scholarly journals Water sampling techniques for continous monitoring of pesticides in water

2017 ◽  
Vol 32 (2) ◽  
pp. 85-93
Author(s):  
Dragana Sunjka ◽  
Sanja Lazic
Keyword(s):  
Surface Waters ◽  
Continuous Monitoring ◽  
Water Status ◽  
Monitoring Program ◽  
Weighted Average ◽  
Sampling Techniques ◽  
Time Period ◽  
Pesticides In Water ◽  
Time Weighted Average

Good ecological and chemical status of water represents the most important aim of the Water Framework Directive 2000/60/EC, which implies respect of water quality standards at the level of entire river basin (2008/105/EC and 2013/39/EC). This especially refers to the control of pesticide residues in surface waters. In order to achieve the set goals, a continuous monitoring program that should provide a comprehensive and interrelated overview of water status should be implemented. However, it demands the use of appropriate analysis techniques. Until now, the procedure for sampling and quantification of residual pesticide quantities in aquatic environment was based on the use of traditional sampling techniques that imply periodical collecting of individual samples. However, this type of sampling provides only a snapshot of the situation in regard to the presence of pollutants in water. As an alternative, the technique of passive sampling of pollutants in water, including pesticides has been introduced. Different samplers are available for pesticide sampling in surface water, depending on compounds. The technique itself is based on keeping a device in water over a longer period of time which varies from several days to several weeks, depending on the kind of compound. In this manner, the average concentrations of pollutants dissolved in water during a time period (time-weighted average concentrations, TWA) are obtained, which enables monitoring of trends in areal and seasonal variations. The use of these techniques also leads to an increase in sensitivity of analytical methods, considering that pre-concentration of analytes takes place within the sorption medium. However, the use of these techniques for determination of pesticide concentrations in real water environments requires calibration studies for the estimation of sampling rates (Rs). Rs is a volume of water per time, calculated as the product of overall mass transfer coefficient and area of the receiving phase exposed to the external environment, and it is substance specific.

scholarly journals Optimization of Time-Weighted Average Air Sampling by Solid-Phase Microextraction Fibers Using Finite Element Analysis Software

Molecules ◽  
2018 ◽  
Vol 23 (11) ◽  
pp. 2736 ◽  
Author(s):  
Bulat Kenessov ◽  
Jacek Koziel ◽  
Nassiba Baimatova ◽  
Olga Demyanenko ◽  
Miras Derbissalin
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Solid Phase Microextraction ◽  
Solid Phase ◽  
Weighted Average ◽  
Internal Diameter ◽  
Analysis Software ◽  
Element Analysis ◽  
Time Weighted Average

Determination of time-weighted average (TWA) concentrations of volatile organic compounds (VOCs) in air using solid-phase microextraction (SPME) is advantageous over other sampling techniques, but is often characterized by insufficient accuracies, particularly at longer sampling times. Experimental investigation of this issue and disclosing the origin of the problem is problematic and often not practically feasible due to high uncertainties. This research is aimed at developing the model of the TWA extraction process and optimization of TWA air sampling by SPME using finite element analysis software (COMSOL Multiphysics, Burlington, MA, USA). It was established that sampling by porous SPME coatings with high affinity to analytes is affected by slow diffusion of analytes inside the coating, an increase of their concentrations in the air near the fiber tip due to equilibration, and eventual lower sampling rate. The increase of a fiber retraction depth (Z) resulted in better recoveries. Sampling of studied VOCs using 23 ga Carboxen/polydimethylsiloxane (Car/PDMS) assembly at maximum possible Z (40 mm) was proven to provide more accurate results. Alternative sampling configuration based on 78.5 × 0.75 mm internal diameter SPME liner was proven to provide similar accuracy at improved detection limits. Its modification with the decreased internal diameter from the sampling side should provide even better recoveries. The results obtained can be used to develop a more accurate analytical method for determination of TWA concentrations of VOCs in air using SPME. The developed model can be used to simulate sampling of other environments (process gases, water) by retracted SPME fibers.

Errors in microsphere determination of cardiac output: a computer simulation in fetal sheep

1989 ◽  
Vol 256 (1) ◽  
pp. H302-H310 ◽  
Author(s):  
I. D. Hope ◽  
F. J. Huikeshoven ◽  
R. D. Gilbert ◽  
G. G. Power ◽  
L. D. Longo
Keyword(s):  
Cardiac Output ◽  
Blood Volume ◽  
Weighted Average ◽  
Fetal Sheep ◽  
Artifactual Changes ◽  
Time Weighted Average ◽  
The Moment ◽  
Distribution Of Cardiac Output ◽  
Measured Distribution

Through use of a compartmental model, we simulated the measurement of cardiac output and distribution by means of radioactively labeled microspheres in fetal lambs with weights between 0.5 and 3 kg. A systematic error in measured cardiac output caused by artifactual changes in blood volume caused by the injection and withdrawal of fluids during the procedure was less than 5% for fetal weights greater than or equal to 1 kg but increased for fetal weights less than 1 kg and when hypovolemia was simulated at all fetal weights. Sensitivity analysis disclosed no significant effect of changes in vascular resistance. We examined the effects of recirculation of microspheres and found no significant increase in error in the measured value of cardiac output due to 20% recirculation of all spheres entering a single isolated organ system; however, errors between 7 and 14% were observed with simulations of 20% recirculation in more than one compartment simultaneously. Recirculation also introduced significant errors in the measured distribution of cardiac output in certain cases. The effect on the measured cardiac output of a temporary change in the true cardiac output was dampened by the artifactual blood volume changes mentioned above and the fact that the measurement is a time-weighted average. We also evaluated four different experimental designs. We conclude that the microsphere technique provides a remarkably reliable means of quantifying cardiac output and individual organ flow in the fetus. The nonrandom errors inherent in the procedure examined in this study are of the order of 10%, which is likely to be less than the moment-to-moment variation in the true cardiac output.

Time-Weighted Average SPME Analysis for in Planta Determination of cVOCs

2012 ◽  
Vol 46 (6) ◽  
pp. 3319-3325 ◽  
Author(s):  
Emily M. Sheehan ◽  
Matt A. Limmer ◽  
Philipp Mayer ◽  
Ulrich Gosewinkel Karlson ◽  
Joel G. Burken
Keyword(s):  
Weighted Average ◽  
In Planta ◽  
Time Weighted Average

Fluctuations of Annual Precipitation and Water Resources Quality in Ukraine

2016 ◽  
Vol 10 (4s) ◽  
pp. 621-629
Author(s):  
Valentina Pidlisnyuk ◽  
◽  
John Harrington JR ◽  
Yulia Melnyk ◽  
Yuliya Vystavna ◽  
...  
Keyword(s):  
Water Resources ◽  
Surface Waters ◽  
Precipitation Amount ◽  
Ion Concentration ◽  
Annual Precipitation ◽  
Resource Quality ◽  
Phosphate Ion ◽  
Regional Trends

The article focuses on examining the influence of fluctuations in annual precipitation amount on the quality of surface waters. Water quality was estimated with data on BOD, COD and phosphate–ion concentration within five selected regions of Ukraine. Analysis of the precipitation data (1991 – 2010) showed different regional trends. Using the statistics, determination of the interconnection between precipitation amount and water resources quality were done. The obtained regularities and associated uncertainties can be used for prediction of changes in water resource quality and as a guide for future adaptation to possible climate change.

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