Microwave-assisted Sample Preparation Research Articles

Characterization and quantification of microplastics and organic pollutants in mussels by microwave-assisted sample preparation and analytical pyrolysis

We developed a method to isolate and quantify various classes of both non-polymeric contaminants and polymers from mussel flour using microwave-assisted extraction/digestion and analytical pyrolysis-GC-MS.

Deep eutectic solvent dispersive liquid–liquid microextraction methods for the analysis of chlorophyll natural colorant (E140) via microwave assisted sample preparation

In the current research paper, extraction and analysis of chlorophyll, one of the bioactive compounds that is usually utilized as natural pigments (E140) and obtained from many leafy green plants and seaweeds, have been carried out via deep eutectic solvent-based dispersive liquid–liquid phase microextraction (DES-UA-DLLME) from plants and food pruducts. The DES-UA-DLLME method was developed by utilizing deep eutectic solvent (DES) which was prepared by heating process with a 1:1 ratio of choline chloride and urea (ChCl: U). Analytical parameters such as pH, DES volume, sample volume, centrifugation and mixing time, DES type, matrix effect, etc. were optimized to ensure the extraction efficiency of chlorophyll. The limit of detection (LOD), limit of quantification (LOQ), intra-day and inter-day relative standart devision (RSD) were found as 0.007 µg/mL, 0.023 µg/mL, 1.3 %, and 1.9 %, respectively. The accuracy of the method was tested with water sample addition/recovery studies. The DES-UA-DLLME method has been applied to food, water, and plant samples. The food products and plants were prepared with the help of ultrasonic and microwave extraction for spectrophotometric analysis of chlorophyll. According to literature survey, the DES-UA-DLLME method and the MWAE method combination was used to the first time for extraction of chlorophyll (E140) from plants.

Fast and green microwave-assisted digestion with diluted nitric acid and hydrogen peroxide and subsequent determination of elemental composition in brown and white rice by ICP-MS and ICP-OES

For the elemental determination of rice, a microwave-assisted sample preparation method employing diluted HNO3 and H2O2 under high temperature and pressure was developed in a rapid and eco-friendly manner. The analysis was performed using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). At 280 °C and 160 bar, the optimal condition for microwave-assisted wet digestion in a single reaction chamber was achieved with a mixture consisting of 3 mL of 0.1 mol L−1 HNO3 and 5 mL of 30% H2O2 (0.25 g rice sample). The optimized procedure yielded a low residual acidity (RA) of 0.017 mol L−1 and low residual carbon content (RCC) of 355 mg L−1. The limits of detection (LODs) were from 0.159 (Sb) to 9.863 (Fe) μg kg−1. Additionally, the developed method received a total score of 85 on the analytical Eco-Scale, indicating an excellent green analysis method. Furthermore, the method was validated by determining 19 elements (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, P, Pb, S, Sb, Se, and Zn) in brown and white rice cultivated in South Korea.

Microwave-assisted sample preparation of α-spodumene: A simple procedure for analysis of a complex sample

Lithium-ion industry requires high amounts of lithium in high purity and spodumene, together with brine, are the major sources. Spodumene has three polymorphic forms, the one occurring in nature is α-spodumene. This form is highly resistant to chemical attack due to its compact structure containing silicon and aluminium oxides. Chemical analysis of this material is usually performed by combining fusion followed by acid digestion. However, microwave radiation converts α-spodumene to β-spodumene and it is known that this latter form can be chemically attacked using less critical reaction conditions. Based on this behaviour, it was developed a microwave-assisted procedure for chemical analysis of α-spodumene aiming the determination of lithium and other metals of interest by using an acid mixture composed by sulphuric and phosphoric acids and diluted hydrofluoric acid solution. The feasibility of using ammonium fluoride, a less critical reagent, instead of HF was also demonstrated. The heating program was implemented in 60 min at a maximum temperature of 230 °C using closed vessels for digestion of α-spodumene. All elements were determined by inductively coupled plasma optical emission spectrometry.

Evaluation of Partial Digestion as a Strategy for Elemental Analysis of Inorganic Samples by Inductively Coupled Plasma–Optical Emission Spectrometry (ICP OES)—A Proof of Concept Study

This study discusses the application of microwave-assisted sample preparation for inorganic samples using concentrated or diluted HNO3 solutions followed by determination of Al, Ca, Cu, Cr, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, and Zn using inductively coupled plasma–optical emission spectrometry (ICP OES). Aiming the total digestion (reference procedure), samples were decomposed in a heating block using a mixture of 2 mL of 40% v v−1 HF and 5 mL of 14 mol L−1 HNO3. Four digestion mixtures composed by (1) 14, (2) 7.0, (3) 4.0, and (4) 2.0 mol L−1 HNO3 plus 3 mL of concentrated H2O2 were evaluated as alternatives for microwave-assisted digestion of six inorganic samples (partial digestion). Considering all evaluated procedures, quantitative recoveries were obtained applying reference and partial digestion procedures. Therefore, the use of HNO3 dilute solutions as an alternative for HF is a feasible procedure for quantitative analysis of zinc oxide, kaolin, zinc residue, and zinc sulfide. However, tailored procedures must be taken into consideration, since quantitative determination depends on digestion mixture, sample matrix, and analytes.

Microwave-assisted sample preparation of Hungarian raw propolis in quartz vessels and element analysis by ICP-OES and ICP-MS for geographical identification

One of the aims of this study was to improve the sample throughput of a microwave-assisted closed vessel digestion system by using small quartz vials in polytetrafluoroethylene (PTFE) vessels for the sample preparation of raw propolis samples in small amounts. The digested samples were measured by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) analyzing 36 elements. Limit of detection was low enough to measure all the elements, with the exception of La, in all raw propolis samples. There were no cross-contamination between the quartz vials, therefore independent samples can be prepared in the same PTFE vessel. Accuracy of the method was checked by spike recoveries and by analyzing BCR 189 wholemeal flour and two plant samples from a collaborative study. The means of RSDs were 5.3%–14.4% in the case of measured elements. The sample throughput was increased by three times using quartz vials in PFTE vessels besides matching with the requirements of green chemistry.Another goal was the characterization of the element content and thereby geographical identification of Hungarian raw propolis. In total, 252 samples were analyzed and their statistical characteristics were described. We cannot find globally such results of propolis element content, which is representing one country and with such a number of elements and samples. All the elements have positive skew and positive kurtosis. Concentration range is above two orders of magnitude in the case of Ba, Zn, V, Cr, Ni, Cd and Eu elements. The decimal logarithm of element concentrations was used for geographical identification of raw propolis samples originating from seven regions of Hungary by linear discriminant analysis (LDA). Grouping of the samples of the Northern Great Plain was the most effective with 96.3% and 77.8% based on the original method and the cross validation, respectively. The same indicators for all the groups are 76.6% and 61.5%.

Multielement Analysis of Oil by ICP–AES and ICP–MS with Microwave-Assisted Sample Preparation

To obtain detailed information on the elemental composition of oil, we developed ICP–AES and ICP–MS procedures for the determination of a wide range of elements in oil after microwave sample digestion. We found a possibility and selected the conditions of the microwave decomposition of samples of light and superviscous oils, weighing up to 1000 mg. The effect of residual acidity and residual carbon on the formation of an analytical signal in ICP–AES and ICP–MS (high resolution) was studied. We found that 20 elements can be determined by ICP–AES at a level of n × 10–2–m × 102 μg/g and 42 elements can be determined by ICP–MS at a level of n × 10–2–m × 102 ng/g.

Microwave-based strategies for sample preparation and halogen determination in blood using ICP-MS

In this work, two microwave-assisted sample preparation methods based on combustion and ultraviolet digestion for futher determination of Br, Cl, and I in blood by inductively coupled plasma mass spectrometry were proposed. For microwave-induced combustion (MIC), blood was spotted on square pieces of Munktell TFN paper, and water and diluted NH4OH were evaluated as absorbing solutions. The stability of the analytes in the spotted blood was also evaluated. During 90 days, no changes of halogen content were observed for samples (with and without anticoagulant) on paper stored in a desiccator at 20 ± 5 °C. Whole blood was also digested by microwave-assisted ultraviolet digestion (MAD-UV). Some parameters as the volume of HNO3 solution, the influence of H2O2, and the effect of UV radiation were investigated. The interferences caused by C and K on halogen determination were carefully investigated. The results for MIC and MAD-UV and Br, Cl and I determination by ICP-MS presented no difference. The accuracy of MIC and MAD-UV was also evaluated by analyte spike with reference solutions of Br, Cl and I using inorganic species and also organic I standard (T4-levothyroxine). For both methods, recoveries were 94 and 108% for Br, 96 and 103% for Cl, and 104 and 97% for I. In case of organic I, recoveries were 99 and 111% for MIC and MAD-UV, respectively. The limits of quantification for MIC and MAD-UV after ICP-MS determination were 0.06 and 0.04 μg g−1 for Br, 14 and 30 μg g−1 for Cl and 12 and 8 ng g−1 for I, respectively. The proposed methods provide a suitable digestion approach, assuring safety and high digestion efficiency for further halogen determination in blood, with the possibility to use in clinical analysis.

Multivariate optimization for the development of a sample preparation procedure and evaluation of calibration strategies for nutrient elements determination in handmade chocolate

This study presents a procedure for microwave-assisted sample preparation of handmade chocolates with different levels of cocoa (30 to 85%) using 2.5 mol L−1 of HNO3 followed by determination of nutrient elements (Ca, Cu, Fe, K, Mg, Mn, P and Zn). The determinations were perfomed using inductively coupled plasma optical emission spectrometry (ICP OES). The optimization of the sample preparation procedure was performed using a Doehlert design, for evaluation of the following variables: volume de H2O2 and concentration of HNO3. The best condition for digestion of 200 mg of samples were obtained using only 5 mL of HNO3 at 2.5 mol L−1. In addition, three calibration strategies were evaluated: external calibration (EC), internal standardization (IS) and one-point standard addition (OP SA), and the EC showed the best results for the determination of the evaluated elements. The proposed procedure was validated and applied for the determination of Ca, Cu, Fe, Mg, Mn, P and Zn in 11 samples of handmade chocolates with different levels of cocoa produced in south region of Bahia State, Brazil. The concentration ranges for Ca, Cu, Fe, K, Mg, Mn, P, S and Zn found in the samples were compared with the values of recommended diary intake (RDI), inferring that handmade chocolates is a good nutrients source.

Microwave-assisted digestion using dilute nitric acid solution and investigation of calibration strategies for determination of As, Cd, Hg and Pb in dietary supplements using ICP-MS

This study proposes an analytical procedure for microwave-assisted sample preparation of dietary supplements for athletes using dilute nitric acid solution followed by determination of elemental impurities (As, Cd, Hg and Pb) by inductively coupled plasma mass spectrometry (ICP-MS) according to the United States Pharmacopeia Chapters 2232 and 233. Calibration strategies as internal standardization (IS), multi-isotope calibration (MICal), and one-point standard addition (OP SA) were applied for correction of matrix effects. The optimization of the sample preparation procedure was performed using Doehlert experimental design based on overall desirability results (residual acidity, dissolved organic carbon and recoveries reached for certified reference material of Typical Diet) for each calibration method evaluated. Accuracy was also evaluated by recovery experiments according to the permissible daily exposure specific for each element and samples were spiked with element concentrations of 0.5J and 1.5J in order to check accuracies for As, Cd, Hg and Pb. Recoveries ranged from 82 to 120% using IS, 90 to 125% using MICal, 88 to 120% using OP SA and the repeatability was demonstrated by a precision lower than 10% RSD. Ten samples of dietary sport supplements were analyzed using the three calibration methods evaluated and the concentrations of As, Cd and Pb determined in eight samples were lower than the limits established by the Chapter 2232.

Edible Spruce (Morchella esculenta), Accumulator of Toxic Elements in the Environment

Abstract In this study we examined the dried fruiting bodies of Morchella esculenta, collected in the area of the coal and biomass based thermal power plant in Vojany from the nearby Bahoň marsh, in the Slovak Republic. The area is characterized by a high environmental burden, especially because of air pollutant emissions from the power plant operation. Twenty-three (23) chemical elements were found in the dried fruiting bodies after microwave-assisted sample preparation using an Inductively Coupled Plasma Mass Spectrophotometer ICP-MS AGILENT 7500c system. The mercury content was determined employing a special AMA 254 apparatus intended for the determination of Hg directly in dry powdered fruiting bodies without microwave digestion. The content of toxic elements expressed in mg.kg−1 DW (dry weight) were as follows: Hg 0.048—0.052 (RSD—Relative Standard Deviation = 4.80 %); Cd 4.543—6.169 (RSD = 3.35 %); Pb 0.261—0.291 (RSD = 2.67 %); As 0.455—0.469 (RSD = 5.79 %); Cr 1.585—1.616 (RSD = 2.33 %); and Ni 8.166—9.276 (RSD = 3.03 %). The contents of cadmium, nickel and mercury exceeded the hygiene limits, while the contents of arsenic and lead approached the hygiene limits. Due to the high levels of toxic elements, the fruiting bodies collected in the location are not suitable for culinary purposes. The mushroom Morchella esculenta acts as an accumulator of toxic elements from the environment in which it grows and can be considered as an indicator of environmental pollution.

Microwave-assisted sample preparation of medicines for determination of elemental impurities in compliance with United States Pharmacopeia: How simple can it be?

This work proposed a procedure for microwave-assisted sample preparation of medicines using diluted nitric acid followed by determination of elemental impurities using inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS) according to the United States Pharmacopeia Chapters 232 and 233. Three solutions, i.e. inverse aqua regia, 7.0 and 2.0 mol L−1 HNO3, were evaluated for microwave-assisted digestion of nine drugs samples. The applicability of each digestion procedure was assessed by comparison of analyte concentrations determined using total (reference procedure) and partial digestions (proposed procedure) as well as by determining dissolved carbon content and evaluating matrix effects. There were none significant differences at a 95% confidence level among the concentrations determined applying reference and proposed procedures. Internal standardization (ICP OES) and aerosol dilution (ICP-MS) were applied for minimization and correction of matrix effects. Addition and recovery experiments were performed according to oral permissible daily exposures values specific for each element and each sample was spiked with element concentrations of 0.5J and 1.5J in order to check accuracies for 24 analytes. Recoveries ranged from 70 to 138% for ICP OES and from 72 to 128% for ICP-MS, for all elements but Os. All analytes were below the respective limits of quantification when applying all sample preparation procedures, except As, Ba, Co, Cu, Cr, Mo, Ni, Pb, Sb, Sn, Tl and V, however the determined concentrations for these elements were lower than the limits proposed by Chapter 232.

Experimental design for metal extraction from facial cosmetics samples and determination by square wave voltammetry

An alternative microwave-assisted sample preparation procedure is proposed for the rapid, reliable and easy extraction of metals from facial cosmetics samples.

Determination of arsenic, chromium, lead, manganese, and mercury in certifiable color additives by inductively coupled plasma/mass spectrometry.

Specifications in the Code of Federal Regulations limit the levels of As, Pb, and Hg in most certifiable color additives, and some have additional specification limits for Cr and Mn. A new ICP/MS method was developed and validated for the quantitative determination of these elements in various certifiable color additives. One dissolution and two microwave-assisted digestion sample preparation procedures were optimized to address initial low Hg and enhanced As recoveries. Results using the three sample preparation procedures were generally equivalent for all of the elements determined. LOQ values were 0.3 mg/kg for As, 0.7 mg/kg for Cr, 0.4 mg/kg for Pb, 0.7 mg/kg for Mn, and 0.1 mg/kg for Hg.

Automated Radioanalytical System Incorporating Microwave-Assisted Sample Preparation, Chemical Separation, and Online Radiometric Detection for the Monitoring of Total 99Tc in Nuclear Waste Processing Streams

An automated fluidic instrument is described that rapidly determines the total (99)Tc content of aged nuclear waste samples, where the matrix is chemically and radiologically complex and the existing speciation of the (99)Tc is variable. The monitor links microwave-assisted sample preparation with an automated anion exchange column separation and detection using a flow-through solid scintillator detector. The sample preparation steps acidify the sample, decompose organics, and convert all Tc species to the pertechnetate anion. The column-based anion exchange procedure separates the pertechnetate from the complex sample matrix, so that radiometric detection can provide accurate measurement of (99)Tc. We developed a preprogrammed spike addition procedure to automatically determine matrix-matched calibration. The overall measurement efficiency that is determined simultaneously provides a self-diagnostic parameter for the radiochemical separation and overall instrument function. Continuous, automated operation was demonstrated over the course of 54 h, which resulted in the analysis of 215 samples plus 54 hly spike-addition samples, with consistent overall measurement efficiency for the operation of the monitor. A sample can be processed and measured automatically in just 12.5 min with a detection limit of 23.5 Bq/mL of (99)Tc in low activity waste (0.495 mL sample volume), with better than 10% RSD precision at concentrations above the quantification limit. This rapid automated analysis method was developed to support nuclear waste processing operations planned for the Hanford nuclear site.

Mercury speciation in whole blood by gas chromatography coupled to ICP-MS with a fast microwave-assisted sample preparation procedure

A simple and fast method is described for simultaneous determination of methylmercury (MeHg), ethylmercury (Et-Hg) and inorganic mercury (Ino-Hg) in blood samples by using capillary gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS) after derivatization and alkaline digestion. Closed-vessel microwave assisted digestion conditions with tetramethylammonium hydroxide (TMAH) have been optimized. Derivatization by using ethylation and propylation procedures have also been evaluated and compared. The absolute detection limits (using a 1 μL injection) obtained by GC-ICP-MS with ethylation were 40 fg for MeHg and Ino-Hg, respectively, and with propylation were 50, 20 and 50 fg for MeHg, Et-Hg and Ino-Hg, respectively. Method accuracy is traceable to Standard Reference Material (SRM) 966 Toxic Metals in Bovine Blood from the National Institute of Standards and Technology (NIST). Additional validation is provided based on the comparison of results obtained for mercury speciation in blood samples with the proposed procedure and with a previously reported LC-ICP-MS method. With the new proposed procedure no tedious clean-up steps are required and a considerable improvement of the time of analysis was achieved compared to other methods using GC separation.

Analysis of silicate materials using the microwave-assisted sample preparation

A technique of microwave-assisted preparation of natural and commercial silicate materials for subsequent spectrophotometric determination of the major rock-forming components (silicon, aluminum, iron, titanium, and phosphorus) is described. The total duration of analysis is several times less than for a standard technique. In particular, the time taken for the digestion is shortened to 1 h for ten samples undergoing digestion simultaneously; the time of complexation of aluminum with aluminon and of phosphorus with molybdenum heteropoly acid is reduced from a few hours to 12 min.

Microwave-assisted sample preparation for rapid and sensitive analysis of H. pylori lipid A applicable to a single colony

The lipid A of Gram-negative bacteria plays a major role in the pathogenesis of bacterial infections. Lipid A diversity is observed both in the number and length of fatty-acid side chains and in the presence of terminal phosphate residues and associated modifications. In this report, we describe a new sample preparation method based on microwave-assisted enzymatic digestion and detergent-free mild hydrolysis, in conjunction with a MALDI-time-of-flight (TOF)/TOF analysis, to determine the structures of lipid A from Helicobacter pylori. The total time for sample preparation and mass spectrometric analysis is within 2 h and applicable to profiling the lipid A structures from dried bacterial cells on as little as 1 microg. The reliability of the technique was further demonstrated through the analysis of the lipid A from bacterial cells of different H. pylori strains. The phosphorylation and acylation patterns of lipid A could be elucidated using material from a single colony. Furthermore, we found unusual heptaacyl lipid A species present in H. pylori mutant that have not been previously reported, although the abundance was relatively low. The present study provides the first characterization of the lipid A component from a single bacterial colony sample by mass spectrometry.

Microwave-assisted digestion procedures for biological samples with diluted nitric acid: Identification of reaction products

Microwave-assisted sample preparation using diluted nitric acid solutions is an alternative procedure for digesting organic samples. The efficiency of this procedure depends on the chemical properties of the samples and in this work it was evaluated by the determination of crude protein amount, fat and original carbon. Soybeans grains, bovine blood, bovine muscle and bovine viscera were digested in a cavity-microwave oven using oxidant mixtures in different acid concentrations. The digestion efficiency was evaluated based on the determination of residual carbon content and element recoveries using inductively coupled plasma optical emission spectrometry (ICP OES). In order to determine the main residual organic compounds, the digests were characterized by nuclear magnetic resonance ( 1H NMR). Subsequently, studies concerning separation of nitrobenzoic acid isomers were performed by ion pair reversed phase liquid chromatography using a C18 stationary phase, water:acetonitrile:methanol (75:20:5, v/v/v) + 0.05% (v/v) TFA as mobile phase and ultraviolet detection at 254 nm. Sample preparation based on diluted acids proved to be feasible and a recommendable alternative for organic sample digestion, reducing both the reagent volumes and the variability of the residues as a result of the process of decomposition. It was shown that biological matrices containing amino acids, proteins and lipids in their composition produced nitrobenzoic acid isomers and other organic compounds after cleavage of chemical bonds.

Sample preparation of sewage sludge and soil samples for the determination of polycyclic aromatic hydrocarbons based on one-pot microwave-assisted saponification and extraction

A microwave-assisted sample preparation (MASP) procedure was developed for the analysis of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge and soil samples. The procedure involved the simultaneous microwave-assisted extraction of PAHs with n-hexane and the hydrolysis of samples with methanolic potassium hydroxide. Because of the complex nature of the samples, the extracts were submitted to further cleaning with silica and Florisil solid-phase extraction cartridges connected in series. Naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene, were considered in the study. Quantification limits obtained for all of these compounds (between 0.4 and 14.8 microg kg(-1) dry mass) were well below of the limits recommended in the USA and EU. Overall recovery values ranged from 60 to 100%, with most losses being due to evaporation in the solvent exchange stages of the procedure, although excellent extraction recoveries were obtained. Validation of the accuracy was carried out with BCR-088 (sewage sludge) and BCR-524 (contaminated industrial soil) reference materials.