Wet Ashing Methods Research Articles

Speciation of copper in soils and relation with its concentration in fruits

Different extraction reagents were studied in soils and the results obtained were compared with copper (Cu) contents of seven type fruits grown in these soils. For fruits, wet and dry ashing methods were applied and acceptable results were obtained by using dry ashing. The speciation is based on the dissolution of the soil samples in HNO3/H2O2, oxalic acid, acetic acid, EDTA and citric acid as extraction reagents at hot and cold conditions. Mean total Cu concentrations for all fruits studied were (mg kg‐1) in the range of 3.0–7.0 (dried weight basis). Significant positive correlations have been found between Cu contents of various fruits and different extractants studied. Flame atomic absorption spectrometry was used for determination of Cu in digestions. Probable chemical forms of Cu in soils were evaluated.

Effect of method of analysis on iron content of beef from advanced meat recovery systems

A field survey was conducted by the USDA, Food Safety Inspection Service (FSIS) to provide analytical data on meat obtained from beef cervical vertebrae processed by advanced meat recovery (AMR) systems. As a result, an added iron performance standard was proposed to limit the amount of marrow in AMR products. The performance standard was based on iron content of hand boned lean compared to AMR lean. Iron content was determined by a hydrochloric wet ash digestion method. The same samples were then analyzed using dry ash digestion. The objectives of the study were to determine differences in iron content of the survey samples due to the digestion method and the impact of this difference on the added iron performance standard. Iron values by the dry ash method were approximately double those of the wet ash method. The difference was a result of incomplete volatilization of the organic matrix by hydrochloric acid in the wet ash procedure. The performance standards developed from the wet and dry ash methods were 1.8 and 3.2 mg added iron 100 −1 g, respectively. Added iron levels from the dry ash method greater than 3.2 mg 100 −1 g were present in 60% of the AMR lean indicating that some marrow was present or that factors other than amount of iron in hand boned lean should be considered before a performance standard is established.

Determination of trace elements by inductively coupled plasma mass spectrometry of biomass and fuel oil reference materials using milligram sample sizes.

Most of the analytical techniques used to quantify elements associated with solid samples suffer from high detection limits and cannot be used for trace elements in biomass samples, particularly when only 20 mg are available for analysis. Inductively coupled plasma mass spectrometry (ICP-MS) can achieve detection limits of parts-per-trillion with liquid sample introduction by solution nebulisation. This technique was therefore tested with two standard biomass reference materials: oriental tobacco leaves and cabbage leaves. Two preparations successfully used on coal standards were used to digest the solid samples: a total digestion method (wet ashing digestion) and a partial leaching (microwave extraction). The concentrations of up to seventeen elements (As, Ba, Be, Cd, Co, Cr, Cu, Ga, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn) were measured after the two preparations. The accuracy and sensitivity of the measurements improved when the dilution factor decreased from 5000 to 1000 and to 500. Since the proportion of mineral matter in biomass samples is small (5%), the microwave digestion extracted elements that are generally not completely extracted from coal samples (e.g. Sb). However, some trace element concentrations were below the limit of quantification after microwave extraction, even with a reduced dilution factor (As, Se and Mo) and could not be quantified. A fuel oil was also digested. The trace element concentrations were very low (between 28 and 0.1 microgram g(-1)) but acceptable results were obtained by applying a dilution factor of 100. Only six elements in the fuel oil (As, Ba, Co, Ni, Se and V) had certified or indicated values. Factors affecting the accuracy and sensitivity of the analyses are discussed. The reproducibility of analysis of the tobacco leaf standard was checked over a period of nine months by both digestion methods. The wet ashing method gave acceptable reproducibility for Ba, Cd, Co, Cu, Ga, Mn, Mo, Ni, Pb, V and Zn but poor precision for Cr, Se and Sn and showed evidence of residual chloride interference for As. The microwave extraction gave good reproducibility for As, Ba, Cd, Co, Cr, Cu, Mo, Ni and Zn but poor precision for Se and low recoveries for Ga, Mn, Sn and V. In spite of the small quantities of material analysed, it proved possible to determine the trace elements at levels down to 0.1 microgram g(-1) in the reference materials.

Comparison of digestion methods for the determination of selenium in fish tissue by cathodic stripping voltammetry

A certified reference material (NIST-RM-50 Albacore Tuna) was analysed for selenium by cathodic stripping voltammetry (CSV), after digestion of the material by a number of methods that avoid the use of perchloric acid. The digestion techniques tested included wet and dry ashing methods, oxygen bomb digestion, ultraviolet (UV) digestion, and methods involving elevated pressure. The only method that reliably produced results that agreed with the certified value for selenium in the reference material was the combination wet/dry ashing method incorporating elevated pressure recommended by the Association of Official Analytical Chemists (AOAC) for determination using hydride generation atomic absorption spectrometry (AAS). Recoveries using the other methods were low and variable, apparently because of incomplete destruction of organic matter and losses caused by volatilisation of selenium.

Isotope ratio determination in boron analysis.

Traditionally, boron (B) isotope ratios have been determined using thermal ionization mass spectrometry (TIMS) and, to some extent, secondary ion mass spectrometry (SIMS). Both TIMS and SIMS use a high-resolution mass analyzer, but differ in analyte ionization methods. TIMS uses electrons from a hot filament, whereas SIMS employs an energetic primary ion beam of Ga+, Cs+, or O- for analyte ionization. TIMS can be used in negative or positive ion modes with high sensitivity and precision of B isotope ratio determination. However, isobaric interferences may be a problem, if the sample is not well purified and/or memory of the previous sample is not removed. Time-consuming sample preparation, analyte (B) purification, and sample determination processes limit the applications of TIMS for routine analyses. SIMS can determine B and its isotope ratio in intact solid samples without destroying them, but has poorer resolution and sensitivity than TIMS, and is difficult to standardize for biological samples. Development of plasma-source mass spectrometry (MS) enabled the determination of B concentration and isotope ratio without requiring sample purification. Commonly used plasma-source MS uses an Ar inductively coupled plasma (ICP) as an ionization device interfaced to a low-resolution quadrupole mass analyzer. The quadrupole ICP-MS is less precise than TIMS and SIMS, but is a popular method for B isotope ratio determination because of its speed and convenience. B determination by ICP-MS suffers no spectroscopic interferences. However, sample matrices, memory effects, and some instrument parameters may affect the accuracy and precision of B isotope ratio determination if adequate precautions are not taken. New generations of plasma-source MS instruments using high-resolution mass analyzers provide better sensitivity and precision than the currently used quadrupole ICP-MS. Because of the convenience and high sample throughput, the high-resolution ICP-MS is expected to be the method of choice for B isotope ratio determination. The current state of instrumental capabilities is adequate for B isotope determination. However, precision and accuracy are primarily limited by sample preparation, introduction, and analytical methodology, including 1. Analyte loss and isotope fractionation during sample preparation. 2. The precision of B isotope determination in small samples, especially those containing low concentrations. 3. Difficult matrices. 4. Memory effects. Sample preparation by alkali fusion allows rapid and complete decomposition of hard-to-digest samples, but high-salt environments of the fused materials require extensive sample purification for B ratio determination. The alternative wet-ashing sample decomposition with HF also results in B loss and isotopic fractionation owing to the high volatility of BF3. Open-vessel dry- or wet-ashing methods usually do not work well for animal samples, and are also prone to B loss and contamination. Closed-vessel microwave digestion overcomes these problems, but the digests of biological materials have high C contents, which cause spectral interference on 11B and affect 11B/10B ratios. Exchange separation/preconcentration of B using exchange (cation or anion exchange, B-specific resin, e.g., Amberlite IRA-743) tend to cause B isotope fractionation, and C eluting from these resin columns may interfere with B isotope ratio determination. Memory effects of B that occur during sample determination may cause serious errors in B isotope ratio determination, especially when samples varying in B concentrations and/or isotope composition are analyzed together. Although the utilization of high-resolution plasma-source MS will undoubtedly improve analytical precision, it is the sample preparation, sample introduction, and analytical methodology that represent the primary limitation to accurate and precise B isotope ratio determination.

Determination of Sr, K, Mg And Na In Human Teeth by Atomic Spectrometry Using a Microwave-Assisted Digestion in a Closed Flow System.

A procedure is proposed to improve the acid digestion of human teeth. A closed flow system is used to digest samples inside a microwave oven which allow us more rapid treatment of samples than classical pressurized wet ashing methods, not requiring the use of long cooling periods and also reducing the sample handling. The content of Sr, K, Mg and Na in human teeth samples has been determined by atomic spectrometry and precise and accurate results have been obtained.

Determination of Chromium and Molybdenum in Medical Foods by Graphite Furnace Atomic Absorption Spectrophotometry

Graphite furnace atomic absorption spectrophotometry was used to determine chromium and molybdenum in 7 medical foods from 5 manufacturers. Linear standard curves were obtained for both elements for concentrations between 5 and 25 ng/mL. Detection limits were 0.24 ng/mL for Cr and 0.67 ng/mL for Mo. Characteristic masses were 3.1 and 14.7 pg for Cr and Mo, respectively. No difference was detected between wet and dry ashing methods, and dry ashing was used to complete the study. The method was validated by assaying various National Institute of Standards and Technology standard reference materials. Analysis of these products for Cr and Mo were within certified values. One product was evaluated by this method for reproducibility (n = 5). Relative standard deviations were 6.8 and 4.8% for Cr and Mo, respectively. This product contained 0.31 +/= 0.02 micrograms Cr/g and 0.63 +/- 0.03 micrograms Mo/g. The remaining products contained 0.09-1.28 micrograms Cr/g and 0.07-2.3 micrograms Mo/g. Mean recovery values were 98 +/- 14% (n = 14) for Cr at spike levels of 0.20-1.89 micrograms/g and 102 +/- 24% (n = 10) for Mo at spike levels of 0.30-1.89 micrograms/g.

Effects of CBMIDA and Zn-DTPA in Drinking Water on Removal of Plutonium in Rats.

The effects of the oral administration of CBMIDA [catechol-3, 6-bis (methyleiminodiacetic acid)], given in drinking water, on the removal of plutonium in rats were compared to those of Zn-DTPA. Male Wistar rats received a daily dose of 120μmol/kg or 1, 200μmol/kg of CBMIDA or Zn-DTPA, given in drinking water, for 4 weeks after plutonium injection. The content of plutonium in bone, liver, kidney, spleen, and testis was measured by a liquid scintillation spectrometry after treatment of the organs by a wet ash method. The plutonium content of each organ in the 120μmol/kg groups of CBMIDA and Zn-DTPA was not significantly reduced. The content of plutonium in the 1, 200μmol/kg groups of both CBMIDA and Zn-DTPA was, however, significantly reduced, to 65.7% (p<0.001) and 76.8% (p<0.05), respectively of the control in bone, and to 66.6% (p<0.05) and 44.0% (p<0.01), respectively, in liver. There were no significant decreases in kidney, spleen, and testis in the 1, 200μmol/kg dose CBMIDA group, but there were significant decreases in these organs in the 1, 200μcmol/kg dose Zn-DTPA group. These results showed that, when given orally, CBMIDA was more effective in removing plutonium from bone than Zn-DTPA, a finding similar to the results were achieved with the intravenous injection of both agents in our previous study.

Effects of CBMIDA(Catechol-3,6-bis(methyleiminodiacetic acid)) on Removal of Plutonium in Rats.

Effects of CBMIDA [catechol-3, 6-bis(methyleiminodiacetic acid)] on injected 239Pu were examined in rats; in our previous studies, CBMIDA had almost the same toxicity as those of DTPA and EDTA. Rats were injected intravenously with 239Pu (1.85×104Bq/kg) and divided into four groups of five rats each. Three groups were each injected intraperitoneally with a daily dose of 150μmol/kg of CBMIDA, Ca-DTPA or Zn-DTPA for 2 weeks, beginning at about 1h after plutonium injection. Rats were sacrificed 14 days later and the femur and liver were removed. All excreta were collected at 24-h intervals during the experimental period. Plutonium contents of the femur, liver, feces and urine treated by a wet ashing method were measured by a liquid scintilation spectrometry.The plutonium contents in the skeleton of administered dose were 11.5% for CBMIDA group, 19.0% for Ca-DTPA group, and 26.9% for Zn-DTPA group, whereas that was 63.9% for the control; those in the liver were 0.62% for CBMIDA group, 0.35% for Ca-DTPA group and 0.54% for Zn-DTPA group, whereas that was 7.74% for the control. The data obtained indicate that CBMIDA is superior to Ca-DTPA and Zn-DTPA on removing plutonium from bone, and also has almost the same effectiveness on removing it from liver as those of both Ca-DTPA and Zn-DTPA. The higher effectiveness of CBMIDA on removal of plutonium from the skeleton might be, besides the stronger chelating action, due to the inhibition of plutonium deposition into bone, judging from the results of our previous study wherein the effects of CBMIDA on bone metabolism were examined in beagle dogs.In conclusion, taking together the results obtained in this study and those from our previous studies on the toxicity, it was demonstrated that CBMIDA could be utilized, as a new chelating agent, to remove plutonium from human body.

Comparison of some wet digestion and dry ashing methods for voltammetric trace element analysis

Several wet digestion and dry ashing methods were compared for the precise and accurate determination of some trace elements in biological and environmental materials. The wet digestion methods were generally faster than the dry ashing methods, but required the use of large amounts of reagents and, therefore, gave higher blank contributions for some elements. The main advantages of the dry ashing method were the lower blank levels, improved (lower) background current and its ability to handle considerably larger amounts of sample. However, careful dissolution of the sample ash in a suitable reagent was necessary. Under suitable conditions, both decomposition methods allowed the reliable voltammetric determination of trace elements in biological and environmental materials with relative standard deviations of between 1 and 3%. The ultimate choice of decomposition method was influenced by the amount of sample available, the nature of the sample, the sample matrix and the analysis time available.

Heating and the Distribution of Total and Heme Iron Between Meat and Broth

ABSTRACTThe effect of heat on movement of total and heme iron from meat to broth was investigated. Total iron by a wet ash method was nearly identical to the sum of heme iron plus nonheme iron. The total amount of nonheme iron increased with cooking temperature (r = 0.98), as did the amount of nonheme iron in the broth (r = 0.93). Leaching of heme pigments into the broth was greatest at 60°C. Boiling (97°C) rapidly coagulated the meat pigments and minimized the leaching of heme pigments into the broth. More total iron (85.3%) was retained in boiled (97°C) meat than in meat heated 1 hr at 60°C (81.6%), 77°C (78.2%) or autoclaved (77.5%).

Slurry Method for Rapid DCP Atomic Emission Determination of Residual Bone Fragments in Mechanically Separated Turkey

A slurry atomization direct current plasma (DCP) emission method is reported which involves a minimum of sample preparation for the spectroscopic determination of residual bone solids (as calcium) in mechanically separated turkey. Lengthy wet-ashing methods have been replaced here by a simple approach involving a 2-min “Polytron” homogenization step followed by shaking of the meat homogenate for ∼10 s with dilute nitric acid at room temperature. The sample bulk remains as a suspension of solids that is immediately and directly pumped to a clog-free Babington-type nebulizer installed in a three-electrode DCP emission spectrometer for Ca determination. Before homogenizing, mechanically separated turkey (MST) normally contains bone fragments in the particle size range 0.1 to 0.8 mm. For these MST samples, quantitative Ca recoveries are achieved by the new matrix-modified slurry atomization DCP atomic emission method within about 10 min of the time the meat product is received for bone solids analysis by the lab.

Simplified Slurry Method for Direct Flame Emission Determinations of Dietary Salt in Processed Meat

The rapid, direct slurry atomization flame emission procedure for Na and K determination is shown to give accurate results for a variety of processed meats including bologna, salami, sausage, ham, bacon, and pizza products. Wet and dry ashing methods are found to be unnecessary in this application. The sample preparation scheme for the elements Na and K has been even further simplified over our previous slurry atomization report (Ref. 1) by elimination of the sonic/cavitational homogenizer in favor of an ordinary household food processor (meat grinder). Ground meat or pizza is simply suspended by being shaken in some deionized water followed immediately by direct flame emission analysis of the suspension using a slurry nebulizer and a high-solids premixed natural-gas/air flame. A simple clinical-type filter photometer is evaluated as a substitute for the grating instrument previously used for the determination of dietary salt in processed meat by slurry atomization.

Extraction and Flameless AAS Determination of Germanium in Lignite Fly Ash

Abstract The use of dicyclohexyl-18-crown-6 methyl isobutyl ketone solution in extraction and flamelessatomic absorption spectrophotometry (AAS) determination of germanium in lignite fly ashes have been studied. Germanium is usually determined in lignites after the carbonaceous part of the sample has been burnt by a dry or wet ashing method. However, methods are described for direct determination of germanium. In the present paper a wet ashing method is reported for the determination of germanium in lignite fly ashes by flameless AAS after extraction into dicyclohexyl-18-crown-6 methyl isobutyl ketone (MIBK) solution. Solvent extraction is a known hydrometallurgical method that could be applied in germanium recovery.

Stoichiometry of iron binding by uteroferrin and its relationship to phosphate content.

The analysis of uteroferrin's iron content by an acid-release method used in previous studies shows a critical dependence on phosphate, i.e. the native phosphate-free enzyme yields two irons/molecule, while enzyme with one tightly bound phosphate gives closer to one iron. In contrast, two irons/molecule of protein are found in samples assayed by a wet ash method. When iron assays are carried out on samples of purple two-iron protein reductively stripped of their phosphate, both methods again yield two iron atoms/molecule. However, the discrepancy between the two methods recurs when phosphate is added to samples of pink protein which were formerly free of phosphate. These results suggest that phosphate bound to native uteroferrin may have interfered with iron determinations in some earlier studies. Furthermore, enzyme samples with one tightly bound phosphate have the optical purity index (i.e.A280/A545 approximately less than 14.0) and extinction coefficient at 280 nm, characteristic of putative one-iron preparations. There is little doubt, therefore, that previous EPR, magnetic susceptibility, and iron titration experiments thought to have been carried out on genuine one-iron preparations were in fact done on samples of two-iron protein bearing a single tightly bound phosphate. Reassessment of earlier studies indicates that the properties of putative one-iron preparations may be reconciled with those of the two-iron phosphate-laden protein studied here.

A comparative examination of sample treatment procedures for ICAP-AES analysis of biological tissue

The objective of this study was to contribute to the evaluation of existing sample preparation procedures for ICAP-AES analysis of biological material. Performance characteristics were established of current digestion procedures comprising extraction, solubilization, pressure digestion, and wet and dry ashing methods. Apart from accuracy and precision, a number of criteria of special interest for the analytical practice was applied. As a test sample served SRM bovine liver. In this material six elements were simultaneously determined. Results showed that every procedure has its defects and advantages. Hence, unambiguous recommendation of standard digestion procedures can be made only when taking into account the specific analytical problem.

A Low Temperature Ashing Pretreatment Method for the Analysis of Heavy Metals in Foods

A low temperature ashing (LTA) pretreatment method was developed for the analysis of heavy metals in foods, and the results were compared with those obtained by the conventional wet and dry ashing methods.1) The LTA method requires few reagents, and utilizes oxygen plasma. Ashing can thus be done easily and simply, with little risk of contamination of samples by metals.2) Before LTA, treatments may be necessary to remove moisture from samples and to prevent losses from samples with high contents of oils.3) There was no significant loss of metals in the LTA method except in the case of arsenic. The recoveries of added cadmium, zinc, manganese, lead, chromium, nickel and copper were nearly 100%.4) Loss of arsenic could be avoided in LTA by using a radio frequency power (R. F. power) of less than 100W.5) Analysis of standard samples made available by the joint FAO/WHO investigation group showed that the present method gives accurate results.

Pressure dissolution and real sample matrix calibration for multielement analysis of raw agricultural crops by inductively coupled plasma atomic emission spectrometry

A method utilizing a pressure dissolution technique to minimize sample pretreatment is described for multielement analysis of raw agricultural crops by inductively coupled argon plasma atomic emission spectrometry. The procedure employs a 30-min pressure dissolution of sample composite with 6 M HCI at 80/sup 8/C in 60-mL linear polyethylene bottles. A sample introduction system is also described which permits direct atomization of complex organic matrices. Combined with a real sample matrix callbration technique, this introduction system allows rapid and accurate multielement analysis of complex HCl sample matrix solutions. The procedure compares favorably to more time-consuming conventional wet ashing methods for the determination of major, minor, and trace elements occurring in lettuce, potatoes, peanuts, soybeans, spinach, sweet corn, and wheat. Recoveries for spiked samples, precision studies, and analyses of NBS reference materials demonstrate the reliability and accuracy of the procedure. Advantages and limitations of this technique relative to conventional wet ashing methods are discussed. 2 figures, 7 tables.

Sample Preparation in Determination of Lead in Garden Vegetables by Flame Atomic Absorption Spectrophotometry

Dry and wet ashing methods have been used in the analysis of garden vegetables for Pb. The reliability of wet ashing has been verified by the method of standard additions. Comparison of dry and wet ashing showed good agreement for a variety of garden vegetables. Sample size was more strictly limited for the wet-ashed samples, which led to lower sensitivity. Vegetable samples are commonly analyzed for a number of trace elements, which introduces additional constraints on sample preparation, notably because of Cd loss on dry ashing. Pretreatment with HNO3/H2SO4 ash aid eliminated Cd loss. Reliability of dry ashing with pretreatment was shown with NBS SRM Orchard Leaves, Pine Needles, Spinach, and Tomato Leaves. The analysis was insensitive to ashing temperature in the range 480-625 degrees C. A practical detection limit for the method is about 2 ppm Pb, dry weight basis (DWB). Care must be exercised to avoid contamination of the sample with lead at this level by improper handling. Segregation and acid washing of glassware and protection of the sample from contact with any object not demonstrably clean was necessary. No evidence was found of Pb contamination at this level from tap water washing of fresh vegetables, forced-air oven drying, or grinding with mortar and pestle. No special clean room facilities or laboratory air purification measures were used. Sensitivity was increased 3-fold by extraction with dithizone in CHCl3 followed by back-extraction into dilute HCl. Detection limits were not improved, however, because of variation in the extraction results. The instrumental method for assessing effective correction for back-ground absorbance showed adequate compensation, although comparison of direct and extractive determinations showed a small but significant difference between the methods of about 1 ppm Pb (DWB).

Characterization of Petroleum Sulfonates by a Nonaqueous Titration Method

Abstract A new method is described for the determination of the equivalent weight for petroleum sulfonates. The method is based on the direct acidimetric titration of the sulfonate in acetic acid/acetic anhydride solvent using a titrant of perchloric acid in dioxane. From the titration, the moles of perchloric acid required to react with the sulfonate is measured. The equivalent weight is calculated from the grams of sample titrated and the moles of acid used. The potentiometric titration can be carried out in less than 10 minutes and can be done with 10 to 100 mg of sample. The accuracy and precision of the procedure were examined by the titration of sodium salts of p-toluene sulfonate, 2-naphthalene sulfonate, and petroleum sulfonates. In general, values for the equivalent weight were within 2% of those values determined by the Epton titration, by wet ashing methods, or from the theoretical value. The relative standard deviation (RSD) for the procedure is estimated to be 0.5%. For p-toluene sulfonate, an RSD of 0.15% was calculated. The new method was used to determine the equivalent weights for three fractions of a petroleum sulfonate obtained by the preferential elution from silica gel with alcohol. A series of samples with varying equivalent weight was prepared by proportional combination of the three fractions. Analysis by high-performance liquid chromatography (HPLC) gave a set of data points of peak areas for the series. A plot of equivalent weight as a function of disulfonate to total peak area ratio resulted in a straight line. The slope of this line is descriptive of the molecular weight range for the petroleum sulfonate.