Sample Flow Rate Research Articles

Increasing flow rates in polydimethylsiloxane-based deterministic lateral displacement devices for sub-micrometer particle separation

In this study, we show the design and manufacturing of microfluidic deterministic lateral displacement (DLD) devices for sub-micrometer particle separation. For that purpose, devices with pillar gaps of 4 µm and a periodicity of 50 were designed. After photolithographic manufacturing of SU-8 masters with different heights (15 and 30 µm) and vertical sidewalls for soft-lithographic replication with polydimethylsiloxane (PDMS) the influence of flow rate on the separation efficiency of 0.45 and 0.97 µm particles was investigated. The 15 µm devices were operated at 0.125 and 0.5 µl/min sample flow rate and the 30 µm devices at 0.5 and 2.0 µl/min, respectively. Excellent separation efficiencies were observed for both device heights at the lower sample flow rates, while separation efficiencies decreased at the respective higher sample flow rates. The decrease in separation efficiency was attributed to deformation of the soft PDMS pillars, which causes an increase in pillar gaps at the higher sample flow rates as shown by microscopy imaging. The advantage of the 30 µm devices over the 15 µm devices is clearly shown by the separation of 0.45 and 0.97 µm particles at 0.5 µl/min. Due to reduced hydrodynamic resistance in the 30 µm devices and thus less pillar deformation, the displacement efficiency of 0.97 µm particles was above 99% compared to 46–57% for the 15 µm devices. Our 30 µm devices demonstrated excellent separation at a tenfold higher sample flow rate with 0.5 µl/min compared to comparable PDMS-based devices operating in the same size regime.

Study on the influence of sampling methods for measuring soil radon exhalation rates

Soil is the primary source of radon in the atmosphere, and soil radon exhalation rate (E) is a key indicator to evaluate the radon hazard in soil. Radon can also be used as a tracer to analyze atmospheric processes and monitor greenhouse gas emissions. Therefore, improving the accuracy of measuring E is significant for radon protection and radon pollution management as well as public health. In this study, three different sampling methods were compared to determine the most suitable sampling method for E measurement under different conditions. The results indicated that the closed-loop gas-flow method can be used to measure E and required correction for leakage and counterdiffusion; E was found to vary from 13.25 ± 1.44 to 30.46 ± 2.19 mBq·m−2 s−1. For the open-loop gas-flow method, a low sampling flow rate was selected, and the sampling flow rate derived from this experiment was less than 0.2 l min−1; E varied from 36.11 ± 0.99 to 52.67 ± 1.68 mBq·m−2 s−1. For the activated-carbon adsorption method, the counterdiffusion effect had a negligible influence on the measurement results, and the measurement error due to the uneven distribution of radon in the carbon layer could be eliminated by changing the waiting time for the measurement; the measurement showed E of about 23 mBq·m−2 s−1. Moreover, the influence of water absorption of the activated carbon on the measurement results should be considered, and the water absorption rate should be less than 9%. The obtained values will serve as a reference for the rapid and accurate measurement of E.

Determination of K, Na, and Mg in Brine by Liquid Cathode Glow Discharge—Optical Emission Spectrometry (LCGD-OES) with Interference Suppression

The determination of K, Na, and Mg in brine is important for its effective utilization. Liquid cathode glow discharge—optical emission spectrometry (LCGD-OES) is a successful approach for the determination of these elements in brine. However, matrix interferences reduce the accuracy using a standard curve. Here a correction method based upon the mutual interferences between K, Na, and Mg is reported to improve the accuracy of brine analysis. To verify the performance, LCGD-OES was employed to analyze four samples using the optimized operating voltage and sample flow rate. The results showed that the relative errors of the concentrations of K and Na in the brine were from 1.79% to 8.65% and 3.88% to 6.49% compared to inductively coupled plasma optical—emission spectrometry (ICP-OES). The reported correction method significantly reduced matrix interferences for the determination of K and Na. Additionally, Mg in brine was determined using Al as the internal standard.

Advanced setup for safe breath sampling and patient monitoring under highly infectious conditions in the clinical environment

Being the proximal matrix, breath offers immediate metabolic outlook of respiratory infections. However, high viral load in exhalations imposes higher transmission risk that needs improved methods for safe and repeatable analysis. Here, we have advanced the state-of-the-art methods for real-time and offline mass-spectrometry based analysis of exhaled volatile organic compounds (VOCs) under SARS-CoV-2 and/or similar respiratory conditions. To reduce infection risk, the general experimental setups for direct and offline breath sampling are modified. Certain mainstream and side-stream viral filters are examined for direct and lab-based applications. Confounders/contributions from filters and optimum operational conditions are assessed. We observed immediate effects of infection safety mandates on breath biomarker profiles. Main-stream filters induced physiological and analytical effects. Side-stream filters caused only systematic analytical effects. Observed substance specific effects partly depended on compound’s origin and properties, sampling flow and respiratory rate. For offline samples, storage time, -conditions and -temperature were crucial. Our methods provided repeatable conditions for point-of-care and lab-based breath analysis with low risk of disease transmission. Besides breath VOCs profiling in spontaneously breathing subjects at the screening scenario of COVID-19/similar test centres, our methods and protocols are applicable for moderately/severely ill (even mechanically-ventilated) and highly contagious patients at the intensive care.

Microextraction of organophosphorus pesticides on a screw coated with PAN/calcined ZnMgAl-LDH electrospun nanofibers.

The present research is an attempt to expand the recently reported microextraction on screw method. For this purpose, polyacrylonitrile/calcined ZnMgAl-LDH nanofiber was fabricated by the electrospinning technique on the surface of a screw. It was applied tothe extraction of organophosphorus pesticides (OPP)from agricultural samples. The separation and determination of OPPs were carried out by gas chromatography-mass spectrometry. The characterization of the fabricated nanofiber was performed utilizing Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction instruments. Effective parameters on the extraction efficiency of the analytes including sample pH, ionic strength, sample flow rate and number of cycles, type, volume, and flow rate of desorption solvent were optimized by one-variable-at-a-time method. Under optimized conditions, the limits of detection were 0.03 and 0.07μg L-1 for diazinon and chlorpyrifos, respectively. This method showed wide linearity in the range 0.10-1000μg L-1 for diazinon and 0.25-1000μg L-1 for chlorpyrifos with R2 > 0.996. The intra- and inter-day precisions (RSD%, n = 3) were ≤ 6.4% and ≤ 7.7%, respectively. Also, RSD% values less than 11.1% were obtained for screw-to-screw reproducibility. The applicability of the method for the extraction and determination of the analytes in complex agricultural environments such as cabbage, potato, tomato, cucumber, and beetroot was investigated. The results led to acceptable relative recoveries in the range 81.0-108.2%.

A non-invasive method for the detection of glucose in human exhaled breath by condensation collection coupled with ion chromatography

An analytical method for the detection of glucose in human exhaled breath by non-invasive condensation collection coupled with ion chromatography was developed. A self-designed exhaled breath condensation device was constructed, through which human exhaled breath was condensed and collected. And the glucose in collected human exhaled breath condensate (EBC) was analyzed by ion chromatography with a pulsed amperometric instrument. The standard EBC collection method was established, and the key factors such as cooling temperature and sampling flow rate during condensation collection were investigated deeply, and a good linear correlation between blood glucose levels and exhaled breath glucose levels was obtained. The intra-day precision was 3.37%, and the inter-day precision was 3.83%. Furthermore, EBC from healthy people and diabetic patients was collected in fasting state and after meal. We found the breath glucose level in healthy volunteers was 0.11–2.34 ng/L and that in diabetic patients was 0.23–135.92 ng/L. In after meal samples, the breath glucose level is 10–100 times higher than that of healthy subjects, which offering the prospect of a non-invasive approach to the monitoring of diabetes.

Adsorption performance of Enterobacter cloacae towards U(VI) ion and application of Enterobacter cloacae/carbon nanotubes to preconcentration and determination of low-levels of U(VI) in water samples

Keeping the high potential of some microorganisms in adsorption of radionuclides in view, the adsorption properties of Enterobacter cloacae towards uranium were attentively scrutinized, and then it was used for preconcentration of uranium in different samples, using Enterobacter cloacae/carbon nanotube composite. First, using ultrasonic agitation, the effects of operational factors on biosorption of uranium on the inactive Enterobacter cloacae were appraised and modeled by central composite design, and a comprehensive study was performed on the equilibrium, kinetics, thermodynamic, and selectivity aspects of biosorption. The optimization studies along with the evaluations of the adsorption properties revealed that Enterobacter cloacae have a high affinity for fast and selective biosorption of uranium ions, at pH 5.1. Second, the Enterobacter cloacae/carbon nanotube was synthesized, characterized, and utilized for preconcentration of uranium in different samples, using a mini-column packed with the composite. The optimization of operational factors on recovery of uranium, using the central composite design, showed that uranium can be quantitively adsorbed at a sample flow rate lower than 4.5 mL min−1 and the desorption could be accomplished with 3.0 mL HCl 0.6 M solution. Finally, the mini-column was exploited for preconcentration and determination of uranium in different samples. The results revealed the low detection limit (0.015 μg.L−1), high precision (RSDs ≤3.92%), and good accuracy of the proposed procedure.

Separation of heavy metals by amino acid functionalized polymer: Experimental and theoretical insights

A chloromethylated polystyrene resin was chemically functionalized with glycine molecules to introduce metal ions chelating sites. The functionalized resin (PsGly) was loaded in a glass column and successfully used for the extraction of heavy metal ions. Several experimental parameters like solution pH, sample flow rate, adsorbent dose and breakthrough volume was studied and optimized. The adsorption capacity observed for Ni(II), Cu(II) and Zn(II) were 0.72, 0.68 and 0.60 mmol g−1, respectively. The chelating mechanism for metal ion adsorption was studied by density functional theory. The metal-ligand interaction energy, entropy, and Gibbs energy were estimated by employing the B3LYP basis set of density functional theory and suggest that the studied metal ions form strong complexes with the adsorbent. The column procedure was employed for the extraction of heavy metal ions from wastewater with detection limit of 0.2 μg L−1.

Novel core–shell SiO2@dSiO2@NH2-MIL-53(Al) packed into solid phase extraction column for enrichment of non-steroidal anti-inflammatory drugs prior to UPLC-MS/MS

NH2-MIL-53(Al) was in situ synthesized on the SiO2@dSiO2 with a simple solvothermal method. The prepared composite was packed into column solid phase extraction as adsorbent. After introduction of SiO2@dSiO2 as the support, the drawbacks of adsorbent loss and high backpressure were overcome. Using ultra-high performance liquid chromatography-mass spectrometry, the proposed method was employed to analyze trace non-steroidal anti-inflammatory drugs (NSAIDs) in water samples. Extraction parameters, including type of adsorbent, pH of sample solution, flow rate, sample volume, type and volume of elution solvent, were optimized. Then commendable sensitivity was obtained with limits of detection from 0.5 to 4.0 pg·mL−1, and limits of quantification from 1.5 to 13.3 pg·mL−1. Moreover, the correlation coefficient (r) of linearity was 0.9916–0.9974. Satisfactorily, the recoveries of the target compounds were between 75.3 % and 109.3 %, and the relative standard deviation was less than 7.8 %. Furthermore, naproxen was chosen as a nominee to evaluate adsorption behavior of SiO2@dSiO2@NH2-MIL-53(Al). Molecular docking simulation calculations were conducted to explore adsorption mechanism between NH2-MIL-53(Al) and five NSAIDs.

Virtual impaction in compressible flows with pressure recovery

Virtual impactors have been utilized towards classifying and increasing aerosol concentrations in sampling and measurement systems for half a century; in an ideal virtual impactor, sampled particles larger than a critical diameter (known as the cutsize) are directed inertially into a small fraction of the sample flow, known as the minor flow. Concentrating submicrometer particles with virtual impactors while maintaining near-atmospheric pressure downstream in the minor flow remains a challenge, due the low mass-to-drag ratios of these particles. Increased inertial behavior for small mass-to-drag ratio particles can be overcome by increasing flow velocities; however, in most prior work with virtual impaction of submicrometer particles, pressure recovery (keeping the aerosol outlet pressure similar to the inlet pressure) in the receiving tube at high sample flow rates was not investigated. Here, we describe the development and testing of virtual impactors functioning with flow velocities near the sonic limit, capable of submicrometer particle concentration, and with near-complete pressure recovery in the minor flow. We specifically designed, built, and tested two round-nozzle virtual impactors (denoted as VI-1 and VI-2) and evaluated their performances using fluorescent polystyrene latex particles and uranine-doped oleic acid particles with varying particle diameter. The results show that both virtual impactors, operating with 12 L per minute sample flow and a 10:1 sample flow-to-minor flow ratio, have submicrometer cutsizes (∼700 nm and 200 nm for VI-1 and VI-2, respectively) and near-complete pressure recovery. However, significant particle losses were observed in VI-2 with larger particle diameters. To understand such losses and particle trajectories in compressible flow virtual impactors, we also carried out computational fluid dynamics (CFD) simulations coupled with particle trajectory simulations. Importantly, trajectory calculations incorporated a recently developed drag model capable of predicting particle drag coefficients in a wide Mach number and Knudsen number (and hence Reynolds number) range. Trajectory calculations yielded cutsizes and large particle penetration curves in good agreement with experiments, indicating that large particle losses are due to overfocusing (radial inertial motion leading to deposition) within the nozzle and major flow chamber. Overfocusing always leads to an upper size limit in any virtual impactor system, but it is of greater concern in higher velocity systems. In addition to comparing simulations to measurements sampling at atmospheric pressure, we used trajectory calculations to examine compressible flow virtual impactor performance with variable sampling flow pressure and varying the driving pressure in the major flow. Such simulations reveal that sub-atmospheric pressure sampling leads to a reduced penetration “window” for virtual impaction, such that although it is possible for virtual impactor operation in reduced pressure environments, virtual impactors are applicable to a decreasing range of sizes at low pressure.

INFLUENCE OF SAMPLING FLOW RATE ON THORON EXHALATION RATE MEASUREMENTS BY THE CIRCULATION METHOD.

Researchers have used various methods to obtain the exhalation rates of radon and thoron from soil and building materials. One of the typical methods for radon exhalation rate is the circulation method using an accumulation container, an external or internal sampling pump and a continuous radon monitor. However, it is necessary to consider sampling flow rate if this method is applied to exhalation rate measurement for thoron due to its short half-life. Based on a calibration experiment, the measured thoron concentrations obtained by an electrostatic collection type radon and thoron monitor (RAD7) were found to be influenced strongly by the sampling flow rate. It was also found that the thoron exhalation rate from a soil sample depended on the pressure difference which was proportional to the increasing sampling flow rate. The thoron exhalation rate measured at the generally used sampling flow rate of the internal sampling pump of the RAD7 was overestimated compared with the value at 0 L min-1.

Enrichment of lead and cadmium from water using [formula omitted] nanoparticles/alginate beads: Optimization and determination of significant factors and interaction using response surface methodologies

The optimization, determination of significant factors and interactions between factors of the solid phase extraction method for the enrichment of lead and cadmium in water using P−ZrO2CeO2ZnO nanoparticles/alginate beads was evaluated using Half factorial and Taguchi designs as response surface methodologies in this study. Methods. The beads were characterized using Fourier Transform Infra-Red spectroscopy, Brunauer-Emmet-Teller analysis, Scanning Electron Microscopy and Powder X-ray Diffraction. The amount of adsorbent (50, 100, 150 mg), sample volume (10, 50, 100 mL), eluent volume (10 mL), sample pH (3, 6, 9), eluent concentration (0.5, 1.0 and 2.0 M) and sample flow rate 2 rpm and eluent flow 3 rpm were used during the optimization experiments. The Half factorial design was used to screen for the most significant variables and the Taguchi design was then used to optimize the screened significant variables. Findings The sample volume was the most significant variable for cadmium recovery at p = 0.05. Interactions were noted between sample volume and sorbent dosage, sample volume and pH as well as sorbent dosage and pH. The method was validated by spiking cadmium and lead into borehole and well water samples. The recoveries for metal ions ranged from 57.0 -147.70% for cadmium and 33.12–116.5% forlead, limits of detection were 0.0297 ng/L for cadmium and 0.1022 ng/L for lead. This method exhibits potential for the enrichment of lead and cadmium from water samples.

Microwave Digestion and ICP-MS Determination of Major and Trace Elements in Waste Sm-Co Magnets

In this article, inductively coupled plasma mass-spectrometry (ICP-MS) and inductively coupled plasma optical-emission spectrometry (ICP-OES) were used for the development of an analytical procedure for analysis of the waste of Sm-Co magnets. Experimental parameters related to microwave digestion processes and acid concentrations were optimized. Microwave digestion was carried out in mixtures of HF, HCl, HNO3 and H2SO4. The complete dissolution of the samples occurred in the system: 10 mL H2O, 2 mL HNO3, 10 mL HCl and 1 mL H2SO4. The dependence of the matrix effect on the ICP-MS analysis of waste Sm-Co magnets was studied and optimal instrumental parameters were investigated (nebulizer gas flow, sampling depth and potential at the extractor lens). The optimal conditions were a nebulizer gas flow of 0.85–0.90 L/min, a sampling depth of 101, potential at the extractor lens of −400 V and a sample flow rate of 50 rpm. A recovery test and inter-method experiments were performed to verify the accuracy of the proposed method.

Effects of pipeline geometry, sample volume, and flow rate on pb monitoring outcomes in copper pipe drinking water supply systems

Pb in drinking water is one of the main sources of Pb in human bodies. Besides excess lead incidents caused by lead service lines, Pb contamination in non-lead pipe systems (e.g. copper and PVC) is also on the rise. Brass fixtures and lead-solder connections are the primary sources of lead in non-lead systems, which cause intermittent peaks of Pb at the consumer tap. The concentrations of lead in tap water depend on pipeline geometry, sampling methods, and the characteristic of the pipe flow. Using a 3-dimensional computational fluid dynamics model, this study analyzes the Pb concentration variations at taps of copper water supply systems. The turbulent diffusion and shear flow dispersion are fully simulated in the model to provide the most accurate prediction. Water parcels containing lead (clouds) are formed adjacent to lead sources during stagnation and are then dispersed with the flow of water through the pipe when the tap is opened. The geometry of the pipeline has a significant impact on the monitored Pb levels. The complex flow condition in elbow areas leads to a more intense mixing of lead ions. Therefore, the Pb levels at consumer taps in complex plumbing systems in high-rise buildings are higher than in straight pipelines. When the sampling flow rate is large, the peak height of Pb is slightly higher due to higher turbulent intensity. Pb concentrations in sequential samples are predicted with sample volumes of 50, 250, 500, and 1000 mL. Lead levels may be diluted significantly when samples are taken in large volumes (e.g. 500 mL or 1 L), resulting in an underestimation of Pb levels at taps. A sample volume of 250–500 mL is recommended in sequential sampling programs on non-lead service lines in order to identify Pb sources.

Development of a sampling probe with a small non-isokinetic sampling error in variable flow velocity environments

The flow velocity of exhaust gas from an industrial stack varies from facility to facility and can easily change over time, even in a stack. To accurately measure the concentration of fine particles such as PM10 or PM2.5 emitted in such environments, the conditions for isokinetic sampling must be satisfied. In this study, a novel sampling probe that generates a small error in particle concentration in variable flow velocity environments was developed, even though isokinetic sampling was not performed. The mass distributions obtained by isokinetic sampling using a conventional sampling probe at a flow velocity of 0–6 m/s were compared with those measured using the developed probe to verify the performance of the proposed probe. It was confirmed that the two mass distributions are similar within an error of 5% under all flow velocity conditions. The mass concentrations estimated through theoretical correction considering sampling loss or gain in non-isokinetic environments were also compared, and the distributions were quite similar within approximately 5%. This verifies that the proposed sampling probe can perform nearly perfect sampling of fine particles without changing the sampling flow rates, with minimal particle under- or overestimation caused by non-isokinetic sampling for variable flow velocity conditions.Copyright © 2022 American Association for Aerosol Research

Fast and stable real time monitoring of gaseous mercury in its catalytic oxidation using a fully modified cold-vapor atomic absorption mercury analyzer

A commercially-available cold-vapor atomic absorption mercury analyzer had many difficulties in monitoring real-time gaseous mercury (Hg0) in its oxidation over a V2O5/TiO2-based catalyst under conditions additionally containing HCl, NO and NH3. Thus we made extensive modifications to the original analyzer so that this is suitable for fast and stable real-time Hg0 detections even at low sample flow rates as well as at the harsh conditions. Our fully modified analyzer gave Hg0 signals very similar to those based upon the factory-certified permeation rate of the mercury permeation tube. Gaseous Hg0 could react, only to a small extent, with HCl over a quartz powder and the measured Hg0 oxidation activity was almost associated with the catalyst depending on concentrations of HCl fed to gas streams with NO and NH3. This study can offer useful solutions to academic and industrial research groups to attempt real-time Hg0 measurements at such chosen conditions.

Effect of process parameters on separation efficiency in a deterministic lateral displacement device

Deterministic lateral displacement (DLD) is a hydrodynamic method known for its high-resolution sorting of particles. It achieves this through a periodic array of obstacles and laminar flow that passively directs particles along in two different directions depending on the particles’ diameter. Many prior publications have been dedicated to the structural and geometrical development of DLD arrays to improve separation performance; however, a successful separation requires much more than a well-designed array. This paper shows how separation performance is affected by process parameters. For this purpose, the design and fabrication of a DLD device are described. Then three experiments show how process parameters affect the performance of the device. The first experiment uses dye solutions to visualize the formation of a hydrodynamically focused sample stream. The second experiment shows that the particle separation performance (of 7- & 15-µm particles) is affected by the way output fluids are collected. Finally, the third experiment looks at the particle separation efficiency as the input flow rates and the ratio of buffer to sample are changed. The results show that the proper range for buffer and sample flow rate in this device is 1–10 and 0.1–1 (µl/min), respectively. The buffer to sample flow rate ratio of 10 gives the highest separation efficiency, but at a lower sample throughput. The optimized values are specific for our device but demonstrate processes that we believe are universal for DLD separations.

Recovery of cobalt from spent lithium ion batteries utilizing surface modified graphene oxide

Metal content present in the spent lithium ion batteries (LIBs) make their recycling vital for resources conservation and environmental sustainability. Cobalt, grouped among critical, valuable and strategic metals, is the basic part of the LIBs cathode and defines its recycling economic capacity. In the present work, an attempt has been made to develop an efficient hydrometallurgical technique based on solid phase extraction method for the recovery of cobalt from leach solution of waste LIBs. An adsorbent was synthesized by diazotization of p-phenylenediamine modified graphene oxide (GO-PPDA) sheets with disodium 1-nitroso-2-naphthol-3-6-disulphonate (nitroso R-salt, NRS) in one pot process of Mill's reaction. Maximum retention of cobalt (99.9%) was achieved at pH 5.5–6.5. Adsorption kinetics favour complexation as a separation mechanism following second order kinetics model with R2 value of 0.9999 with sample flow rate of 1.5 mL/min. Langmuir isothermal model (R2 = 0.998) also confirm monolayer chemisorption mechanism with 29.7 mg/g adsorption capacity. The two-step elution mechanism enables us to achieve 99.5% extraction efficiency with ~98% purity. The chelating adsorbent was found reasonably stable even after the 30th cycle of adsorption and desorption with <2% decrease in removal efficiency. The results show that the proposed adsorbent is successful in terms of selectivity, reusability, analytical merit and stability.

A low cost, easy-to-assemble, open-source modular mobile sampler design for thermal desorption analysis of breath and environmental VOCs

Exhaled breath vapor contains hundreds of volatile organic compounds (VOCs), which are the byproducts of health and disease metabolism, and they have clinical and diagnostic potential. Simultaneous collection of breath VOCs and background environmental VOCs is important to ensure analyses eliminate exogenous compounds from clinical studies. We present a mobile sampling system to extract gaseous VOCs onto commercially available sorbent-packed thermal desorption tubes. The sampler can be connected to a number of commonly available disposable and reusable sampling bags, in the case of this study, a Tedlar bag containing a breath sample. Alternatively, the inlet can be left open to directly sample room or environmental air when obtaining a background VOC sample. The system contains a screen for the operator to input a desired sample volume. A needle valve allows the operator to control the sample flow rate, which operates with an accuracy of −1.52 ± 0.63% of the desired rate, and consistently generated that rate with 0.12 ± 0.06% error across repeated measures. A flow pump, flow sensor and microcontroller allow volumetric sampling, as opposed to timed sampling, with 0.06 ± 0.06% accuracy in the volume extracted. Four samplers were compared by sampling a standard chemical mixture, which resulted in 6.4 ± 4.7% error across all four replicate modular samplers to extract a given VOC. The samplers were deployed in a clinical setting to collect breath and background/environmental samples, including patients with active SARS-CoV-2 infections, and the device could easily move between rooms and can undergo required disinfection protocols to prevent transmission of pathogens on the case exterior. All components required for assembly are detailed and are made publicly available for non-commercial use, including the microcontroller software. We demonstrate the device collects volatile compounds, including use of chemical standards, and background and breath samples in real use conditions.

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min−1 providing a sample throughput of more than 15 samples h−1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.