Chemical Concentration Measurements Research Articles

Portable digital lock-in instrument to determine chemical constituents with single-color absorption measurements for Global Health Initiatives

Innovations in international health require the use of state-of-the-art technology to enable clinical chemistry for diagnostics of bodily fluids. We propose the implementation of a portable and affordable lock-in amplifier-based instrument that employs digital technology to perform biochemical diagnostics on blood, urine, and other fluids. The digital instrument is composed of light source and optoelectronic sensor, lock-in detection electronics, microcontroller unit, and user interface components working with either power supply or batteries. The instrument performs lock-in detection provided that three conditions are met. First, the optoelectronic signal of interest needs be encoded in the envelope of an amplitude-modulated waveform. Second, the reference signal required in the demodulation channel has to be frequency and phase locked with respect to the optoelectronic carrier signal. Third, the reference signal should be conditioned appropriately. We present three approaches to condition the signal appropriately: high-pass filtering the reference signal, precise offset tuning the reference level by low-pass filtering, and by using a voltage divider network. We assess the performance of the lock-in instrument by comparing it to a benchmark device and by determining protein concentration with single-color absorption measurements. We validate the concentration values obtained with the proposed instrument using chemical concentration measurements. Finally, we demonstrate that accurate retrieval of phase information can be achieved by using the same instrument.

Continuous-wave cavity ring-down evanescent-field sensing with a broadband source based on frequency-shifted interferometry

We demonstrate that all-fiber cavity ring-down (CRD) evanescent-field sensing can be performed using frequency-shifted interferometry (FSI). In contrast to conventional CRD schemes, without the need for any optical pulse or fast electronics, this FSI–CRD technique allows one to monitor the intensity decay of a continuous lightwave traveling inside a fiber loop ring-down cavity (RDC), from which the cavity loss information can be deduced. By incorporating a fiber taper as the sensing element inside a RDC, we carried out FSI–CRD experiments with an amplified spontaneous emission source, an acousto-optic modulator, and a slow detector, successfully applying the technique to the measurement of chemical solution concentration based on absorption, solution refractive index change, or a combination of both. A minimum detectable 1-octyne concentration of 0.29% (or 0.020M) was achieved in decane, while refractive index sensitivity of 1dB/RIU with a measurement error of 1×10−4dB was attained in sodium chloride solutions (NaCl in water). The 1-octyne detection limit is better than previously reported values measured by conventional fiber-based CRD techniques.

Duration of Greenland Stadial 22 and ice-gas Δage from counting of annual layers in Greenland NGRIP ice core

Abstract. High-resolution measurements of chemical impurities and methane concentrations in Greenland ice core samples from the early glacial period allow the extension of annual-layer counted chronologies and the improvement of gas age-ice age difference (Δage) essential to the synchronization of ice core records. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses in order to constrain the duration of the Greenland Stadial 22 (GS-22) between Greenland Interstadials (GIs) 21 and 22, for which inconsistent durations and ages have been reported from Greenland and Antarctic ice core records as well as European speleothems. Depending on the chronology used, GS-22 occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21). From annual layer counting, we find that GS-22 lasted between 2696 and 3092 years and was followed by a GI-21 pre-cursor event lasting between 331 and 369 yr. Our layer-based counting agrees with the duration of stadial 22 as determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr) or an alternative chronology based on gas-marker synchronization to EPICA Dronning Maud Land ice core. These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the possible ranges of NorthGRIP Δdepth (5.49 to 5.85 m) and Δage (498 to 601 yr) at the warming onset of GI-21 as well as the Δage range at the onset of the GI-21 precursor warming (523 to 654 yr), observing that temperature (represented by the δ15N proxy) increases before CH4 concentration by no more than a few decades.

Odour Impact Assessment in Industrial Areas

Odours emitted by multi-source facilities, like industrial complexes, have become a major concern for local authorities because the resulting annoyance in the neighbourhood is generally high compex compared to a single source one. In the case of such multi-source odour emissions especially, common chemical analyses or odour concentration measurement methods are not often applicable.This paper describes the methodology adopted for assessing the odour impact on the industrial area of the city of Salerno (Italy), caused by the co-presence of two strategic plants: wastewater treatment plant and composting plant of organic fraction of solid waste. The combination of olfactometric analyses and dispersion modelling allowed both the quantification of the odour emissions and the evaluation of their potential impact on the surrounding areas. Odour impact criteria, input parameters and emissive rate were evaluated. Results discuss and compare different emissive scenarios to assessment odour impacts in the industrial area.

Hydrogen-Peroxide-Enhanced Nonthermal Plasma Effluent for Biomedical Applications

A novel nonthermal plasma dielectric-barrier discharge (DBD) system for decontamination, sterilization, and medical applications has been developed. The discharge is physically removed from the disinfection zone, and plasma-induced free radicals are delivered through an air stream. The physical distance between the discharge and the treatment surface can be up to 3 m, making the technology robust and flexible for applications in the medical clinic. The bactericidal properties of the free-radical effluent are enhanced by hydrogen peroxide additives. We report a 6-log reduction in Staphylococcus aureus and Pseudomonas aeruginosa bacteria strains in under 1 min of exposure in vitro and inactivation of Bacillus atrophaes spores and Escherichia coli biofilms. The concentration of hydrogen peroxide additives is seen to be a key variable in inactivation efficacy, suggesting that active species in our experiment may be different than in other DBD configurations. Precise chemical concentration measurements using direct frequency comb spectroscopy show presence of ozone ( O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ), hydrogen peroxide (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), nitrous oxide (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O), and nitrogen dioxide (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). In vivo multiple exposures of mouse skin to the plasma effluent do not yield any adverse effects.

Variations in time and space of trace metal aerosol concentrations in urban areas and their surroundings

Abstract. Using an unprecedentedly large geochemical database, we compare temporal and spatial variations in inhalable trace metal background concentrations in a major city (Barcelona, Spain) and at a nearby mountainous site (Montseny) affected by the urban plume. Both sites are contaminated by technogenic metals, with V, Pb, Cu, Zn, Mn, Sn, Bi, Sb and Cd all showing upper continental crust (UCC) normalised values &gt;1 in broadly increasing order. The highest metal concentrations usually occur during winter at Barcelona and summer in Montseny. This seasonal difference was especially marked at the remote mountain site in several elements such as Ti and Rare Earth Elements, which recorded campaign maxima, exceeding PM10 concentrations seen in Barcelona. The most common metals were Zn, Ti, Cu, Mn, Pb and V. Both V and Ni show highest concentrations in summer, and preferentially fractionate into the finest PM sizes (PM1/PM10 &gt; 0.5) especially in Barcelona, this being attributed to regionally dispersed contamination from fuel oil combustion point sources. Within the city, hourly metal concentrations are controlled either by traffic (rush hour double peak for Cu, Sb, Sn, Ba) or industrial plumes (morning peak of Ni, Mn, Cr generated outside the city overnight), whereas at Montseny metal concentrations rise during the morning to a single, prolonged afternoon peak as contaminated air transported by the sea breeze moves into the mountains. Our exceptional database, which includes hourly measurements of chemical concentrations, demonstrates in more detail than previous studies the spatial and temporal variability of urban pollution by trace metals in a given city. Technogenic metalliferous aerosols are commonly fine in size and therefore potentially bioavailable, emphasising the case for basing urban background PM characterisation not only on physical parameters such as mass but also on sample chemistry and with special emphasis on trace metal content.

Groundwater quality assessment of one former industrial site in Belgium using a TRIAD-like approach

Contaminated industrial sites are important sources of pollution and may result in ecotoxicological effects on terrestrial, aquatic and groundwater ecosystems. An effect-based approach to evaluate and assess pollution-induced degradation due to contaminated groundwater was carried out in this study. The new concept, referred to as “Groundwater Quality TRIAD-like” (GwQT) approach, is adapted from classical TRIAD approaches. GwQT is based on measurements of chemical concentrations, laboratory toxicity tests and physico-chemical analyses. These components are combined in the GwQT using qualitative and quantitative (using zero to one subindices) integration approaches. The TRIAD approach is applied for the first time on groundwater from one former industrial site located in Belgium. This approach will allow the classification of sites into categories according to the degree of contaminant-induced degradation. This new concept is a starting point for groundwater characterization and is open for improvement and adjustment.

Chemical sensor resolution requirements for near-surface measurements of turbulent fluxes

Abstract. Businger and Delany (1990) presented an approach to estimate the sensor resolution required to limit the contribution of the uncertainty in the chemical concentration measurement to uncertainty in the flux measurement to 10 % for eddy covariance, gradient, and relaxed eddy accumulation flux measurement methods. We describe an improvement to their approach to estimate required sensor resolution for the covariance method, and include disjunct eddy covariance. In addition, we provide data to support selection of a form for the dimensionless scalar standard deviation similarity function based on observations of the variance of water vapor fluctuations from recent field experiments. We also redefine the atmospheric parameter of Businger and Delany in a more convenient, dimensionless form. We introduce a "chemical parameter" based on transfer velocity parameterizations. Finally, we provide examples in which the approach is applied to measurement of carbon dioxide, dimethylsulfide, and hexachlorobenzene fluxes over water. The information provided here will be useful to plan field measurements of atmosphere-surface exchange fluxes of trace gases.

Coating-by-parts method for experimental study of internal mechanisms of water gas shift fuel processor

An innovative coating-by-parts (CBP) sampling method is proposed to improve the experimental study of water gas shift (WGS) systems used in systems in packed-bed and monolithic reactors. The CBP method enables detailed measurements of chemical species concentrations and operating conditions inside a reactor. Chemical kinetics-coupled CFD model has been set up for simulation to evaluate the performance of CBP. The model was first validated by the experimental data and subsequently run for multiple cases to simulate the use of CBP. The results show that the CBP method has an acceptable accuracy in packed-bed reactor and monolithic reactors. Meanwhile, another commonly used experimental method, namely, the central line sampling method, is found to achieve a high accuracy in the monolithic reactor, but a lower accuracy in the packed-bed reactor with low inlet velocity and packed by larger pellets. Copyright © 2010 John Wiley & Sons, Ltd.

Chemical Sensing Using Fiber Cavity Ring-Down Spectroscopy

Waveguide-based cavity ring-down spectroscopy (CRD) can be used for quantitative measurements of chemical concentrations in small amounts of liquid, in gases or in films. The change in ring-down time can be correlated to analyte concentration when using fiber optic sensing elements that change their attenuation in dependence of either sample absorption or refractive index. Two types of fiber cavities, i.e., fiber loops and fiber strands containing reflective elements, are distinguished. Both types of cavities were coupled to a variety of chemical sensor elements, which are discussed and compared.

Attenuated total reflection Fourier transform infrared spectroscopy for on-chip monitoring of solute concentrations

We report a cost-efficient Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) method for monitoring concentrations of solutes in solutions flowing through microfluidic channels. The method allows rapid acquisition of spectra and enables chemical characterisation and concentration measurements that are independent of the flow rate of liquids. The method enables independent measurement of concentrations of solutes with distinct spectral features in mixed solutions. For the polymer solutes studied in the present work, the method has a sensitivity of at least 10 microM (0.01 wt%). We also propose the applicability of the method for the differentiation between dissolved and adsorbed amphiphilic species.

Experimental study of chemical concentration variation of ASP flooding

A physical modeling system of long slim tube was established. Several pressure measuring and sampling points were laid out at different positions along the tube. Through real-time measurements of pressures and chemical concentrations at different points, the mass transfer and chemical concentration of ASP flooding in porous media are studied. The concentration of chemicals declines gradually during the fluid flow from the inlet to the outlet of the model. The concentration increases in the front edge of the slug faster than the concentration decreases in the rear edge of the slug. The concentration variation of the chemicals is an asymmetrical and offset process. The order of motion velocities of the chemicals from fast to slow is polymer, alkali and surfactant. The motion lag and comprehensive diffusion are strong in the vicinity of the inlet, the motion velocities of the chemicals are high, the difference of flow velocities among the three chemicals is significant and the chromatographic separation of the chemicals is obvious. In the area near the outlet, the comprehensive diffusion and motion lag become weak, the concentrations of the chemicals decrease, the motion velocities of the chemicals are slow, the difference among the motion velocities of the chemicals becomes small, the chromatographic separation is not obvious, the adsorption and retention of chemicals gradually increase as the chemical slug moves further along the tube, the adsorption and retention of polymer is the most serious.

A Wireless, Passive pH Sensor Based on Magnetic Higher-Order Harmonic Fields

A wireless, passive sensor was fabricated for remote monitoring of chemical analytes in the human body. The sensor was made of a magnetically soft film (sensing element) and a permanent magnetic film (biasing element) sandwiching a reversibly swelling hydrogel. When subjected to a low frequency magnetic AC field, the sensing element generated higher-order harmonic magnetic fields that were detected with a remotely located detection coil. In the presence of a DC magnetic field (biasing field), such as that generated from the biasing element, the pattern of the higher-order harmonic magnetic fields varied, and the magnitude of change (referred to as the harmonic field shift) was proportional to the strength of the biasing field. The hydrogel, which acted as a transducer that converted variations in the chemical concentration into changes in dimensions, physically varied the separation distance between the sensing and the biasing elements. This causes a change in the magnitude of biasing field experienced by the sensing element, thus changing its higher-order harmonic field shift allowing remote measurement of chemical concentrations. The novelty of this sensor was its wireless and passive nature, which allows it to be used inside a human body for long term chemical monitoring. A scaled-up prototype was fabricated and tested to demonstrate the pH monitoring capability of the sensor. The main structure of the prototype sensor was a polycarbonate substrate containing a larger rectangular well of 36mm×8mm×4mm on top of a smaller well of 30mm×5mm×2mm (see Fig. 1). The smaller well was filled with hydrogel made of (poly)vinyl alcohol and (poly)acrylic acid. A commercial magnetoelastic thick film, Metglas 2826MB from Metglas Inc., was attached to the step at the bottom of the larger well and allowed to rest on the hydrogel. The DC magnetic field was provided by an Arnokrome III film (Arnold Magnetic Technologies) of 30mm×6mm attached at the bottom of the sensor structure. The sensor was placed on the detection coil, and its response was measured with a spectrum analyzer while exposed to test solutions of varying pH. The sensor's harmonic field shift, when cycled between pH 7 and pH 3, was measured and plotted in Fig. 2. As shown in the figure, the hydrogel swelled when the sensor was exposed to pH 3, decreasing the harmonic field shift. The response and recovery times of the hydrogel were below 2 minutes. This experiment proves the feasibility of the technology for real-time, remote monitoring of pH. Further work includes improving the response time and sensitivity of the hydrogel, as well as miniaturization of the sensor.

Biomarkers of exposure to combustion by-products in a human population in Shanxi, China

Emissions of complex mixtures of polycyclic aromatic hydrocarbons (PAHs) and other compounds into the environment represent a potential threat to the health of humans. Information regarding the dose and duration of exposure is essential to determine the degree of risk and to identify sensitive receptors within a population. Although measurements of chemical concentrations in air may be used to estimate exposures, internal biomarkers provide more accurate information regarding the dose of exposure and retention of toxic chemicals. This study was conducted in a population in rural China exposed to PAHs from a variety of sources. The study population was located in an area known to have an elevated incidence of birth defects. Parents of children born with a neural tube defect (NTD) were recruited as case participants and parents of children born with no visible birth defect were recruited as controls. The study was designed to test the hypothesis that parents of children born with a NTD would exhibit a biomarker of exposure at higher levels than the parents of a child with no visible birth defect. A total of 35 mothers and 32 fathers were recruited as case participants, and 18 mothers and 19 fathers were recruited as control participants. Venous blood was collected from the study participants by hospital staff as soon as possible following the birth of the child. PAHs were isolated from the whole blood by solvent extraction and DNA was isolated from a separate aliquot of blood for (32)P-postlabeling to measure bulky adducts. Single Nucleotide Polymorphisms (SNPs) in phase II enzymes were also monitored in an attempt to identify sensitive receptors. Both total and carcinogenic PAH (cPAH) concentrations were elevated in the parents of case children. Both values were elevated significantly in mothers, whereas only cPAH concentrations were elevated significantly in fathers. Levels of DNA adducts were highly variable and displayed a reverse pattern to that of PAH levels in blood. None of the polymorphisms evaluated were correlated with PAH levels or DNA adducts. For mothers, whose total PAH concentration was above the median concentration, the age-adjusted odds ratio (OR) for having a child with a NTD was 8.7. Although this suggests that PAHs may be a contributing factor to the risk of NTDs, the lack of a correlation with DNA adducts would suggest a possible non-genotoxic mechanism. Alternatively, the PAHs may be a surrogate for a different exposure that is more directly related to the birth defects. The results have shown that blood levels of PAHs may be used to identify populations exposed to elevated concentrations of combustion by-products.

Thermoelectric Properties of Directionally Solidified Half-Heusler (M 0.5 a ,M 0.5 b )NiSn (Ma, Mb = Hf, Zr, Ti) Alloys

To evaluate the effect of the substitution of the M-site atoms Ti, Zr, and Hf on thermoelectric properties, nearly single-phase (M0.5a,M0.5b)NiSn alloys (Ma, Mb = Hf, Zr, Ti) were fabricated by directional solidification. The lattice thermal conductivity can be most effectively reduced in the (Ti0.5,Hf0.5)NiSn alloy, probably due to the solid-solution effect, since the difference in atomic size and atomic mass are maximized between Ti and Hf. Moreover, we have found the phase separation between Ti-rich and Ti-poor half-Heusler phases in (Ti0.5,Hf0.5)NiSn and (Ti0.5,Zr0.5)NiSn alloys through observation of microstructure, chemical concentration measurement, and x-ray diffractometry.

Evaluating consistency of best professional judgment in the application of a multiple lines of evidence sediment quality triad

The bioavailability of sediment-associated contaminants is poorly understood. Often, a triad of chemical concentration measurements, laboratory sediment toxicity tests, and benthic infaunal community condition is used to assess whether contaminants are present at levels of ecological concern. Integration of these 3 lines of evidence is typically based on best professional judgment by experts; however, the level of consistency among expert approach and interpretation has not been determined. In this study, we compared the assessments of 6 experts who were independently provided data from 25 California embayment sites and asked to rank the relative condition of each site from best to worst. The experts were also asked to place each site into 1 of 6 predetermined categories of absolute condition. We provided no guidance regarding assessment approach or interpretation of supplied data. The relative ranking of the sites was highly correlated among the experts, with an average correlation coefficient of 0.92. Although the experts' relative rankings were highly correlated, the categorical assessments were much less consistent, with only 1 site out of 25 assigned to the same absolute condition category by all 6 experts. Most of the observed categorical differences were small in magnitude and involved the weighing of different lines of evidence in individual assessment approaches, rather than interpretation of signals within a line of evidence. We attribute categorical differences to the experts' use of individual best professional judgment and consider these differences to be indicative of potential uncertainty in the evaluation of sediment quality. The results of our study suggest that specifying key aspects of the assessment approach a priori and aligning the approach to the study objectives can reduce this uncertainty.

Chemical concentration measurement in blood serum and urine samples using liquid-core optical fiber Raman spectroscopy

We report measurements of chemical concentrations in clinical blood serum and urine samples using liquid-core optical fiber (LCOF) Raman spectroscopy to increase the collected signal strength. Both Raman and absorption spectra were acquired in the near-infrared region using the LCOF geometry. Spectra of 71 blood serum and 61 urine samples were regressed via partial least squares against reference analyzer values. Significant correlation was found between predicted and reference concentrations for 13 chemicals. Using absorption data to normalize the LCOF enhancement made the results more accurate. The experimental geometry is well suited for high-volume and automated chemical analysis of clear biofluids.

Modeling agricultural air quality: Current status, major challenges, and outlook

Agricultural air quality is an important emerging area of atmospheric sciences that represents significant challenges in many aspects of research including measurements, modeling, regulations, emission control, and operation managements. This work presents a review of current status, major challenges, and future research needs and opportunities of several important aspects of agricultural air quality modeling including chemical species, concentration and deposition measurements for model verification, emission inventories, major physical and chemical processes, model application and evaluation, and policy implications.

The resonant behavior of silicon tubes under two-phase microfluidic conditions with both microbeads and gas bubbles

This paper examines the behavior of the gain, Q and frequency of resonating microtubes during two-phase, both liquid–gas and liquid–solid, fluidic conditions. The presence of both gas bubbles and solid particles are found to shift the resonant frequency and dampen the resonator signal under static conditions. Going from air to a pure liquid depressed the resonator Q-value by 7–50%. The addition of a significant amount of a second phase, either gas or solid could depress the Q-value by 96% from that of the pure liquid filled resonator. New Q loss mechanisms for microresonators were uncovered, via either internal liquid damping or two-phase damping. Ferromagnetic beads in an external magnetic field are observed to have a significant, variable affect on the gain and Q of the resonator and bead motion of the vibrating microtube. A variety of sensor and transducer applications for the results will be discussed and include Coriolis mass flow, density, chemical concentration, lubricity and viscosity measurements, testing of slurries and carbonated or aerated liquids, mixing, and cell lysing.

The bacterial chemotactic response reflects a compromise between transient and steady-state behavior

Swimming bacteria detect chemical gradients by performing temporal comparisons of recent measurements of chemical concentration. These comparisons are described quantitatively by the chemotactic response function, which we expect to optimize chemotactic behavioral performance. We identify two independent chemotactic performance criteria: In the short run, a favorable response function should move bacteria up chemoattractant gradients; in the long run, bacteria should aggregate at peaks of chemoattractant concentration. Surprisingly, these two criteria conflict, so that when one performance criterion is most favorable, the other is unfavorable. Because both types of behavior are biologically relevant, we include both behaviors in a composite optimization that yields a response function that closely resembles experimental measurements. Our work suggests that the bacterial chemotactic response function can be derived from simple behavioral considerations and sheds light on how the response function contributes to chemotactic performance.