Diogo Pompéu de Moraes

Evaluation of sample preparation methods for polymer digestion and trace elements determination by ICPMS and ICPOES

In this work, sample preparation methods for polymer digestion based on microwave-induced combustion (MIC) and microwave-assisted acid digestion (MW-AD) were evaluated for further As, Bi, Cd, Co, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Sr, Ti, V and Zn determination by inductively coupled plasma mass spectrometry (ICPMS) and inductively coupled plasma optical emission spectrometry (ICPOES). Samples of low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET, colorless and green), polyetheretherketone (PEEK) and nylon 6,6 were digested using MIC and MW-AD in closed quartz vessels. The type and concentration of acids used for MIC were investigated and better results were achieved using a 4 mol l−1 HNO3 + 4 mol l−1 HCl solution. Microwave-assisted acid digestion was also evaluated for polymer digestion using concentrated acids. Both sample preparation methods were considered suitable for polymer digestion but MIC was preferable in view of the possibility of using diluted acids as absorbing solution and allowing higher sample mass to be digested and consequently better limits of detection. Residual carbon content in digests of polymers obtained by MIC was lower in comparison with the values obtained after MW-AD. Accuracy for all the analytes determined by ICPOES and ICPMS after MIC digestion was better than 95% (analysis of certified reference materials and by neutron activation analysis). It was possible to digest up to 8 samples by MIC in less time (in 25 min) in comparison with MW-AD (more than 50 min) and also using diluted acids (4 mol l−1 HNO3 and HCl) instead of concentrated acids.

Bromine and chlorine determination in cigarette tobacco using microwave-induced combustion and inductively coupled plasma optical emission spectrometry

(NH4)2CO3 as absorbing solution and 5 min of reflux. Temperature during combustion was higher than 1400 °C and the residual carbon content in digest obtained after MIC was lower than 1%. Up to eight samples could be processed simultaneously and a single absorbing solution was suitable for both Br and Cl. Limit of quantification by MIC and further ICP OES determination was 12 and 6 µg g -1 for Br and Cl, respectively.

Direct analysis of methylated trivalent arsenicals in mouse liver by hydride generation-cryotrapping-atomic absorption spectrometry

Growing evidence suggest that the methylated trivalent metabolites of inorganic arsenic (iAs), methylarsonite (MAs(III)) and dimethylarsinite (DMAs(III)), contribute to adverse effects of iAs exposure. However, the lack of suitable methods has hindered the quantitative analysis of MAs(III) and DMAs(III) in complex biological matrices. Here, we show that hydride generation-cryotrapping-atomic absorption spectrometry can quantify both MAs(III) and DMAs(III) in livers of mice exposed to iAs. No sample extraction is required, thus limiting MAs(III) or DMAs(III) oxidation prior to analysis. The limits of detection are below 6 ng As/g of tissue, making this method suitable even for studies examining low exposures to iAs.

Focused microwave-induced combustion for digestion of botanical samples and metals determination by ICP OES and ICP-MS.

The advantages and shortcomings of focused microwave-induced combustion (FMIC) for digestion of plant samples were studied. The effects of sample mass, absorbing solution, oxygen gas flow-rate, and time of reflux step on recoveries of major, minor and trace metals were systematically evaluated. Afterwards, Al, Ba, Ca, Co, Cr, Cu, Mg, Mn, Ni, Sr, V, and Zn were determined by inductively coupled plasma optical emission spectrometry (ICP OES) and by inductively coupled plasma mass spectrometry (ICP-MS). The main advantages of FMIC when compared to microwave-assisted wet digestion (MAWD) and focused-microwave-assisted wet digestion (FMAWD) are the possibility to digest larger masses of samples (up to 3g) using shorter heating times and diluted nitric acid solution for absorbing all analytes. Using the selected experimental conditions for FMIC, residual carbon content was lower than 0.7% for all samples and relative standard deviation (RSD) varied from 1.5 to 14.1%. Certified reference materials (NIST 1515 apple leaves and NIST 1547 peach leaves) were used for checking accuracy and determined values for all metals were in agreement with certified values at a 95% confidence level. No statistical difference (ANOVA, 95% of confidence level) was observed for results obtained by FMIC, FMAWD, and MAWD. Limits of detection were lower when using FMIC in the range of 0.02-0.15 μg g(-1) for ICP OES and 0.001-0.01 μg g(-1) for ICP-MS, which were about 3 and 6 times lower than the values obtained by FMAWD and MAWD, respectively. It is important to point out that FMIC was a suitable sample preparation method for major, minor and trace metals by both determination techniques (ICP OES and ICP-MS). Additionally, since it allows lower LODs (because up to 3g of sample can be digested) and diluted acid solutions are used (without any further dilution), the use of ICP-MS is not mandatory.

Preconcentration and determination of As, Cd, Pb and Bi using different sample introduction systems, cloud point extraction and inductively coupled plasma optical emission spectrometry

This study deals with the development of a method for As, Bi, Cd and Pb preconcentration and determination using cloud point extraction (CPE) and inductively coupled plasma optical emission spectrometry (ICP OES). Hydride generation, pneumatic nebulization and micronebulization/aerosol desolvation were investigated for introducing the surfactant rich phase into the ICP. O,O-Diethyldithiophosphate (DDTP) was used as complexant and octylphenoxypolyethoxyethanol (Triton X-114) as surfactant. The influence of concentration of HNO3, HCl, DDTP, Triton X-114, surfactant rich phase in methanol, reductant of As, and NaBH4 was evaluated. The enrichment factors obtained were 10, 18, 12 and 14 for As, Bi, Cd and Pb, respectively. The limits of detection (LODs) of As, Bi, Cd and Pb were 0.055, 0.063, 0.047 and 0.28 μg L−1, respectively. Precision and accuracy were assessed by analysis of certified enriched water (NIST 1643e), oyster tissue (NIST 1566b), tobacco leaves (CTA-OTL-1), bush branches and leaves (GBW 07602) and analyte spiking. Microwave-induced combustion (MIC), sonication, and acid digestion were used for sample preparation. The developed method was applied for extraction and determination of As, Bi, Cd and Pb in river water, wine, fertilizer and urine. Analyte recovery close to 100% and relative standard deviation (RSD) lower than 5% were observed.

Speciation of inorganic arsenic in rice using hydride generation atomic absorption spectrometry (HG-AAS)

Inorganic arsenic (iAs) concentration in rice is a current concern worldwide. A method for iAs determination in rice using hydride generation atomic absorption spectrometry (HG-AAS) is proposed. Arsenic species were extracted from rice using 0.14 mol L−1 HNO3 assisted by microwave radiation or 0.28 mol L−1 HNO3 and heating in a water bath prior to As determination by HG-AAS. Selective generation of arsine of As(III) was achieved with 0.1% (m/v) NaBH4 and 10 mol L−1 HCl. iAs was determined by pre-reduction of all inorganic arsenic and determination under the same conditions used for As(III). By difference, the concentration of As(V) was estimated. Ascorbic acid (1% m/v) and KI (0.2% m/v) in the presence of 1.2 mol L−1 HCl were used for As pre-reduction. The limit of detection (LOD) of As(III) was 1.96 ng g−1 and that of iAs was 3.85 ng g−1, which are feasible for As(III) and iAs speciation in rice. The accuracy was evaluated by analyte recovery tests and analysis of certified reference rice. Total arsenic (tAs) was quantified using alkaline extraction with K2S2O8 and HNO3, followed by As detection by HG-AAS. Thirteen samples of different types of rice (polished, brown, organic, and parboiled) grown in southern Brazil were analyzed. The iAs, As(III) and As(V) concentrations found were consistent with those already reported for rice.

Toxic and micronutrient elements in organic, brown and polished rice in Brazil

Concentration levels of As, Cd, Hg, Pb, Tl, Sn, Sb Co, Cu, Mn, Se, Zn, Cr, Ni and Mo in different types of rice cultivated in irrigated fields in Brazil were evaluated. Arsenic, Cd, Pb, Zn, Mn and Cu were found in higher concentrations in brown rice samples, suggesting the prevalence of these elements in the bran. Meanwhile, lower concentrations of Pb, Mo, Cr, Se and Co were found in parboiled rice. Organic rice did not differ of cultivated conventionally rice. Thallium, Hg and Sb were not detected in any rice sample whose limits of detection were 0.7 μg kg−1, 2.5 μg kg−1 and 8 μg kg−1, respectively. The concentrations of the investigated elements were compared with those reported for polished rice and brown rice from other countries, unveiling concentrations in general at the same level for rice produced at non-contaminated sites.

Selective generation of substituted arsines-cryotrapping-atomic absorption spectrometry for arsenic speciation analysis in N-methylglucamine antimonate

Hydride generation-cryotrapping-gas chromatography-atomic absorption spectrometry (HG-CT-AAS) was applied for arsenic speciation analysis in an injectable drug, N-methylglucamine antimonate. The method employs generation of substituted hydrides and selective hydride generation, which makes possible an analysis of arsenites and arsenates and their mono-, di-, and trimethyl substituted species. Interference of the antimony matrix was eliminated using the T-valve to prevent supply of the stibine interferent to the atomizer. The limits of detection in measured sample solutions were 70 ng L−1 for inorganic arsenate, 42 ng L−1 for mono- and dimethylarsenates and 30 ng L−1 for all the other determined species. Concentrations of all methylated species in all samples were below their detection limits. A significant but different amount of inorganic As was found in different batches of the drug: between 0.9 and 2.3 mg L−1 with 7% to 10% of the content present as the trivalent form. The accuracy was assessed by the comparison of the determined inorganic arsenic content with the total arsenic content determined by the conventional inductively coupled plasma mass spectrometry. Both methods yielded for individual samples equal values within experimental error. The HG-CT-AAS procedure showed good performance with minimum sample pretreatment at low investment and running costs.

Wet Digestion Using Microwave Heating

Abstract The use of microwave energy to sample preparation is already consolidated and allows the decomposition of many matrices at high pressure and temperature with safety. The combination of inorganic acids and hydrogen peroxide is widely used and enables the decomposition of organic and inorganic materials. This chapter gives an overview about important aspects for sample preparation using microwave heating with concentrated and diluted acids. Special details will be given for samples of food, petroleum, polymers, carbon nanotubes, and advanced materials.

Microwave-assisted ultraviolet digestion: an efficient method for the digestion of produced water from crude oil extraction and further metal determination

A sample preparation method based on microwave-assisted ultraviolet digestion (MW-UV) was evaluated for the first time to treat produced waters from crude oil extraction containing variable salinity and organic carbon content for the subsequent determination of Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sr, V and Zn by inductively coupled plasma optical emission spectrometry (ICP-OES). Some parameters of the proposed MW-UV method were evaluated, such as the concentrations of HNO3 and H2O2, microwave power and heating time in order to obtain high efficiency of digestion, which was verified by the determination of total organic carbon content (TOC) in the final solutions. Digestion was performed using about 8 g of produced water, 0.8 mol L−1 of HNO3 and 0.4 mL of H2O2 in high-pressure quartz vessels at 700 W for 15 min (5 min of ramp). Under these conditions, the TOC in solution was reduced by 98, 80, 78 and 48% for samples A, B, C and D, respectively, and residual acidity was lower than 0.41 mol L−1 for all samples evaluated. Conventional microwave-assisted acid digestion (MW-AD) was also performed under the same conditions as MW-UV for comparison, and it was observed that some samples were not completely digested. For analyte determination by ICP-OES, the use of an internal standard was investigated, and better results were obtained using Sc. The accuracy of the proposed method was evaluated using a spiked sample and certified reference material (CRM). Using MW-UV, recoveries for the spiked sample were better than 90% for all analytes, and the results obtained for the CRM were in agreement, better than 94%, with the certified reference values (t-test, 95% confidence level). It was possible to use diluted reagents to treat complex samples, like produced waters, in only 15 min for further determination of sixteen metals by ICP-OES.