Microwave-assisted Acid Extraction Research Articles

Microwave-assisted acid extraction of high-methoxyl kinnow (Citrus reticulata) peels pectin: Process, techno-functionality, characterization and life cycle assessment

The present study assessed the efficacy of kinnow peel pectin-acetic acid extraction using microwave heating at 110 °C, pH 2.2 for 10 min with a 1:2 ratio supernatant to ethanol for higher yield. The kinnow peel was freeze dried and grinded to fine powder for pectin extraction. The microwave extracted (ME) kinnow pectin showed 833 mg equivalent weight, 7.44 % methoxyl content, 66.67 % degree of esterification, 63.15 % galacturonic acid content and evinced higher purity than commercial citrus pectin. ME kinnow pectin exhibited shear thinning behaviour while higher apparent viscosity (Pa. s) at 20 % concentration. The ME kinnow pectin showed characteristic functional groups and a less crystalline structure as deduced from FT-IR, SEM and XRD respectively, and a higher thermal decomposition analysed from TGA. Further, life cycle assessment (LCA) predicted that the ethanol and acetic acid were major contributors toward climate change in this study. ME kinnow pectin has the potential to be used as a commercial pectin in various food applications.

Microwave-assisted extraction of pectin from onion and garlic waste under organic, inorganic and dual acid mixtures

This study aims to investigate pectin extraction from garlic (GW) and onion waste (OW) by microwave-assisted (MAE) and sequential microwave assisted-hot acid extraction (MAHE) methods. All extractions were performed under three different media including organic acids [citric (CA) and acetic (AA)], inorganic acids [sulfuric (H2SO4) and hydrochloric (HCl)] and their mixtures. GW provided more pectin yields compared with OW. While the highest pectin yields from GW and OW by MAE in H2SO4 were respectively 24.62 ± 0.65 and 24.93 ± 0.59%, these yields under MAHE were 27.99 ± 0.36 and 28.43 ± 0.42%, respectively. Higher pectin yields and galacturonic acid (Gal-A) contents were mostly achieved in inorganic acids. However, degree of esterification (DE), methoxyl content (MeO) and equivalent weight (EW) values were higher for the pectins extracted under organic acids. Extraction of pectin from GW and OW was also accomplished in dual acidic media by MAE. Addition of inorganic acids to the organic acid solutions resulted in increasing pectin yields. The highest pectin yields from GW and OW under dual acid solutions were respectively 23.36 ± 0.66 and 21.88 ± 0.52%, and achieved in 1/3 HCl-H2SO4 and 1/3 CA-H2SO4 mixtures by MAE. While increasing inorganic acid contents in dual acid solutions resulted in enhanced Gal-A contents, increasing organic acid volume also generated higher DE and MeO values of the pectins. Obtained successful outcomes indicate that MAHE method could be used as an efficient extraction technique for the higher pectin yields, and utilization of organic-inorganic dual acid mixtures during MAE provides enhanced yields and controlled physicochemical properties of pectin.Graphical abstract

Distribution of Minor and Major Metallic Elements in Residential Indoor Dust: A Case Study in Latvia.

The coronavirus disease 2019 (COVID-19) pandemic has not only brought considerable and permanent changes to economies and healthcare systems, but it has also greatly changed the habits of almost the entire society. During the lockdowns, people were forced to stay in their dwellings, which served as a catalyst for the initiation of a survey on the estimation of the metallic element content in residential indoor dust in different parts of Latvia. This article presents the study results obtained through the analysis of collected dust samples from 46 dwellings, both in the capital of Latvia, Riga, and in smaller cities. Two methods were employed for indoor dust collection: vacuum sampling and manual sampling with a brush and plastic spatula. After microwave-assisted acid extraction, the samples were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) in terms of the major (Na, K, Ca, Mg, Al and Fe) and minor (Mn, Ni, Co, Pb, Cr, As, Ba, Li, Be, B, V, Cu, Zn, Se, Rb, Sr, Cd, La, Ce and Bi) elements. For the data analysis, principal component analysis was performed. Among the measured metals, the highest values were determined for the macro and most abundant elements (Na > K > Ca > Fe > Mg > Al). The concentration ranges of the persistently detected elements were as follows: Pb, 0.27-1200 mg kg-1; Cd, 0.01-6.37 mg kg-1; Ni, 0.07-513 mg kg-1; As, 0.01-69.2 mg kg-1; Cu, 5.71-1900 mg kg-1; Zn, 53.6-21,100 mg kg-1; and Cr, 4.93-412 mg kg-1. The critical limit values of metallic elements in soil defined by the legislation of the Republic of Latvia (indicating the level at or above which the functional characteristics of soil are disrupted, or pollution poses a direct threat to human health or the environment) were exceeded in the following numbers of dwellings: Pb = 4, Ni = 2, As = 1, Cu = 16, Cr = 1 and Zn = 28.

Emulsification characteristics of soy hull polysaccharides obtained by membrane separation

Membrane separation technology was used to separate and purify the microwave-assisted oxalic acid extraction of soy hull polysaccharides (MOSP) in order to obtain samples of different molecular weights. The emulsification characteristics of the MOSP were investigated including protein adsorption, polysaccharide adsorption, interfacial tension, emulsion index, and particle size; optical microscopy and Phenom electron microscopy were used to elucidate the emulsion structures. In addition, Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and high-performance gel-filtration chromatography (HPGFC) were used to study the differences in the components and structures of MOSP in different molecular weights. The molecular weight had several important effects on the emulsifying properties of MOSP. The adsorption capacities of the emulsion droplets containing low molecular weight MOSP (L-MOSP), middle molecular weight MOSP (M-MOSP), and high molecular weight MOSP (H-MOSP) were relatively low, and those of H-MOSP were slightly higher than those of L-MOSP. With extended storage time, the particle sizes of the emulsions rich in L-MOSP, M-MOSP, and H-MOSP increased. L-MOSP, M-MOSP, and H-MOSP were mainly composed of furans. The conformation of the molecular chain was spherical. The emulsions formed with H-MOSP were the most stable.

Mobility, spatial variation and human health risk assessment of mercury in soil from an informal e-waste recycling site, Lagos, Nigeria.

Spatial variations and mobility of mercury (Hg) and Hg associations with other potentially toxic elements (PTEs) were studied in soil samples from Alaba, the largest e-waste recycling site in Nigeria and West Africa. Total Hg concentration was determined in surface soil samples from various locations using cold vapour atomic absorption spectrometry (CVAAS) following microwave-assisted acid extraction, while sequential extraction was used to determine operationally defined mobility. The concentrations of the PTEs arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn) metals were determined using inductively coupled plasma mass spectrometry (ICP-MS) following microwave-assisted digestion with aqua regia. Total Hg concentration ranged from < 0.07 to 624mg/kg and was largely dependent on the nature and intensity of e-waste recycling activities carried out. Mobile forms of Hg, which may be HgO (a known component of some forms of e-waste), accounted for between 3.2 and 23% of the total Hg concentration, and were observed to decrease with increasing organic matter (OM). Non-mobile forms accounted for >74% of the total Hg content. In the main recycling area, soil concentrations of Cd, Cd, Cu, Hg, Mn, Ni, Pb and Zn were above soil guideline values (Environment Agency in Science Report, 2009; Kamunda et al.,2016). Strong associations were observed between Hg and other PTEs (except for Fe and Zn) with the correlational coefficient ranging from 0.731 with Cr to 0.990 with As in April, but these correlations decreased in June except for Fe. Hazard quotient values > 1 at two locations suggest that Hg may pose health threats to people working at the e-waste recycling site. It is therefore recommended that workers should be investigated for symptoms of Hg exposure.

Determination of arsenic chemical species in rice grains using high-performance liquid chromatography coupled to hydride generator with atomic fluorescence detector (HPLC-HG-AFS)

The objective of this work is the validation and implementation of an analytical method for the determination of arsenic chemical species in rice grain samples using High-performance liquid chromatography coupled to a hydride generator with atomic fluorescence detector (HPLC-HG-AFS). The extraction protocol developed was based on HNO3 0.28 M (90 °C, 2 h), microwave-assisted. The results showed recovery percentages of arsenite (As (III)) (99–101%), arsenate (As (V)) (91–96%), dimethylarsinic acid (DMA) (92–102%) and monomethylarsonic acid (MMA) (94–97%). The precision of the method presented coefficients of variation lower than 7% and 8% for repeatability and reproducibility respectively. The detection limits were 2.5, 3.75, 7.5 and 4.0 µg kg−1 for As (III), As (V), DMA and MMA respectively. The proposed methodology is reliable for the quantification of As species, because they are conserved during the extraction.•The extraction protocol developed was based on Microwave-assisted acid extraction.•This methodology offers good sensitivity, precision, accuracy, detection and quantification limits.•It was successfully applied to determination of arsenic chemical species in rice grains.

Performance Parameters of Inductively Coupled Plasma Optical Emission Spectrometry and Graphite Furnace Atomic Absorption Spectrometry Techniques for Pd and Pt Determination in Automotive Catalysts.

Palladium (Pd) and platinum (Pt) are extensively used as catalysts in the petrochemical and automotive industries, and due to high demand for them on the market, their recycling from spent supported catalysts is clearly needed. To assess the content of Pd and Pt in catalysts in order to establish their commercial value or to evaluate the recovery efficiency of technologies used for recycling, reliable analytical methods for determination of these elements are required. Spectrometric methods, such as inductively coupled plasma optical emission spectrometry (ICP-OES) and graphite furnace atomic absorption spectrometry (GFAAS) are powerful tools that can be employed for the determination of Pd and Pt in various sample matrices. However, these methods allow only the injection of liquid samples. In this regard, the digestion of solid sample by microwave-assisted acid extraction procedures at high pressures and temperatures is often used. In this study, a microwave acid digestion method was optimized for the extraction of Pd and Pt from spent catalysts, using a four-step program, at a maximum 200 °C. The resulting solutions were analyzed using ICP-OES, at two different wavelengths for each metal (Pd at 340.458 and 363.470 nm, and Pt at 265.945 and 214.423 nm, respectively) and using GFAAS (Pd at 247.64 nm, Pt at 265.94 nm). Five types of spent catalyst were analyzed and the standard deviations of repeatability for five parallel samples were less than predicted relative standard deviations (PRSD%) calculated using Horvitz’s equation for all the analyzed samples.

A novel method for metals extraction from municipal solid waste using a microwave-assisted acid extraction

This paper investigated the development and evaluation of an extraction process for copper, chromium, cobalt, iron, manganese, zinc, lead, cadmium, barium, magnesium, and vanadium from municipal solid waste incineration ash (bottom and fly ashes) based on microwave-assisted acid extraction method. In this study, a novel conventional microwave-mediated technique was applied by using various acidic extracting agents, namely, hydrochloric acid, nitric acid, and phosphoric acid. Several experimental conditions and parameters were modified and optimized to determine the most effective conditions for maximizing metal extraction. The results were also compared with our preliminary research, which investigated the optimization of conventional heating for extracting the same metals. The current study concluded that the microwave-assisted acid extraction method was much more effective than conventional heating. The metals from the bottom ash were much easier to extract in contrast with the fly ash. For the bottom ash, 71 wt% of Co, 75.69 wt% of Cr, 56.19 wt% of Cd, 35.23 wt% of Ba, 30.2 wt% of Pb, and 5.41 wt% of Mn were effectively extracted using the protocol C (2 M HCl and 3 M H3PO4). 13.87 wt% of Al, 10.59 wt% of Cu, 7.2 wt% of Fe, 5.25 wt% of Mg were also extracted using the protocols D and E (3 M HNO3 and 3 M H2O2) from MSW-BA. On the other hand, for the fly ash, 2.27 wt% of Cu, 0.93 wt% of Fe, 2.32 wt% of Zn, 6.28 wt% of Cd, 1.98 wt% of Ba, 3.46 wt% of Mg and 4.7 wt% of V were extracted by using the protocol A (5 M HCl and 5 M HNO3). 1.48 wt% of Cr, 0.93 wt% of Fe, 1.19 wt% of Mn, and 1.18 wt% of Al were extracted using the protocol C (2 M HCl and 3 M H3PO4). It was also confirmed that higher microwave power levels had a positive effect on the metal extraction, and longer contact times had an adverse effect. When comparing the cost analyses for both methods, it was found that the microwave-assisted acid extraction was less expensive than the conventional heating. The present study offers a promising method, which is simple and cost-effective and presents a minimal environmental risk to extract metals from municipal solid waste incineration ash.

A Single Digestion Procedure for Determination of Major, Trace, and Rare Earth Elements in Sediments

The simultaneous determination of major, trace, and rare earth elements in sediments requires the development of specific procedures to prevent interferences. A single digestion method adapted from the EPA method 3051A is proposed for the quantification of 42 elements in sediments by inductively coupled plasma techniques associated with optical emission spectroscopy (ICP-OES) and mass spectrometry (ICP-MS). A combination of different acids and microwave-assisted acid extraction following hot plate extraction was tested. Evaluation of applicability range, linearity, limits of detection and quantification, selectivity, repeatability, intermediate precision, and trueness showed the accurate determination of all elements. Selectivity, precision, and trueness values were below the criteria established by the laboratory. The applicability of the proposed method was tested in real sediment samples. For each element, difference between duplicates was lower than the corresponding repeatability limit, with the coefficients of variation ranging between 1.7 and 14%. These results point to the usefulness of this method in multi-element determination of major, minor, trace, and REE in sediment samples, showing its applicability in environmental studies related, namely to sediment characterization, monitoring programs, assessment of environmental impacts, sediment provenance, and post-depositional mechanisms.

Types, occurrence, and distribution of microplastics and metals contamination in sediments from south west of Kerkennah archipelago, Tunisia.

Microplastics (MPs) are one of the most significant solid waste pollutants in the marine environment and accumulate in sediments around worldwide. In this study, the pollution level, the type, occurrence, and distribution of MPs in sediments from the southwestern Kerkennah archipelago, Tunisia, were investigated. Sediment samples were collected from 20 adjacent sites through three "lines L1, L2, and L3." MPs were separated from sediment by density flotation (NaCl, 1.2gcm-3) and characterized in terms of shape, size, and color using microscope. The accumulation of toxic chemicals such as trace metals on microplastics was measured by atomic absorption microwave-assisted acid extraction. Polymer types were identified using FTIR-ATR spectroscopy. This study showed that microplastics were found in all samples, which emphasized that their extensive distribution throughout three lines by an average abundance of "MPs" was 611 items/m2. Among the shape categories of plastic particles, fiber and fragment were the most dominant frequent shapes (94%). The more frequent colors found were white (52.7%) and transparent (35.1%). Regarding the sizes, the microplastics below 1mm were the most common accounting for 97% of all plastics. Results of trace metals Zn, Cu, Pb, Cr, and Ni in sediments with concentrations were reported as 3.48μg/g, 0.41μg/g, 0.38μg/g, 0.33μg/g, and 0.12μg/g, respectively. Graphical abstract.

The effect of hemicellulose content on mechanical strength, thermal stability, and water resistance of cellulose-rich fiber material from poplar

The hemicellulose content of cellulosic material from poplar chemi-thermomechanical pulp (CTMP) was controlled by a microwave-assisted formic acid (MFA) extraction process. The environmentally friendly, self-bonded, and cellulose-rich fiber sheets (around 0.3 mm thick and 280 g/m2 grammage) were fabricated via a molding and compression process. The results showed that the MFA treatment effectively controlled the hemicellulose content in the range from 6.8% to 20.4%. Mechanical testing results showed a good linear relationship between the tensile strength and the hemicellulose content, where a higher hemicellulose content obtained a stronger tensile strength. Meanwhile, as hemicellulose content decreased, the onset temperature, representing the thermal stability, increased from 318.1 °C to 335.7 °C and the elastic modulus, representing the mechanical stiffness, increased from 0.047 MPa to 0.068 MPa. Additionally, as the hemicellulose content decreased, the water-resistance of the cellulose-rich fiber sheets improved. During the hemicellulose removal process, the strength of single fibers was found to have a dominant role in the mechanical strength of the cellulose-rich fiber sheets, rather than the inter-fiber bonding strength. This was contrary to research on the delignification process, where the inter-fiber bonding strength was found to be more important than the strength of single fibers in deciding the material strength.

Microwave-assisted formic acid extraction for high-purity cellulose production

The effective separation of hemicelluloses and cellulose is the prerequisite for creating high-value products using wood wastes. In this study, a novel process including mechanical pre-beating, microwave-assisted formic acid (MAFA) extraction, and bleaching treatment was developed for producing high-purity cellulose from the pulp fibers of hardwood waste. Most hemicelluloses and lignin were simultaneously removed (i.e., hemicelluloses were separated from cellulose) due to the MAFA treatment. The pulp fibers were pre-beaten for a loose fiber structure for the formic acid impregnation. The results showed that the introduction of microwave could significantly enhance hemicellulose removal and separation from pulp fibers. The MAFA treatment was performed under atmospheric pressure and mild condition (≤ 100 °C), which led to the significant increase in the lignin yield, cellulose content, crystallinity index, and crystallite homogeneity. After the beating pretreatment and MAFA process (88% formic acid, 100 °C, 4 + 4 h), the hemicellulose removal rate reached 75.5%, and the cellulose purity was as high as 93.2% along with a maximal cellulose crystallinity index (77.5%) and minimum crystallite cross-sectional area (12.40 nm2).

Wheat Straw Bio-refining. Part I: Optimization of the Microwave Radiation Process with Sulphuric Acid Pre-treatment

Background: This study investigates the microwave-assisted acid extraction of lignin from wheat straw. Methods: Two experimental design methods, the Central Composite Design (CCD) and the Response Surface Method (RSM) methods were used to select conditions and optimise the process. The parameters studied were: the stirring rate, H2SO4 concentration, microwave radiation power and residence time. Results: The optimum conditions found to achieve the maximum lignin yield (wt%) from wheat straw were: 0.46M H2SO4 under microwave radiation power of 602 W at 65% of stirring rate (3200rpm) and residence time of 39min. These conditions led to a delignification of 78.5% (by weight) of the parent lignin content, which accounted for 11.8wt% on dry biomass basis; this compares to a yield of 3.35wt% for the conventional H2SO4 pre-treatment method under similar conditions. Conclusion: This work is a first step to demonstrate the potential of innovative microwave methods to overcome the high cost of acid extraction of lignin from biomass waste.

The Simultaneous Analysis of Eight Essential Trace Elements in Human Milk by ICP-MS

Trace elements are commonly present as components of metabolic enzymes, hormones and antioxidants in human milk. Previous studies have reported single or few elements in relatively large volumes of human milk using complex, time-consuming and expensive methods involving microwave-assisted acid digestion and extraction using tetramethylammonium hydroxide at various temperatures. We report here a validated alkaline dissolution method using ethylenediaminetetraacetic acid, ammonia solution, isopropanol and Triton X-100 to simultaneously determine trace elements in 0.2 mL samples of human milk by inductively coupled plasma mass spectrometry (ICP-MS). The trace elements zinc (Zn), copper (Cu), selenium (Se), manganese (Mn), iodine (I), iron (Fe), molybdenum (Mo), bromine (Br), chromium (Cr), cobalt (Co), lead (Pb), nickel (Ni), silver (Ag), cadmium (Cd), arsenic (As), bismuth (Bi), aluminium (Al), antimony (Sb), vanadium (V), thallium (Tl) and uranium (U) were detected, and the method was applied quantitatively to 12 samples of human milk. The results for method validation showed good sensitivity, accuracy and repeatability for Zn, Cu, Se, Mn, I, Fe, Mo and Br. The mean ± SD of these elements in the above human milk samples (μg/L) were 1390.6 ± 211.5, 220.8 ± 32.9, 14.3 ± 5.8, 1.37 ± 0.14, 113.5 ± 17.1, 47.3 ± 99.9, 0.37 ± 0.12 and 812.6 ± 127.7, respectively. This method is precise, reliable, straightforward and cost-effective in the determination of trace elements simultaneously in small sample volumes of human milk. Method application permits routine monitoring of several elements and the ongoing assessment of trace element nutrition in breast milk. It is the first method to highlight the relatively high Br levels present in human milk.

Microwave-assisted acid extraction of the major metal elements in herbal extracts followed by flame atomic absorption spectrometric (FAAS) determination

The content of As, Cd, Cr, Cu, Fe, Hg, Mg, Mn, Pb, and Zn was determined in Rosa damascena, Vitis vinifera, Crocus sativus, and Olea europaea L. herbal extracts produced in different areas in Greece. Samples were mineralized in a closed microwave system using nitric acid, and the concentration of all metals was determined by flame atomic absorption spectrometry. The herbal extracts contained As, Cd, Cr, Hg, Mn, and Pb at concentrations below their respective limits of detection, whereas Cu, Fe, Mg, and Zn were determined in varying quantities. The proposed method is precise and accurate, thus it can be used for the determination of metals in Rosa damascena, Vitis vinifera, Crocus sativus, and Olea europaea L. herbal extracts.

Evaluation of different microwave-assisted dilute acid extracting reagents on simultaneous coal desulphurization and demineralization

Coal combustion is one of the largest anthropogenic contributors to SOx and some other volatile elemental emissions to the atmosphere. Therefore, the current study investigated the effect of different dilute acidic reagents (HCl, HNO3, HCl–HNO3, HCl–H2O2, HNO3–H2O2 and HCl–HNO3–H2O2) on simultaneous coal demineralization and desulphurization under microwave irradiation. The applied conditions for microwave-assisted dilute acid extraction (MW-ADAE) process were as follows: 180°C, 5min, 3molL−1, 3molL−1, 0.1g and 2:1 for microwave temperature, extraction time, acid concentration, [H2O2], coal amount and acid-hydrogen peroxide volume ratios, respectively. The leachate solutions obtained from the MW-ADAE process were then analysed by using ICP–OES for multi-element determination. The ICP–OES analysis was performed in order to investigate the acidic reagent that resulted in highest extraction recoveries of the examined multi-element. All extracting reagents that contained HNO3 showed accepted extraction efficiencies (% R⩾80%) as indicated by the ICP–OES results. The proposed MW-ADAE procedure with HNO3–H2O2 reagent showed excellent desulphurization efficiency parallel to the other literature reported methods. The raw and acid treated coals were then characterized by Elemental analyser (CHNS), FT-IR, SEM, P-XRD and TGA to examine the influence of different acids on the coal structure. The FT-IR, SEM and P-XRD results showed insignificant changes throughout all the studied acidic reagents. However, the CHNS results of HNO3–H2O2 treated coal revealed sufficient coal desulphurization as compared to the other investigated acids. Alternatively, thermal studies of raw coal (A) showed high quantity of unburned mineral matter. In addition, most of the acid treated coals such as B (HCl), C (HNO3), E (HCl–H2O2 and F (HNO3–H2O2) indicated moderate removal of mineral matter while aqua-regia based extracting reagents (G (HCl–HNO3–H2O2) and D (HCl–HNO3)) caused drastic extraction of both carbon and mineral content. Therefore, the mixture of HNO3–H2O2 was selected as the potential extracting reagent for the proposed simultaneous coal desulphurization and demineralization process as it showed moderate attack on the carbon content of the coal and sufficient desulphurization (102%) and demineralization (70–115%).

A rapid microwave-assisted acid extraction method based on the use of diluted HNO3-H2O2 followed by ICP-MS analysis for simultaneous determination of trace elements in coal samples

Before coal processing such as pyrolysis, liquefaction, gasification and combustion, it is very crucial to monitor the trace element concentration levels as that determines the coal quality. Therefore, the current study describes the development of microwave-assisted acid extraction (MW-AAE) method for extraction of 15 trace elements in coal samples prior to their determination using inductively coupled plasma-mass spectrometry. Diluted HNO3-H2O2 was used in order to reduce reagents amount used, eliminate matrix interferences caused by concentrated acids and to decrease waste produced in analytical laboratories. The optimisation of the proposed extraction method was carried out by using a full factorial design (24) involving four factors; that is, temperature, extraction time, HNO3 and H2O2 concentrations. The optimum conditions for the MW-AAE procedure were found to be 200°C, 5 min, 5 mol L−1 and 2 mol L−1 for temperature, extraction time, HNO3 and H2O2 concentrations, respectively. Under optimum conditions, the accuracy of the MW-AAE method was examined by analysing three coal certified reference materials (SARM 18, 19 and 20) and recoveries of 80–115% were achieved for V, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Zr, Cs, Ba, Pb and U, except for Ti (10–25%) and Hf (27–70%). In addition, the precision of the proposed method, expressed in terms of relative standard deviation (SD) (n = 15), was within the accepted range (≤3.5%). The method detection limits of 0.001–0.57 µg g−1 for all trace elements under the investigation were similar to the literature reported work, except for Ti (4.00 µg g−1).

A single-step microwave-assisted acid extraction of total sulphur in coal samples followed by ICP-OES determination

A rapid microwave-assisted acid extraction (MW-AAE) procedure using a dilute [HNO3–H2O2] mixture followed by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis has been developed for the determination of total sulphur in coal samples. Parameters affecting the MW-AAE such as extractant concentration, microwave temperature, extraction time, coal amount and HNO3 : H2O2 volume ratio were optimized by using a certified reference material (SARM 20) in order to attain total sulphur quantitative recoveries. The optimum conditions for the extraction procedure were found to be 180 °C, 5 min, 3 mol L−1, 3 mol L−1, 0.05 g and 2 : 1 for microwave temperature, extraction time, [HNO3], [H2O2], coal amount and HNO3 : H2O2 volume ratio, respectively. Under optimum conditions, the accuracy of the MW-AAE method was examined by analyzing three coal certified reference materials (SARM 18, 19 and 20) and quantitative recoveries (83–102%) were achieved. Additionally, the precision of the proposed method, expressed in terms of relative standard deviation (n = 15), was satisfactory (≤3%). The method limit of detection (0.026 μg g−1) and method limit of quantification (0.087 μg g−1) for sulphur analysis were relatively good as compared to work reported in the literature.

Elemental analysis of nanodiamonds by inductively-coupled plasma atomic emission spectroscopy

A 68-element survey study was carried out on micro-impurities from 20 commercial nanodiamond samples from eight international manufacturers. The measurements were made using inductively coupled plasma atomic emission spectroscopy with detection limits for most elements below 1ppm. Various methods of sample preparation were compared: direct introduction of suspensions, ashing with microwave-assisted acid digestion, and microwave-assisted acid extraction, and their advantages and disadvantages evaluated. The work demonstrates the feasibility of nanodiamond analysis by direct slurry nebulization, which provides a multi-element, rapid, simple, and relatively low-cost route for nanodiamond purity estimation. Most of the samples contain relatively high amounts of Fe, Na, Ca, Si, Cu, Al, S, and Ti (>100ppm), while Pb, Zn, K, Mn, B, Cr, Mg, Mo, Sn, W, Ba, Sb, Co, and Sr are at low but significant amounts. In addition, in several samples, we found some uncommon elements like Ag, Ce, Y, Hf, Zr, and Hg. This study provides new possibilities for certifying nanodiamond purity, understanding their properties and behavior, and advancing their production technology.

Optimization of Extraction and Determination of Chloramphenicol in Livestock Meat Samples using Aqueous Two-Phase System ofn-propanol and Potassium Citrate Coupled with HPLC

A slurry sampling flame atomic absorption spectrometric method for sequential determination of Cu and Fe in airborne particulate matter (APM) collected on glass fiber filters is proposed. The method optimization was carried out using a dry powdered sample (filter + APM) mass of 50 mg, dispersed in 0.5 mol L-1 nitric acid solution and under ultrasonic bath for 10 min. The limits of detection (n = 10) were 4 and 14 µg g-1 for Cu and Fe on the filter, respectively. The repeatability expressed as the relative standard deviation was better than 7 and 8% (n = 3) for Cu and Fe, respectively. The accuracy of the method was confirmed by analysis of the fly ash certified reference material (BCR 176R). The results obtained for six samples of APM using the proposed method showed no significant differences with those obtained after microwave-assisted acid extraction and determination by inductively coupled plasma mass spectrometry. The analytical method proved to be simple, fast and reliable.