Simultaneous mass bias and fractionation corrections utilizing isotopic solid standards and laser ablation ICPMS

Homogeneous incorporation of analytes of known isotopic abundance into sol-gel-derived standards that mimic important mineral systems has the potential to contribute significantly to providing solid standard benchmarks for a range of applications. This preliminary study reports on the synthesis of solid glass standards produced via the sol-gel method and their doping with Standard Reference Material (SRM) 981 Common Lead Isotopic Standard and SRM 982 Equal-Atom Lead Isotopic Standard. Custom isotopic materials were also prepared using mixtures of the two isotopic SRMs. Particles from these solid samples were then introduced into an inductively coupled plasma mass spectrometer via laser ablation to determine whether materials of suitable homogeneity could be developed as isotopic reference materials. Preliminary results for Pb isotope ratios show that these solid isotopic reference standards are capable of correcting for instrumental mass bias and laser ablation-induced bias due to fractionation simultaneously. Correction factors generated from the quotient of the certified and measured Pb isotopic ratios in sol-gel disks spiked with SRMs 981 and 982 were successfully applied to produce accurate isotope ratios using comparative control/unknown checks. These correction factors were also used to assign Pb isotopic ratios in NIST SRM 612 Trace Elements in Glass that were in excellent agreement with published measurements, suggesting that tunable matrix sol-gel disks can serve as adequate control matrixes for evaluation of isotope ratios in glass samples.     

Development of SRM 2907 trace terrorist explosives simulants for the detection of Semtex and triacetone triperoxide

Effective and accurate detection of trace explosives is crucial in the effort to thwart terrorist explosives attacks. A National Institute of Standards and Technology (NIST) standard reference material (SRM) has been developed for the evaluation of trace explosives detectors that sample by collection of residue particles using swiping or air filtration. SRM 2907 Trace Terrorist Explosives Simulants consists of two materials individually simulating the residues of the plastic explosive Semtex [for pentaerytritol tetranitrate (PETN)] and the improvised explosive triacetone triperoxide (TATP). Unique challenges were encountered in the development of these materials, including the selection of suitable inert substrates, material preparation, thermal stability testing, and analytical method development. Two independent analytical methods based on liquid chromatography with ultraviolet absorbance and mass spectrometric detection, LC-UV and LC/MS, respectively, were developed and used to certify the mass fractions of PETN and TATP. These materials were further evaluated for their suitability on a field swipe-sampled trace explosives detectors based on ion mobility spectrometry (IMS).     

Determination of aluminum by chemical and instrumental neutron activation analysis in biological standard reference material and human brain tissue.

Since aluminum is an extremely difficult element to determine reliably in biological samples, no National Institute of Standards and Technology (NIST) biological standard reference material for tissue has yet been certified for aluminum. A chemical neutron activation analysis procedure employing anion-exchange chromatography was developed. The procedure proved successful in decontaminating radioactivatable sodium and chlorine and phosphorus which can produce aluminum via a fast neutron bombardment. For bovine liver (NIST SRM 1577 a) a value of 2.1 +/- 0.2 micrograms of aluminum/g of sample was determined, comparing favorably to the uncertified value 2 micrograms/g sample. For freeze-dried urine (NIST SRM 2670) a value of 0.18 +/- 0.01 micrograms of aluminum/mL of urine was observed. Its uncertified value is 0.18 micrograms of aluminum/mL of sample. Twenty three individual samples in three different human brains were analyzed for their aluminum content.     

Determination of mercury in water and fish samples by cold vapor atomic absorption spectrometry after solid phase extraction on agar modified with 2-mercaptobenzimidazole

Due to the consumption of chicken and chicken products in Turkey at high ratio, trace metal content of chicken and chicken products from Turkey were determined by atomic absorption spectrometry after microwave digestion. The accuracy of the method was confirmed by analysis of standard reference material (NIST SRM 1577b Bovine liver). Trace element content in various parts of chicken samples and chicken products were to be in the range of 0.10-114 microg/g for copper, 0.25-6.09 microg/kg for cadmium, 0.01-0.40 microg/g for lead, 0.10-0.91 microg/g for selenium, 0.05-3.91 microg/g for manganese, 0.06-0.10 microg/g for arsenic, 0.01-0.72 microg/g for chromium, 0.01-2.08 microg/g for nickel, 0.01-0.02 microg/g for cobalt, 0.10-1.90 microg/g for aluminium, 1.21-24.3 microg/g for zinc, 2.91-155 microg/g for iron. The levels of lead in some analyzed chicken products were higher than the recommended legal limits for human consumption.     

Development of standard reference materials for rheological measurements of cement-based materials

Rotational rheometers are routinely used for homogeneous materials, but their usage for characterization of a granular fluid like concrete is a relatively new phenomenon. As measurements with rheometers can involve flow in a complex geometry, it is important that they are calibrated with a reference material or an SRM. NIST has produced an SRM for cement paste (SRM 2492) as the first step for the development of a reference material for concrete rheometers. The second step is the development of a reference material for mortar, composed of the SRM 2492 with added spherical beads. Here, material properties, such as viscosity, cannot be measured in fundamental units with certainty, thus modeling was used to determine the plastic viscosity of the SRM mortar which in turn could be compared with experiments. This paper will present the process used to develop the mortar reference material. Measurements and modeling will be presented.     

牛肝标准物质中氯含量的定值方法研究

针对基体标准物质中氯含量的准确定值问题,采用高温燃烧水解-离子色谱法和干灰化-电位滴定法对牛肝标准物质中的氯含量进行了测定。对两种方法的前处理和测定条件进行了优化,实验结果表明两种方法的测定结果一致,测定结果的相对标准偏差分别为0.7%和1.1%。采用NIST牛肝标准物质(SRM1577c)对两种方法进行了验证,两种方法的测定结果与标准值相符。对两种方法测定结果的不确定度进行了评定,氯测定结果的相对扩展不确定度(k=2)分别为1.6%和2.2%。两种方法测定牛肝中氯含量都准确可靠,能够满足标准物质定值的要求。     

拉曼光谱仪相对强度标准物质量值表达及不确定度评定

拉曼光谱仪常用于纯定性分析、高度定量分析和测定分子结构。然而,相对强度未经校准的拉曼谱图会出现变形和失真,造成不同仪器的测量结果缺乏可比性。选用中国计量科学研究院研制的标准物质候选物,使用激光共聚焦拉曼光谱校准装置对标准物质候选物进行定值、均匀性和稳定性检验,并评定了其不确定度。结果显示标准物质候选物具有良好的均匀性,且在1年的有效测量内具有良好的稳定性,与NIST的标准物质SRM2243相比,校准结果等效、一致。     

Development of isotope dilution cold vapor inductively coupled plasma mass spectrometry and its application to the certification of mercury in NIST standard reference materials

An isotope dilution cold vapor inductively coupled plasma mass spectrometry (ID-CV-ICPMS) method featuring gaseous introduction of mercury via tin chloride reduction has been developed and applied to the quantification and certification of mercury in various NIST standard reference materials: SRM 966 Toxic Metals in Bovine Blood (30 ng x mL(-1)); SRM 1641d Mercury in Water (1.6 microg x mL(-1)); and SRM 1946 Lake Superior Fish Tissue (436 ng x g(-1)). Complementary mercury data were generated for SRMs and NIST quality control standards using cold vapor atomic absorption spectroscopy (CVAAS). Certification results for the determination of mercury in SRM 1641d using two independent methods (ID-CV-ICPMS and CVAAS) showed a degree of agreement of 0.3% between the methods. Gaseous introduction of mercury into the ICPMS resulted in a single isotope sensitivity of 2 x 10(6) counts x s(-1)/ng x g(-1) for 201Hg and significantly reduced the memory and washout effects traditionally encountered in solution nebulization ICPMS. Figures of merit for isotope ratio accuracy and precision were evaluated at dwell times of 10, 20, 40, 80, and 160 ms using SRM 3133 Mercury Spectrometric Solution. The optimum dwell time of 80 ms yielded a measured 201Hg/202Hg isotope ratio within 0.13% of the theoretical natural value and a measurement precision of 0.34%, on the basis of three replicate injections of SRM 3133.     

Determination of gallium in human urine by supercritical carbon dioxide extraction and graphite furnace atomic absorption spectrometry

This study presents supercritical carbon dioxide (scCO(2)) extraction as an inherently safer and cleaner sample treatment method for identifying trace gallium in urine samples. Extraction is performed in the presence of a fluorinated beta-diketones chelating agent, 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (HFOD), by unmodified scCO(2). Quantitative extractions are conducted at 80 degrees C and 20.7 MPa with 15 min static plus 15 min dynamic extractions, and are followed by analysis via graphite furnace atomic absorption spectroscopy (GFAAS). The proposed procedure is successfully applied to determine the concentrations of gallium in real urine samples spiked with various levels of gallium with satisfactory recoveries of 90.8-100.3% (n=6) and relative standard deviations <10%. A standard reference material (SRM), Seronorm Trace Elements Urine, is used to validate the accuracy of the proposed method.     

Sorbent extraction of rubeanic acid-metal chelates on a new adsorbent: Sepabeads SP70

A sorbent extraction procedure for lead, iron, cadmium and manganese ions on Sepabeads SP70 adsorption resin has been presented prior to their flame atomic absorption spectrometric determinations. By the passage of aqueous samples including analyte ions-rubeanic acid chelates through Sepabeads SP70 column, metal chelates adsorb quantitatively and almost all matrix elements will pass through the column to drain. The influence of potential interfering ions was also studied. The validation of the method was made though the analysis of LGC 6010 Hard drinking water, SRM 1577b Bovine liver and GBW 07603 Bush branches and leaves standard reference materials (SRM). The method was applied to the determination of analyte ions from various water, wastewater, cow meat and milk, red wine, and tobacco samples with successfully results.     

Use of sol-gels as solid matrixes for simultaneous multielement determination by radio frequency glow discharge optical emission spectrometry: determinations of suspended particulate matter

A new approach for the analysis of particulate matter by radio frequency glow discharge optical emission spectrometry (rf-GD-OES) is described. Dispersion of the particles in a sol-gel sample matrix provides a convenient means of generating a thin film suitable for sputter-sampling into the discharge. Acid-catalyzed sol-gel glasses synthesized from tetramethyl orthosilicate were prepared and spun-cast on glass substrates. The resultant thin films on glass substrates were analyzed to determine the discharge operating conditions and resultant sputtering characteristics while a number of optical emission lines of the film components were monitored. Slurries of powdered standard reference materials NIST SRM 1884a (Portland Cement) and NIST SRM 2690 (Coal Fly Ash) dispersed in the sols were cast into films in the same manner. Use of the sol-gels as sample matrixes allows for background subtraction through the use of analytical blanks and may facilitate the generation of calibration curves via readily synthesized, matrix-matched analytical standards in solids analysis. Detection limits were determined for minor elements via the RSDB method to be in the range of 1-10 microg/g in Portland Cement and Coal Fly Ash samples for the elements Al, Fe, Mg, S, and Si. Values for Ca were in the range of 15-35 microg/g. This preliminary study demonstrates the possibility of incorporating various insoluble species, including ceramics and geological specimens in powder form, into a solid matrix for further analysis by either rf-GD-OES or MS.     

Lithium isotope composition of basalt glass reference material

We present data on the lithium isotope compositions of glass reference materials from the United States Geological Survey (USGS) and the National Institute of Standards and Technology (NIST) determined by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), thermal ionization mass spectrometry (TIMS), and secondary ionization mass spectrometry (SIMS). Our data on the USGS basaltic glass standards agree within 2 per thousand, independent of the sample matrix or Li concentration. For SIMS analysis, we propose use of the USGS glasses GSD-1G (delta(7)Li 31.14 +/- 0.8 per thousand, 2sigma) and BCR-2G (delta(7)Li 4.08 +/- 1.0 per thousand, 2sigma) as suitable standards that cover a wide range of Li isotope compositions. Lithium isotope measurements on the silica-rich NIST 600 glass series by MC-ICPMS and TIMS agree within 0.8 per thousand, but SIMS analyses show systematic isotopic differences. Our results suggest that SIMS Li isotope analyses have a significant matrix bias in high-silica materials. Our data are intended to serve as a reference for both microanalytical and bulk analytical techniques and to improve comparisons between Li isotope data produced by different methodologies.     

Development and certification of a standard reference material for vitamin D metabolites in human serum

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health's Office of Dietary Supplements (NIH-ODS), has developed a Standard Reference Material (SRM) for the determination of 25-hydroxyvitamin D [25(OH)D] in serum. SRM 972 Vitamin D in Human Serum consists of four serum pools with different levels of vitamin D metabolites and has certified and reference values for 25(OH)D(2), 25(OH)D(3), and 3-epi-25(OH)D(3). Value assignment of this SRM was accomplished using a combination of three isotope-dilution mass spectrometry approaches, with measurements performed at NIST and at the Centers for Disease Control and Prevention (CDC). Chromatographic resolution of the 3-epimer of 25(OH)D(3) proved to be essential for accurate determination of the metabolites.     

六种多环芳烃溶液标准物质的研制

本文介绍了荧蒽、苯并（b)荧蒽、苯并（k)荧蒽、苯并（a)芘、苯并（ghi)Bai和茚并（1,2,3－cd)芘六种环保用多环芳烃甲醇溶液标准物质的定值测定及均匀性和稳定性考察。定值采用美国国家标准研究院（NIST）的SRM2260和SRM1491作为高一级的标准物质进行量值传递,使用高效液相色谱法（HPLC）,测量不确定度约为3％。     

Atmospheric pressure microwave sample preparation procedure for the combined analysis of total phosphorus and kjeldahl nitrogen

An atmospheric pressure microwave digestion method has been developed for the combined analysis of total phosphorus and Kjeldahl nitrogen in complex matrices. In comparison to the digestion steps in EPA Methods 365.4 (total phosphorus) and 351.x (Kjeldahl nitrogen), this method requires less time, eliminates the need for a catalyst, and reduces the toxicity of the waste significantly. It employs a microwave-assisted digestion step, using refluxing borosilicate glass vessels at atmospheric pressure. Traditionally, this method has a time-consuming sample preparation step and generates toxic waste through the use of heavy metal catalysts. These advantages are gained by the combination of a high boiling point acid (sulfuric acid) and the application of focused microwave irradiation, which enhances the digestion process by direct energy coupling. NIST standard reference materials 1572 (citrus leaves), 1577a (bovine liver), and 1566 (oyster tissue) and tryptophan were analyzed to validate the method. Phosphorus concentrations were determined by the colorimetric ascorbic acid method outlined in EPA Method 365.3. Kjeldahl nitrogen concentrations were determined using EPA Method 351.1. The results of the analyses showed good precision and are in excellent agreement with the NIST published values for both elements.     

用HXCF测量物质X射线质量衰减系数

X射线质量衰减系数是研究X射线的一个重要物理量,硬X射线探测器地面标定装置由于其单色性、稳定性以及其可测的绝对光子数,成为了研究质量衰减系数的一套理想装置.使用Cu、A12种不同材料分别在X射线能量为30 keV、50 keV、80 keV、100 keV和110 keV的情况下对其质量衰减系数进行测量,并将测量值与NIST的参考值进行了对比,得到了其标准偏差.根据NIST提供的质量衰减系数曲线,验证了Cu和Al在110keV处的质量衰减系数,为进一步研究做好了基础.     

Standards for bullets and casings

The National Institute of Standards and Technology is developing reference standards through its Office of Law Enforcement Standards with funding provided by the National Institute of Justice. The standard reference materials are used by crime laboratories to verify that results obtained when using their protocols and methodologies meet legal requirements and that equipment is operating properly. The NIST Reference Materials 8240/8250 standard bullets and casings is an example of materials that will assist laboratories in calibrating their instruments and ensuring quality control.The Office of Law Enforcement Standards (OLES) at the National Institute of Standards and Technology (NIST) manages research in many different disciplines of forensic science. One of these projects supports the National Integrated Ballistics Information Network (NIBIN). NIST digitized six bullet signatures from samples provided by the Bureau of Alcohol, Tobacco, and Firearms (ATF) and the Federal Bureau of Investigation (FBI). Using these signatures as a virtual standard, NIST’s Instrument Shop manufactured 20 reference materials (RM) 8240 standard bullets using a numerically-controlled diamond turning machine. Test results show high reproducibility of the bullet signatures on standard bullets. NIST has also developed a new parameter for bullet signature comparisons, using autocorrelation functions, and proposed a diagram for tracing local ballistics measurements to the National Laboratory Center of the ATF and to the FBI. Using an electro-forming process, NIST has manufactured prototype standard casings and test results show high reproducibility for the casing signatures.     

Critical examination of the quantification of aromatic compounds in three standard reference materials

Three standard reference materials from the National Institute of Standards and Technology (NIST), namely, SRM 1597 coal tar, 1582 crude oil, and 1580 shale oil, were investigated in detail to determine the concentration of polycyclic aromatic sulfur heterocycles using gas chromatography with the atomic emission detector in the carbon- and sulfur-selective modes. Coelution problems were found to be common, and the use of two capillary gas chromatographic columns with stationary phases of widely differing polarity was necessary for the separation of the important analytes phenanthrene, anthracene, dibenzothiophene, and the naphthothiophenes. On the commonly used nonpolar stationary phases, phenanthrene and dibenzothiophene coelute with the isomeric naphthothiophenes and this leads to too high concentrations being measured for the two major analytes and must be corrected for. For (sulfur and oxygen) heterocycles, individual response factors must be used if the flame ionization detector is employed. The NIST values were obtained without regard to those factors. This is done here for the three SRMs, and it is shown that the adjusted NIST values agree very well with the GC/AED values. It is suggested that the (noncertified) NIST values for several polycyclic aromatic compounds (PACs) should be reexamined. Very probably many other determinations of PACs might suffer from the same shortcomings.     

Molar mass and molar mass distribution of polystyrene particle size standards

Monodisperse polystyrene microspheres and nanospheres are often used as particle size standards for calibration of size-measuring instruments. They are potentially useful as the mass standards for particle mass spectrometry as well. We demonstrated in this work that it is possible to achieve high-precision mass determination for single polystyrene spheres using a quadrupole ion trap. We introduced the particles into the trap by laser-induced acoustic desorption and probed them with light scattering. Mass-to-charge ratios of the individual particles were determined from applied trap-driving frequencies, voltage amplitudes and the observed starlike oscillatory trajectories projected on the radial plane. Creation of one-electron differentials through charge-state changes by electron bombardment allowed determination for the absolute mass of a single trapped particle to a precision better than 0.1%. Both molar mass and molar mass distribution were deduced from a large number of measurements for NIST polystyrene particle size standards (SRMs 1690 and 1691). Our results are in excellent agreement with the size measurement for the 0.895-microm spheres (NIST SRM 1690), but a small discrepancy (4%) in number-average mass was found for the 0.269-microm spheres (NIST SRM 1691).     

Evaluation of radiochemical neutron activation analysis methods for determination of arsenic in biological materials

Radiochemical neutron activation analysis (RNAA) with retention on hydrated manganese dioxide (HMD) has played a key role in the certification of As in biological materials at NIST. Although this method provides very high and reproducible yields and detection limits at low microgram/kilogram levels, counting geometry uncertainties may arise from unequal distribution of As in the HMD, and arsenic detection limits may not be optimal due to significant retention of other elements. An alternate RNAA procedure with separation of arsenic by solvent extraction has been investigated. After digestion of samples in nitric and perchloric acids, As(III) is extracted from 2 M sulfuric acid solution into a solution of zinc diethyldithiocarbamate in chloroform. Counting of (76)As allows quantitation of arsenic. Addition of an (77)As tracer solution prior to dissolution allows correction for chemical yield and counting geometries, further improving reproducibility. The HMD and solvent extraction procedures for arsenic were compared through analysis of SRMs 1577c (bovine liver), 1547 (peach leaves), and 1575a (pine needles). Both methods gave As results in agreement with certified values with comparable reproducibility. However, the solvent extraction method yields a factor of 3 improvement in detection limits and is less time-consuming than the HMD method. The new method shows great promise for use in As certification in reference materials.