Xueying Mao

Quantitative analysis of metal impurities in carbon nanotubes: efficacy of different pretreatment protocols for ICPMS spectroscopy.

Metal impurities in carbon nanotubes (CNTs) are undesirable for their uses in diverse applications, for instance, they may potentially have a negative health impact when using in biomedical fields. However, so far there is a lack of analysis methods able to quantify metallic impurities in CNTs. In this paper, using the neutron activation analysis (NAA) technique as a nondestructive standard quantification method and inductively coupled plasma mass spectrometry (ICPMS) as a practical approach, we established an analytical method for quantitative determination of metallic impurities in CNTs. ICPMS, one of the most sensitive analytical techniques used for coincident multielement measurements, has become a common tool in many laboratory, and thus it is easily available and a good selection for determining the metal impurities in CNTs. However, because of their extremely stable structure and the encapsulated metals in the defect structure, CNTs must undergo special pretreatments before ICPMS. We investigated different sample pretreatment procedures for ICPMS analysis, including dry ashing coupled with acid extraction, wet digestion, and a combination of dry ashing with acid digestion. With the reference data from the nondestructive analytical method of NAA, we found that the quantitative determination of metal impurities in CNTs is highly dependent on the sample pretreatment in which the conditions are largely different from those used for conventional biological samples or environmental materials. This paper not only provides the practical method and analysis conditions for quantifying the metal impurities of CNTs but also the first protocol for pretreatment processes of CNT samples.

A new preconcentration method for platinum and gold based on a macropore anion resin HHY-10A

The ion exchange behavior of Au and Pt on a new China-made macropore anion resin was studied using radiotracer technique. The conditions for adsorption and desorption, such as acidity, flow-rate and concentration of desorbing agents were studied carefully. Using the established method, the contents of Au and Pt in two Chinese ultrabasic SRMs were determined by ICP-MS and the results found in good agreement with the reference values.

Chemical speciation study of platinum group elements in geological samples by stepwise dissolution and inductively coupled plasma mass spectrometry

A chemical speciation study method for platinum group elements in geological samples was developed, including stepwise dissolution, nickel sulphide fire assay preconcentration and inductively coupled plasma mass spectrometry (ICP-MS) determination. Samples were firstly separated into eight components (water-soluble phase, exchangeable phase, carbonate phase, Fe/Ni metal phase, sulfide phase, oxide phase, silicate phase and HF-insoluble residue) by a newly-revised selective chemical dissolution procedure. The separated components were pretreated and subjected to nickel sulphide fire assay to preconcentrate platinuim group elements, which were determined by ICP-MS. The chemical speciation of platinum group elements in a Danish Cretaceous/Tertiary (K/T) boundary sample was studied as a demonstration

An α-amino pyridine resin preconcentration method for iridium in environmental and geological samples

The adsorption behavior of iridium on an cw-amino pyridine (AP) resin at very low Ir concentrations (0.24 ng ml(-1)) was studied by using the Ir-192 radiotracer technique. A preconcentration procedure was established, and the overall yield was 91.0 +/- 1.8% for Ir. Inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the measurement of Ir in reference materials, and a good agreement between the reference values and our results was obtained. This method is also suitable for the analyses of trace Au and Pd in environmental and geological samples

A study on the relationship between iridium concentration in hen eggshell and iridium-enriched feed by NAA

Four hens were fed by adding ammonium hexachloroiridate into their forage. After two weeks, we measured the Ir concentration in three fractions (eggshell, albumen, egg yolk) of their eggs by instrumental neutron activation analysis (INAA). Ir was present in all the three parts of the eggs. Further, the highest concentration of Ir was found in the egg yolk fraction, about 10 times higher than that in the eggshell and albumen. Moreover, the longer the Ir-containing feed was used, the higher the Ir concentration in the egg fractions was. After 4-6 day feeding, the Ir concentration became stable. The experimental results indicated that the Ir concentration was about 2-7·10-10 g/g in the eggshell fraction compared to 5.6·10-7 g/g in feed. Therefore, we can estimate the ratio from the feed over the eggshell via gastrointestinal pathway to be about 0.08%. The new result is useful to evaluate the iridium-enriched eggshell fossils of dinosauria and to interpret the origin of the mass extinction of dinosauria at the end of Cretaceous.

Neutron activation analysis of extractable organohalogens in milk from China

Instrumental neutron activation analysis (INAA) has been used for the determination of extractable organohalogens (EOX) in milk. The detection limits are 50 ng, 8 ng and 3.5 ng for Cl, Br and I, respectively. The EOX concentrations in milk samples from various regions of China were determined. Meanwhile, organochlorine pesticides residues were detected by gas chromatography. The concentrations of the EOX in the milk samples are decreasing in the order of EOCl >> EOBr > EOI, and EOCl accounts for 95% of the total EOX. The average concentration of EOCl in milk is 4.44 ·g/g expressed as fat weight basis, with the highest value of 17.6 ·g/g from South China. The mean concentrations of total HCH and DDT are 0.038 ·g/g and 0.046 ·g/g, respectively. Organochlorine pesticides account only for 1.6% of the EOCl, indicating the very high proportion of the unknown EOCl in the milk sample.

Coulometric titration study of the redox behavior and precise determination of hexachloroiridate(IV) ion and its monoaquo-chloro complex with electrogenerated bi-intermediates

The redox behavior of IrCl62- and Ir(H2O)Cl-5(-) ions is investigated. Based on the reversibility of the IrCl62-/IrCl63- couple, the reusable reduction and oxidation titrations of iridium(IV,III) can be realized in the same HCl solution with electrogenerated CuCln(n-1)- and Cl-2 as bi-intermediates, using biamperometric end point detection. The first reduction titration among the determinations of IrCl62- can be used for precise coulometric analysis. For the determinations of 0.5-5.0 mg of iridium, the relative average errors of the results are less than or equal to+/-0.06%, and the relative standard deviation (n=5-6) is 0.18-0.04%. The method is applied to the determination of iridium in the metal and its compounds

Effect of calcium supplements on osteoporosis by using nuclear analytical techniques

Neutron activation analysis (NAA) and dual energy X-ray absorptiometry (DEXA) have been used to study the effects of different calcium supplements on osteoporosis, including calcium carbonate, calcium threonate, calcium gluconate, calcium lactate, calcium acetate and a traditional Chinese medicine. Animal test results showed that calcium carbonate, calcium gluconate, calcium acetate and the Chinese medicine notably increased osteoporotic rats femoral bone mineral density (BMD). Also, calcium carbonate, calcium acetate and the Chinese medicine significantly increased osteoporotic rats vertebral BMD. But calcium L-threonate and calcium lactate had no such effects. Calcium gluconate, calcium acetate and the Chinese medicine improved the bone mechanical intensity of osteoporotic rats. The results of NAA showed that the loss of elements in spongy bones was more seriously than that in compact bone and was difficult to be improved.

Determination of Iridium in Environmental and Geological Samples by NAA with α-Amino Pyridine Resin Preconcentration

The Ir, Au and Pd concentrations in three certified reference materials SARM-7, FC-1 and DZΣ-1 were determined by neutron activation analysis using α-amino pyridine preconcentration. Good agreement between the reference values and our results was obtained, and the reliability of our method was confirmed. This method is suitable for ppb or sub-ppb levels of Ir and Au analyses in environmental and geological samples. The Ir and Au levels in a Chinese coastal sediment GBW07314 were also analyzed.

Study of interfering nuclear reactions in determination of platinum group elements by neutron activation analysis

Eighteen interfering nuclear reactions that likely occur in neutron activation analysis of platinum group elements are studied. Their degrees are calculated by the basic principle of activation analysis. The calculation results indicate that most of the nuclear interferences become significant only if the interfering elements exist in major amount and the elements of interest in trace amount. However, the second-order interference to platinum analysis from gold and the fission interference to analysis of ruthenium and palladium from uranium cannot be neglected even if the gold and uranium exist as trace constituents in samples.