Determination of Metallic Impurities in Carbon Nanotubes by Glow Discharge Mass Spectrometry.

A method for the rapid assessment of metallic impurities in carbon nanotubes (CNTs) by pin-cell source geometry glow discharge mass spectrometry (GDMS) is presented. Pins were prepared by pressing CNT powder onto an indium substrate. GDMS analysis was performed using high-carbon-content nanotube and coal-certified reference materials for calibration purposes. This approach enables the calibrated measurement of 41 elemental impurities in CNTs. The method was validated by the analysis of NIST SRM 2483 single-wall CNTs (raw soot) with good agreement with the certified values. The proposed measurement approach could also be applied not only for CNTs but also for the assessment of precursor materials used in the synthesis of CNTs and for quality control during the entire manufacturing process. The ability to assess the presence of all metallic impurities in a simple, reliable, high-throughput manner will allow the industry to real-time monitor any changes in the product process, access its toxicity, and environmental impact. As sample preparation is maintained to a minimum, this allows the determination of metallic impurities at concentration levels that are usually not attainable by most techniques.

Collaborative determination of trace element mass fractions and isotope ratios in AQUA-1 drinking water certified reference material.

The Isotrace CNRS workgroup in collaboration with National Research Council of Canada has characterized a number of trace element mass fractions and isotope ratios currently not certified in AQUA-1 natural drinking water reference material (NRC Canada). This survey further expands the use of this material as a tool for environmental quality control, method validation, and method development tool for the international community. Simultaneously, the SLRS-6 river water was analyzed as quality control and also in order to compare both water characteristics, which were sampled in the same area but having undergone different treatment. Mass fractions for B, Cs, Li, Ga, Ge, Hf, Nb, P, Rb, Rh, Re, S, Sc, Se, Si, Sn, Th, Ti, Tl, W, Y, Zr, REEs, and six isotopic ratios are proposed for Sr and Pb. Measurements were mostly performed using ICP-MS with various calibration approaches. The results are reported as consensus or indicative values depending on the number of available datasets, with their associated uncertainties.

Evaluation of different strategies for determination of selenomethionine (SeMet) in selenized yeast by asymmetrical flow field flow fractionation coupled to inductively coupled plasma mass spectrometry (AF4-ICP-MS).

This manuscript exemplifies the prospective use of asymmetrical flow field flow fractionation (AF4) coupled to inductively coupled plasma mass spectrometry (ICP-MS) as a simple tool for chemical speciation of selenomethionine (SeMet) in selenized yeast. Several popular sample preparation methods were evaluated for their suitability to determine selenomethionine (SeMet) in selenized yeast by AF4-ICP-MS. These included water, methanesulfonic acid (MSA), formic acid (FA) and alkaline extractions. Alkaline extraction (using sodium dodecyl sulfate buffer) provided the best recovery/determination conditions for SeMet based on analysis of NRC certified reference material (CRM) SELM-1 since it minimized hydrolysis of the protein peptide bonds optimally required for the AF4 separation. The analytical performance of three different AF4 membranes (5, 10 and 500 kDa regenerated cellulose) was also evaluated. No significant difference in the recovery of SeMet was observed when using 5 and 10 kDa RC membranes, whereas the 500 kDa membrane resulted in a significant loss. The proposed method presents appropriate instrument and intra-assay precisions of 4.4-9.2% and 3.8% RSD, respectively, a detection limit of 0.49 µg L-1 SeMet as Se and good linearity with correlation coefficients (R) between 0.996 - 0.999. This is the first report of use of AF4-ICP-MS for species specific quantitation of SeMet in selenized yeast demonstrating its efficient use as an alternative method to other traditional chromatographic techniques.

CRM rapid response approach for the certification of arsenic species and toxic trace elements in baby cereal coarse rice flour certified reference material BARI-1.

With recently legislated maximum levels of inorganic arsenic (iAs) in white and brown rice in Canada, the regulatory bodies are evaluating the need for regulation of As levels in infant food products. Rice is a major part of infants' diet, and therefore, the presence of As in this staple food causes concerns. So far, the scientific community was lacking suitable certified reference material (CRM) which could be used to assess the accuracy of developed analytical methods for As speciation in infants' food products. As a result, we have developed BARI-1, a baby cereal coarse rice flour reference material which was certified for total arsenic (0.248 ± 0.018 mg kg-1), cadmium (0.0134 ± 0.0014 mg kg-1), mercury (0.0026 ± 0.0003 mg kg-1), lead (0.0064 ± 0.0016 mg kg-1), inorganic As (0.113 ± 0.016 mg kg-1) and dimethylarsinic acid (DMA) (0.115 ± 0.010 mg kg-1), and reference value for monomethylarsonic acid (MMA) (0.0045 ± 0.0008 mg kg-1) was reported. We also observed trace amounts of an unknown As compound, with chromatographic retention time close to DMA. Participating laboratories were allowed to use their in-house-validated extraction and/or digestion methods, and the detection of total metals was done by ICP-MS whereas HPLC-ICP-MS was used for As speciation. Despite the diversity in sample preparation and quantitation methods, reported values were in good agreement. For iAs measurement, the comparison between hydride generation ICP-MS and HPLC-ICP-MS found iAs overestimation with the former method, possibly due to interference from DMA. The certification was accomplished with a CRM rapid response approach in collaborative, focused effort completing the CRM development in few months instead of the typical multiyear project. This approach allowed to respond to measurement needs in a timely fashion. Graphical abstract.

Diagnostic detection systems and QuEChERS methods for multiclass pesticide analyses in different types of fruits: An overview from the last decade.

This manuscript is a bibliographic review about analyses of different classes of pesticide in fruits using QuEChERS as sample preparation methodology. The aim is to clarify different trends and facilitate decision-making by the scientific community in order to carry out further studies in this field. It is well known that different countries have different pesticides regulations for maximum level of pesticide residue permitted. The comparative analysis amongst the main producer countries reveals that for some fruits they are not studied enough. Recent improvements to QuEChERS make it possible to minimize the pesticides instability due the matrix pH, and achieving cleaner extracts. Regarding the detection systems, the tandem MS are preferred once they have high sensitivity and selectivity, although traditional techniques (GC-ECD and HPLC-DAD) are still commonly used due to their accessibility and good sensitivity to some pesticides. Also, studies involving metabolites usually show that they are more toxic than their precursor compounds.

Inter-laboratory study for the certification of trace elements in seawater certified reference materials NASS-7 and CASS-6.

Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 is described. At the National Research Council Canada (NRC), column separation was performed to remove the seawater matrix prior to the determination of Cd, Cr, Cu, Fe, Pb, Mn, Mo, Ni, U, V, and Zn, whereas As was directly measured in 10-fold diluted seawater samples, and B was directly measured in 200-fold diluted seawater samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) was used for elemental analyses, with double isotope dilution for the accurate determination of B, Cd, Cr, Cu, Fe, Pb, Mo, Ni, U, and Zn in seawater NASS-7 and CASS-6, and standard addition calibration for As, Co, Mn, and V. In addition, all analytes were measured using standard addition calibration with triple quadrupole (QQQ)-ICPMS to provide a second set of data at NRC. Expert laboratories worldwide were invited to contribute data to the certification of trace metals in NASS-7 and CASS-6. Various analytical methods were employed by participants including column separation, co-precipitation, and simple dilution coupled to ICPMS detection or flow injection analysis coupled to chemiluminescence detection, with use of double isotope dilution calibration, matrix matching external calibration, and standard addition calibration. Results presented in this study show that majority of laboratories have demonstrated their measurement capabilities for the accurate determination of trace metals in seawater. As a result of this comparison, certified/reference values and associated uncertainties were assigned for 14 elements in seawater CRMs NASS-7 and CASS-6, suitable for the validation of methods used for seawater analysis.

Elemental characterization of single-wall carbon nanotube certified reference material by neutron and prompt γ activation analysis.

Instrumental neutron activation analysis with both relative and k0 standardization was used in four experienced laboratories to determine element mass fractions in single-wall carbon nanotube certified reference material (CRM) SWCNT-1. Results obtained were evaluated using the National Institute of Standards and Technology (NIST) "Type B On Bias" approach and yielded consensus values in agreement with National Research Council Canada (NRCC) certified values for Fe, Co, Ni, and Mo and provided mass fraction values for 13 additional elements, namely, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Br, La, W, and Au. In addition, prompt γ neutron activation analysis was employed to determine mass fractions of H, B, Co, Ni, and Mo. Results of this work provide a basis for the establishment of reference values of element mass fractions in CRM SWCNT-1, thus expanding its usability for more accurate characterization and benchmarking of similar nanotechnology materials.

Determination of trace elements in fluoropolymers after microwave-induced combustion.

An effective approach to the digestion of fluoropolymers for the determination of Ag, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, and Ni impurities has been developed using microwave-induced combustion (MIC) in closed quartz vessels pressurized with oxygen. Samples that were examined included the following: polytetrafluorethylene (PTFE); polytetrafluoroethylene with an additional modifier, perfluoropropylvinylether (PTFE-TFM); and fluorinated ethylene propylene (FEP). A quartz device was used as a sample holder, and the influence of the absorber solution was evaluated. Determination of trace elements was performed by inductively coupled plasma-optical emission and mass spectrometry. Neutron activation analysis (NAA) was used for validation purposes. Results were also compared to those obtained using microwave-assisted acid extraction in high-pressure closed systems. Dilute nitric acid (5 mol L(-1)), which was selected as the absorbing medium, was used to reflux the sample for 5 min after the combustion. Using these conditions, agreement for all analytes was better than 98% when compared to values determined by NAA. The residual carbon content in the digests was lower than 1%, illustrating the high efficiency of the method. Up to 8 samples could be digested within 30 min using MIC, providing a suitable throughput, taking into account the inertness of such samples.

Determination of moisture content of single-wall carbon nanotubes.

Several techniques were evaluated for the establishment of reliable water/moisture content of single-wall carbon nanotubes. Karl Fischer titration (KF) provides a direct measure of the water content and was used for benchmarking against results obtained by conventional oven drying, desiccation over anhydrous magnesium perchlorate as well as by thermogravimetry and prompt gamma-ray activation analysis. Agreement amongst results was satisfactory with the exception of thermogravimetry, although care must be taken with oven drying as it is possible to register mass gain after an initial moisture loss if prolonged drying time or elevated temperatures (120 °C) are used. Thermogravimetric data were precise but a bias was evident that could be accounted for by considering the non-selective loss of mass as volatile carbonaceous components. Simple drying over anhydrous magnesium perchlorate for a minimum period of 8-10 days is recommended if KF is not available for this measurement.

The determination of total Se in urine and serum by graphite furnace atomic absorption spectrometry using Ir as permanent modifier and in situ oxidation for complete trimethylselenonium recovery.

The present work evaluated the use of iridium (Ir) as permanent modifier for the determination of total selenium in urine and serum by graphite furnace atomic absorption spectrometry. Concerning urine, the presence of trimethylselenonium (TMSe(+)) was especially considered. Pyrolysis and atomization temperatures of 1,000 and 2,100 degrees C, respectively, were used. For nondigested urine and serum samples, 0.2% v/v HNO(3) and Triton X-100 were used as diluents, respectively, and the same initial platform Ir treatment was effective for up to 1,100 atomization cycles. Good precision [less than 5% relative standard deviation (RSD)] can be achieved with the proposed method. Low TMSe(+) recovery was observed for nondigested urine samples. Thus, if this species is to be considered in urine analysis, a previous external mineralization step was found to be necessary. Alternatively, an in situ oxidation treatment was developed. Detection limits of 8, 10, and 7 mug l(-1) were obtained after dilution, microwave-assisted digestion, and in situ oxidation procedures, respectively. The accuracy of the method was validated by the analysis of certified reference or commercial quality control materials and spiked samples.

Determination of thorium and uranium in ultrapure lead by inductively coupled plasma mass spectrometry.

A method for the determination of U and Th at sub-ppt levels in high-purity Pb samples using extraction chromatography with ICPMS detection is described. Following acid digestion, uranium and thorium are separated from the lead matrix using UTEVA resin. Sorption and elution procedures were optimized, the potential reusability of the chromatographic resin was evaluated, and a performance comparison between prepacked and freshly prepared UTEVA column was made. Uranium could be eluted with 0.025 M HCl and Th then recovered using 0.5% oxalic acid. Recovery yields for U exceed 80% whereas those for Th were typically 60%. Procedural detection limits of 0.5 and 1.5 pg g(-)(1) were obtained for U and Th, respectively. For purposes of comparison, GD-MS analysis of samples was also performed, yielding results consistent with those generated by ICPMS but with inferior detection power.