scholarly journals The reversed-axis method to estimate precision in standard additions analysis

2016 ◽  
Vol 124 ◽  
pp. 155-158 ◽  
Author(s):  
Daniel A. Goncalves ◽  
Bradley T. Jones ◽  
George L. Donati
Keyword(s):  
Standard Additions ◽  
Estimate Precision

Optimization of Ultrasound-Assisted Extraction of Cr, Cu, Zn, Cd, and Pb from Sediment, Followed by FAAS and GFAAS Analysis

2016 ◽  
Vol 99 (1) ◽  
pp. 252-259 ◽  
Author(s):  
Aparecida M S Mimura ◽  
Marcone A L Oliveira ◽  
Virginia S T Ciminelli ◽  
Julio C J Silva
Keyword(s):  
Atomic Absorption Spectrometry ◽  
Atomic Absorption ◽  
Matrix Effects ◽  
Graphite Furnace ◽  
Absorption Spectrometry ◽  
Ultrasound Assisted Extraction ◽  
Flame Atomic Absorption ◽  
Assisted Extraction ◽  
Graphite Furnace Atomic Absorption ◽  
Standard Additions

Abstract An ultrasound method for simultaneous extraction of Cr, Cu, Zn, Cd, and Pb from sediment, and determination by flame atomic absorption spectrometry (FAAS) and graphite furnace atomic absorption spectrometry (GFAAS) was proposed. The experimental results obtained using analytical curves and the method of standard additions agreed at a confidence level of 95% for all the analytes, as determined by FAAS and GFAAS, indicating no significant matrix effects. Recoveries ranged from 80.1 to 93.7% (certified reference material) and from 89 to 107% (spike tests). The LOD and LOQ results from the method were consistent with the techniques used (FAAS and GFAAS), with high analytical throughput. The proposed method was then used to determine Cr, Cu, Zn, Cd, and Pb in river sediment samples from Rio Doce, Minas Gerais, Brazil. The results indicated levels below those permitted by Brazilian legislation for all the analytes, with the exception of Cr.

scholarly journals Universal PCR and antibody testing demonstrate little to no transmission of SARS-CoV-2 in a rural community

2020 ◽  
Author(s):  
Ayesha Appa ◽  
Saki Takahashi ◽  
Isabel Rodriguez-Barraquer ◽  
Gabriel Chamie ◽  
Aenor Sawyer ◽  
...  
Keyword(s):  
Rural Community ◽  
The United States ◽  
Rural Setting ◽  
Antibody Testing ◽  
Cross Sectional Survey ◽  
Cross Sectional ◽  
Rural Town ◽  
Low Prevalence ◽  
Prior Infection ◽  
Estimate Precision

Abstract Background Limited systematic surveillance for SARS-CoV-2 in the early months of the United States epidemic curtailed accurate appraisal of transmission intensity. Our objective was to perform case detection of an entire rural community to quantify SARS-CoV-2 transmission using PCR and antibody testing. Methods We conducted a cross-sectional survey of SARS-CoV-2 infection in the rural town of Bolinas, California (population 1,620), four weeks following shelter-in-place orders. Participants were tested between April 20 th – 24 th, 2020. Prevalence by PCR and seroprevalence from two forms of antibody testing were performed in parallel (Abbott ARCHITECT IgG and in-house IgG ELISA). Results Of 1,891 participants, 1,312 were confirmed Bolinas residents (>80% community ascertainment). Zero participants were PCR positive. Assuming 80% sensitivity, it would have been unlikely to observe these results (p<0.05) if there were >3 active infections in the community. Based on antibody results, estimated prevalence of prior infection was 0.16% (95% CrI: 0.02%, 0.46%). The positive predictive value (PPV) of a positive result on both tests was 99.11% (95% CrI: 95.75%, 99.94%), compared to PPV 44.19%-63.32% (95% CrI range 3.25%-98.64%) if one test was utilized. Conclusions Four weeks following shelter-in-place, SARS-CoV-2 infection in a rural Northern California community was extremely rare. In this low prevalence setting, use of two antibody tests increased seroprevalence estimate precision. This was one of the first community-wide studies to successfully implement synchronous PCR and antibody testing, particularly in a rural setting. Widespread testing remains an underpinning of effective disease control in conjunction with consistent uptake of public health measures.

scholarly journals Simultaneously quantifying ferrihydrite and goethite in natural sediments using the method of standard additions with X-ray absorption spectroscopy

2018 ◽  
Vol 476 ◽  
pp. 248-259 ◽  
Author(s):  
Jing Sun ◽  
Brian J. Mailloux ◽  
Steven N. Chillrud ◽  
Alexander van Geen ◽  
Aaron Thompson ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
X Ray ◽  
Standard Additions ◽  
X Ray Absorption

scholarly journals Identification-Robust Estimates of the Canadian Natural Rate of Interest

2016 ◽  
Vol 91 (1-2) ◽  
pp. 161-176
Author(s):  
Maral Kichian
Keyword(s):  
Interest Rate ◽  
Robust Methods ◽  
Errors In Variables ◽  
Natural Rate ◽  
Real Rate ◽  
Point Estimates ◽  
Natural Rate Of Interest ◽  
Best Fitting ◽  
Estimate Precision ◽  
Fitting Model

The natural rate of interest is an unobservable entity and its measurement presents some important empirical challenges. In this paper, we use identification-robust methods and central bank real-time staff projections to obtain estimates for the equilibrium real rate from contemporaneous and forward-looking Taylor-type interest rate rules. The methods notably account for the potential presence of endogeneity, under-identification, and errors-in-variables concerns. Our applications are conducted on Canadian data. The results reveal some important identification difficulties associated with some of our models, reinforcing the need to use identification-robust methods to estimate such policy functions. Despite these challenges, we are able to obtain fairly comparable point estimates for the real equilibrium interest rate across our different models, and in the case of the best fitting model, also remarkable estimate precision.

scholarly journals Evaluation of the accuracy of thermal dissociation CRDS and LIF techniques for atmospheric measurement of reactive nitrogen species

2017 ◽  
Vol 10 (5) ◽  
pp. 1911-1926 ◽  
Author(s):  
Caroline C. Womack ◽  
J. Andrew Neuman ◽  
Patrick R. Veres ◽  
Scott J. Eilerman ◽  
Charles A. Brock ◽  
...  
Keyword(s):  
Conversion Efficiency ◽  
Reactive Nitrogen Species ◽  
Thermal Dissociation ◽  
Ambient Air ◽  
Reactive Nitrogen ◽  
Organic Nitrates ◽  
Nitrogen Species ◽  
Operating Characteristics ◽  
Experimental Conditions ◽  
Standard Additions

Abstract. The sum of all reactive nitrogen species (NOy) includes NOx (NO2 + NO) and all of its oxidized forms, and the accurate detection of NOy is critical to understanding atmospheric nitrogen chemistry. Thermal dissociation (TD) inlets, which convert NOy to NO2 followed by NO2 detection, are frequently used in conjunction with techniques such as laser-induced fluorescence (LIF) and cavity ring-down spectroscopy (CRDS) to measure total NOy when set at > 600 °C or speciated NOy when set at intermediate temperatures. We report the conversion efficiency of known amounts of several representative NOy species to NO2 in our TD-CRDS instrument, under a variety of experimental conditions. We find that the conversion efficiency of HNO3 is highly sensitive to the flow rate and the residence time through the TD inlet as well as the presence of other species that may be present during ambient sampling, such as ozone (O3). Conversion of HNO3 at 400 °C, nominally the set point used to selectively convert organic nitrates, can range from 2 to 6 % and may represent an interference in measurement of organic nitrates under some conditions. The conversion efficiency is strongly dependent on the operating characteristics of individual quartz ovens and should be well calibrated prior to use in field sampling. We demonstrate quantitative conversion of both gas-phase N2O5 and particulate ammonium nitrate in the TD inlet at 650 °C, which is the temperature normally used for conversion of HNO3. N2O5 has two thermal dissociation steps, one at low temperature representing dissociation to NO2 and NO3 and one at high temperature representing dissociation of NO3, which produces exclusively NO2 and not NO. We also find a significant interference from partial conversion (5–10 %) of NH3 to NO at 650 °C in the presence of representative (50 ppbv) levels of O3 in dry zero air. Although this interference appears to be suppressed when sampling ambient air, we nevertheless recommend regular characterization of this interference using standard additions of NH3 to TD instruments that convert reactive nitrogen to NO or NO2.

Sign in / Sign up

Export Citation Format

Share Document