Ultrasound-assisted Digestion Research Articles

Optimization of Selective Hydrometallurgical Tantalum Recovery from E-Waste Using Zeolites.

To protect future high-tech metal demand, a selective and efficient recovery method for tantalum from a tantalum-rich e-waste component sample was developed. Ultrasound-assisted digestion of the component sample was optimized, and the highest dissolution rate was achieved using a mixture of 8 mol/L H2SO4 and HF at a temperature of 60 °C. The determined amount of tantalum was as high as 11000 ± 1000 mg/kg, which results in a high potential for recyclable tantalum. The other major elements of this complex e-waste fraction were silicon, iron, aluminum, and tin. Efficient recovery of tantalum from the leachate was performed using the zeolite material ZSM-5. Extremely high selectivity and a recovery rate of over 98% were obtained. In terms of adsorption efficiency, selectivity, and durability of the material, optimal adsorption was obtained using the diluted sample at 0.5 mol/L of H2SO4. The adsorption capacity of ZSM-5 for tantalum was determined to be 10.5 ± 0.6 mg/g, and tantalum was selectively eluted with 1:4 diluted ethanolamine with a yield of 87.2 ± 1.5%.

Composite Hydrogels of Ultrasound-Assisted-Digested Formic Acid-Decellularized Extracellular Matrix and Sacchachitin Nanofibers Incorporated with Platelet-Rich Plasma for Diabetic Wound Treatment.

In this study, an ultrasound-assisted digestion method of a formic acid-decellularized extracellular matrix (dECM) of porcine skin was developed and optimized to form UdECM hydrogels for diabetic wound healing. Results demonstrated that ultrasonication improved the extraction rate of collagen from dECM samples, preserved the collagen content of dECM, reduced residual cells, and extracted greater DNA contents. Scanning electron microscope (SEM) analyses were performed, which demonstrated the optimal porosity on the surface and density of the cross-section in the hydrogel structure, which could control the release of growth factors embedded in UdECM hydrogels at desirable rates to boost wound healing. A wound-healing study was conducted with six different composite hydrogels, both empty materials and materials enriched with rat platelet-rich plasma (R-PRP), sacchachitin nanofibers (SCNFs), and TEMPO-oxidized sacchachitin in diabetic rats. The assessment based on scars stained with hematoxylin and eosin (H&E), Masson's trichrome (MT), and a cluster of differentiation 31 (CD31) staining showed that the UdECM/SC/R-PRP treatment group had the most significant efficacy of promoting healing and even recovery of diabetic wounds to normal tissues. UdECM/R-PRP and UdECM/SCNFs demonstrated better healing rates than UdECM hydrogel scaffolds, which had only recovered 50% resemblance to normal skin. Treatment with both UdECM/TEMPO 050 and UdECM/TEMPO 050/R-PRP hydrogel scaffolds was ranked last, with even poorer efficacy than UdECM hydrogels. In summary, formulated UdECM and SCNF hydrogels loaded with PRP showed synergistic effects of accelerating wound healing and ultimately stimulating the wound to recover as functional tissues. This newly UdECM/SCNF composite hydrogel has promising potential for healing and regenerating diabetic wounds.

Sequential ultrasound-assisted digestion procedure for determination of cadmium and lead contaminants in sea grapes and some seaweed products

Sequential ultrasound-assisted digestion procedure for determination of cadmium and lead contaminants in sea grapes and some seaweed products

A quantitative strategy of ultrasound-assisted digestion combined UPLC-MS/MS for rapid identifying species-specific peptide markers in the application of food gelatin authentication

Gelatins are important and frequently-used food additives, but the quality control of gelatins is always an intractable problem in routine analysis. In this work, a new strategy for simultaneously rapid identification and quantification of gelatins from various species using ultrasound assisted digestion-UPLC-MS/MS was described. Fourteen peptide markers were used for authenticity of gelatins by the presence or absence of these species-specific peptides. In the meantime, adulteration ratios could be calculated based on the peak area of different species peptide markers. With 10 g/L trypsin and ultrasound application, digestion time could be decreased from >12 h (traditional method) to 5 min, and the determination of animal gelatins could be achieved in 20 min with a single analysis run. Twenty-five commercial gelatin samples were screened, among which two deer-hide gelatin samples were adulterated with 900 g/kg and 265 g/kg cattle-hide gelatin (CHG); two donkey-hide gelatin (ACC) samples were adulterated with 66 g/kg and 381 g/kg horse-hide gelatin; and one ACC sample was adulterated with 786 g/kg CHG. This strategy provides an efficient and sensitive authentication and traceability of gelatin-containing products, and could also be applied to processed meat or protein food.

Chemometric optimization of trypsin digestion method applying infrared, microwave and ultrasound energies for determination of caseins and ovalbumin in wines

Caseins and ovalbumin are frequently used as wine fining agents to remove undesirable compounds like polymeric phenols. Their presence in wines is a subject of concern because may cause adverse effects on susceptible consumers, especially when their presence is not labeled. A key step for its determination is trypsin digestion, which is considered the bottleneck of bottom-up approach workflow because usually requires several hours. To reduce this time, the objective of this work was to carry out a chemometric optimization of trypsin digestion method applying infrared, microwave and ultrasound energies to determine caseins and ovalbumin in wines. The conditions of each accelerated digestion method were optimized using a Response Surface Methodology based on central composite design. The parameters optimized were digestion time and trypsin: protein ratio. The response variable evaluated was digestion yield, which was determined through the peak area of each protein transition determined by liquid chromatography-mass spectrometry. The most effective technique was microwave followed by ultrasound and infrared. Since optimal values of microwave and ultrasound-assisted digestion were the same, the later was chosen considering sample preparation and cost. Applying the proposed approach, a reduction of ca. 140 and 240-fold on digestion time was achieved compared with optimized and non-optimized conventional methods, respectively. With this workflow, both proteins were digested in a single 3min process allowing its detection by liquid chromatography-mass spectrometry at µgL-1 level, which is ca. 60 times lower than the current limit of 0.25mgL-1.

Nutritional analysis of Spirulina dietary supplements: Optimization procedure of ultrasound-assisted digestion for multielemental determination

Arthrospira platensis and Arthrospira maxima are a type of blue-green microalga used as a dietary supplement (Spirulina). A low time-consuming ultrasound-assisted digestion (UAD) of Spirulina supplements for multielemental determination by microwave induced plasma atomic emission spectrometry (MPAES) was performed. Several parameters such as acid concentration (AC), thermostated water bath (TWB), digestion time (DT) and UAD – probe or bath – affecting the digestion process were evaluated through a full factorial design. Under the optimal conditions −100 °C for TWB, 5% for AC and 10 min for DT- and selecting the bath as the proper UAD system, the concentrations of 15 analytes (Al, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, V, Zn) were reported. The values are in accordance with the recommendation established by Food and Drug Administration (FDA) excepting for Cd. The knowledge of Spirulina multielemental composition contributes to an outstanding nutritional and toxicological report for human health.

A qualitative and quantitative evaluation of the peptide characteristics of microwave- and ultrasound-assisted digestion in discovery and targeted proteomic analyses.

Fast digestion methods can dramatically accelerate enzyme digestion and increase the throughput of proteomic analysis. However, the peptide characteristics of fast digestion methods and their performance in discovery and targeted proteomic analysis must be systematically evaluated. Three digestion methods, including overnight digestion, microwave-assisted protein enzymatic digestion (MAPED), and high-intensity focused ultrasonic-assisted enzymatic digestion (HIFUSAED), in trypsin or in trypsin/Lys-C were comprehensively compared in both discovery and targeted proteomics analysis using the HeLa cell proteome. In discovery proteomic analysis, the highest numbers of peptides and proteins were identified when the sample was digested via the MAPED method with trypsin/Lys-C. The fast digestion methods showed a higher mis-cleavage rate and a lower semi-tryptic rate than the overnight digestion method. In both label-free quantitative analysis and targeted proteomic analysis, both fully cleaved peptides (FCPs) and mis-cleaved peptides (MCPs) from the fast digestion methods and the overnight digestion method showed good reproducibility if they showed good abundance. When both the FCPs and MCPs were included in the analysis, the MAPED with trypsin/Lys-C method showed the best results for both discovery proteomic analysis and relative quantitative targeted proteomic analysis. These results will be beneficial for the application of fast digestion methods to proteomics.

Stripping voltammetric determination of trace cadmium and lead in Thai organic unpolished rice after ultrasound-assisted digestion

A cost-effective and environmentally friendly method was developed for the simultaneous determination of trace cadmium and lead contaminants in unpolished rice. An ultrasound-assisted digestion (UAD) procedure was ultilized for sample preparation prior to determination of Cd(II) and Pb(II) by anodic stripping voltammetry (ASV) using an eco-friendly bismuth film electrode (BiFE). The efficiency of the proposed UAD procedure was evaluated by certified reference material of glutinous rice powder. The parameters influencing UAD such as solvent system, sample mass, presonication time and sonication time were evaluated. Using the deposition time of 300s for ASV, linear calibration graphs in a range of 10–200μgL−1 for Cd(II) and 5–200μgL−1 Pb(II) were obtained with detection limits of 0.11 and 0.06μgL−1 for Cd(II) and Pb(II), respectively. Relative standard deviations were 3.5 and 2.3% for 10μgL−1 of Cd(II) and Pb(II), respectively. The developed system was successfully applied to the analysis of Cd(II) and Pb(II) in various types of organic unpolished rice samples and validated by flame atomic absorption spectrometric method. All studied Thai organic unpolished rice samples were not contaminated with Cd(II) and Pb(II).

Quality assessment of trace Cd and Pb contaminants in Thai herbal medicines using ultrasound-assisted digestion prior to flame atomic absorption spectrometry

A simple, efficient, and reliable ultrasound-assisted digestion (UAD) procedure was used for sample preparation prior to quantitative determination of trace Cd and Pb contaminants in herbal medicines using flame atomic absorption spectrometry. The parameters influencing UAD such as the solvent system, sample mass, presonication time, sonication time, and digestion temperature were evaluated. The efficiency of the proposed UAD procedure was evaluated by comparing with conventional acid digestion (CAD) procedure. Under the optimum conditions, linear calibration graphs in a range of 2–250 μg/L for Cd, and 50–1000 μg/L for Pb were obtained with detection limits of 0.56 μg/L and 10.7 μg/L for Cd and Pb, respectively. The limit of quantification for Cd and Pb were 1.87 μg/L and 40.3 μg/L, respectively. The repeatability for analysis of 10 μg/L for Cd and 100 μg/L for Pb was 2.3% and 2.6%, respectively. The accuracy of the proposed method was evaluated by rice flour certified reference materials. The proposed method was successfully applied for analysis of trace Cd and Pb in samples of various types of medicinal plant and traditional medicine consumed in Thailand. Most herbal medicine samples were not contaminated with Cd or Pb. The contaminant levels for both metals were still lower than the maximum permissible levels of elements in medicinal plant materials and finished herbal products sets by the Ministry of Public Health of Thailand. The exception was the high level of Cd contamination found in two samples of processed medicinal plants.

Determination of macronutrients, micronutrients, non-essential elements in milk based-infant formulas by atomic absorption and inductively coupled plasma-optical emission spectroscopy after microwave and ultrasound assisted digestion

ABSTRACTMicrowave and ultrasound procedures for samples preparations were adopted and the elements were determined by validated flame atomic absorption and inductively coupled plasma–optical emission spectrometry. Student’s t-test was established whether there was a difference between the sample preparation methods. Trueness of certified values by all methods was ensured which were not differing significantly at 95% level of confidence interval. The highest intensity ratio of magnesium (II)/magnesium (I) was obtained at 1120 radiofrequency value to achieve accurate and reproducible results by inductively coupled plasma–optical emission spectrometry. The value of corresponding correlation coefficient (r2) were obtained as >0.990 indicating the excellent linearity for concentration range chosen for each element to be determined in commercial samples. Results showed that concentrations of calcium, magnesium, potassium, sodium, chromium, copper, iron, manganese, selenium, and zinc found in commercially available products are in good agreement with label as declared by the manufacturers. Exposure to aluminum, cadmium, and lead from consumption of products under evaluation was estimated and it was in compliance with permissible level suggested by European Commission regulations. Regarding the food safety monitoring, the proposed methods are rapid and met green chemistry approach so that can be implemented in laboratories easily for routine analysis.

Ultrasound-assisted digestion of biodiesel samples for determination of metals by stripping voltammetry

Room-temperature ultrasound-assisted digestion of biodiesel for stripping voltammetry of metals with adequate recovery values (94–108%) and low residual carbon content is demonstrated.

Characterization and leaching of real fluorescent lamp waste for the recovery of rare earth metals and mercury

Current resource issues and the growing demand for metals used in advanced technologies have focused attention towards more efficient processing of end-of-life products and waste streams. Fluorescent lamp waste is a viable target for the recovery of rare earth metals (REMs); specifically cerium, europium, gadolinium, lanthanum, terbium, and yttrium. Waste originating from a discarded lamp processing facility was investigated using Scanning Electron Microscopy/Energy Dispersive Spectroscopy and X-ray Diffraction. Total dissolution experiments were carried out with aqua regia at elevated temperatures in order to estimate an average metal content and assess the recycling potential of the material.Leaching using different solutions (pure water, ammonium chloride, acetic acid, nitric and hydrochloric acid) and parameters (temperature, ultrasound-assisted digestion, solid:liquid ratio and leaching agent concentration) was investigated for the recovery of REMs and mercury. Cerium, europium, gadolinium, lanthanum, terbium, and yttrium were the REMs identified, with a total average content of 8.4±0.4g/kg dry waste. An average of 0.7±0.1g mercury/kg dry waste was quantified. Partial removal of impurities from the material raised the average REMs content to 105.7±5.3g/kg waste. Pure water and ammonium chloride solution (1M) performed poorly as leachants. Efficient leaching of europium and yttrium (over 95%, respectively 97% dissolution) was achieved in less than 24h at 20±1°C, using weak nitric and hydrochloric acid solutions (0.5M). Leaching of cerium, gadolinium and terbium occurred slowly and did not reach equilibrium even after 96h. An increased acid concentration and increased temperature, and ultrasound-assisted digestion improved the leaching efficiency for all investigated elements. Hydrochloric acid proved to be as efficient as nitric acid when it comes to solubilizing most REMs. The former showed better efficiency for mercury: 89.6±3.3% vs. 23.2±0.3%, when using a 4M solution. Acetic acid (25% v/v solution) dissolved approx. 50% of the europium, 75% of all yttrium, between 2 and 10% of the other REMs, and just over 2% of the mercury. Based on the observations, several processing methods are suggested for the samples investigated.

Determination of toxic elements in glass beads used for pavement marking by ICP OES

A simple and rapid method for the simultaneous determination of As, Sb and Pb in glass beads used for pavement markings on highway surfaces by axial view inductively coupled plasma optical emission spectrometry is presented. Three sample preparation approaches using a 3:1 mixture of HNO3 and HF were evaluated: (01) an open beaker approach; (02) a microwave-assisted digestion system, based on EPA method 3052 and (03) an ultrasound-assisted digestion. To react with the excess of residual fluoride, H3BO3 and ZrOCl2 were investigated. Spectral interference was evident when ZrOCl2 was used for determination of As. Ultrasound-assisted digestion using 3mL of HNO3 and 1mL of HF for 1h at 40kHz followed by addition of H3BO3 was chosen for in-depth study. Quantification limits (10s, n=10) based on a 0.1g subsample diluted to 50mL were: 30mgkg−1 for As (193.696nm), 10mgkg−1 for Sb (206.834nm) and 5mgkg−1 for Pb (220.353nm). Analysis of spiked samples provided recoveries in the range of 87 to 104% for all analytes. Of nineteen Brazilian and imported samples analyzed, As was present above the quantification limit in five, Sb in one and Pb in almost all. Some samples, all imported, showed values above the limit allowed by the Brazilian legislation, i.e., 200mgkg−1 for As, Sb and Pb. Solubility tests showed high levels of As leaching for all imported samples, above the specification limit. Leachability tests showed that the glass beads cannot be classified as toxic materials; however, the release of potentially toxic elements could cause some environmental risks.

Ultrasound-assisted extraction for total sulphur measurement in mine tailings

A sample preparation method for percentage recovery of total sulphur (%S) in reactive mine tailings based on ultrasound-assisted digestion (USAD) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) was developed. The influence of various methodological factors was screened by employing a two-level and three-factor (23) full factorial design and using KZK-1, a sericite schist certified reference material (CRM), to find the optimal combination of studied factors and %S. Factors such as the sonication time, temperature and acid combination were studied, with the best result identified as 20min of sonication, 80°C temperature and 1ml of HNO3:1ml of HCl, which can achieve 100% recovery for the selected CRM. Subsequently a fraction of the 23 full factorial design was applied to mine tailings. The percentage relative standard deviation (%RSD) for the ultrasound method is less than 3.0% for CRM and less than 6% for the mine tailings. The investigated method was verified by X-ray diffraction analysis. The USAD method compared favorably with existing methods such as hot plate assisted digestion method, X-ray fluorescence and LECO™-CNS method.

The determination of antimony and arsenic concentrations in fly ash by hydride generation inductively coupled plasma optical emission spectrometry

Hydride generation inductively coupled plasma optical emission spectrometry (HG-ICP-OES) was used in the determination of As and Sb concentrations in fly ash samples. The effect of sample pre-treatment reagents and measurement parameters used for hydride generation was evaluated. Due to memory effects observed, the appropriate read delay time was adjusted to 60 s resulting in RSDs 0.6% and 2.3% for As and Sb, respectively. The most suitable volumes of pre-reduction reagents for 10 mL of sample were 4 mL of KI/ascorbic acid (5%) and 6 mL of HCl (conc.). The determination of Sb was significantly interfered by HF, but the interference could be eliminated by adding 2 mL of saturated boric acid and heating the samples to 60 °C at least 45 min. The accuracy of the method was studied by analyses of SRM 1633b and two fly ash samples with the recovery test of added As and Sb. As high a recovery as 96% for SRM 1633b was reached for As using 193.696 nm with two-step ultrasound-assisted digestion. A recovery rate of 103% was obtained for Sb using 217.582 nm and the pre-reduction method with the addition of 2 mL of saturated boric acid and heating. The quantification limits for the determination of As and Sb in the fly ash samples using two-step ultrasound-assisted digestion followed with HG-ICP-OES were 0.89 and 1.37 mg kg −1, respectively.

Determination of metals in coal fly ashes using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry

A method for determination of Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn in coal fly ash samples using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) is proposed. The digestion procedure consisted in the sonication of the previously dried sample with hydrofluoric acid and aqua regia at 80 °C for 30 min, elimination of fluorides by heating until dryness for about 1 h and dissolution of the residue with nitric acid solution. A classical digestion method, used as comparative method, consisted in the addition of HCl, HNO 3 and HF to 1 g of sample, and heating on a hot plate until dryness for about 6 h. The proposed method presents several advantages: it requires lower amounts of sample and reagents, and it is faster. It is also advantageous when compared to the published methods, which also use ultrasound-assisted digestion procedure: lower detection limits for Co, Cu, Ni, V and Zn, and it does not require shaking during the digestion. The detection limits (μg g −1) for Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn were 0.06, 0.37, 1.0, 25, 0.93, 0.45, 4.0, 1.7 and 4.3, respectively. The results were in good agreement with those obtained by the classical method and reference values. The exception was Cr, which presented low recoveries in classical and proposed methods (83 and 87%, respectively). Also, the concentration for Cu obtained by the proposed method was significantly different from the reference value, in spite of the good recovery (91 ± 1%).

Ultrasound assisted pseudo-digestion for determination of iron and manganese in citric acid fermentation mediums by electrothermal atomic absorption spectroscopy

Abstract A sensitive, simple and rapid method for ultra-trace determination of iron and manganese based on ultrasound assisted pseudodigestion in citric acid fermentation medium samples (beet and cane molasses and raw sugar based mediums) is described. Parameters influencing pseudo-digestion, such as sonication time, sample mass and solvent system were fully optimized. Final solutions obtained upon sonication were analyzed by electrothermal atomic absorption spectrometry (ETAAS). The best conditions for metal pseudo-digestion were as follows: a 25, 30 and 20 min sonication time for beet molasses, cane molasses and raw sugar based medium samples, respectively, 0.7 g sample mass of raw sugar based samples, 0.5 g sample mass of molasses based samples and an extraction mixture of concentrated HNO3-H2O2, in 25 mL of solvent. Analytical results obtained for the two metals by ultrasound assisted pseudo-digestion and conventional wet digestion methods showed a good agreement. This method reduces the time required for all treatments (heating to dryness, cooling and separation) in comparison with conventional wet digestion method. The accuracy of the method was tested by comparing the obtained results with that of conventional wet digestion method.

The determination of trace element concentrations in fly ash samples using ultrasound-assisted digestion followed with inductively coupled plasma optical emission spectrometry

A method of ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of trace element (chromium, copper, lead, nickel, vanadium and zinc) concentrations in fly ash samples was developed. All the measurements were performed in robust plasma conditions. Ultrasound-assisted digestion procedures using digestion solutions of aqua regia and hydrofluoric acid (HF) resulted in recovery rates of over 80% for all the analyte elements. Ultrasound-assisted two-step digestion with digestion solutions of 6 mL of HNO 3 (Step 1) and 3 mL of HNO 3 + 3 mL of HF (Step 2) resulted in recovery rates of over 92% for all the analyte elements with one exception, chromium, which had a recovery of about 85%. The analysis of SRM 1633b showed that the two-step ultrasound-assisted digestion method developed resulted in chromium, copper, nickel and zinc concentrations higher than the microwave digestion method standardized by the United States Environmental Protection Agency (USEPA method 3052). This is the very first time when a digestion method using ultrasound resulted in higher efficiency than microwave (USEPA method 3052) for chromium and nickel in very hard to dissolve samples. The major advantages of the ultrasound-assisted digestion over microwave digestion is the high treatment rate (about 30 samples simultaneously with a sonication time of 18 min) and the possibility to use new sample vessels without a significant increase in costs.

Trivalent manganese as an environmentally friendly oxidizing reagent for microwave- and ultrasound-assisted chemical oxygen demand determination

In the present work manganese(III) has been used as oxidant and microwave radiation and ultrasound energy have been assessed to speed up and to improve the efficiency of digestion step for the determination of chemical oxygen demand (COD). Microwave (MW) and ultrasound-assisted COD determination methods have been optimized by means of experimental design and the optimum conditions are: 40 psi pressure, 855 W power and 1 min irradiation time; and 90% of maximum nominal power (180 W), 0.9 s (s −1) cycles and 1 min irradiation time for microwaves and ultrasound, respectively. Chloride ion interference is removed as hydrochloric acid gas from acidified sample solutions at 150 °C in a closed reaction tube and captured by bismuth-based adsorbent suspended above the heated solution. Under optimum conditions, the evaluated assisted digestion methods have been successfully applied, with the exception of pyridine, to several pure organic compounds and two reference materials. COD recoveries obtained with MW and ultrasound-assisted digestion for five real wastewater samples were ranged between 86–97% and 68–91%, respectively, of the values obtained with the classical method (open reflux) used as reference, with relative standard deviation lower than 4% in most cases. Thus, the Mn(III) microwave-assisted digestion method seems to be an interesting and promising alternative to conventional COD digestion methods since it is faster and more environmentally friendly than the ones used for the same purpose.

Determination of mineral and trace element concentrations in pine needles by ICP-OES: evaluation of different sample pre-treatment methods

In the present study, the determination of mineral and trace elements (Al, B, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn) from pine needles using three sample pre-treatment methods followed by inductively coupled plasma optical emission spectrometry, was examined. Sample pre-treatment methods tested were microwave digestion, ultrasound-assisted digestion and dry ashing. The new ultrasound-assisted digestion method was optimised by the analysis of the standard reference material (SRM) 1575a (pine needles) sample. The speed of dry ashing method was significantly increased by ultrasound dissolution after ashing. All the ICP-OES measurements were performed in robust plasma conditions which were tested by measuring the Mg II 280.270 nm/Mg I 285.213 nm line intensity ratios. The microwave digestion resulted generally in slightly higher element concentrations than ultrasound-assisted digestion. B, Cu and Na resulted in such low concentrations that they could not be accurately determined by using the microwave digestion method. The t-tests found no significant differences between the certified and the determined element concentrations of the SRM 1575a using the dry ashing method followed with ultrasound dissolution.