A simple and precise method for measuring ammonium in marine and freshwater ecosystems

1999 ◽  
Vol 56 (10) ◽  
pp. 1801-1808 ◽  
Author(s):  
Robert M Holmes ◽  
Alain Aminot ◽  
Roger Kérouel ◽  
Bethanie A Hooker ◽  
Bruce J Peterson
Keyword(s):  
Matrix Effects ◽  
Freshwater Ecosystems ◽  
Sodium Borate ◽  
Sample Collection ◽  
Fluorometric Method ◽  
Simple Method ◽  
Temperature Matrix ◽  
Wide Range ◽  
Substantial Error ◽  
Reaction Proceeds

The accurate measurement of ammonium concentrations is fundamental to understanding nitrogen biogeochemistry in aquatic ecosystems. Unfortunately, the commonly used indophenol blue method often yields inconsistent results, particularly when ammonium concentrations are low. Here, we present a fluorometric method that gives precise measurements of ammonium over a wide range of concentrations and salinities emphasizing submicromolar levels. The procedure not only solves analytical problems but also substantially simplifies sample collection and preservation. It uses a single working reagent (consisting of orthophthaldialdehyde, sodium sulfite, and sodium borate) that is stable for months when stored in the dark. The working reagent and sample can be mixed immediately after sample collection and the reaction proceeds to completion within 3 h at room temperature. Matrix effects and background fluorescence can be corrected without introducing substantial error. This simple method produces highly reproducible results even at very low ammonium concentrations.

scholarly journals ASSESSMENT OF ECOLOGICAL STATE OF THE VELIKAYA RIVER DELTA BASED ON HYDROCHEMICAL INDICATORS AND STRUCTURE OF PHYTOPLANKTON

2017 ◽  
Vol 1 ◽  
pp. 82
Author(s):  
Tatiana Drozdenko ◽  
Sergei Mikhalap ◽  
Larisa Nikolskaya ◽  
Anna Chernova
Keyword(s):  
Water Quality ◽  
High Speed ◽  
Shannon Index ◽  
Freshwater Ecosystems ◽  
River Delta ◽  
Ecosystem Dynamics ◽  
Polluted Water ◽  
Ecological State ◽  
Sample Collection ◽  
Wide Range

The basis of the existence of freshwater ecosystems is phytoplankton, which produces most of the primary biological production, participates in repair processes and provides a wide range of ecosystem services. The short life cycle and high speed metabolism of microalgae make them ideal objects for ecological monitoring. The aim of the present study is to research the ecological state of the Velikaya river delta based on the species composition of phytoplankton community and some hydrochemical parameters. The sample collection for phytoplankton study and physicochemical measurements was carried out in summer 2016 at five stations representing different ecological locations of the Velikaya river delta. One hundred sixty five species taxa of microalgae belonging to 8 phylums were identified during the research: Bacillariophyta (37%), Chlorophyta (33.9%), Cyanophyta/Cyanobacteria (9.7%), Chrysophyta (6.1%), Euglenophyta (6.1%), Cryptophyta (3%), Dinophyta (3%), Xanthophyta (1.2%). The values of Shannon index indicate the average complexity of the microalgae communities structure. Values of Margalef index characterize the Velikaya river delta as an area of high species richness. Compared to the previous studies, a significant increase in the level of information diversity is observed, indicating an increase in the number of possible flows of substance and energy in the ecosystem. Dynamics of biogen substances in the water shows a slight increase of their concentrations. Ecological and geographical analysis proves that absolute dominance of cosmopolitan freshwater forms is typical for the algoflora of the Velikaya river delta. In relation to the pH-reaction inhabitants of neutral and slightly alkaline water dominate. Pantle–Buck saprobity index is applied for water quality assessment, which shows beta-mesosaprobic water quality in the ecosystem. Thus, the water of the Velikaya river delta could be referred to the category of moderately polluted water (class II of water quality). This is confirmed by the data of hydrochemical analysis.

Alkene Difunctionalization Directed by Free Amines: Diamine Synthesis via Nickel-Catalyzed 1,2-Carboamination

2021 ◽  
Author(s):  
Taeho Kang ◽  
José Manuel González ◽  
Zi-Qi Li ◽  
Klement Foo ◽  
Peter Cheng ◽  
...  
Keyword(s):  
Nickel Catalyst ◽  
Room Temperature ◽  
Kinetic Studies ◽  
Fine Tuning ◽  
Secondary Amines ◽  
Protecting Group ◽  
Wide Range ◽  
Leaving Group ◽  
Primary And Secondary Amines ◽  
Reaction Proceeds

A versatile method to access differentially substituted 1,3- and 1,4-diamines via a nickel-catalyzed three-component 1,2-carboamination of alkenyl amines with aryl/alkenylboronic ester nucleophiles and N–O electrophiles is reported. The reaction proceeds efficiently with free primary and secondary amines without needing a directing auxiliary or protecting group, and is enabled by fine-tuning the leaving group on the N–O reagent. The transformation is highly regioselective and compatible with a wide range of coupling partners and alkenyl amine substrates, all performed at room temperature. A series of kinetic studies support a mechanism in which alkene coordination to the nickel catalyst is turnover-limiting.

scholarly journals Sesquiterpene emissions from vegetation: a review

2008 ◽  
Vol 5 (3) ◽  
pp. 761-777 ◽  
Author(s):  
T. R. Duhl ◽  
D. Helmig ◽  
A. Guenther
Keyword(s):  
Plant Species ◽  
Emission Rates ◽  
Sample Collection ◽  
Ambient Temperatures ◽  
Relative Contribution ◽  
Environmental Controls ◽  
Weather Events ◽  
Wide Range ◽  
Experimental Protocols ◽  
Selection Of Species

Abstract. This literature review summarizes the environmental controls governing biogenic sesquiterpene (SQT) emissions and presents a compendium of numerous SQT-emitting plant species as well as the quantities and ratios of SQT species they have been observed to emit. The results of many enclosure-based studies indicate that temporal SQT emission variations appear to be dominated mainly by ambient temperatures although other factors contribute (e.g., seasonal variations). This implies that SQT emissions have increased significance at certain times of the year, especially in late spring to mid-summer. The strong temperature dependency of SQT emissions also creates the distinct possibility of increasing SQT emissions in a warmer climate. Disturbances to vegetation (from herbivores and possibly violent weather events) are clearly also important in controlling short-term SQT emissions bursts, though the relative contribution of disturbance-induced emissions is not known. Based on the biogenic SQT emissions studies reviewed here, SQT emission rates among numerous species have been observed to cover a wide range of values, and exhibit substantial variability between individuals and across species, as well as at different environmental and phenological states. These emission rates span several orders of magnitude (10s–1000s of ng gDW-1 h−1). Many of the higher rates were reported by early SQT studies, which may have included artificially-elevated SQT emission rates due to higher-than-ambient enclosure temperatures and disturbances to enclosed vegetation prior to and during sample collection. When predicting landscape-level SQT fluxes, modelers must consider the numerous sources of variability driving observed SQT emissions. Characterizations of landscape and global SQT fluxes are highly uncertain given differences and uncertainties in experimental protocols and measurements, the high variability in observed emission rates from different species, the selection of species that have been studied so far, and ambiguities regarding controls over emissions. This underscores the need for standardized experimental protocols, better characterization of disturbance-induced emissions, screening of dominant plant species, and the collection of multiple replicates from several individuals within a given species or genus as well as a better understanding of seasonal dependencies of SQT emissions in order to improve the representation of SQT emission rates.

scholarly journals Automatic and Online Detection of Rotor Fault State

2018 ◽  
Vol 7 (1) ◽  
pp. 43 ◽  
Author(s):  
Ali Ouanas ◽  
Ammar Medoued ◽  
Salim Haddad ◽  
Mourad Mordjaoui ◽  
D. Sayad
Keyword(s):  
Induction Motor ◽  
Dimensional Space ◽  
Operating Conditions ◽  
Online Detection ◽  
K Nearest Neighbor ◽  
Simple Method ◽  
Important Place ◽  
Motor Test ◽  
Wide Range ◽  
Fault State

In this work, we propose a new and simple method to insure an online and automatic detection of faults that affect induction motor rotors. Induction motors now occupy an important place in the industrial environment and cover an extremely wide range of applications. They require a system installation that monitors the motor state to suit the operating conditions for a given application. The proposed method is based on the consideration of the spectrum of the single-phase stator current envelope as input of the detection algorithm. The characteristics related to the broken bar fault in the frequency domain extracted from the Hilbert Transform is used to estimate the fault severity for different load levels through classification tools. The frequency analysis of the envelope gives the frequency component and the associated amplitude which define the existence of the fault. The clustering of the indicator is chosen in a two-dimensional space by the fuzzy c mean clustering to find the center of each class. The distance criterion, the K-Nearest Neighbor (KNN) algorithm and the neural networks are used to determine the fault type. This method is validated on a 5.5-kW induction motor test bench.Article History: Received July 16th 2017; Received: October 5th 2017; Accepted: Januari 6th 2018; Available onlineHow to Cite This Article: Ouanas, A., Medoued, A., Haddad, S., Mordjaoui, M., and Sayad, D. (2017) Automatic and online Detection of Rotor Fault State. International Journal of Renewable Energy Development, 7(1), 43-52.http://dx.doi.org/10.14710/ijred.7.1.43-52

scholarly journals Determination of Arsenic, Chromium and Lead in titanium dioxide pigments by ICP- OES with Concomitant Metals Analyser

2019 ◽  
pp. 296-305
Author(s):  
Beena Sunilkumar ◽  
S. B. Singh
Keyword(s):  
Titanium Dioxide ◽  
Matrix Effects ◽  
Mineral Acid ◽  
Icp Oes ◽  
Acid Decomposition ◽  
Simple Method ◽  
Sample Dissolution ◽  
The Matrix ◽  
Generating System

A simple method has been developed for the determination of trace toxic elements like arsenic, lead and chromium in titanium dioxide pigment samples by ICP OES attached with a Concomitant Metals Analyser. Open mineral acid decomposition was used for sample dissolution employing a mixture of nitric and hydrofluoric acids. The continuous online generation of hydrides into the plasma was achieved through a concomitant metals analyser. The recovery of arsenic, lead and chromium and the matrix effects of titanium on these elements have been studied with spiking experiments. The proposed method has been successfully applied to the determination of arsenic and other elements in titanium pigment samples. The continuous hydride generating system, Concomitant Metals Analyser (CMA) improved the sensitivity of analysis nearly five times in pigment samples. The precision of the measurements was found to be less than 10% RSD.

Detection of Fourth Generation Synthetic Halocarbons in the Upper Troposphere

2021 ◽  
Author(s):  
Tanja Schuck ◽  
Katharina Meixner ◽  
Peter van Velthoven ◽  
Simon O’Doherty ◽  
Martin Vollmer ◽  
...  
Keyword(s):  
Degradation Products ◽  
Stratospheric Ozone ◽  
Montreal Protocol ◽  
Gas Chromatography Mass Spectrometry ◽  
Fourth Generation ◽  
Oh Radicals ◽  
Sample Collection ◽  
Upper Troposphere ◽  
Wide Range ◽  
Air Sample

<p>Synthetic halocarbons are used for a wide range of applications, for example air conditioning or foam blowing. Many of them are long-lived greenhouse gases contributing to climate change and, in addition, may contribute to stratospheric ozone depletion if containing chlorine or bromine. Therefore, their production and use are regulated by the Montreal Protocol and its amendments. These long-lived halocarbons are increasingly replaced by a fourth generation of unsaturated short-lived halocarbons, the hydrochlorofluoroolefines (HCFOs) and hydrofluoroolefines (HFOs). The main removal process of these compounds in the atmosphere is reaction with OH radicals, and their average lifetimes are of the order of up to a few tens of days.</p><p>As part of the IAGOS-CARIBIC instrument package we operate an automated air sample collection system during regular flights in the upper troposphere and lowermost stratosphere. At altitudes around 10-12 km, samples are collected in stainless steel and glass flasks at predefined times. Post-flight laboratory analyses include gas chromatography - mass spectrometry measurements of a wide range of halocarbons. The short-lived compounds HFO-1234ze(E) and HCFO-1233zd(E) were detected in a small number of samples, indicating that these compounds are sufficiently long lived for transport into the upper troposphere. There were not found in stratospheric samples.</p><p>At this altitude, low abundance of OH and low temperatures may slow down chemical decay, and tracer lifetimes may increase significantly. Based on average temperatures and OH abundance, we estimate local lifetimes of HFO-1234ze(E) and HCFO-1233zd(E)  in the mid-latitudes of up to 75 days and 200 days, respectively. Short-lived H(C)FOs reaching the upper troposphere could thus be transported over large distances and their degradation products may be deposited  far from their emission sources.</p>

Convenient Synthesis of Fluorescent Chromeno[4,3-d]pyrimidines from Electron-Deficient 3-Vinylchromones

Synthesis ◽  
2019 ◽  
Vol 52 (01) ◽  
pp. 40-50 ◽  
Author(s):  
Nikita M. Chernov ◽  
Roman V. Shutov ◽  
Anastasia E. Potapova ◽  
Igor P. Yakovlev
Keyword(s):  
Stokes Shift ◽  
Mild Conditions ◽  
Convenient Synthesis ◽  
Acid Fragment ◽  
Wide Range ◽  
Powerful Approach ◽  
Reaction Proceeds ◽  
Electron Withdrawing Group ◽  
Blue Range ◽  
Acetic Acids

We report an easy and powerful approach to the synthesis of novel chromeno[4,3-d]pyrimidine-5-acetic acids through ANRORC reaction of electron-deficient 3-vinylchromones and 1,3-N,N-binucleophiles. The reaction proceeds under mild conditions (EtOH, rt) and is applicable to a wide range of substrates. The described compounds show fluorescence in the violet-blue range (390–460 nm) with Stokes shift of 40–80 nm and moderate quantum yield (0.15–0.20). As the electron-withdrawing group is conserved in the form of an acetic acid fragment, these compounds may readily be functionalized or conjugated to a required substrate for (bio)analytical purposes.

Simplified approach to confidence limited in radioimmunassay.

1980 ◽  
Vol 26 (6) ◽  
pp. 763-765 ◽  
Author(s):  
R C Baxter
Keyword(s):  
Quality Control ◽  
Mean Value ◽  
Confidence Limits ◽  
Simple Method ◽  
Response Variable ◽  
Simplified Approach ◽  
Quadratic Curve ◽  
Wide Range ◽  
Advanced Computing ◽  
Routine Quality Control

Abstract A simple method of calculating confidence limits for radioimmunoassay data is presented. The method involves the use of the within-assay variation in dose estimate of three routine quality-control specimens, measured in repeated assays, to estimate the confidence limits for results on unknown samples. Results for control specimens are combined by calculating the unique quadratic curve fitting a graph of within-assay standard deviation vs mean value for each control. This method requires no special data accumulation or advanced computing equipment. For cortisol, lutropin, and thyroxine radioimmunoassays, confidence limits calculated in this way have been compared with those calculated from the variance of the response variable “B/B0” in repeated standard curves. Both methods agree well with actual limits observed when plasma pools containing a wide range of hormone concentrations are assayed repeatedly.

scholarly journals Wearable Potentiometric Sensors for Medical Applications

Sensors ◽  
2019 ◽  
Vol 19 (2) ◽  
pp. 363 ◽  
Author(s):  
María Cuartero ◽  
Marc Parrilla ◽  
Gaston Crespo
Keyword(s):  
Sport Performance ◽  
Medical Utilization ◽  
Potentiometric Sensors ◽  
Sensor Calibration ◽  
Medical Applications ◽  
Sample Collection ◽  
Medical Settings ◽  
Wide Range ◽  
The Individual

Wearable potentiometric sensors have received considerable attention owing to their great potential in a wide range of physiological and clinical applications, particularly involving ion detection in sweat. Despite the significant progress in the manner that potentiometric sensors are integrated in wearable devices, in terms of materials and fabrication approaches, there is yet plenty of room for improvement in the strategy adopted for the sample collection. Essentially, this involves a fluidic sampling cell for continuous sweat analysis during sport performance or sweat accumulation via iontophoresis induction for one-spot measurements in medical settings. Even though the majority of the reported papers from the last five years describe on-body tests of wearable potentiometric sensors while the individual is practicing a physical activity, the medical utilization of these devices has been demonstrated on very few occasions and only in the context of cystic fibrosis diagnosis. In this sense, it may be important to explore the implementation of wearable potentiometric sensors into the analysis of other biofluids, such as saliva, tears and urine, as herein discussed. While the fabrication and uses of wearable potentiometric sensors vary widely, there are many common issues related to the analytical characterization of such devices that must be consciously addressed, especially in terms of sensor calibration and the validation of on-body measurements. After the assessment of key wearable potentiometric sensors reported over the last five years, with particular attention paid to those for medical applications, the present review offers tentative guidance regarding the characterization of analytical performance as well as analytical and clinical validations, thereby aiming at generating debate in the scientific community to allow for the establishment of well-conceived protocols.

Screening of 104 New Psychoactive Substances (NPS) and Other Drugs of Abuse in Oral Fluid by LC–MS-MS

2020 ◽  
Vol 44 (7) ◽  
pp. 697-707
Author(s):  
Kelly Francisco da Cunha ◽  
Karina Diniz Oliveira ◽  
Marilyn A Huestis ◽  
Jose Luiz Costa
Keyword(s):  
Oral Fluid ◽  
Drugs Of Abuse ◽  
Matrix Effects ◽  
Synthetic Cannabinoids ◽  
Screening Method ◽  
Simultaneous Detection ◽  
New Psychoactive Substances ◽  
Major Public Health Problem ◽  
Psychoactive Substances ◽  
Wide Range

Abstract New psychoactive substances (NPS) are a major public health problem, primarily due to the increased number of acute poisoning cases. Detection of these substances is a challenge. The aim of this research was to develop and validate a sensitive screening method for 104 drugs of abuse, including synthetic cannabinoids, synthetic cathinones, fentanyl analogues, phenethylamines and other abused psychoactive compounds (i.e., THC, MDMA, LSD and their metabolites) in oral fluid by liquid chromatography–tandem mass spectrometry (LC–MS-MS). The Quantisal™ oral fluid device was used to collect oral fluid samples. The oral fluid–elution buffer mixture (500-μL sample) was extracted with t-butyl methyl ether, and chromatographic separation was performed on a Raptor™ biphenyl column (100 × 2.1 mm ID, 2.7 μm), with a total run time of 13.5 min. Limits of detection were established at three concentrations (0.05, 0.1 or 1 ng/mL) for most analytes, except for acetyl norfentanyl and mescaline (5 ng/mL). Matrix effects were generally <20% and overall extraction recoveries >60%. The highest matrix effect was observed within the synthetic cannabinoid group (PB22, −55.5%). Lower recoveries were observed for 2C-T (47.2%) and JWH-175 (58.7%). Recoveries from the Quantisal™ device were also evaluated for all analytes (56.7–127%), with lower recoveries noted for 25I-NBOMe, valerylfentanyl and mCPP (56.7, 63.0 and 69.9%, respectively). Drug stability in oral fluid was evaluated at 15, 60 and 90 days and at 25, 4 and −20°C. As expected, greater stability was observed when samples were stored at −20°C, but even when frozen, some NPS (e.g., synthetic cannabinoids) showed more than 20% degradation. The method was successfully applied to the analysis of seven authentic oral fluid samples positive for 17 different analytes. The method achieved good sensitivity and simultaneous detection of a wide range of NPS.

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