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101.
Michele M. Schantz Gauthier Eppe Jean-François Focant Coreen Hamilton N. Alan Heckert Rebecca M. Heltsley Dale Hoover Jennifer M. Keller Stefan D. Leigh Donald G. Patterson Jr Adam L. Pintar Katherine E. Sharpless Andreas Sjödin Wayman E. Turner Stacy S. Vander Pol Stephen A. Wise 《Analytical and bioanalytical chemistry》2013,405(4):1203-1211
Four new Standard Reference Materials (SRMs) have been developed to assist in the quality assurance of chemical contaminant measurements required for human biomonitoring studies, SRM 1953 Organic Contaminants in Non-Fortified Human Milk, SRM 1954 Organic Contaminants in Fortified Human Milk, SRM 1957 Organic Contaminants in Non-Fortified Human Serum, and SRM 1958 Organic Contaminants in Fortified Human Serum. These materials were developed as part of a collaboration between the National Institute of Standards and Technology (NIST) and the Centers for Disease Control and Prevention (CDC) with both agencies contributing data used in the certification of mass fraction values for a wide range of organic contaminants including polychlorinated biphenyl (PCB) congeners, chlorinated pesticides, polybrominated diphenyl ether (PBDE) congeners, and polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) congeners. The certified mass fractions of the organic contaminants in unfortified samples, SRM 1953 and SRM 1957, ranged from 12 ng/kg to 2200 ng/kg with the exception of 4,4′-DDE in SRM 1953 at 7400 ng/kg with expanded uncertainties generally <14 %. This agreement suggests that there were no significant biases existing among the multiple methods used for analysis. Figure
Comparison of Concentrations of Selected Compounds in Human Serum and Human Milk Standard Reference Materials (SRMs) 相似文献
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104.
Research combining the areas of separation science and microfluidics has gained popularity, driven by the increasing need to create portable, fast, and low analyte-consumption devices. Much of this research has focused on the developments in electrophoretic separations, which use the electrokinetic properties of analytes to overcome many of the problems encountered during system scale-down. In addition, new physical phenomenon can be exploited on the microscale not available in standard techniques. In this study, the innovative developments, including electrophoretic concentration, sample preparation/conditioning, and separation on-chip are reviewed, along with some introductory discussions, from January 2008 to July 2010. 相似文献
105.
Bhat SH Gelhaus SL Mesaros C Vachani A Blair IA 《Rapid communications in mass spectrometry : RCM》2011,25(1):115-121
4‐(Methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK) is a carcinogenic nitrosamine produced upon curing tobacco. It is present in tobacco smoke and undergoes metabolism to 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol (NNAL) in the lungs. NNAL undergoes further uridine diphosphate glucuronosyltransferase (UGT)‐mediated metabolism to give N‐ and O‐glucuronide metabolites, which together with free (non‐conjugated) NNAL are then excreted in the urine. The ability to conduct validated analyses of free and conjugated NNAL in human urine is important in order to assess inter‐individual differences in lung cancer risk from exposure to cigarette smoke. The use of stable isotope dilution (SID) methodology in combination with liquid chromatography/multiple reaction monitoring/mass spectrometry (LC/MRM‐MS) provides the highest bioanalytical specificity possible for such analyses. We describe a novel derivatization procedure, which results in the formation of a pre‐ionized N‐propyl‐NNAL derivative. The increased LC/MS sensitivity arising from this derivative then makes it possible to analyze free NNAL in only 0.25 mL urine. This substantial reduction in urine volume when compared with other methods that have been developed will help preserve the limited amounts of stored urine samples that are available from on‐going longitudinal biomarker studies. The new high sensitivity SID LC/MRM‐MS assay was employed to determine free and conjugated NNAL concentrations in urine samples from 60 individual disease‐free smokers. Effects of inter‐individual differences in urinary creatinine clearance on NNAL concentrations were then assessed and three metabolizer phenotypes were identified in the 60 subjects from the ratio of urinary NNAL glucuronides/free NNAL. Poor metabolizers (PMs, 14 subjects) with a ratio of NNAL glucuronides/free NNAL <2 (mean = 1.3), intermediate metabolizers (IMs, 36 subjects) with a ratio between 2 and 5 (mean = 3.4), and extensive metabolizers (EMs, 10 subjects) with a ratio >5 (mean = 11.1). Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
106.
Juliana Utley Stacy Reeder Adrienne Redmond-Sanogo 《School science and mathematics》2020,120(6):345-355
Teachers need the opportunity to reflect, rethink, and adapt as they continually develop their image of their role in their mathematics classrooms. Thus, the purpose of this research was to examine how the Draw-a-Mathematics-Teacher-Test (DAMTT) and rubric can be used to assess preservice elementary teachers’ images of and beliefs about their future mathematics classrooms and validate the Draw-a-Math-TeacherTest-Rubric (DAMTT-R). Results suggest that the DAMTT-R is a valid measure and yields consistent results. Additionally, analysis of preservice elementary teachers’ (PETs) DAMTT revealed that only slightly more than one-third (36.9%) drew a picture and described their classroom in such a way that it reflected beliefs aligned with student-centered pedagogic practices. While mathematics educators may aim for the majority of PETs to leave their programs having developed beliefs aligned with and supportive of student-centered pedagogic practices, the results of this study revealed that 25% of PETs held beliefs that align with teacher-centered pedagogic practices. Lastly, 38.1% of the PETs reflected beliefs about their pedagogic practices, as measured by the DAMTT and the DAMTT-R, aligned with a transition between teacher-centered and student-centered. 相似文献
107.
A SPME-GC-MS method was developed to quantify nitrous oxide (N(2)O) to evaluate denitrification rates. There is a need for this sensitive and definitive N(2)O detection method to accurately measure the soil and sediment ability to convert anthropogenic mineral nitrogen loads to N(2) through denitrification hence decreasing estuarine waterway pollution loading. This method is applied to measure denitrification, which is a major pathway for inorganic nitrogen removal, by incorporating the acetylene (C(2)H(2)) block method on anaerobic assays. Currently, denitrification is largely measured using GCs fitted with TCD or ECD detectors. With a mean R(2) value of 0.996, the calibration curve spanned over three orders of magnitude (4.1-2030 nM) with a limit of detection (LOD) of 4.1 nM N(2)O (18 ppb) and a limit of quantification (LOQ) of 16 nM N(2)O (72 ppb). This detection method was valid with less than 15% relative standard deviation (RSD) and error for middle and high quality control (QC) points and less than 20% for low QC points on three experimental days. Measuring N(2)O using SPME-GC-MS technology allows for confidence in identification, high sensitivity, reproducibility, and short run times. 相似文献
108.
Stacy Simai Reginald Yoo Seok Lee Hyeryeong Lee Nulee Jang In Seop Chang 《Electroanalysis》2019,31(9):1635-1640
Herein, an enzyme‐electrode based on the oxygen‐insensitive carbon monoxide dehydrogenase (CODH) containing molybdenum (Mo) and copper (Cu), flavin adenine dinucleotide (FAD) and two different [2Fe‐2 S] clusters as cofactors from the aerobic bacterium Hydrogenophaga pseudoflava, is proposed as a platform for dissolved CO concentration monitoring. The immobilized CODHs on Au electrode retain their catalytic activity and demonstrates changes to cyclic voltammetry and amperometry signals upon interactions with various dissolved CO concentrations. Cyclic voltammetry shows that CODHs are capable of direct electron transfer without any mediator use as oxidative current which starts around ?0.268 V (vs Ag/AgCl) is observed in the presence of CO. When CO‐saturated standard solution was spiked sequentially into the gas‐tight reactor, amperometry analysis shows current increased accordingly with response time within 5 s. Our study demonstrates that this enzyme‐electrode is promising to serve as platform for developing an on‐line dissolved CO concentration monitoring tool which is essential to fill in the gap for conventional technologies which are limited to off‐line measurement. 相似文献
109.
Second virial coefficients have been measured in tetrahydrofuran for a series of anionically polymerized narrow distribution homopolymers and copolymers of butadiene and styrene. The results fit the general empirical equation A2 = M?1/4(0.0216wB + 0.00995wS + CwBwS), where M is the polymer molecular weight, wB and ws are the weight fractions of butadiene and styrene, and C is a constant which is zero for block polymers and equal to 7.9 × 10—3 for random copolymers. The equation is independent of the degree of 1,2 addition of butadiene and fits data on both linear and tetrachain star-branched polymers within experimental error. 相似文献
110.
Nadine P. Connor Kerrin L.P. Palazzi-Churas Stacy B. Cohen Glen E. Leverson Diane M. Bless 《Journal of voice》2007,21(2):189-202
OBJECTIVES: Extraesophageal reflux disease (EERD) is linked with serious and varied health concerns. The authors' goal was to determine the prevalence of EERD and the effect on health-related quality of life in adults within a large community-based sample. STUDY DESIGN: Survey study conducted in a community setting. METHODS: In the Madison, Wisconsin area, 1845 adult subjects were surveyed. Main outcome measures were frequently of GERD and laryngeal symptoms, the Medical Outcomes Trust Short Form 12 (SF-12), Voice Handicap Index (VHI), and Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaires. RESULTS: More than 66% of subjects reported either GERD or laryngeal symptoms, and 26% reported both GERD and laryngeal symptoms (which reflect symptoms commonly reported for EERD). In addition, 39% of our sample took medicine for heartburn. Forty-four percent of subjects with both GERD and laryngeal symptoms reported occasional breathing difficulties, and 38% of these subjects reported a voice disorder. Significant reductions in perceived quality of general health, digestive health, and voice-related quality of life were found in subjects with both GERD and laryngeal symptoms, in comparison with subjects manifesting each symptom group alone, or in subjects with no symptoms. CONCLUSIONS: The presence of GERD and laryngeal symptoms, and their concurrence, was identified in a substantial number of subjects. The GERD and laryngeal symptoms surveyed represent those most commonly reported for EERD. Because EERD has been linked with tissue damage and reductions in health-related quality of life, it is important to identify these persons and provide treatment before progression of the condition. 相似文献