NBS Standard Reference Materials Research Articles

Scanning microcalorimetry at high cooling rate

Heat capacity measurements at fast cooling and heating were realized for linear polyethylene NBS SRM (standard reference material) 1484 sample, ca. 120 ng, in the melting-crystallization region. A commercial vacuum sensor, thermal conductivity gauge TCG-3880, Xensor Integrations, was utilized as a cell for a micro-calorimeter suitable for such measurements. The cell consists of a thin-film Si 3N x membrane with a film-thermopile and a film-heater, which are formed at the membrane center. The current at the heater as well as the signal from the thermopile were monitored in real time during fast scanning of temperature of the central part of the membrane. The measurements were performed in an ambient gas, so that controlled cooling and heating rates up to 5×10 3 K/s were achieved. As conditions were not adiabatic, the heat leakage from the sample was calibrated and was taken into account for heat capacity measurements. A simple calibration algorithm was developed for such measurements. Thus, a step towards ultra fast cooling scanning calorimetry was made.

Copper Oxide Precipitates in NBS Standard Reference Material 482.

Copper oxide has been detected in the copper containing alloys of NBS Standard Reference Material (SRM) 482. This occurrence is significant because it represents heterogeneity within a standard reference material that was certified to be homogeneous on a micrometer scale. Oxide occurs as elliptically to spherically shaped precipitates whose size differs with alloy composition. The largest precipitates occur in the Au20-Cu80 alloy and range in size from submicrometer up to 2 μm in diameter. Precipitates are observed using light microscopy, electron microscopy, and secondary ion mass spectrometry (SIMS). SIMS has demonstrated that the precipitates are present within all the SRM 482 wires that contain copper. Only the pure gold wire is precipitate free. Initial results from the analysis of the Au20-Cu80 alloy indicate that the percentage of precipitates is less than 1 % by area. Electron probe microanalysis (EPMA) of large (2 μm) precipitates in this same alloy indicates that precipitates are detectable by EPMA and that their composition differs significantly from the certified alloy composition. The small size and low percentage of these oxide precipitates minimizes the impact that they have upon the intended use of this standard for electron probe microanalysis. Heterogeneity caused by these oxide precipitates may however preclude the use of this standard for automated EPMA analyses and other microanalysis techniques.

Inductively coupled plasma magnetic sector mass spectrometry method for stable lead isotope tracer studies

Studies in our laboratory and elsewhere require the analyses of stable lead (Pb) isotopes at sub-ppb levels as tracers of lead metabolism and therapeutic chelation treatment in animal models and humans. While analytical alternatives such as thermal ionization mass spectrometry (TIMS) provide excellent isotope measurement sensitivity and precision, TIMS is not well-suited for rapid throughput of large numbers of biological samples. Here we report the development of an inductively coupled plasma magnetic sector mass spectrometry (Finnigan MAT Element) method, possessing suitable lead isotope measurement sensitivity and precision for use in biologically stable lead isotope tracer studies in which the natural relative abundance of one or more isotopes (i.e., 204Pb, 206Pb, 207Pb, or 208Pb) has been enriched by >5%. Standard reference materials (SRMs) NBS 981 lead isotope standard and four different NIST biological SRM materials were spiked with bismuth-209 as an internal standard, and analyzed at lead concentrations of 1–10 ppb. The method consisted of 300 passes per sample for masses 201, 204, 206, 207, 208 and 209, with a total analysis time of about five minutes per sample. Concentrations for 204Pb, 206Pb, 207Pb, and 208Pb were determined by comparison to a certified lead concentration standard that had been isotopically characterized by TIMS. Analyses of lead concentrations in the NIST biological SRMs yielded a measurement accuracy (recoveries) of 96–101%, with a detection limit of 0.013 ppb total lead. Accuracy of isotope abundance analyses of NBS SRM 981 (n=12) was 99.92–99.99% of that expected for all four isotopes, with a measurement precision of 0.07–0.22% RSD. Thus, this method is ideally suited for the rapid, accurate, and precise measurements of lead concentrations and stable isotope abundances in lead isotope tracer studies in animals and humans, where one or more lead isotopes are enriched above natural levels.

Accumulation of Trace Elements in the Peripheral and Central Parts of a Foliose Lichen Thallus

Accumulation of Trace Elements in the Peripheral and Central Parts of a Foliose Lichen Thallus

Neutron activation analysis for determination of trace elements in sediments in the Sea of Galilee, Israel

The feasibility of applying both thermal and epithermal neutron activation analysis for simultaneous determinations of elemental composition in sediments, collected from the Sea of Galilee (Kineret Lake), Israel, during 1988–1993, was experimentally investigated. In the present work, the concentrations of 30 elements (Al, Ba, Br, Ca, Ce, Co, Cs, Cr, Eu, Fe, Hf, K, La, Lu, Mg, Mn, Na, Nd, Rb, Sc, Si, Sr, Ta, Tb, Th, Ti, U, V, Yb and Zn) in sediments were determined. The validity of the method was checked by analyzing the U.S. NBS Standard Reference Material SRM-1633a; the elemental content found agreed well with the published certified data. Aluminium was determined by reactor neutron activation analysis (RNAA) taking into account the contribution of silicon to the total28Al activity by the28Si(n,p)28Al reaction. Measurements of irradiated mixtures of Si and Al showed that the dependence of log Si∶Al mass ratio vs. log cadmium ratio (RCd) of28Al is almost linear. The data can be analyzed more accurately by a parabolic correlation (log Si:Al mass ratio vs logRCd). The concentrations of fission radionuclide137Cs, an activation radionuclide134Cs (derived from Chernobyl accident) and the naturally occuring radionuclides40K,226Ra and232Th in sediments were also measured by γ-ray spectrometry using Marinelli (Reentrant) Beaker-Sample Containers.

Preparation of standard samples and standard reference materials for microbeam analysis

Metal, alloy and compound films were prepared by vacuum evaporation. Homogeneities of the films were examined by synchrotron radiation-induced X-ray emission (SRIXE) and scanning electron microscope (SEM). Elemental areal densities were determined by tube X-ray fluorescence (XRF), and were checked by NBS standard reference materials. The film samples have been used as standard samples and standard reference materials at Beijing Synchrotron Radiation Facility (BSRF_, Institute of High Energy Physics (IHEP).

Studies on the reaction between cadmium and potassium tetrahydroborate in aqueous solution and its application in atomic fluorescence spectrometry

The conditions for the vapour generation of cadmium by the reaction with potassium tetrahydroborate in aqueous solution were investigated using a programmable intermittent flow reactor. It was found that thiourea together with cobalt ion greatly enhanced the generation efficiency of the volatile species. Based upon the results of the investigation, the vapour generation system was used for the determination of ultra-trace amounts of cadmium by atomic fluorescence spectrometry. A detection limit of 8 pg ml −1 was obtained under optimized conditions and the precision of the measurements for 5 ng ml −1 of Cd was 1.2% R.S.D. The effects of 28 diverse ions on the generation of the cadmium volatile species were investigated. Serious signal depressions were observed from copper and lead but these were decreased by using potassium cyanide as masking agent for copper and by coprecipitation with barium sulphate for lead. The method was successfully applied to the determination of cadmium in NBS standard reference material (SRM) 1577a bovine liver, NBS SRM 1645 river sediment and other Chinese origin SRMs. The method was also applied to tap water analysis with full recovery of spiked samples.

Boron analysis in biological material: microwave digestion procedure and determination by different methods

Investigations were made on the determination of boron in biological material. A procedure using the microwave digestion technique was optimised. The analyses were performed by photometry with azomethine-H, fluorimetry with carminic acid, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. The matrix interferences, the interferences caused by iron and the detection limits were investigated for these methods. Determinations were performed for plant material, wheat, milk, meat and blood plasma. Recoveries and precision of all methods were studied. To test accuracy and precision, four NBS reference materials were analysed and the results compared with the values in literature. Good recoveries were found with all methods, except the fluorimetric technique. The boron content found in the NBS standard reference materials agreed well with data reported before. Best precision was obtained for the two ICP methods. The azomethine-H method gave good results when material of high boron content was analysed. With the carminic acid method no reliable results were achieved.

Chemical composition of wet and dust deposition in Athens, Greece

In the present study a wet/dry precipitation collector was used (Canadian MIC) to collect wet and dust deposition samples in one station in the center of the Athens basin, Greece, for the period September 1987–August 1988. Concentrations of the main cations (H +, NH 4 +, Na +, K +, Ca 2+ and Mg 2+) and main anions (Cl −, NO 3 − and SO 4 2−) were determined. The analytical chemical methods were evaluated with NBS standard reference material and with rainwater samples from EMEP (European Monitoring Evaluation Programme). Statistical analyses of correlation between the concentration of chemical species and correlation diagrams between chemical species concentrations and wind directions were made in order to estimate the origin of the determined ions both in wet and dust deposition. In all samples non-marine molar sulfate concentrations exceed nitrate concentrations despite the dominance of low sulfur oil burning in the region (0.3% for domestic heating, 0.7% for industrial uses). For 37% of the samples the pH was lower than 4.5 and for 69% of samples was lower than 5.6. The wet flux of sulfur was calculated to be 0.67 gm −2yr −1. The results support the conclusion that chemical constituents in rain and dust deposition are a combination of emissions from natural and anthropogenic sources.

Determination of elemental composition of settling particles in Israel following Saharan dust storms by neutron activation analysis

Several cases of transporation and deposition of settling particles following dust storms over Israel, occurring between 1973 and 1987, were experimentally investigated. The storm particles were collected in Jerusalem and Ramat Hasharon, north of Tel Aviv. Meteorological conditions during the storms were examined and classified according to their trajectories into two types: (a) North African and (b) Arabian Desert. The North African type is by far the most common. In the present work, the concentrations of 26 elements (Al, Ba, Br, Ca, Ce, Co, Cl, Cr, Eu, Fe, Hf, K, La, Mg, Mn, Na, Rb, Sb, Sc, Si, Ta, Th, Ti, U, V, and Yb) in settling particles were determined by instrumental neutron activation analysis. The validity of the method was checked by analyzing U.S. NBS Standard Reference Material SRM-1633a; the elemental content found agreed well with the published certified data. Since Al as well as Si were determined through the reactions27Al(n, γ)28Al(2.24 min) and28Si(n, p)28Al, respectively, thermal and epithermal neutron activation was applied in order to determine the contribution of silicon to the total28Al activity. Interpretation of the chemical analyses using Enrichment Factors reveals that settling particles are relatively enriched in Ca probably from the local terrain and in Cl derived from the Mediterranean Sea.

Level of some minor and trace elements in Bangladeshi meat products

An investigation on the level of some minor and trace elements in some varieties of meat (beef, mutton and chicken) consumed in Bangladesh is reported. In this study, protoninduced X-ray emission (PIXE) and radioisotope-induced X-ray fluorescence (XRF) techniques were used for analytical measurements. In PIXE measurements, the samples were exposed to the proton beam in air as 1 mm thick pellets and irradiated with 2.0 MeV protons having the beam intensity of 30 nA for characteristic X-ray excitation, whereas in XRF, the samples were excited for 5000 seconds with a 10 mCi109Cd annular X-ray source. The elemental concentrations of Ca, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Rb and Sr were determined in the samples by comparison with X-ray yield curves constructed from IAEA and NBS standard reference materials. The significance of the results is dicussed in relation to human health and diseases.

Computer-Assisted Quantitative and Qualitative Analyses of Complex Sample Using a Multi-Wavelength Detector

A new computer-assisted analytical strategy has been proposed for both quantitative and qualitative analyses of complex mixture samples. This method is based on simultaneous peak detection at 6 different wavelengths using a photodiode-array multiwavelength detector. It was applied to the analysis of polycyclic aromatic hydrocarbons in petroleum pitch with reference to the NBS standard reference material (SRM-1647). Our new strategy has allowed a tentative identification of 14 compounds among 16 Priority Pollutants contained in pitch through a retention comparison. However, the identification of 4 components was cancelled due to a comparison with the UV spectrum. The method proposed here allows even an inexperienced operator to do analysis work on complex mixture samples with the aid of a computer.

Instrumental neutron activation analysis of biological samples

The elemental compositions of 18 biological reference materials have been processed, for 14 stepped combinations of irradiation/decay/counting times, by the INAA Advance Prediction Computer Program. The 18 materials studied include 11 plant materials, 5 animal materials, and 2 other biological materials. Of these 18 materials, 14 are NBS Standard Reference Materials and four are IAEA reference materials. Overall, the results show that a mean of 52% of the input elements can be determined to a relative standard deviation of +/- 10% or better by reactor flux (thermal plus epithermal) INAA.

Measurement of the spectral emissivity of solid materials

A novel method has been employed to measure accurately the spectral emissivity of a range of metal and non-metal solid materials. The method is particularly well suited to poor thermal conductors with high emissivity since these cannot normally be measured very accurately owing to large uncertainties associated with the measurement of surface temperature. Results are reported on two NBS standard reference materials. Some preliminary measurements on bare or coated V-grooved specimens of aluminium are also reported and the results compared with a theory that assumes perfectly specularly or diffusely reflecting surfaces. The specimen design has been chosen to enable the effects of the V-groove shape and the surface emissivity to be distinguished experimentally.

Simultaneous multielement atomic-emission spectrometry with a charge-injection device detector

Simultaneous multielement atomic-emission spectrometry with a charge-inection device (CID) as a multichannel optical detector is described. The system used in this study employs a standard commercial D.C. plasma source, a modified echelle spectrometer, and a special digital camera system that uses a two-dimensional CID array sensor. A description of the modified spectrometer is given along with performance results. Computer algorithms for acquiring and analysing spectral information are described. Detection limits for several elements are determined simultaneously. Results of simultaneous determination of several elements in an NBS standard reference material (SRM 1643A) are given. These results indicate that the CID detector is capable of reasonably good accuracy and high sensitivity in the simultaneous determination of several elements in complex samples.

Study of a toroidal argon MIP and a cylindrical helium MIP for atomic emission spectrometry—II: Combination with graphite furnace vaporization and use for analysis of biological samples

The capabilities of a toroidal argon and a diffuse helium microwave induced plasma (MIP) operated in a TM 010 resonator and in combination with electrothermal vaporization have been studied for atomic emission spectrometry (AES). The 75 W toroidal MIP has been found to improve the power of detection with respect to the filament argon MIP by a factor of 3–10. The detection limits using 50 μl solution aliquots for a large series of elements are between 0.1 and 100 ng ml . With a diffuse helium MIP in combination with graphite furnace vaporization the detection limit for P is 10 ng ml and for Pb 1 ng ml . In the toroidal argon MIP, matrix effects due to alkali elements occur already at concentrations of 10 μg ml of Na and could not be eliminated satisfactorily by the use of NH 4NO 3. In. the helium MIP, also volatilization interferences in the case of Ca and P were found. After separation of the alkali elements by sorption of the trace elements as hexamethylene-dithiocarbamates (HMDC) on acetylated cellulose, MIP-AES with the toroidal argon MIP coupled to electrothermal vaporization has been found to be suitable for multielement determinations in biological samples, subsequent to wet chemical sample decomposition in closed PTFE (Teflon) vessels. This is demonstrated by the determination of Fe, Cu and Zn in the NBS standard reference materials of bovine liver, orchard leaves and tomato leaves.

The status of trace and minor elements in some Bangladeshi foodstuffs

An investigation is conducted on the status of trace and minor elements in some foodstuffs (cereals, vegetables, milk, egg and fish), commonly consumed in Bangladesh, using proton induced X-ray emission (PIXE) and radioisotope-induced X-ray fluorescence (XRF) techniques. In PIXE measurements, the samples were irradiated in air with 2.0 MeV (energy on the target) protons having the beam intensity of 30 nA for characteristic X-ray excitation, while in XRF analysis, the samples were excited for 5000 seconds with a 10 mCi Cd-109 annular X-ray source. The elemental concentration of K, Ca, Mn, Fe, Ni, Cu, Zn, Se, As, Br, Rb, Sr, Mo, and Pb were determined in the samples by comparison with X-ray yield curves constructed from IAEA and NBS standard reference materials. The validity of the analytical procedures (PIXE and XRF) followed in this study has been confirmed by comparative measurements of Cu, Zn and Mn in some varieties of rice with atomic absorption spectrophotometry. The results indicate that none of the food regimes investigated here is burdened with heavy metals beyond permissible limits except five species of vegetables with chromium having the range of 0.99–3.59 mg/kg compared to the literature value of 0.0–0.36 mg/kg (dry weight basis). An average value of 0.2 mg/kg of arsenic was observed both in IRRI (n=16) and local Aman (n=12) varieties of rice and only one hen egg contained 1.7 mg/kg of lead in yolk. The zinc content in some marine fish from Bay of Bengal was reported to be 5.4–19.5 mg/kg, whereas in the present study of sweet-water fish, the level is found to be 15.2–62.1 mg/kg (fresh weight basis) for five species. In human milk, both Cu (0.12–0.25 mg/l, n=8) and Zn (0.28–1.80 mg/l, n=8) levels appear to be almost half the literature values (n=25). On the other hand formula milk has higher values of Cu (0.32–1.63 mg/kg, n=16) and Zn (5.16–19.8 mg/kg, n=16).

Calibration of the NBS 10-μm “space beads”

A summary of the procedures used to certify NBS Standard Reference Material 1960, nominal 10-μm “space beads,” is presented. Three independent micrometrology techniques were used, with the results agreeing to about 0.1%. Center distance finding, a method based on optical microscopy, gave a value of 9.89 ± 0.04 μm, which was chosen as the certified mean diameter. Two supporting measurements, made using metrology electron microscopy and resonance light scattering, yielded mean diameters of 9.886 ± 0.029 and 9.898 ± 0.029 μm, respectively. The main peak of the size distribution for this material is nearly Gaussian, with a certified standard deviation of 0.09 μm, excluding outlying particles. The SRM 1960 microspheres were grown in microgravity aboard the NASA space shuttle “Challenger,” making the material the first commercial product to be made in space.

Facile synthesis of 1‐nitropyrene‐d9 of high isotopic purity

Abstract1‐Nitropyrene‐d9, 1,3‐dinitropyrene‐d8, 1,6‐dinitropyrene‐d8, and 1,8‐dinitropyrene‐d8, used as internal standards for the determination of nitropolycyclic aromatic hydrocarbons (NPAH) in simple and complex mixtures, and required for GC/MS measurements used in the certification of NBS Standard Reference Material (SRM) 1596 (a mixture of nitropyrenes), were synthesized in one step from commercially available pyrene‐d10 and nitric acid‐d1. The electron impact mass spectra and isotopic purity of 1‐nitropyrene‐d9 and the deuterated dinitropyrenes were determined; the compounds were characterized by gas chromatpgraphy‐mass spectrometry (GC‐MS) and by high performance liquid chromatography (HPLC).

The measurement of latex particle sizes using scattering ratios in the rayleigh scattering size range

The diameters of polystyrene latex (PSL) particles in the size range of 0.065–0.460 μm were determined by scattering measurements using open cavity laser aerosol spectrometers operating at wavelengths of 633 and 1152 nm. A recently available NBS standard reference material (SRM) was adopted as a primary standard PSL size. By comparing the ratio of light scattered by various PSL sizes to the SRM, the sizes of large samples of PSL could be rapidly determined. Comparisons of various PSL samples confirmed that the measured diameters can differ from the nominal diameters a considerable degree. Differences as large as 20% were observed for sub-tenth micrometer sizes but typically less than 5% at sizes between 0.2 and 0.4 μm. The size of 0.1 μm particles was also determined from the direct measurement of the scattered power. The resulting size difference was less than the uncertainty of the NBS SRM.