Development of a Standard Reference Material for metabolomics research.

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health (NIH), has developed a Standard Reference Material (SRM) to support technology development in metabolomics research. SRM 1950 Metabolites in Human Plasma is intended to have metabolite concentrations that are representative of those found in adult human plasma. The plasma used in the preparation of SRM 1950 was collected from both male and female donors, and donor ethnicity targets were selected based upon the ethnic makeup of the U.S. population. Metabolomics research is diverse in terms of both instrumentation and scientific goals. This SRM was designed to apply broadly to the field, not toward specific applications. Therefore, concentrations of approximately 100 analytes, including amino acids, fatty acids, trace elements, vitamins, hormones, selenoproteins, clinical markers, and perfluorinated compounds (PFCs), were determined. Value assignment measurements were performed by NIST and the Centers for Disease Control and Prevention (CDC). SRM 1950 is the first reference material developed specifically for metabolomics research.

Pressurized liquid extraction of diesel and air particulate standard reference materials: effect of extraction temperature and pressure.

Four particulate matter Standard Reference Materials (SRMs) available from the National Institute of Standards and Technology (NIST) were used to evaluate the effect of solvent, number of static cycles and static times, pressure, and temperature when using pressurized liquid extraction (PLE) for the extraction of polycyclic aromatic hydrocarbons (PAHs) and nitrated-PAHs. The four materials used in the study were SRM 1648a Urban Particulate Matter, SRM 1649b Urban Dust, SRM 1650b Diesel Particulate Matter, and SRM 2975 Diesel Particulate Matter (Industrial Forklift). The results from the study indicate that the choice of solvent, dichloromethane compared to toluene and toluene/methanol mixtures, had little effect on the extraction efficiency. With three to five extraction cycles, increasing the extraction time for each cycle from 5 to 30 min had no significant effect on the extraction efficiency. The differences in extraction efficiency were not significant (with over 95% of the differences being <10%) when the pressure was increased from 13.8 to 20.7 MPa. The largest increase in extraction efficiency occurred for selected PAHs when the temperature of extraction was increased from 100 to 200 °C. At 200 °C naphthalene, biphenyl, fluorene, dibenzothiophene, and anthracene show substantially higher mass fractions (>30%) than when extracted at 100 °C in all the SRMs studied. For SRM 2975, large increases (>100%) are also observed for some other PAHs including benz[a]anthracene, benzo[k]fluoranthene, benzo[e]pyrene, benzo[a]pyrene, benzo[ghi]perylene, and benzo[b]chrysene when extracted at the higher temperatures; however, similar trends were not observed for the other diesel particulate sample, SRM 1650b. The results are discussed in relation to the use of the SRMs for evaluating analytical methods.

Comparison of orthogonal liquid and gas chromatography-mass spectrometry platforms for the determination of amino acid concentrations in human plasma.

Concentrations of amino acids in a human plasma pool were determined using four independent quantification methods. Orthogonal separation schemes (LC, GC, or GC x GC) and detection systems (triple quadrupole or time-of-flight mass spectrometry) are shown to demonstrate excellent consistency among platforms for quantifying 18 amino acids in NIST Standard Reference Material (SRM) 1950 Metabolites in Human Plasma using a well-characterized isotope dilution (ID) quantification method. Measured levels were consistent with reference values in plasma from the literature. Individual amino acid concentrations in plasma varied by over an order of magnitude ranging from 1.83 microg/g to 28.0 microg/g (7.78 micromol/L to 321 micromol/L). Average variability (coefficient of variation) between experimental amino acid concentrations (excluding cysteine) among all methods was 6.3%. Certified mass fraction values for amino acids in NIST SRM 1950 will be established from statistically weighted means of all experimental results.

Characterization of undigested particulate material following microwave digestion of recycled document papers.

Recycled document paper was microwave digested in a solution of HNO(3) and H(2)O(2) prior to analysis by inductively coupled plasma mass spectrometry (ICP-MS) to determine the trace elemental concentrations within the paper. Undigested particulate material was observed and subsequently characterized as a mixture of kaolin (clay) and TiO(2) by Fourier transform infrared spectroscopy and X-ray diffraction spectroscopy. The effect of the particulate material on the elemental concentrations was then investigated. Paper samples were completely digested in hydrofluoric acid (HF) and element concentrations determined in the HF and HNO(3)/H(2)O digests were statistically compared using Student's t-test (95% confidence limit). Statistical differences in element concentrations between the two digests were observed for only four elements and there was no evidence of element adsorption by the particulate material. Hence, the HNO(3)/H(2)O(2) digestion proved sufficient to digest paper for ICP-MS analysis, eliminating the need to use the hazardous and corrosive HF matrix.

Determination of trace elemental concentrations in document papers for forensic comparison using inductively coupled plasma-mass spectrometry.

With improvements in manufacturing procedures, comparing physical characteristics of paper samples may not offer sufficient discrimination among different vendors. In this work, the potential to differentiate paper samples based on trace element concentrations was investigated. Paper samples from two different vendors were microwave-digested and trace element concentrations (Mg, Al, Mn, Fe, Sr, Y, Ba, Ce, and Nd) were determined using inductively coupled plasma-mass spectrometry. Differences in concentration were assessed statistically using two-way ANOVA and Tukey's honestly significant differences test. Elemental concentrations were shown to be consistent across a single sheet as well as within a single ream of paper for each vendor. Reams from vendor A were differentiated based on Al and Ba concentration while reams from vendor B were differentiated based on Mg, Mn, and Sr concentrations. Paper was differentiated according to vendor based on significant differences in Ba, Sr, Ce, and Nd concentrations.

A comparison of boron-doped diamond thin-film and Hg-coated glassy carbon electrodes for anodic stripping voltammetric determination of heavy metal ions in aqueous media.

The performance of boron-doped diamond (BDD) for the anodic stripping voltammetric (ASV) determination of heavy metal ions (Zn2+, Cd2+, Pb2+, Cu2+, Ag+) was compared with that of Hg-coated glassy carbon (Hg-GC). Hg has historically been the electrode of choice for ASV but there is an ongoing search for alternate electrodes and diamond is one of these. Despite the fundamentally different nature of the metal reduction and oxidation reactions on these two electrodes, BDD provides as good or superior analytical detection figures of merit when compared to Hg. The stripping peak potentials for all the metals studied were similar at both electrodes indicating that BDD is as active as Hg for metal phase formation and oxidation. Due to the more heterogeneous chemical and electrical properties across the BDD surface, the stripping peaks were broader and more asymmetric than they were for Hg-GC. The linear dynamic range for BDD was three to four orders of magnitude (r2>0.995), similar to Hg-GC, but the sensitivity for BDD was three to five times lower. However, the lower background current and noise for BDD enabled detection limits as low as those seen for Hg-GC. The minimum concentration of each metal ion detectable (S/N> or =3) with BDD was in the mid to low ppb range (e.g., 50 ppb Zn2+, 1.0 ppb Cd2+, 5.0 ppb Pb2+, 10 ppb Cu2+ and 1.0 ppb Ag+). BDD exhibited an electrode-to-electrode and run-to-run variability of less than 5%, which is comparable to that for Hg-GC. The possibility of incomplete metal oxidation and metal phase detachment from BDD was investigated using double step chronoamperometry. Neither of these processes was found to occur to any appreciable extent. The results demonstrate that BDD is a viable alternate electrode to Hg for ASV.