Home About us Contact
|
Home About us Contact | ||
|
|
||
Standard Reference Materials (standard + reference_material)
Selected AbstractsSingle Laboratory Method Performance Evaluation for the Analysis of Total Food Folate by Trienzyme Extraction and Microplate AssayJOURNAL OF FOOD SCIENCE, Issue 5 2007L. Chen ABSTRACT:, Single laboratory method performance parameters, including the calibration curve, accuracy, recovery, precision, limit of detection (LOD), and limit of quantification (LOQ), were evaluated for the analysis of total food folate by the trienzyme extraction and microplate assay with Lactobacillus casei subsp. rhamnosus. Standard Reference Material (SRM) 1546 (meat homogenate), SRM 2383 (baby food composite), SRM 1846 (infant formula), Certified Reference Material (CRM) 121 (wholemeal flour), and CRM 485 (mixed vegetables), representing a broad selection of food matrices, were used to evaluate the performance of the method. A generated 4-parameter logistic equation of the calibration curve was y= (0.0705 , 1.0396)/(1 + (x/0.0165) 1.3072) + 1.0396 (P < 0.0001). The test of parallelism demonstrated that matrix components in the food extracts did not affect the accuracy. Measured values of the SRMs and CRMs were within their certified or reference values. Recoveries for all reference materials met the requirements of the AOAC guidelines for single laboratory validation. Precision measured as repeatability, including simultaneous and consecutive replicates for each SRM and CRM, met the Horwitz criterion. LOD and LOQ values were 0.3 and 0.6 ,g/100 g, respectively. The results showed that trienzyme digestion using ,-amylase, PronaseR, and conjugase from chicken pancreas coupled with a 96-well microplate assay provided a highly accurate, reproducible, and sensitive method for the determination of folate in a variety of foods. [source] Elements in the Sera of Preschool Children Living in Central TaiwanCHINESE JOURNAL OF CHEMISTRY, Issue 4 2007Chien-Yi Chen Abstract This study assessed elemental concentrations in the serum of 154 preschool children in central Taiwan via instrumental neutron activation analysis (INAA). A total of eight elements, Br, Cl, Fe, Na, Rb, Sc, Se and Zn of sera for Taiwanese preschool children living at four residential areas:Taichung city, Taichung urban townships and in a remote area inhabited by two groups of aborigines, Atayal and Bunun were determined. Standard reference materials (tomato leaves, NIST-SRM 1570a, and lichen, IAEA-336) were used as quality control standards to crosscheck the accuracy. Residential area, socioeconomic status and gender were shown to significantly influence serum levels of the eight trace elements. Statistical analysis revealed several different gender patterns via the two-tailed student's test. A quantified index of agreement (AT) was used to classify these elements. Small AT indicated a close consistency, while large AT indicated a larger fluctuation, or less agreement, such that the correlation between the elements could be interpreted using a series of quantified indices at the serum levels of preschool children. [source] Limitations of asymmetric parallel-beam geometryJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2004N. A. Raftery Bragg diffraction peak profiles and intensities in asymmetric (,,2,) diffraction using a mirror-based parallel-beam geometry were compared with symmetric parallel-beam (,,2,) and conventional Bragg,Brentano (,,2,) diffraction for a powdered quartz sample and the NIST standard reference material (SRM) 660a (LaB6, lanthanum hexaboride). A comparison of the intensities and line widths (full width at half-maximum, FWHM) of these techniques demonstrated that low incident angles (,,<,5°) are preferable for the parallel-beam setup. For higher , values, if 2,,<,2,, mass absorption reduces the intensities significantly compared with the Bragg,Brentano setup. The diffraction peak shapes for the mirror geometry are more asymmetric and have larger FWHM values than corresponding peaks recorded with a Bragg,Brentano geometry. An asymmetric mirror-based parallel-beam geometry offers some advantages in respect of intensity when compared with symmetric geometries, and hence may be well suited to quantitative studies, such as those involving Rietveld analysis. A trial Rietveld refinement of a 50% quartz,50% corundum mixture was performed and produced adequate results. [source] Bias-free results in the spectrophotometric determination of chemical oxygen demand in bleached textile mill effluentsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2002Francesc Torrades Abstract A calibration methodology that enables validation of the analytical procedure used in those cases where no placebo or standard reference material is available is applied here. The total Youden blank is used to eliminate the constant error component, and analytical measurements in the presence of the matrix at two different levels of the test portion, in order to avoid its interactive interference, are made. Moreover, the results obtained in the determination of chemical oxygen demand following a closed reflux spectrophotometric method are compared with those obtained when a definitive analytical method is applied, in order to show the absence of direct interference from the matrix. © 2002 Society of Chemical Industry [source] Heavy Metals in Matrices of Food Interest: Sequential Voltammetric Determination at Trace and Ultratrace Level of Copper, Lead, Cadmium, Zinc, Arsenic, Selenium, Manganese and Iron in MealsELECTROANALYSIS, Issue 18 2004Clinio Locatelli Abstract The voltammetric methods are very suitable and versatile techniques for the simultaneous metal determination in complex matrices. The present work, regarding the sequential determination of Cu(II), Pb(II), Cd(II), Zn(II) by square-wave anodic stripping voltammetry (SWASV), As(III), Se(IV) by square-wave cathodic stripping voltammetry (SWCSV) and Mn(II), Fe(III) by square-wave voltammetry (SWV) in matrices involved in foods and food chain as wholemeal, wheat and maize meal, are an interesting example of the possibility to sequentially determine each single element in real samples. Besides the set up of the analytical method, particular attention is aimed either at the problem of possible signal interference or to show that, using the peak area Ap as instrumental datum, it is possible to achieve lower limits of detection. The analytical procedure was verified by the analysis of the standard reference materials: Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a. Precision, as repeatability, and accuracy, expressed as relative standard deviation and relative error, respectively, were lower than 6% in all cases. In the presence of reciprocal interference, the standard addition method considerably improved the resolution of the voltammetric technique. Once set up on the standard reference materials, the analytical procedure was transferred and applied to commercial meals sampled on market for sale. A critical comparison with spectroscopic measurements is also discussed. [source] Effect of artificial mixtures of environmental polycyclic aromatic hydrocarbons present in coal tar, urban dust, and diesel exhaust particulates on MCF-7 cells in cultureENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 2 2004Brinda Mahadevan Abstract Human exposure to polycyclic aromatic hydrocarbons (PAHs) occurs through complex mixtures. The National Institute of Standards and Technology has established standard reference materials (SRMs) for selected PAH mixtures that are composed of carcinogenic, noncarcinogenic, and weakly carcinogenic compounds, such as those derived from coal tar (SRM 1597), atmospheric particulate matter (SRM 1649), and diesel particulate matter (SRM 1650). To study the effects of PAHs with different carcinogenic potential in complex mixtures, and to investigate the metabolic activation of noncarcinogenic and weakly carcinogenic PAHs to DNA-binding derivatives, artificial mixtures (1597H, 1649H, and 1650H) were prepared in the laboratory. These artificial mixtures contained the same relative ratios of noncarcinogenic and weakly carcinogenic PAHs present in SRM 1597, SRM 1649, and SRM 1650. The human mammary carcinoma-derived cell line MCF-7 was treated with these artificial mixtures and analyzed for PAH-DNA adduct formation and the induction of cytochrome P450 (CYP) enzymes. We found that the artificial mixtures formed lower but detectable levels of DNA adducts 24 and 48 hr after treatment than benzo[a]pyrene. Induction of CYP enzyme activity was measured by the ethoxyresorufin- O -deethylase assay, and the expression of CYP1A1 and CYP1B1 was confirmed by immunoblots. Both noncarcinogenic and weakly carcinogenic PAHs present in the artificial mixtures have the ability to induce CYP1A1 and CYP1B1 in MCF-7 cells and contribute to DNA binding. Therefore, it is necessary to take into account the noncarcinogenic and weakly carcinogenic PAHs present in environmental mixtures in assessing the potential risk associated with human exposure. Environ. Mol. Mutagen. 44:99,107, 2004. © 2004 Wiley-Liss, Inc. [source] Determination of in-plane thermal conductivity of Nax Co2O4 single crystals via a parallel thermal conductance (PTC) techniquePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008Xiaofeng Tang Abstract A novel parallel thermal conductance ("PTC") system was specifically developed to conduct the steady state thermal conductivity measurement on small size samples such as single crystals of Nax Co2O4 as reported here. The accuracy and reproducibility of the PTC system has been confirmed by measuring several standard reference materials. The in-plane thermal conductivity , of Nax Co2O4 single crystals grown by a NaCl flux method was measured from 10 K to 300 K and , was found to be ,5 W m,1 K,1 at 300 K. The phonon mean free path (MFP) is estimated to be lph , 9 Å at 300 K, which is comparable to the lattice constant but much smaller than the reported MFP of conducting carriers. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||