Coefficients Of Variation For Concentrations Research Articles

Urban stormwater microplastic size distribution and impact of subsampling on polymer diversity.

Understanding not only microplastic (MP) concentration but also size distribution, morphology, and polymer profiles is desirable for stormwater, which is an important pathway of entry for MP into the aquatic environment. A challenge is that subsampling is often required for analysis of environmental samples and the impact of subsampling on the stormwater MP concentration determined and the polymer types identified is poorly characterized. To address this, MP were extracted from urban and suburban stormwater, including from green infrastructure. Fourier Transform Infrared microscopy was performed to characterize MP. In addition, particle dimensions and morphology were recorded. Varying the number of 63-250 μm particles subsampled per sample demonstrated the coefficient of variation for concentration (standard deviation/mean) for most samples was <0.3 when 20 particles (0.8-15% of total particles) or <0.2 when 30 particles (1.2-24% of total particles) per sample were analyzed. MP concentrations in the 63-250 μm size class ranged from 15 to 303 MP/L, one to two orders of magnitude greater than observed in previously reported paired samples from the 250-500 or 500-2000 μm size classes. A total of 25 plastic polymer types were observed across samples, more than observed in the large size classes. Spectral signatures of surface oxidation indicative of weathering were observed on most polyethylene, polypropylene, and polystyrene particles, which were the most abundant polymer types. Fragments were the dominant morphology with an average maximum length of 158 ± 92 μm. Overall, these results may help inform subsampling methods and be useful in future exposure assessments for aquatic organisms or design of MP removal technologies for urban and suburban stormwater.

Multi-reagents dispensing centrifugal microfluidics for point-of-care testing

Point-of-care testing (POCT) has shown great advantages for public health monitoring in resource-limited settings. However, developing of POCT tools with automated and accurate quantitative dispensing of multiple reagents and samples is challenging. Here, we demonstrate a novel multi-reagents dispensing centrifugal microfluidics (MDCM) that allows rapid and automated dispensing of multiple reagents and samples with high throughput and accuracy. The MDCM was designed with multiple aliquoting units with the hydrophobic valve at different radial positions. All reagents and samples were loaded simultaneously, dispensed in parallel by centrifugation at low speed, and then introduced into the reaction chamber sequentially by centrifugation at high speed. Two MDCM chips are demonstrated, including a uniform concentration generator and a gradient concentration generator. The concentration coefficient of variation (CV) among the independent reaction chambers was lower than 0.56%, and the theoretical quantitative concentration gradient was strongly correlated with the actual concentration gradient (R2 = 0.9938). We have successfully applied the MDCM to loop-mediated isothermal amplification (LAMP)-based nucleic acid detection for multiple infectious pathogens and antimicrobial susceptibility testing (AST) for kanamycin sulfate against E. coli. To further extend the applications, the MDCM has also been applied to bicinchoninic acid (BCA) protein assays with online calibration, reducing the detection time from 2 h to 10 min with a twenty-fold reduction in reagent consumption. These results indicated that the MDCM is a high potential platform for POCT.

A Theoretical Study about Ergodicity Issues in Predicting Contaminant Plume Evolution in Aquifers

A large-time Eulerian–Lagrangian stochastic approach is employed to: (1) estimate centroid position uncertainty of contaminant plumes that originate from instantaneous point sources in statistically stationary and isotropic porous formations; (2) assess the time needed for achieving ergodic conditions, which would allow for the evaluation of local concentration values based on the only ensemble mean distribution; (3) derive the concentration coefficient of variation (CV) as a function of asymptotic macro-dispersion coefficients and centroid trajectory variances. The results indicate that the decay time of plume position uncertainty is so large that there is practically no chance for effective ergodicity. The concentration coefficient of variation is zero at the centroid but rapidly increases when moving away from it. The dissipative effect of local dispersion in the presence of relatively high Péclet numbers is considerably exalted by marked flow field heterogeneity, which confirms the previously postulated synergic, non-additive effect of advection and local dispersion in passive solute dilution. A further result from this study is the derivation of the power law that relates dimensionless concentration micro-scale to dimensionless local dispersive area. The exponent of this power law is the same that appears in the relationship between dimensionless Kolmogorov turbulent micro-scale and flow Reynolds number.

Evaluating concentration estimation errors in ELISA microarray experiments

BackgroundEnzyme-linked immunosorbent assay (ELISA) is a standard immunoassay to estimate a protein's concentration in a sample. Deploying ELISA in a microarray format permits simultaneous estimation of the concentrations of numerous proteins in a small sample. These estimates, however, are uncertain due to processing error and biological variability. Evaluating estimation error is critical to interpreting biological significance and improving the ELISA microarray process. Estimation error evaluation must be automated to realize a reliable high-throughput ELISA microarray system.In this paper, we present a statistical method based on propagation of error to evaluate concentration estimation errors in the ELISA microarray process. Although propagation of error is central to this method and the focus of this paper, it is most effective only when comparable data are available. Therefore, we briefly discuss the roles of experimental design, data screening, normalization, and statistical diagnostics when evaluating ELISA microarray concentration estimation errors.ResultsWe use an ELISA microarray investigation of breast cancer biomarkers to illustrate the evaluation of concentration estimation errors. The illustration begins with a description of the design and resulting data, followed by a brief discussion of data screening and normalization. In our illustration, we fit a standard curve to the screened and normalized data, review the modeling diagnostics, and apply propagation of error.We summarize the results with a simple, three-panel diagnostic visualization featuring a scatterplot of the standard data with logistic standard curve and 95% confidence intervals, an annotated histogram of sample measurements, and a plot of the 95% concentration coefficient of variation, or relative error, as a function of concentration.ConclusionsThis statistical method should be of value in the rapid evaluation and quality control of high-throughput ELISA microarray analyses. Applying propagation of error to a variety of ELISA microarray concentration estimation models is straightforward. Displaying the results in the three-panel layout succinctly summarizes both the standard and sample data while providing an informative critique of applicability of the fitted model, the uncertainty in concentration estimates, and the quality of both the experiment and the ELISA microarray process.

Amino acid release in the rat oral pontine reticular nucleus across various vigilance states

To understand the mechanisms determining states of vigilance, we investigated the dynamics of extracellular amino acids from the oral pontine reticular nucleus in five freely moving rats by using a microdialysis technique. Samples were collected at 1-min intervals for 70 min and measured by using high-performance liquid chromatography with an electrochemical detector. The glycine level fluctuated remarkably over the time-course, and the concentration coefficient of variation in the 70 samples was significantly higher than that of glutamate and glutamine. This fluctuation on a minute-by-minute basis tended to be more obvious during the vigilance state transition periods. This fluctuation of the extracellular glycine level could influence local neuronal activity.

Transport of a Passive Scalar in a Stratified Porous Medium

A uniform and horizontal head gradient J is applied to a stratified formation whose given random conductivity K is function of the vertical coordinate x 3 only. K is assumed to be stationary and of finite integral scale I v. By Darcy's law, the velocity field V 1(x 3)=JK depicts a fluctuating shear flow. A solute body is injected instantaneously in the formation. In a Lagrangean framework, the second spatial moment of the mean concentration 〈C(x,t)〉 can be related to the one-particle trajectories variance X 11(t,Pe) where Pe = 〈V1〉Iv/D dT and dT is the transverse pore-scale dispersion coefficient. X 11 was determined in the past by Matheron and de Marsily (1980). The present study is concerned with determining the local concentration variance σ C 2 , that depends on the two-particles trajectories covariance Z 11(t). The latter is derived exactly and langle Crangle and σ C 2 are determined by assuming normal or lognormal probability distribution of trajectories. The results are illustrated for small and very large (ergodic) solute plumes. For large travel time the concentration coefficient of variation at the center of the plume tends asymptotically to a constant value, unlike formations with finite horizontal correlation length of the hydraulic conductivity. The results may serve for benchmarking of numerical codes and in applications for short travel distances in highly anisotropic formations.

A sensitive diffusion sampler for the determination of volatile organic compounds in ambient air

We developed a diffusive sampling device (DSD-voc) for volatile organic compounds (VOCs) which is suitable for collection of low level VOCs and analysis with thermal desorption. This sampling device is composed of two parts, an exposure part made of a porous polytetrafluoroethylene (PTFE) filter, and an analysis part made of stainless-steel tubing. The DSD-voc collects VOCs through the mechanism of molecular diffusion. Collection is controlled by moving the adsorbent from the exposure part to the analysis part by changing the posture of the DSD-voc. Adsorbates in the DSD-voc were analyzed by GC/MS with a thermal desorption cold trap injector (TCT). The TCT has the advantage of being able to accept the entire quantity of VOCs. We connected a condenser between the DSD-voc and the trap tube to prevent moisture from freezing in the trap tube when the sampler was packed with strong adsorbent. We also examined the desorption efficiency for VOCs from several types of adsorbents (Carboxen TM 1000, Carbosieve TM G, Carbosieve S III, Carbotrap TM B, and activated carbon) over a wide range of temperatures. Carboxen 1000 was suitable for the determination of VOCs with a low boiling point range, from CFC12 to hexane, while Carbotrap B was suitable for VOCs from hexane to 1,4-dichlorobenzene. The limits of detection with Carboxen 1000 and Carbotrap B were 0.036–0.046 and 0.0035–0.014 ppb, respectively, for a sampling duration of 24 h. Coefficients of variation for concentrations of major VOCs ranged from 3.8 to 14%. It is possible to estimate atmospheric VOCs at sub-parts per billion (sub-ppb), with high sensitivity, by using both adsorbents in combination.

A review of the use of fentanyl analgesia in the management of acute pain in adults.

A review of the use of fentanyl analgesia in the management of acute pain in adults.

The influence of pore‐scale dispersion on concentration statistical moments in transport through heterogeneous aquifers

Transport of an inert solute in a heterogeneous aquifer is governed by two mechanisms: advection by the random velocity field V(x) and pore‐scale dispersion of coefficients Ddij. The velocity field is assumed to be stationary and of constant mean U and of correlation scale I much larger than the pore‐scale d. It is assumed that Ddij=αdijU are constant. The relative effect of the two mechanisms is quantified by the Peclet numbers Peij=U/Ddij=I/αdij, which as a rule are much larger than unity. The main aim of the study is to determine the impact of finite, though high, Pe on 〈C〉 and σC2, the concentration mean and variance, respectively. The solution, derived in the past, for Pe=∞ is reconsidered first. By assuming a normal X probability density function (p.d.f.), closed form solutions are obtained for 〈C〉 and σC2. Recasting the problem in an Eulerian framework leads to the same results if certain closure conditions are adopted. The concentration moments for a finite Pe are derived subsequently in a Lagrangean framework. The pore‐scale dispersion is viewed as a Brownian motion type of displacement Xd of solute subparticles, of scale smaller than d, added to the advective displacements X. By adopting again a normal p.d.f. for the latter, explicit expressions for 〈C〉 and σC2 are obtained in terms of quadratures over the joint p.d.f. of advective two particles trajectories. While the influence of high Pe on 〈C〉 is generally small, it has a significant impact on σC2. Simple results are obtained for a small V0, for which trajectories are fully correlated. In particular, the concentration coefficient of variation at the center tends to a constant value for large time. Comparison of the present solution, obtained in terms of a quadrature, with the Monte Carlo simulations of Graham and McLaughlin [1989] shows a very good agreement.

Stochastic analysis of solute transport in heterogeneous, variably saturated soils

Statistical moments of solute plumes from small sources in variably saturated, heterogeneous porous media are analyzed by using a newly developed, efficient high‐resolution Monte Carlo technique. In agreement with previous theoretical work, it is illustrated that the prediction of such solute plumes is associated with large uncertainties for dimensionless travel times, t′, exceeding 40, particularly predictions of plumes in highly heterogeneous soils (σy2&gt;2). Uncertainty about the travel path of the plume center contributes significantly to overall concentration uncertainty as flux fields become more variable. It is shown that the concentration coefficient of variation at the center of the plume initially increases but stagnates or decreases at later times. For highly heterogeneous soil flux conditions or for the common case of soils with strongly anisotropic conditions, analytical models underestimate transverse spreading of the mean concentration plume at any given time, while overestimating longitudinal spreading. At identical mean plume displacement distances, analytical models underestimate both transverse and longitudinal spreading and overestimate the variance of solute flux (breakthrough curve) by up to a factor 4. As an alternative to the statistical analysis of solute flux, we propose to analyze statistical properties of time associated with peak solute flux and with first exceedance of a given solute flux level.

High-performance liquid chromatographic determination of a potent and selective HIV protease inhibitor (L-735,524) in rat, dog and monkey plasma

A high-performance liquid chromatographic method coupled with liquid-liquid sample extraction and ultraviolet detection has been developed for the quantification of L-735,524 (I), a potent, highly selective and orally bioavailable inhibitor of recombinant human immundefficiency virus (HIV) protease in rat, dog and monkey plasma. The present method is reproducible and reliable with limits of quantification of 25, 12.5 and 6.25 ng/ml, respectively for rat, dog and monkey plasma. The standard curve was linear over the range of 6.25–2000 ng/ml in the biological fluid. The mean coefficients of variation for concentration within the range of standard curve were 7.94, 6.91 and 4.52%, respectively, for intra-day analysis and 5.58, 9.27 and 5.45%, respectively, for inter-day analysis. The recoveries of I and L-707,943 (II), an analog of I used as the internal standard, from plasma samples were all over 88% through the extraction procedure. I and I are stable in mobile phase over a 48-h period while waiting for injection at ambient temperature and over a 144-h period in rat, dog and monkey plasma while stored at −20°C. Aqueous solubility of I is pH dependent, 60 mg/ml at pH 3.5 and 0.3 mg/ml at pH 4.8. The analytic procedures described in this report have been successfully employed to quantify the concentration of I in rat, dog and monkey plasma and provide the kinetic information for toxicological and pharmacological studies.

Internal quality control of semen analysis

ObjectiveTo test a scheme for quality control of semen analysis. DesignThe reproducibility of assessment of sperm concentration, motility, and morphology was obtained for the same sample measured by different technicians (between or intertechnician variation) and for different samples assessed by each technician with time (within or intratechnician variation). SettingAndrology Laboratory. PatientsSemen samples were analyzed from all patients attending the clinic. InterventionsNone. Main Outcome MeasuresWithin technician and between technician coefficients of variation for concentration, motility, and morphology. ResultsWhen 100 sperm were routinely assessed, both intratechnician variation, as assessed from the precision of duplicate measurements, and intertechnician variation revealed hyperbolic curves with increasing variation at low percentages (<20) of motile or morphological forms. When these low values were excluded, mean intratechnician variations were 5.0%, 8.4%, and 2.8% for concentration, motility, and morphology, respectively, and mean intertechnician variations were, respectively, 6.1%, 5.6%, and 5.6%. Similar mean intertechnician variation for morphology was obtained for repeated assessment of prestained (7.3%) or presmeared (5.9%) slides. The use of cryopreserved semen to monitor longitudinal changes in the technicians’ assessments revealed variations of 8.1% to 12% in concentration and 9.7% to 14% in motility. Computing the monthly means for sperm concentration, motility, and morphology over a 4.5-year period revealed a marked reduction in percentage of normal morphological forms, unrelated to the sperm count or mean age of the men attending the clinic. This was shown to be a result of a shift in the assessment by technicians. ConclusionsQuality control is necessary and possible in an andrology clinic.

Quantitation of a new cholecystokinin and gastrin receptor antagonist (L-365,260) in dog and rat plasma by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) procedure has been developed for the quantification of L-365,260 (I), a cholecystokinin and gastrin receptor antagonist, in dog and rat plasma. The method involves liquid—liquid extraction and HPLC with ultraviolet detection. Standard curves were linear over the range 7.5–2000 ng/ml for rat and dog plasma. The method is reproducible and reliable with a detection limit of 7.5 ng/ml in biological fluids. The mean coefficients of variation for concentrations within the range of the standard curve range were 3.84 and 2.56%, respectively, for intra-day analysis and 4.48 and 4.26%, respectively, for inter-day analysis. Application of the development was successfully demonstrated by quantifying the concentration of I in both dog and rat plasma samples following an intravenous or oral dose of 5 mg/kg I.

Determination of Zearalenone and Related Metabolites in Porcine Urine by Modified Enzyme-Linked Immunosorbent Assay

A direct competitive enzyme-linked immunosorbent assay (ELISA) was modified for the determination of zearalenone and zearalenois in porcine urine. In the modified procedure, standard or unknown concentrations of zearalenone were added to all wells, followed by rapid addition of zearalenone-horseradish peroxidase conjugate, whereas in previous methods, zearalenone and zearalenone-horseradish peroxidase were mixed and then added to microtiter wells. The modification increased the number of urine samples that could be analyzed per assay. The linear portion of the modified ELISA standard curve covered the range of 10-500 ng zearalenone/mL. Average recovery of zearalenone from spiked urine was 91, 101, 95, 107, 136, 112, and 120% for 1, 10, 25, 50, 100, 250, and 500 ng zearalenone/mL urine, respectively. Mean within-assay coefficient of variation for each concentration of zearalenone in 5 standard curves was 5.95%. Between-assay coefficients of variation for concentrations of zearalenone equivalents in lower and upper regions of the standard curve were 10.9% (n = 18) and 8.8% (n = 20), respectively. Analysis of urine samples showed that a gilt excreted 5.3% of ingested zearalenone in the 8 h following ingestion, with an average excretion rate of about 100 micrograms zearalenone equivalents/h.

Determination of trazodone in serum by instrumental thin-layer chromatography.

A simple and specific method for trazodone that uses high-performance thin-layer chromatography (TLC) plates for chromatography and the Camag TLC Scanner for fluorescence-reflectance measurements is described. The quantitative method employs quinidine as an internal standard and the calibration line is linear between 0.2 and 2.0 mg/L serum, the usual range encountered in patients treated with the drug. Replicate analyses of single serum specimens demonstrated reproducibility of better than +/- 3% coefficient of variation for concentrations of trazodone in the midrange of the test line.

An enzyme-linked immunosorbent assay (ELISA) for PBS Z1, a defective phage of Bacillus subtilis.

The sensitivity, reproducibility and specificity of an enzyme-linked immunosorbent assay (ELISA) for the defective phage PBS Z1 of Bacillus subtilis have been investigated. It was shown that phages in concentrations between 10(8) and 2.5 X 10(10) particles/ml could be assayed with this method. The coefficient of variation for concentrations between 5 X 10(8) and 5 X 10(9) particles/ml was approx. 10%. From some other Bacillus phages tested, only the defective phages resembling PBS Z1 in morphology were detected efficiently with the ELISA for PBS Z1. A comparison is made between ELISA and other assays for PBS Z1.