−1 at slightly alkaline pH, suggesting that these materials carry variable charges and could be a significant source of charge when they are returned to soil in relatively large quantities. Multiple regressions indicated that phytoliths, to some extents, can together with other soil constituents such as clay minerals, organic matter and iron oxides, regulate the SC of paddy soils. Despite phytoliths being more or less soluble, their SC properties suggest that the annual recycling of rice straw to paddy soils, particularly after burning, can contribute to the negative SC system. The phytolith-derived charge in turn might affect soil cation exchange capacity (CEC), dispersibility of clay particles and transport of solutes.

Metals Contamination in Face Powders and their Associated Health Risks to the Users in Mekelle, Ethiopia

The presence of heavy metals has been reported in cosmetics and their assessment in these products is of significantly important to protect the users. The objective of this study was to assess the levels of cadmium, lead and zinc in face powders and provide information on the risk associated with human exposure to these heavy metals in the products. The samples were pretreated using dry ashing technique and analyzed by flame atomic absorption spectrophotometer. The level of lead in face powders was below the detection limit while the concentrations of cadmium and zinc ranged from 0.13 to 0.215 mg/kg and not detected to 7.05 mg/kg, respectively. The systemic exposure dosage values for these metals in the products were below their respective provisional tolerable daily intake and/or recommended daily intake values. The margin of safety values were higher than 100 which exhibited that the concentrations of metals observed in these products do not cause substantial health risk to the users.

Quantifiable differences between phytolith assemblages detected at species level: analysis of the leaves of nine Poa species (Poaceae)

<p>The taxonomic value of phytolith assemblages and their degree of variability within different species of the same genus is still an undervalued issue in the botanical range of phytolith studies. However the understanding of grass phytolith variance and its implications to plant systematics is doubtless.</p><p>In the present study phytoliths of the lateral shoots (leaves) of nine, globally distributed <em>Poa</em> species (Pooideae – Poaceae) are described. Phytoliths were recovered from <em>Poa</em> specimens by the dry ashing technique. Altogether 6223 disarticulated phytoliths were counted (approximately 500–700 phytoliths per species) in 54 plant samples, which cover six shoots of nine species. Not only the relative frequency of each morphotype was calculated, but measurements were conducted to determine the biogenic silica content of <em>Poa</em> lateral shoots. A phytolith reference collection for the nine selected species of a worldwide importance was also compiled. The description of the most significant phytolith morphotypes and their taxonomic relationships are given here.</p><p>Results suggest that the biogenic silica content of the <em>Poa</em> lateral shoots was determined to be relatively high within all nine species. Phytolith assemblage data was subjected to multivariate statistical analyses (e.g., CA and PCA) in order to find differences and similarities among the nine <em>Poa</em> species. Results show that the two closely related <em>Poa</em> of the <em>P. pratensis</em> species group, namely the <em>P. pratensis</em> and <em>P. angustifolia</em>, only slightly differ from the other <em>Poa</em> species if we consider their rondel-trapeziform short cells (SC) phytolith frequencies.</p>

Determination of some heavy metals in spinach and lettuce from selected markets in Kaduna metropolis

Heavy metals such as copper, zinc, cadmium and lead were analyzed in vegetable samples (lettuce and spinach) obtained from ten major markets within Kaduna metropolis. The samples were digested by dry-ashing techniques and the trace metal were determined using atomic Absorption Spectrophotometry (AAS). The result were compared with the standard set by FAO/WHO (2001) which shows that for spinach sample cadmium and lead are within the permissible limit with the exception of Gumi market with (Cd 0.30 mg/kg). zinc was found to be within the acceptable limit for all spinach sample obtained. Copper was found to have exceeded the stipulated standard in all spinach samples except for sample from Angwan Rimi market with (0.06mg/kg). for lettuce sample, cadmium and zinc were found to be within the stipulated limit. Analysis for copper in the lettuce sample clearly show that samples from all other markets exceeded the acceptable limit, except samples from Gumi and Sabo markets with (0.32mg/kg and 0.32mg/kg) respectively. From the stipulated limits set by WHO/FAO, consumers of vegetables from this study areas were likely to be liable to copper toxicity and some few metals as stated above.

Determination of major and minor ash-forming elements in solid biofuels

The development of reliable and appropriate methods for the accurate determination of major (Al, Ca, Fe, K, Mg, Na, P, Si, Ti) and minor (As, Ba, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Tl, V, Zn) ash-forming elements in solid biofuels was the major goal of Task III.2 of the EU project BioNorm. For this purpose, wood+bark, straw and olive residues were analysed using several digestion and determination methods. The digestion methods included wet decomposition in closed vessels with different acid mixtures as well as dry-ashing techniques. The determination systems included FAAS, GFAAS, CVAAS, ICP-OES, ICP-MS, XRF as well as direct Hg-determination. Tests were carried out to optimise the methods applied. To summarise the outcomes of these tests, different digestion procedures were developed for major and minor elements. Digestion with H2O2/HNO3/HF followed by neutralisation with H3BO3 was validated for major element analyses, while digestion with H2O2/HNO3/HF was validated for minor element analyses. The validation results show that the applied digestion methods can be recommended for solid biofuel analyses. For the determination of the elements investigated in solid biofuels, the following detection systems can be recommended: FAAS for Ca, Fe, K, Mg, Na, Si, Mn, Zn; ICP-OES for Al, Ca, Fe, K, Mg, Na, P, Si, Ti, Mn, Zn, Ba, Cr, Cu, Mn, Ni, V, Zn; GFAAS for Cd, Cr, Cu, Ni, Pb; ICP-MS: P, Ti, As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, V, Zn and direct determination as well as CVAAS for Hg.

Evaluation of Analytical Methods for Total Phosphorus in Organic Amendments

Increased environmental concern regarding the build‐up of soil phosphorus following application of organic amendments based on plant nitrogen (N) requirements will lead to an application strategy that is based on plant phosphorus (P) requirements. This will create demand for a rapid method of analyzing for total P in organic amendments in order to match application rates to plant P requirements. The wet oxidation method was evaluated in comparison with dry ashing technique for measuring total P in six organic amendments (hog, dairy cattle, beef cattle and poultry manures, municipal biosolids, and composted cattle manure) that ranged in P content from 0.25% to 4.5%. The wet oxidation method produced P concentration that was within 7% of that measured by the dry ashed method in 18 of the 24 samples analyzed and within 15% in the remaining samples. The experimental errors associated with both methods were small and the agreement between the two methods leads us to the conclusion that the wet oxidation method can be used for analysis of total P in a wide range of organic amendments. Each amendment was subjected to air drying, freeze drying, and oven drying in order to evaluate the effect of pre‐treatment on the total P content of amendments relative to fresh sample. The effect of pre‐treatment on the P content of organic amendments was small. In general, the P content of fresh sample was the highest with that of oven dry sample being the lowest. In studies where quantitative recovery of P is important, oven drying is not recommended as a method of removing water. In such cases, where samples cannot be analyzed in the fresh form, freeze drying or air drying is recommended.

Evaluation of triacid and dry ashing procedures for determining potassium, calcium, magnesium, iron, zinc, manganese, and copper in plant materials

Dry ashing and wet ashing techniques are routinely used for preparing plant materials for elemental analysis. The two techniques generally give similar results for the analysis of plant materials but differences have been observed in results using the two methods for elements such as calcium (Ca), iron (Fe), and zinc (Zn). We made a study to compare the dry ashing and triacid digestion procedures for determining potassium (K), Ca, magnesium (Mg), Fe, manganese (Mn), copper (Cu), and Zn in sorghum and rice plant samples having a range in concentration of these elements. For sorghum, the two procedures gave similar results for the determination of K, Mg, Mn, and Zn, the dry ashing procedure gave higher values for Ca, Fe, and Cu than those obtained using the triacid digestion procedure. For rice, the two procedures gave similar results for all nutrient elements except Ca for which the values were higher by the dry ashing procedure than with the triacid digestion procedure. Our results suggest that dry ashing technique provides more reliable results for the analysis of sorghum and rice plant materials for Ca and may be preferred over the triacid digestion procedure. Also, for sorghum plant samples dry ashing seemed more reliable for determination of Fe and Cu. Both dry ashing and triacid digestion methods appeared satisfactory for the determination of K, Mg, Mn, and Zn.

A Comparative Analysis of Wet and Dry Ashing Techniques for the Extraction of Phytoliths from Plant Material

Two methods are commonly used for the extraction of phytoliths from plant material to be used as reference in the analysis of archaeological phytolith samples: (1) spodograms or dry ashings; and (2) acid digestions or wet ashing. It has been suggested that these techniques may modify the resultant samples in different ways. Dry ashing, in particular, has been implicated as a cause of shrinkage and warping in phytolith assemblages when incineration occurs at ≥450°C. The results of a morphometric comparative analysis between the dry ashing and wet ashing methods do not support these claims. This study establishes that differences in patterns of dimension and curvature of short bilobate phytoliths and of elongate phytoliths both subjected to dry and wet ash preparation are not statistically significant. There is, therefore, no detectable evidence of morphological impact as a result of these methods. This finding implies that any differences that do occur in phytolith size and curvature are typical, possibly random permutation within assemblages, or that they are the result of variation in leaf cell structure rather than the consequence of a particular extraction procedure. This suggests that the practice of using different methods of preparation of reference samples for fossil analysis can be reliably continued.

Flow Injection Hydride Generation Atomic Absorption Spectrometry for Determination of Arsenic in Water and Biological Samples from Arsenic-Affected Districts of West Bengal, India, and Bangladesh

The increasing concern over human exposure to arsenic in West Bengal and Bangladesh has necessitated the development of a rapid method for determination of trace levels of arsenic in water and biological samples. We have developed a simple indigenous flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) system for the determination of arsenic in parts-per-billion levels in water and biological samples. The technique is fast, simple, and highly sensitive. The accuracy and precision of the method were evaluated by spiking known amounts of arsenic and analyzing different types of environmental and biological standard reference materials. The organic matter in a biological sample was destroyed by acid digestion and dry ashing technique. We analyzed thousands of tubewell water samples from the affected districts of West Bengal and Bangladesh. Most of the water samples contained a mixture of arsenite and arsenate and in none of them could we detect methylated arsenic. We also analyzed thousands of urine (inorganic arsenic and its metabolites), hair, and nail samples and hundreds of skin-scale and blood samples of people drinking arsenic-contaminated water and showing arsenical skin lesions. Quality control was assessed by interlaboratory analysis of hair samples. An understanding of arsenic toxicity and metabolism requires quantitation of individual arsenic species. The techniques we used for the determination and speciation of arsenic are (i) separation of arsenite and arsenate from water by sodium diethyldithiocarbamate in chloroform followed by FI-HG-AAS; (ii) determination of arsenite in citrate/citric buffer at pH 3 and total arsenic in water in 5 M HCl by FI-HG-AAS. Thus, arsenate is obtained from the difference; (iii) for analysis of inorganic arsenic and its metabolites in urine FI-HG-AAS was used after separation of the species with a combined cation-anion exchange column. Total arsenic in urine was also determined by FI-HG-AAS after acid decomposition. The species arsenite and arsenate are present in groundwater in about a 1:1 ratio and about 90% of the total arsenic in urine is present as inorganic arsenic and its metabolites.

Arsenic Determination in Certifiable Color Additives by Dry Ashing Followed by Hydride Generation Atomic Absorption Spectrometry

The preparations of digested samples of certifiable color additives by dry ashing and wet digestion for arsenic analysis by hydride generation atomic absorption spectrometry (AAS) were compared. The dry ashing technique was based on the preparation used in ASTM D4606-86 for determination of As and Se in coal. The acid digestion method used nitric and sulfuric acids heated by microwaves in sealed vessels. The digested color additives were analyzed for As by using hydride generated from sodium borohydride mixed with the acidified solution on a flow injection system leading to an atomic absorption spectrometer. Dry ashing was preferable to wet digestion because wet digestion yielded poor recoveries of added As. Dry ashing followed by hydride generation AAS gave determination limits of 0.5 ppm As in the color additives. At a specification level of 3 ppm As, the precision of the method using dry ashing was +/- 0.4 ppm (95% confidence interval).

Determination of Arsenic in Orange Juice by Dry Ashing Hydride Generation Atomic Absorption Spectrometry

A procedure suitable for routine analysis of arsenic in orange juice using instrumentation available in most control laboratories was developed. Organic matter is destroyed by the dry ashing technique, the ash is dissolved in HCl, and hydrides of arsenic are generated by the addition of sodium borohydride prior to atomization in a flame-heated quartz cell and atomic absorption spectroscopy measurement. Experimental conditions for the destruction of organic matter were established, and an interference study was carried out. Copper and iron do not interfere in arsenic determination at levels found in orange juice. The methodology developed has a detection limit in orange juice of 0.1 ng g−1, a relative standard deviation of 1%, and a recovery percentage of 98 ± 8. The accuracy of the proposed method was checked by analysis of a certified sample of tomato leaves, NIST SRM 1573 (certified 0.27 ± 0.05 μg/g; found 0.26 ± 0.03 μg/g). The arsenic content of orange juice products was determined. The extremely low arsenic levels found (0.3-4.4 ng g−1)do not present problems from a toxicological point of view.

Comparison of dry ashing and wet acid digestion on the determination of boron in plant tissue

Abstract Dry ashing and wet acid digestion of selected plant tissues were conducted and evaluated for their effectiveness in the spectrophotometric determination of boron (B) using the Azomethine‐H method. In dry ashing, two parameters were varied: ashing aids and length of oxidation period. In wet acid digestion, two different mineral acids were used and the length of the oxidation period was varied between 12 and 24 h. Results showed that samples treated with sulfuric acid in dry ashing had the lowest recoveries of B. Boron concentrations in tissues oxidized for 12 h in wet acid digestions were at least 40% higher than the results obtained for any dry ashing technique.

Determination of arsenic in dry ashed seafood products by hydride generation atomic absorption spectrometry and a critical comparative study with platform furnace Zeeman-effect atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry

A hydride generation atomic absorption spectrometric (HG-AAS) method was developed for the determination of arsenic in mussel products as part of a general plan to control this element in seafood products. Organic matter is destroyed by the dry ashing technique, the ash is dissolved in HNO 3, diluted in HCL, and hydrides of arsenic are generated by the addition of sodium tetrahydroborate prior to atomization in a flame-heated quartz cell and measurement by atomic absorption spectrometry. The detection limit (0.017 μg g −1), precision (3%), recovery (100±4%) and accuracy (determined by analysing NIST Oyster Tissue) were evaluated and an interference study was carried out. A comparative study of HG-AAS, platform furnace Zeeman-effect AAS and inductively coupled atomic emission spectrometry (ICP-AES) showed that the most suitable technique for the determination of arsenic in seafood product is ICP-AES. For samples with arsenic levels below the detection limit of this technique (0.1 μg g −1) the alternative is the use of HG-AAS.

Effects of Revegetation on Surficial Soil Salinity in Panspot Soils

Panspots and transition zone panspots (slickspots) from a Leptic/Typic Natriboroll soil complex in western North Dakota were compared to determine the effects of secondary plant succession upon soil properties. Herbage and rooting characteristics were evaluated among panspot, transition zone, and adjacent well-vegetated Belfield soils using point frame data and a modified dry ashing technique. The effects of vegetation upon soil electrical conductivity (EC) were tested using gradient transects aligned perpendicular to boundaries between panspots and transition zones. Transition zones had 40% more total forage and twice the litter found in panspot areas. Thirteen of 17 gradient transects showed an inverse relationship between soil EC and distance into transition zones at the 0 to 5 cm depth. Significantly higher root-mass was obtained in the 0 to 5 cm depth in transition zones compared to panspots. A conceptual model based on subsurface water flow is presented to explain the polygonal cracking that was observed only in transition zone surfaces initiating a series of interactions resulting in natural reclamation of the transition zone soil.

Determination of Arsenic in Beer by Dry Ashing, Hydride Generation Atomic Absorption Spectroscopy

A method has been developed for determination of arsenic in beer. Organic matter is destroyed by the dry-ashing technique, the ash is dissolved in HCl, and hydrides of arsenic are generated by addition of sodium borohydride prior to atomization in a flame-heated quartz cell and atomic absorption spectroscopy measurement. The analytical features of the method are detection limit 0.1 ng/g beer, precision 8%, and recovery 97 +/- 7%. The arsenic contents of different brands from Spain and other European countries were analyzed. In all samples, the arsenic levels found were well below maximum levels allowed in Spanish legislation (100 ng/g). The quantities of arsenic in Spanish beers do not differ from those found in foreign beers. No differences were found between bottled and canned beers, and no correlation exists between metal content and original specific gravity of the beers.

The determination of platinum in biological materials by electrothermal atomic absorption spectroscopy

Methods for determination of platinum in body tissues and fluids by electrothermal atomic absorption spectroscopy are described. Serum and urine could be analyzed without pretreatment or dilution. Wet and dry ashing techniques for tissue digestion were compared. Dry ashing tissues in a furnace resulted in significant and unexplained losses of analyte, whereas there was complete recovery of platinum added to the tissues when the tissues were wet ashed. The wet ashing technique is fast and convenient and requires minimal sample treatment.

OCORRÊNCIA DE CHUMBO E CÁDMIO EM FÍGADO DE AVES ABATIDAS NO RIO DE JANEIRO*

O presente trabalho teve por objetivo precípuo avaliar o grau de contaminação dos frangos comercializados no Grande Rio por metais pesados, determinando-se o seu conteúdo de chumbo e cádmio. Simultaneamente, verificou-se a possibilidade do uso, para fins de análise de rotina em produtos cárneos, de um espectrofotômetro de absorção atômica com menor resolução e. assim, de preço mais accessível, bem como do emprego da mineralização da matéria orgânica por via seca, com auxílio de coadjuvantes, a fim de evi tar o uso de acidos minerais de alta pureza, importados de elevado custo e de difícil obtenção. Os resultados mostraram que as aves analisadas nao continham teores de Pb e Cd detectáveis pelo método empregado, isto é. não continham teores acima do "ruído" de 0.4 ppm para Pb e 0.04 ppm para Cd. (Valores até 8 e 1 ppm respectivamente, são permitidos pela Legislação Brasileira). Quanto à técnica da mineralização da matéria organica por via seca, com auxílio de coadjuvantes. concluiu-se que ela é aplicável à analise de Pb em produtos cárneos, porém não é recomendável análise de Cd.

Recovery of Endogenous Selenium from Fish Tissues by Open System Dry Ashing

Quantitative recovery of endogenous selenium from fish tissues following dry ashing techniques has not been confirmed. An open system dry ashing procedure, using oxidative fusion with Mg(NO3)2 X 6H2O in the presence of MgO, was tested for recovery of selenium from National Bureau of Standards (NBS) Reference Materials (tuna and oyster) and selected fish tissues. Recovery after dry ashing and hydride analysis was complete from NBS Bovine Liver, Tuna, and Oyster Tissues, as well as from Food and Drug Administration cod, haddock, perch, and flounder research materials. Endogenous selenium, injected into rainbow trout (Salmo gairdneri) as 75Se, was recovered after ashing from liver, ovaries, gastrointestinal tract, muscle, bile, and carcass, 3 and 10 days post-injection. Results indicate that open vessel oxidative fusion is a rapid, simple technique applicable to quantitative recovery of selenium from organoselenium compounds that exist in various aquatic species. The diluted digestate is readily amenable to conventional hydride generation analysis.

Precautions in Ashing Techniques for Lead Determination in Food

In determining lead in food, the matrix must be destroyed before quantitation by atomic absorption spectrophotometry. Wet or dry ashing techniques are generally used. Dry ashing assisted by ultrapure H2SO4 or K2SO4 has the advantages of safety, low reagent blanks, rapidity, and good recoveries of added lead. These techniques are also less labor-intensive than wet ashing.

Determination of copper, iron, potassium and sodium in polyimide resins by atomic absorption spectrometry

Polyimide resins (polyimide-isoindoloquinazolincdione) were decomposed by a dry ashing technique and analyzed for the four elements by flame (air-acetylene) atomic absorption spectrometry. A specially designed quartz ashing vessel was used to control the temperature and atmospheric composition for the ashing. Recoveries of four elements decreased with increasing ashing temperature, being dependent on crucible materials. The recoveries of copper and sodium were not satisfactory when the platinum and quartz crucible were used, respectively. These losses were attributed to the retention of respective metal on the crucible used, which was demonstrated by radioisotopic tracer method. The increase of oxygen content in atmospheric gases resulted in a slight increase of temperature and shortened the ashing time. In practice volatile organic solvent in the resin was first removed by increasing the heating temperature from 100 to 500°C and then the oxidant gases consisting of oxygen and air in equivalent volume was supplied to the ashing vessel at a flow rate of 1.2 l/min. The temperature was raised to 600°C to complete the ashing for one hour. The ash was dissolved in 1 ml of nitric acid and stored in 2 N nitric acid, followed by atomic absorption measurements. The standard deviation of (3.37.9) % came out.