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

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.

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 Treatment of thoracolumbar burst fractures: extended follow-up of a randomized clinical trial comparing orthosis versus no orthosis

2017 ◽  
Vol 27 (1) ◽  
pp. 42-47 ◽  
Author(s):  
Jennifer C. Urquhart ◽  
Osama A. Alrehaili ◽  
Charles G. Fisher ◽  
Alyssa Fleming ◽  
Parham Rasoulinejad ◽  
...  
Keyword(s):  
Outcome Measures ◽  
Weighted Average ◽  
Average Treatment Effect ◽  
Secondary Outcome ◽  
Thoracolumbar Burst Fractures ◽  
Treatment Comparison ◽  
Average Treatment ◽  
Burst Fractures ◽  
Time Weighted Average

OBJECTIVEA multicenter, prospective, randomized equivalence trial comparing a thoracolumbosacral orthosis (TLSO) to no orthosis (NO) in the treatment of acute AO Type A3 thoracolumbar burst fractures was recently conducted and demonstrated that the two treatments following an otherwise similar management protocol are equivalent at 3 months postinjury. The purpose of the present study was to determine whether there was a difference in long-term clinical and radiographic outcomes between the patients treated with and those treated without a TLSO. Here, the authors present the 5- to 10-year outcomes (mean follow-up 7.9 ± 1.1 years) of the patients at a single site from the original multicenter trial.METHODSBetween July 2002 and January 2009, a total of 96 subjects were enrolled in the primary trial and randomized to two groups: TLSO or NO. Subjects were enrolled if they had an AO Type A3 burst fracture between T-10 and L-3 within the previous 72 hours, kyphotic deformity < 35°, no neurological deficit, and an age of 16–60 years old. The present study represents a subset of those patients: 16 in the TLSO group and 20 in the NO group. The primary outcome measure was the Roland Morris Disability Questionnaire (RMDQ) score at the last 5- to 10-year follow-up. Secondary outcome measures included kyphosis, satisfaction, the Numeric Rating Scale for back pain, and the 12-Item Short-Form Health Survey (SF-12) Mental and Physical Component Summary (MCS and PCS) scores. In the original study, outcome measures were administered at admission and 2 and 6 weeks, 3 and 6 months, and 1 and 2 years after injury; in the present extended follow-up study, the outcome measures were administered 5–10 years postinjury. Treatment comparison between patients in the TLSO group and those in the NO group was performed at the latest available follow-up, and the time-weighted average treatment effect was determined using a mixed-effects model of longitudinal regression for repeated measures averaged over all time periods. Missing data were assumed to be missing at random and were replaced with a set of plausible values derived using a multiple imputation procedure.RESULTSThe RMDQ score at 5–10 years postinjury was 3.6 ± 0.9 (mean ± SE) for the TLSO group and 4.8 ± 1.5 for the NO group (p = 0.486, 95% CI −2.3 to 4.8). Average kyphosis was 18.3° ± 2.2° for the TLSO group and 18.6° ± 3.8° for the NO group (p = 0.934, 95% CI −7.8 to 8.5). No differences were found between the NO and TLSO groups with time-weighted average treatment effects for RMDQ 1.9 (95% CI −1.5 to 5.2), for PCS −2.5 (95% CI −7.9 to 3.0), for MCS −1.2 (95% CI −6.7 to 4.2) and for average pain 0.9 (95% CI −0.5 to 2.2).CONCLUSIONSCompared with patients treated with a TLSO, patients treated using early mobilization without orthosis maintain similar pain relief and improvement in function for 5–10 years.

scholarly journals In Planta Determination of the mRNA-Binding Proteome of Arabidopsis Etiolated Seedlings

2016 ◽  
Vol 28 (10) ◽  
pp. 2435-2452 ◽  
Author(s):  
Marlene Reichel ◽  
Yalin Liao ◽  
Mandy Rettel ◽  
Chikako Ragan ◽  
Maurits Evers ◽  
...  
Keyword(s):  
In Planta ◽  
Etiolated Seedlings ◽  
Mrna Binding

scholarly journals Exposure to Ultrafine Particles in the Ferroalloy Industry Using a Logbook Method

Nanomaterials ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2546
Author(s):  
Rikke Bramming Jørgensen ◽  
Ida Teresia Kero ◽  
Aleksander Blom ◽  
Esten Eide Grove ◽  
Kristin von Hirsch Svendsen
Keyword(s):  
Exposure Assessment ◽  
Ultrafine Particles ◽  
Weighted Average ◽  
Average Concentration ◽  
Respirable Particles ◽  
Exposure Estimation ◽  
Close Proximity ◽  
Personal Sampling ◽  
Time Weighted Average ◽  
Stationary Sampling

Background: It is difficult to assess workers’ exposure to ultrafine particles (UFP) due to the lack of personal sampling equipment available for this particle fraction. The logbook method has been proposed as a general method for exposure assessment. This method measures the time and concentration components of the time-weighted average concentration separately and could be suitable for investigation of UFP exposure. Objectives: In this study, we have assessed workers’ exposure to UFP in a ferrosilicon plant. The main tasks of the furnace workers were identified, and the logbook method was used in combination with stationary measurements of UFP taken as close to the identified task areas as possible. In order to verify the results, respirable particles were collected using stationary sampling in close proximity to the UFP measuring instrument, and personal full-shift sampling of respirable particles was performed simultaneously. Thus, exposure to respirable particles determined using the logbook method could be compared to the results of standard measurement. Methods: The particle number concentration of ultrafine particles was determined using a NanoScan SMPS. Respirable particle concentration and exposure were determined using a sampling train consisting of a pump, filter, filter cassettes, and SKC Cyclone for the respirable fraction. Attendance times for workers at each work location were registered via thorough observations made by the research team. Results: The logbook method for exposure estimation based on stationary sampling equipment made it possible to calculate UFP exposure for workers operating the furnaces at a ferrosilicon plant. The mid-size furnace and the large furnace were evaluated separately. The workers operating the largest furnace were exposed to 1.47 × 104 particles/cm3, while workers operating the mid-size furnace were exposed to 2.06 × 104 particles/cm3, with a mean of 1.74 × 104 particles/cm3. Substantial contributions from the casting area, ladle transport corridor, and both tapping areas were made. Exposure to respirable particles was 2.04 mg/m3 (logbook); 2.26 mg/m3 (personal sampling) for workers operating the large-sized furnace, 3.24 mg/m3 (logbook); 2.44 mg/m3 (personal sampling) for workers operating the medium-sized furnace, and 2.57 mg/m3 (logbook); 2.53 mg/m3(personal sampling) on average of all tappers. The average ratio of these two methods’ results was 1.02, which indicates that the logbook method could be used as a substitute for personal sampling when it is not possible to perform personal sampling, at least within this industry. Conclusions: The logbook method is a useful supplement for exposure assessment of UFP, able to identify the most polluted areas of the workplace and the contribution of different work tasks to the total exposure of workers, enabling companies to take action to reduce exposure.

Evaluation of a simple, inexpensive, in situ sampler for measuring time-weighted average concentrations of suspended sediment in rivers and streams

2019 ◽  
Vol 33 (5) ◽  
pp. 678-686 ◽  
Author(s):  
Nicholas J.C. Doriean ◽  
Peter R. Teasdale ◽  
David T. Welsh ◽  
Andrew P. Brooks ◽  
William W. Bennett
Keyword(s):  
Suspended Sediment ◽  
Weighted Average ◽  
Measuring Time ◽  
Rivers And Streams ◽  
Time Weighted Average
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