Closed-vessel Microwave Digestion Research Articles

Total Triterpenes, Polyphenols, Flavonoids, and Antioxidant Activity of Bioactive Phytochemicals of Centella asiatica by Different Extraction Techniques.

Obtaining phytochemical-rich plant extracts from natural products where the active ingredients are present in comparatively low levels in the tissue matrix is the critical initial step of any chemical analysis or bioactivity testing. The plant C. asiatica is rich in various phytochemicals, the major constituents being triterpenes and flavonoids, as well as other polyphenols, leading to a number of bioactivities. In this study, an attempt was made to achieve several green technology principles, while optimizing the extraction method for the efficient extraction of bioactive compounds from C. asiatica. Soxhlet extraction (SE), ultrasound-assisted extraction (UAE) with low-frequency sonication, microwave-assisted extraction (MAE) using a closed-vessel microwave digestion system, and subcritical water extraction (SWE) in a high-pressure reactor were employed to extract the bioactive compounds. The solvent system, extraction time, and solid-to-solvent ratio were varied to optimize the extraction. UAE gave the best extraction yield, while MAE gave similar results, with a solid-to-liquid ratio of 1:25, a binary solvent system of 9:1 methanol to water (v/v), and a 20 min extraction time for the extraction of triterpenes, including madecassoside, asiaticoside, madicassic acid, and asiatic acid. Investigation of different solvent systems based on water and methanol also revealed information on the extraction behavior of total triterpene content (TTC), total polyphenolic content (TPC), total flavonoid content (TFC), and the variations in the antioxidant capacity of the extracts. In this study, it was evident that UAE and MAE offer more efficient and effective extraction of bioactive compounds in terms of extraction yield, time, and minimal solvent and energy use. Furthermore, the results showed that the different solvent ratios in the extraction mixture will affect the extraction of bioactive compounds, and a binary solvent system with a combination of methanol and water was the most efficient for the studied compounds in Centella asiatica.

Microwave-Assisted Digestion Using Dilute Nitric Acid and Hydrogen Peroxide for Multielement Determination in Wheat Flour by ICP-MS

A closed-vessel microwave digestion method was developed for the simultaneous determination of macro, micro, and toxic elements (Mg, K, Ca, Al, Mn, Fe, Cu, Zn, Se, Rb, V, Cd, and As) in wheat by inductively coupled plasma mass spectrometry (ICP-MS). A two-level factorial design with four variables was employed to determine the optimal conditions for the significant parameters. The optimal conditions for microwave digestion of ground wheat samples were found to be 0.5 g of the sample, 9 mL of 8 mol/L HNO3, and 3 mL of 33% H2O2 at 210°C. The analytical method was validated, and the accuracy of the method was then evaluated through analysis of wheat flour-certified standard reference materials (NIST SRM 1567b). The validated procedure was subsequently applied to the analysis of 12 wheat samples sourced from local farms in the Al-Qassim region and a further six samples purchased from the Al-Qassim markets, covering six imported brands common in Saudi Arabia. The results of the study showed that the level of minerals in wheat grown in desert areas is higher than in other areas. The concentrations of macroelements and microelements in the Al-Qassim samples exceeded those of the imported samples by 12.41% and those of the samples from other countries by 33.90%. The results were also evaluated using multivariate analysis techniques: principal component analysis (PCA) and hierarchical cluster analysis (HCA).

Determination of 48 elements in 7 plant CRMs by ICP-MS/MS with a focus on technology-critical elements

Seven plant certified reference materials (NIST SRM1515 Apple Leaves, NIST SRM1547 Peach Leaves, BCR-129 Hay Powder, BCR-670 Aquatic Plant, GBW07603 Bush Twigs and Leaves, GBW10015 Spinach Leaves and NCS ZC73036a Green Tea) were analysed for their mass fractions of 48 elements by inductively coupled plasma tandem-mass spectrometry (ICP-MS/MS): Li, Be, Na, Mg, Al, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Nb, Mo, Ag, Cd, Sb, Te, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ta, Tl, Pb, Bi, Th, U. Special focus was put on the determination of technology-critical elements (TCEs), to which, e.g. Li, Be, Ga, Ge, Nb, Sb, Ta, Tl, Bi, and the rare-earth elements (REEs, lanthanides and Y) are counted. Closed-vessel microwave digestion was performed using HNO3, H2O2 and HBF4. The average bias for certified values is − 1% ± 13% (SD). Limits of detection (xL) in the measured solutions lie between 13 fg g−1 (Tb) and 52 ng g−1 (Ca). This article seeks to provide an optimised measurement procedure for the determination of element mass fractions of emerging importance in environmental samples, which are challenging to analyse with more traditional techniques such as single-quad ICP-MS. In addition, it aims to improve the characterisation of commonly used plant reference materials by providing mass fraction data for rarely studied elements.Graphical abstract

Mineral and Isotopic Characterization of Wines From the Douro Demarcated Region

ObjectivesIn the 1960s, the French paradox launched the debate around the benefits of wine consumption. Since then several epidemiological studies have evidenced its potential protective cardiovascular effects. Wine’s characteristics are highly dependent on the terroir. This study aims to characterize the profile of 11 minerals and micronutrients (K, Na, Ca, Fe, P, Mg, Mn, Se, Cu, Cr, and Zn) and the 87Sr/86Sr isotopic ratio, and evaluate suitable tracers of authenticity for the Douro Demarcated Region. It will identify the parameters influenced by processing methods or environmental contamination and the ones common to the region, and fundamentally dependent on the soils and climate. MethodsThe sampling plan comprehended the collection of 15 Port wines and 15 Douro wines. All sample preparation occurred in cleanroom facilities, reagents were of high purity and Ultra-pure water grade I was used. Samples were mineralized using closed vessel microwave digestion. For isotopic analysis, a further purification step was required using Sr-selective resin Eichron®. Minerals and micronutrients were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and ICP-mass spectrometry (ICP-MS), and isotope ratios by multi collector-ICP-MS (MC-ICP-MS). ANOVA was applied to evaluate significant differences between the two types of wine. ResultsResults are within the maximum levels established by the International Organization of Vine and Wine (OIV), when applicable. k was the most abundant element in both types of wine with values ranging from 399 ± 7 to 1458 ± 7 mg/L. Se was the least abundant one presenting levels between the limit of quantification (2.5 μg/L) and 6.2 ± 0.2 μg/L. The statistical analysis showed significant differences between the two types of wine regarding six elements, namely Ca, Na, Zn, Cu, Cr, and Se. ConclusionsSix elements were identified as potential markers for the wines under study. Since all vineyards under study are grown in the same type of geological formation, the soil should not be responsible for these differences. Instead, they may result from agricultural practices, the winemaking process, or the aging of the wines. Funding SourcesThis work was completed under the METROFOOD-PP project frame and received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 871083.

Comparison of DMA-80 and ICP-MS Combined with Closed-Vessel Microwave Digestion for the Determination of Mercury in Coal.

As one of the most widely used techniques for concentration determination of trace elements in coal, inductively coupled plasma mass spectrometry (ICP-MS) has also been used in several studies for the determination of mercury concentration in coal. ICP-MS after closed-vessel microwave digestion and a Milestone DMA-80 are employed in this study to determine the mercury concentration in coal. Three NIST standard references of coal samples were selected as references to verify the accuracy of the test results. The Au rinse solution (200 μg/L, 5% HNO3) can diminish mercury memory effects to a blank level within 80 seconds. The results showed that ICP-MS can accurately determine the mercury content in mercury standard solutions, but the mercury concentration in most NIST samples after microwave digestion is lower than the detection level of the ICP-MS. The inaccuracy may be due to volatilization of mercury during solid sample digestion process. By contrast, the determined concentrations in NIST samples by the Milestone DMA-80 are very close to the verified values. Therefore, ICP-MS is not recommended to analyze mercury in coal after digestion even in a closed-vessel digestion system, but the mercury direct analyzer (without digestion) is recommended to analyze mercury in coal.

Content of biogenic and toxic elements in the leaves of Deschampsia antarctica É. Desv. (Poaceae): a preliminary study

The Antarctic hairgrass (Deschampsia antarctica É. Desv.) is one of two flowering plants native to the Antarctic and therefore it was intensively studied for decades. However, there is still limited information available about the content of biogenic and toxic elements in the leaves of this plant. While being an important component of the Antarctic terrestrial ecosystems, the content of nutrients like K, P, and S in the plants of D. antarctica may significantly affect soil properties, especially in such hot spots like rhizosphere and detritosphere. Moreover, the content of toxic elements and trace metals in particular in the plant is an important criterion to evaluate its indicative role, whether or not D. antarctica may be used as a bio-indicator to monitor the Antarctica environmental state. In this study, we report the preliminary results about the content of K, P, Ca, S, Mg, Na, Si, Fe, Zn, Al, Sr, Mn, Cu, B, Cr, Ba, V, Pb, Cd, and Co in the leaves of D. antarctica from the natural habitats of the maritime Antarctіс. Dry leaves were digested in nitric acid (closed-vessel microwave digestion). Elemental concentration was measured by ICP-OES technique. It was found that differences between the samples taken from one location were far less notable than between samples from different locations. Among the biogenic elements, the content of potassium was the most variable – from 12.2 mg·g-1 on Galindez Island to 28.7 mg·g-1 on the Cape Tuxen (Antarctic Peninsula). The content of trace metals also varied greatly between the samples from different locations. The results of this preliminary study suggest that due to the high content of nutrients, leaves of D. antarctica should be considered as an important precursor of soil organic matter, as well as a possible bioindicator. However, future studies are needed to confirm these preliminary results and hypotheses.

Assessment of microelements in six varieties of sesame seeds using ICP-MS

Sesame seeds are being used since long time worldwide and particularly in China as a food ingredient. However, insufficient information is available with micro mineral concentrations in different varieties of sesame seeds. The study compared the mineral composition in six varieties of black and white sesame seeds in China. Eleven trace elements (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Mo and Ba) were quantified on inductively coupled plasma-mass spectrometry (ICP-MS) after closed-vessel microwave digestion. In general, average levels of Mn, Fe, Cu, Zn and Ba in selected varieties ranged 1.07-7.40 mg/100 g, based on dry weight of the samples. Nevertheless, V, Cr, Co, Ni, Se and Mo were found at lower concentrations (<0.14 mg/100 g). The average concentrations of Mn, Fe and Zn in black sesame varieties were higher than that of the white varieties. No significant variation was noted for V, Cr, Co, Ni, Cu, Se, Mo and Ba contents between black and white sesame seeds. On the whole, black varieties of sesame exhibited similar levels of investigated elements, which could be helpful to suggest the consumption value of sesame seeds based on mineral contents.

Trace Arsenic Determination in a TiO2 Pigment Matrix Using Electrothermal Atomic Absorption Spectrometry.

This work describes the use of electrothermal atomic absorption spectrometry in combination with a pyrolytic graphite-coated tube with a platform for trace arsenic (As) determination in titanium dioxide (TiO2) pigment. This type of matrix is challenging, as complete digestion in hydrofluoric acid-containing solution is needed. First, closed-vessel microwave digestion was performed for the full-sample decomposition. Next, a temperature program was optimized for drying, pyrolysis, and atomization temperatures. Furthermore, the use of a chemical modifier mixture was proposed that reduced the background contribution and prevented significant analyte loss and therefore improved the analytical procedure. The optimized method was validated for the detection (LOD) and quantification (LOQ) limits, the linear concentration range, accuracy, and precision. Special attention was devoted to the matrix-matching solutions in the calibration procedure. Linearity was confirmed in the 5.0 to 100.0 µg/L concentration range (R2 = 0.999). The average recovery for 16 different real TiO2 pigment samples was 92.0%, and the relative standard deviation value for six replicate measurements was ≤10.4%. Moreover, the LOD and LOQ in terms of the TiO2 pigment mass was determined to be 0.2 µg/(g TiO2) and 0.7 µg/(g TiO2), respectively. The latter complies with Commission Directive 2008/128/EC, which does not allow more than 3 µg As/(g product) as the specific criteria of purity. Finally, based on scanning electron microscopy analysis of unused and several times used pyrolytic graphite-coated tubes, usage of the tube 250 times before replacement is recommended.

Determination of 27 Elements in Animal Feed by Inductively Coupled Plasma-Mass Spectrometry.

A method was developed to determine 27 elements (aluminum, arsenic, boron, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, mercury, molybdenum, nickel, phosphorus, potassium, selenium, sodium, sulfur, vanadium, zinc, antimony, uranium, beryllium, thallium, and thorium) in animal feeds and pet foods using closed vessel microwave digestion and inductively coupled plasma-mass spectrometry. These elements can adversely affect animal health when amounts become excessive or deficient in food. For potentially toxic elements, the target LOQ was determined to be 1/10 the lowest maximum tolerable level (MTL) for the most sensitive animal species. For nutritionally essential elements, the target LOQ was determined to be 1/10 the concentration that would be considered deficient in feed if that level is lower than 1/10 the lowest MTL. The targeted high end of the quantitation range was selected as twice the highest MTL. A single-laboratory validation (SLV) was performed to determine the accuracy and precision of the method, and the results were evaluated with respect to predetermined performance characteristics. The test materials used in the SLV included two National Institute of Standards and Technology certified reference materials, two Association of American Feed Control Officials (AAFCO) check samples, and one in-house previously analyzed feed sample. The concentrations of each element determined were the result of spiked analyte, incurred analyte, or a combination of spiked and incurred analyte. All samples were analyzed seven times on different days at 2 × LOQ and at the midrange concentration. For most data, the results of the SLV met or exceeded the criteria for accuracy and repeatability. For accuracy, K at the midrange level had a mean recovery of 95%, which is just below the low preferred accuracy threshold of 97%. For repeatability, all the 2 × LOQ CVr values were below the preferred values. Be, Cr, Ni, Na, Mn, and S all had midrange CVr values exceeding the preferred values. Be had the highest midrange CVr value of 9.93. Eight AAFCO check samples were also analyzed to determine the method's accuracy and repeatability for elements at the manufacturer's claimed levels. For accuracy, all results had z-scores <1.5. For repeatability, three CVr values from two AAFCO check samples were greater than the preferred limits.

Determination of Eu concentrations in coal, fly ash and sedimentary rocks using a cation exchange resin and inductively coupled plasma mass spectrometry (ICP-MS)

Europium (Eu) in coal, coal combustion residues (e.g., fly ash), and sedimentary rocks in coal-bearing sequences has attracted much attention in recent years mainly because of its world-wide demand and use as a geochemical indicator of geological setting for coal deposit studies. This paper presents a method for accurately measuring the concentration of Eu in coal, fly ash, and sedimentary rocks by quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS), plus the use of closed-vessel microwave digestion and a cation exchange resin. To significantly diminish the inference of Ba-based polyatomic ions (137Ba16O, 136Ba17O, 135Ba18O, and 134Ba18OH) on 153Eu in coal, fly ash, and sedimentary rock samples, a Bio-Rad AG50W-x8 cation exchange resin was used to separate Ba from digested solutions of solid samples. The AG50W-x8 cation exchange resin can effectively separate the barium from digested solutions and thus could diminish the inference of Ba on Eu. The determination of Ba and Eu in the National Institute of Standards Technology (NIST) standard references of coal and fly ash samples showed that the use of the AG50W-x8 cation exchange resin combined with quadrupole-based ICP-MS analysis can provide a reliable method for the accurate determination of Eu concentrations in coal and coal-related samples. The method detection limits for Ba and Eu are 0.030 μg/l and 0.006 μg/l, respectively, and the determination coefficient of their calibration curves (linearity range 0–100 μg/l) is >0.9999. A Ba/Eu value of 1000 in the samples is proposed for judging the interference of Ba on Eu. If Ba/Eu > 1000, then Ba in coal, fly ash, and sedimentary rocks significantly interferes with Eu and this interference then needs to be considered when interpreting the analytical results and their significance.

Multivariate data analysis of trace elements in bivalve molluscs: Characterization and food safety evaluation

Four species of bivalve molluscs (Anomalocardia brasiliana, Iphigenia brasiliana, Lucina pectinata and Trachycardium muricatum) were collected in the Todos os Santos Bay (TSB), Bahia, Brazil, in order to evaluate As, Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Se, V and Zn levels and, consequently, the risk of bivalve mollusc consumption in humans. The samples were analyzed by inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS) after closed-vessel microwave digestion. The accuracy was confirmed using the certified reference materials of oyster tissue (NIST 1566b) and mussel tissue (NIST 2977), and the results were statistically equivalent to the certified values. Application of principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed a tendency to form two groups between samples of Lucina pectinata and Trachycardium muricatum. All species showed As and Cr concentrations higher than the maximum tolerable limit specified in Brazilian legislation.

Ultra-low background mass spectrometry for rare-event searches

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) allows for rapid, high-sensitivity determination of trace impurities, notably the primordial radioisotopes 238U and 232Th, in candidate materials for low-background rare-event search experiments. We describe the setup and characterisation of a dedicated low-background screening facility at University College London where we operate an Agilent 7900 ICP-MS. The impact of reagent and carrier gas purity is evaluated and we show that twice-distilled ROMIL-SpATM-grade nitric acid and zero-grade Ar gas delivers similar sensitivity to ROMIL-UpATM-grade acid and research-grade gas. A straightforward procedure for sample digestion and analysis of materials with U/Th concentrations down to 10 ppt g/g is presented. This includes the use of 233U and 230Th spikes to correct for signal loss from a range of sources and verification of 238U and 232Th recovery through digestion and analysis of a certified reference material with a complex sample matrix. Finally, we demonstrate assays and present results from two sample preparation and assay methods: a high-sensitivity measurement of ultra-pure Ti using open digestion techniques, and a closed vessel microwave digestion of a nickel–chromium-alloy using a multi-acid mixture.

Establishing human heart chromium, cobalt and vanadium concentrations by inductively coupled plasma mass spectrometry

ObjectiveChromium, cobalt, and vanadium are used in metallic joint prosthesis. Case studies have associated elevated heart tissue cobalt concentrations with myocardial injury. To document the long term heart metal ion concentrations, a validated inductively coupled plasma mass spectroscopy (ICP-MS) method was needed. MethodThe method utilized a closed-vessel microwave digestion system to digest the samples. An ICP‐MS method utilizing Universal Cell Technology was used to determine our target analyte concentrations. Accuracy was verified using reference materials. Precision, sensitivity, recovery and linearity studies were performed. This method was used to establish a reference range for a non-implant containing cohort of 80 autopsy human heart tissues ResultsThis method demonstrated an analytic measurement range of 0.5–100ng/mL for each element. Accuracy was within ±10% of target value for each element. Within-run precision for each element was below 20% CV. The chromium, vanadium and cobalt concentrations (mean±SD) were 0.1523±0.2157μg/g, 0.0094±0.0211μg/g and 0.1039±0.1305μg/g respectively in 80 non-implant containing human heart tissue samples. ConclusionsThis method provides acceptable recovery of the chromium, cobalt and vanadium in heart tissue; allowing assessment of the effects of metallic joint prosthesis on myocardial health.

Closed vessel microwave digestion of air filters for measurements of elemental iodine

An acid assisted closed vessel microwave digestion procedure was developed for the treatment of fine airborne particulate matter that allows elemental iodine to be solubilised simultaneously with other metallic elements.

Human Health Risk Assessment and Safety Threshold of Harmful Trace Elements in the Soil Environment of the Wulantuga Open-Cast Coal Mine

In this study, soil samples were collected from a large-scale open-cast coal mine area in Inner Mongolia, China. Arsenic (As), cadmium (Cd), beryllium (Be) and nickel (Ni) in soil samples were detected using novel collision/reaction cell technology (CCT) with inductively-coupled plasma mass spectrometry (ICP-MS; collectively ICP-CCT-MS) after closed-vessel microwave digestion. Human health risk from As, Cd, Be and Ni was assessed via three exposure pathways—inhalation, skin contact and soil particle ingestion. The comprehensive carcinogenic risk from As in Wulantuga open-cast coal mine soil is 6.29–87.70-times the acceptable risk, and the highest total hazard quotient of As in soils in this area can reach 4.53-times acceptable risk levels. The carcinogenic risk and hazard quotient of Cd, Be and Ni are acceptable. The main exposure route of As from open-cast coal mine soils is soil particle ingestion, accounting for 76.64% of the total carcinogenic risk. Considering different control values for each exposure pathway, the minimum control value (1.59 mg/kg) could be selected as the strict reference safety threshold for As in the soil environment of coal-chemical industry areas. However, acceptable levels of carcinogenic risk are not unanimous; thus, the safety threshold identified here, calculated under a 1.00 × 10−6 acceptable carcinogenic risk level, needs further consideration.

Trace element composition of PM2.5 and PM10 from Kolkata – a heavily polluted Indian metropolis

Elemental composition of PM2.5 and PM10 was measured from 16 locations in Greater Kolkata in Eastern India. Sampling was carried out in the winter months of 2013–2014. PM2.5 and PM10 mass concentrations ranged from 83–783μg/m3 and 167–928μg/m3 respectively. 20 elements were measured with an Agilent 7700 series ICP–MS equipped with a 3rd generation He reaction/collision cell following closed vessel microwave digestion. In both size fractions Fe, Na, Al, K, Ca were present in high concentrations (>1 000ng/m3), Mn, Zn and Pb demonstrated medium concentrations (>100ng/m3), and Sc, V, Co, Ni, Mo, Cd, Sn and Sb had low concentrations (<100ng/m3). Ca, Al, Mg, Sc, Ti, Mn and Fe were concentrated in the PM10 fraction, while the toxic metals (Cr, Ni, Zn, Mo, Sn, Sb, V, Co, Cu, Cd and Pb) were concentrated in the PM2.5 fraction. Al normalized Enrichment Factors (EF) showed EF<10 for Ti, Mg, Sc, Fe, Mn, Na, K, Ca, V, Co which is indicative of crustal sources, 100>EF>10 for Ni, Cr, Cu is possibly industrial influence and 1 000>EF>100 for Sn, Zn, Mo, Sb, Pb, Cd is related to industrial, high temperature combustion and vehicle sources. Factor analysis identified three possible sources for PM10; (1) abraded vehicular part related road dust, exhaust gases of car and municipal waste incineration (2) industrial emissions, and (3) coal combustion and non–ferrous metal smelting and three possible sources for PM2.5; (1) abraded vehicular part related road dust and industrial emissions (2) exhaust gases of cars and municipal waste incineration, and (3) coal combustion and non–ferrous metal smelting. In a risk evaluation using a U.S. EPA IRIS, chromium was found to have the highest excess cancer risk.

Simultaneous determination of 31 elements in foodstuffs by ICP-MS after closed-vessel microwave digestion: Method validation based on the accuracy profile

This article describes an optimisation and validation process for the simultaneous determination of 31 elements – lithium, boron, sodium, magnesium, aluminium, potassium, calcium, titanium, vanadium, chromium, iron, manganese, cobalt, nickel, copper, zinc, gallium, germanium, arsenic, selenium, strontium, molybdenum, silver, cadmium, tin, antimony, tellurium, barium, mercury, lead and uranium – in food samples by inductively coupled plasma-mass spectrometry (ICP-MS) after closed-vessel microwave digestion. In order to improve the limits of quantification of certain elements for risk assessment in the context of the first French Infant Total Diet Study (iTDS), the analytical conditions of the multi-elemental method were optimised. The validation was conducted using the evaluation of several performance criteria such as linearity, specificity, precision under repeatability conditions, intermediate precision reproducibility and limits of quantification (LOQ), with the use of the accuracy profile. Furthermore, the method was supervised by several external quality controls (EQC). Results indicate that this method could be used in the laboratory for the routine determination of these 31 essential and non-essential elements in foodstuffs with acceptable analytical performance. A more sensitive method will be necessary for Hg and Pb to decrease at the lowest the percentage of left-censored data for this iTDS.

Determination of Ti from TiO2 Nanoparticles in Biological Materials by Different ICP-MS Instruments: Method Validation and Applications

The accurate determination of nanoparticles (NPs) content in biological samples is of great interest for studying its potential impacts on health. This paper describes a method validation process for Ti determination from TiO2 NPs in biological matrixes using a closed-vessel microwave digestion with a mixture of 3 mL of HNO3 and 0.4 mL of HF and a detection by quadrupole inductively coupled plasma-mass spectrometry (Q-ICP-MS), in both standard and collision/ reaction cell (CCT) modes. As no suitable certified reference materials are available, several internal reference materials (IRMs) were prepared precisely and they were used for the optimisation and the analytical quality assurance of the method. Several criteria such as linearity, limits of quantification (LOQ), precision under repeatability conditions and intermediate precision reproducibility were evaluated. Furthermore, the method was compared on different Q-ICP-MS devices and on a high resolution (HR)-ICP-MS using the prepared IRMs and various samples of rat tissues exposed to two different sizes of TiO2 NPs. The results demonstrated that the Q-ICP-MS method evaluated permitted an accurate determination of Ti present as TiO2 NPs in both standard and CCT modes, with a greater accuracy in CCT mode at low concentration levels near the LOQ of 0.10 mg kg-1.

Determination of Boron in Coal Using Closed-Vessel Microwave Digestion and Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

Boron in coal is of great interest, mainly because it can be used as paleosalinity indicator; it is also of environmental concern because of its toxic effects, especially on land plants. This paper describes a new method for determination of the boron concentration in coal by inductively coupled plasma mass spectrometry (ICP-MS) after closed-vessel microwave digestion. Samples of raw coal rather than coal ash were used for the determination to avoid the loss of volatile organically bound boron. Addition of H3PO4 to the HNO3 and HF used as reagents in the process could also significantly diminish boron volatilization during acid-drying after sample digestion. A 2% ammonia solution, which was injected into an ICP-MS spray chamber to eliminate the memory effect of boron, may reduce boron signals to blank levels (within 120 s) during ICP-MS analysis. The boron concentrations of National Institute of Standards and Technology (NIST) standard reference coal samples obtained using the ICP-MS in high-resolution mode and with 103Rh or 115In used as online addition internal standards are in good agreement with the certified values.

Determination of As and Se in coal and coal combustion products using closed vessel microwave digestion and collision/reaction cell technology (CCT) of inductively coupled plasma mass spectrometry (ICP-MS)

Toxic elements arsenic and selenium in coal are of great concern mainly because of their adverse effects on human health during coal combustion. This paper describes the concentration determination of As and Se in coal and coal combustion products (CCPs), performed by collision/reaction cell technology (CCT) of inductively coupled plasma mass spectrometry (ICP-MS; collectively ICP-CCT-MS) after closed vessel microwave digestion. The reagents for 50-mg coal sample digestion are 2-ml 40% (v/v) HF and 5-ml 65% (v/v) HNO3 but for the CCP samples, the reagents include 5-ml 40% HF and 2-ml 65% HNO3. To significantly diminish the argon-based interferences at mass to charge ratios (m/z) 75 (40Ar35Cl) and 78 (40Ar38Ar), a helium and hydrogen mixture was used in the optimized hexapole collision cell. The results showed that CCT technology can effectively diminish the spectral interferences of the Ar-based polyatomic ions 40Ar35Cl and 40Ar38Ar to 75As and 78Se, respectively. The method detection limit of As and Se is 0.024 and 0.095μg/l, respectively, and their linearity of the calibration curves in the range 0–100μg/l has a determination coefficient r2>0.9999. The determination of As and Se in NIST standard reference materials of coal and fly ash samples showed that ICP-CCT-MS plus closed vessel microwave digestion is a reliable method for concentration determination of the two elements in coal and CCPs.