Standard Buffer Research Articles

Which city is the greenest? A multi-dimensional deconstruction of city rankings

The question “which city is the greenest” sounds trivial, but in reality, this question contains statistical ambiguities. In this study, we approach this issue by ranking cities by green space shares. However, we do not base our ranking only on one green parameter and the commonly used administrative boundaries. Instead, we broaden access to rankings through several approaches: First, we calculate two parameters, i.e. green space shares and green space per capita. Second, we apply these parameters for two cases: for all green areas as well as for green areas with a minimum size of one hectare. The latter are considered to have an impact on near-home recreation and the local climate. Third, we relate these parameters on the one hand to administrative spatial units constituting the entity ‘city’, but juxtapose these on the other hand with two alternative spatial reference units: a morphological spatial unit that closely encompasses the built-up pattern of the city, and a standardized buffer unit around the city centers. The variability of these manifold rankings obtained by this study makes clear: the rank of one city in a relational system to other cities depends strongly on these parameters and spatial units applied. In our experiments we rank and compare the 80 major cities in Germany. The diversity of results allows to discuss the susceptibility of spatial statistics to ambiguities that may arise from the use of different concepts. By integrating these multidimensional concepts into one final ranking, we propose a strategy for a more holistic and robust approach while revealing uncertainties.

Validation of a Simple HPLC-Based Method for Lysine Quantification for Ruminant Nutrition

Robust and selective quantification methods are required to better analyze feed supplementation effectiveness with specific amino acids. In this work, a reversed-phase high-performance liquid chromatography method with fluorescence detection is proposed and validated for lysine quantification, one of the most limiting amino acids in ruminant nutrition and essential towards milk production. To assess and widen method applicability, different matrices were considered: namely Li2CO3 buffer (the chosen standard reaction buffer), phosphate buffer solution (to mimic media in cellular studies), and rumen inoculum. The method was validated for all three matrices and found to be selective, accurate (92% ± 2%), and precise at both the inter- and intra-day levels in concentrations up to 225 µM, with detection and quantification limits lower than 1.24 and 4.14 µM, respectively. Sample stability was evaluated when stored at room temperature, 4 °C, and −20 °C, showing consistency for up to 48 h regardless of the matrix. Finally, the developed method was applied in the quantification of lysine on real samples. The results presented indicate that the proposed method can be applied towards free lysine quantification in ruminant feeding studies and potentially be of great benefit to dairy cow nutrition supplementation and optimization.

Anodic stripping voltammetry on a carbon-based ion-selective electrode

In this study, we demonstrated the unique capability of carbon-based ion-selective electrode (ISE) to perform highly sensitive square wave anodic stripping voltammetry, while maintaining all the properties of an ISE, in terms of sensitivity, detection limit, response time and selectivity. Square wave anodic stripping voltammetry involves deposition and dissolution steps of metal ions, which means adsorption and desorption of metal ions on the conductive ion-selective membrane without losing its ion-sensing property. To demonstrate this capability, we chose a Ca2+ ion-selective microelectrode (µISE) as a potentiometric method and Cu2+-stripping voltammetry as an amperometric method. The carbon-based ISE surface is capable of quantifying nanomolar to micromolar Cu2+ in both a standard acetate buffer and a complex water sample. The Ca2+-µISE also showed a Nernstian slope of 29 mV/log [Ca2+] and a detection limit of 1 µM within the linear range of 1 µM to 10 mM. It thus opens an opportunity to use the low detection limit of anodic stripping voltammetry and the high selectivity of ISE-based potentiometry.

A Novel Antibody-Cell Conjugation Method to Enhance Cellular Therapies for the Treatment of Hematological Malignancies

IntroductionCellular therapies including γδ T cells, NK-92 cells, and cytokine-induced killer (CIK) cells have shown modest anti-tumor activity against multiple hematological and solid malignancies in preclinical and phase I/II clinical trials. We investigate whether the antitumor activity of these cellular therapies can be augmented by using a novel method that rapidly affixes tumor-targeting antibodies directly to cell surface proteins.MethodsMonoclonal antibodies including rituximab and daratumumab were conjugated to the cell surface proteins using a three step approach. First, we conjugate single-stranded DNAs (ssDNAs) to the therapeutic monoclonal antibodies, as previously described (ref below). Next, we conjugate complementary ssDNAs to surface proteins of cells being used for cellular therapy. Finally, the modified antibodies are attached to the modified cells via hybridization of the complementary DNA strands.ResultsWe demonstrate that multiple anti-neoplastic monoclonal antibodies including rituximab and daratumumab can be conjugated to the surface proteins on a variety of cell including γδ T cells, NK-92 cells, CIK cells, and primary human T cells. Then we evaluated the killing activity of these conjugated cells in vitro, in vivo, and ex vivo . In vitro, Rituximab-armed γδ T cells and NK-92 cells demonstrated increased cytokine production (IFN-γ and granzyme B) and enhanced cytotoxic killing against of multiple human B-cell non-Hodgkin lymphoma (NHL) and multiple myeloma cell lines. Similar enhanced anti-tumor activity was seen with rituximab-armed or daratumumab-armed CIK cells, as well as increased CD107a expression (a marker of cytotoxicity activity) by the antibody-armed CIK cells. Rituximab-armed primary T cells also show enhanced cytotoxic killing against Raji cells, although not as pronounced as autologous rituximab-armed CIK cells. We next evaluated the therapeutic potential of antibody-armed cell therapies in vivo in a disseminated xenograft mouse model using SCID-beige mice. Rituximab-armed γδ T cells exhibited potent anti-lymphoma activity against Raji cells, which lead to improved overall survival; whereas unarmed γδ T cells alone or with rituximab co-infusion demonstrated limited anti-lymphoma activity. We also evaluated the therapeutic activity of antibody-armed cell therapies against a primary lymphoma target ex vivo. Rituximab-arm CIK cells demonstrated enhanced cytolytic activity against primary follicular lymphoma freshly collected from a patient via fine needle aspiration biopsy.DiscussionWe have demonstrated a novel approach to create tumor-specific cellular immunotherapies without the need for genetic engineering. The antibody to cell conjugation method is straight forward. The modified antibodies can be made and stored until needed. It takes approximately 1 hour to attaching these modified antibodies to the cell surface and is performed in standard aqueous buffers, such as phosphate-buffered saline (PBS). This method is also flexible being able to conjugate multiple different antibodies to the surface proteins of a variety of different cell types. We also see enhanced cell killing across multiple hematological targets using multiple cell populations including γδ T cells, NK-92 cells, CIK cells, and primary human T cells. Overall, our data demonstrate existing monoclonal antibodies can be used to “antibody program” cell therapies for the treatment of hematological malignancies.RefHsiao et al Langmuir 2009,25(12), 6985-6991 DisclosuresHsiao:Acepodia, Inc: Employment.

Catalytic effects of magnetic and conductive nanoparticles on immobilized glucose oxidase in skin sensors

Wearable skin sensors is a promising technology for real-time health care monitoring. They are of particular interest for monitoring glucose in diabetic patients. The concentration of glucose in sweat can be more than two orders of magnitude lower than in blood. In consequence, the scientific and technological efforts are focused in developing new concepts to enhance the sensitivity, decrease the limit of detection (LOD) and reduce the response time (RT) of glucose skin sensors. This work explores the effect of adsorbed superparamagnetic magnetite nanoparticles (MNPs) and conductive nanoparticles (CNPs) on carbon nanotube substrates (CNTs) used to immobilize glucose oxidase enzyme in the working electrode of skin sensors. MNPs and CNPs are made of magnetite and gold, respectively. The performance of the sensors was tested in standard buffer solution, artificial sweat, fresh sweat and on the skin of a healthy volunteer during an exercise session. In the case of artificial sweat, the presence of MNPs accelerated the RT from 7 to 5 s at the expense of increasing the LOD from 0.017 to 0.022 mM with slight increase of the sensitivity from 4.90 to 5.09 μAm M−1 cm−2. The presence of CNPs greatly accelerated the RT from 7 to 2 s and lowered the LOD from 0.017 to 0.014 mM at the expense of a great diminution of the sensitivity from 4.90 to 4.09 μAm M−1 cm−2. These effects were explained mechanistically by analyzing the changes in the concentration of free oxygen and electrons promoted by MNPs and CNPs in the CNTs and its consequences on the the glucose oxidation process.

Stability and Performance Study of Fluorescent Organosilica pH Nanosensors.

Long-term stability and function are key challenges for optical nanosensors operating in complex biological environments. While much focus is rightly placed on issues related to specificity, sensitivity, reversibility, and response time, many nanosensors are not capable of transducing accurate results over prolonged time periods. Sensors could fail over time due to the degradation of scaffold material, degradation of signaling dyes and components, or a combination of both. It is critical to investigate how such degradative processes affect sensor output, as the consequences could be severe. Herein, we used fluorescent core-shell organosilica pH nanosensors as a model system, incubating them in a range of common aqueous solutions over time at different temperatures, and then searched for changes in fluorescence signal, particle size, and evidence of silica degradation. We found that these ratiometric nanosensors produced stable optical signals after aging for 30 days at 37 °C in standard saline buffers with and without 10% fetal bovine serum, and without any evidence of material degradation. Next, we evaluated their performance as real-time pH nanosensors in bacterial suspension cultures, observing a close agreement with a pH electrode for control nanosensors, yet observing obvious deviations in signal based on the aging conditions. The results show that while the organosilica scaffold does not degrade appreciably over time, careful selection of dyes and further systematic investigations into the effects of salt and protein levels are required to realize long-term stable nanosensors.

One and Two-Step In Vitro-In Vivo Correlations Based on USP IV Dynamic Dissolution Applied to Four Sodium Montelukast Products.

Montelukast is a weak acid drug characterized by its low solubility in the range of pH 1.2 to 4.5, which may lead to dissolution-limited absorption. The aim of this paper is to develop an in vivo predictive dissolution method for montelukast and to check its performance by establishing a level-A in vitro-in vivo correlation (IVIVC). During the development of a generic film-coated tablet formulation, two clinical trials were done with three different experimental formulations to achieve a similar formulation to the reference one. A dissolution test procedure with a flow-through cell (USP IV) was used to predict the in vivo absorption behavior. The method proposed is based on a flow rate of 5 mL/min and changes of pH mediums from 1.2 to 4.5 and then to 6.8 with standard pharmacopoeia buffers. In order to improve the dissolution of montelukast, sodium dodecyl sulfate was added to the 4.5 and 6.8 pH mediums. Dissolution profiles in from the new method were used to develop a level-A IVIVC. One-step level-A IVIVC was developed from dissolution profiles and fractions absorbed obtained by the Loo–Riegelman method. Time scaling with Levy’s plot was necessary to achieve a linear IVIVC. One-step differential equation-based IVIVC was also developed with a time-scaling function. The developed method showed similar results to a previously proposed biopredictive method for montelukast, and the added value showed the ability to discriminate among different release rates in vitro, matching the in vivo clinical bioequivalence results.

Zwitterions for impedance spectroscopy: The new buffers in town

Studying the role of buffers in impedance spectroscopy is a relatively unexplored area. We demonstrate a special class of biologically relevant buffers known as Good's zwitterionic buffers that show improved performance over standard electrolyte buffers (e.g. PBS) currently widely used in impedance spectroscopy measurements of bacterial suspensions. Our theoretical and experimental comparisons of conductivity of classical and zwitterionic buffers at various different concentrations show that ion-ion interaction effects are significantly higher in zwitterionic buffers as compared to classical buffers at the concentrations at which they are used. This and the fact that zwitterions have larger sizes leads to the lowering of their conductivity which significantly improves their impedance sensing ability. We illustrate through an example of heat-induced ionic release in model S. typhi and S. aureus bacteria that having a low conductivity buffer is indeed beneficial for biological impedance measurements. In fact, the best buffer for impedance studies can be chosen solely based on their electrical properties as long as they are also biologically compatible. This gives Good's zwitterionic buffers an edge over conventional media as they satisfy both these criteria.

High-Throughput Label-Free Biochemical Assays Using Infrared Matrix-Assisted Desorption Electrospray Ionization Mass Spectrometry.

Mass spectrometry (MS) can provide high sensitivity and specificity for biochemical assays without the requirement of labels, eliminating the risk of assay interference. However, its use had been limited to lower-throughput assays due to the need for chromatography to overcome ion suppression from the sample matrix. Direct analysis without chromatography has the potential for high throughput if sensitivity is sufficient despite the presence of a matrix. Here, we report and demonstrate a novel direct analysis high-throughput MS system based on infrared matrix-assisted desorption electrospray ionization (IR-MALDESI) that has a potential acquisition rate of 33 spectra/s. We show the development of biochemical assays in standard buffers for wild-type isocitrate dehydrogenase 1 (IDH1), diacylglycerol kinase zeta (DGKζ), and p300 histone acetyltransferase (P300) to demonstrate the suitability of this system for a broad range of high-throughput lead discovery assays. A proof-of-concept pilot screen of ∼3k compounds is also shown for IDH1 and compared to a previously reported fluorescence-based assay. We were able to obtain reliable data at a speed amenable for high-throughput screening of large-scale compound libraries.

THE IMPACT OF ISCHEMIA-REPERFUSION ON LANGENDORFF RABBIT HEART WITH EXPERIMENTAL ATHEROSCLEROSIS

Abstract Objective: To examine the effect of hypercholesterolemia (HC)on cardiac function in rabbit model. Design and method: 12 adult rabbits divided into 2 groups of 6 rabbits each:Control(C) fed on normal chow, and (HC) fed on 2% cholesterol (Iard mixed with chow) for 16 weeks. After treatment, rabbits from (C) and (HC) groups were sacrificed and hearts were quicky removed, and perfused with standard Krebs Hanseleit buffer at a rate of 10 ml/minute at 37°C, pH 74 in Langendorff retrograde perfusion system at a constant pressure.45 minutes ischemia was followed by 120 minutes reperfusion and parameters of cardiac function: coronary flow (HC), Heart rate (H.R.) and left ventricle developed pressure (LVDP) of hearts from (C) and (HC) groups were measured. TACS DNA laddering kit was used to assess left ventricle cardiomyocytes from group (HC) for apoptosis, also fragments of left ventricle from (HC) were processed for Electron Microscopy (EM). Results: Evaluation of (C.F.), (H.R.) and (LVDP) in (C) and (HC) groups have pointed out a 50% reduction in (C.F). in (HC) group versus (C) during stabilization period In (HC) group, LVDP was depressed during the whole experiment, while in (C) group is was almost constant. Protection of myocardium against oxidative stress was significantly depressed following (HC) treatment, synthesis and utilization of GSH was limited versus (C). Cardiac hypertrophy experimentally induced with (HC) was related with a decrease in (C.F.) and LVDP associated with an increase in lipid peroxidase, in LDH and CK as markers of myocardial lesion and GGT activity in myocardial tissue. Myocyte apoptosis was present in (HC) group, pointed out by DNA laddering pattern on gel electrophoresis. (E.M.) studies have pointed out perinuclear edema of myocytes, dilated sarcoplasmic reticulum and swollen mitochondria. Conclusions: High cholesterol diet in (HC) rabbits induces cardiac hypertrophy and changes in physiological parameters of heart with a negative impact upon synthesis of antioxidant enzymes as well as changes in ultrastructure of heart muscle and at the molecular level (DNA laddering is present as a sign of apoptosis in ventricular myocytes).

Dimensioning On-Demand Vehicle Sharing Systems

We consider the problem of optimal fleet sizing in a vehicle sharing system. Vehicles are available for short-term rental and are accessible from multiple locations. A vehicle rented at one location can be returned to any other location. The size of the fleet must account not only for the nominal load and for the randomness in demand and rental duration but also for the randomness in the number of vehicles that are available at each location because of vehicle roaming (vehicles not returning to the same location from which they were picked up). We model the dynamics of the system using a closed queueing network and obtain explicit and closed form lower and upper bounds on the optimal number of vehicles (the minimum number of vehicles needed to meet a target service level). Specifically, we show that starting with any pair of lower and upper bounds, we can always obtain another pair of lower and upper bounds with gaps between the lower and upper bounds that are independent of demand and bounded by a function that depends only on the prescribed service level. We show that the generated bounds are asymptotically exact under several regimes. We use features of the bounds to construct a simple and closed form approximation that we show to be always within the generated lower and upper bounds and is exact under the asymptotic regimes considered. Extensive numerical experiments show that the approximate and exact values are nearly indistinguishable for a wide range of parameter values. The approximation is highly interpretable with buffer capacity expressed in terms of three explicit terms that can be interpreted as follows: (1) standard buffer capacity that is protection against randomness in demand and rental times, (2) buffer capacity that is protection against vehicle roaming, and (3) a correction term. Our analysis reveals important differences between the optimal sizing of standard queueing systems (where servers always return to the same queue upon service completion) and that of systems where servers, upon service completion, randomly join any one of the queues in the system. We show that the additional capacity needed to buffer against vehicle roaming can be substantial even in systems with vanishingly small demand. This paper was accepted by Baris Ata, stochastic models and simulation.

Alternative frameworks for measuring credit gaps and setting countercyclical capital buffers

This paper complements the standard Basel countercyclical capital buffer framework by suggesting four additional measures for credit gaps that can be used to measure the financial cycle and to decide on countercyclical capital buffers for banks. The new measures behave similarly to the gaps calculated with the standard Basel one-sided Hodrick-Prescott filter in long samples, but they have the properties desired for countries with relatively short historical samples. While the standard Basel credit gaps have been deep in negative territory for many European Union countries since the Great Recession the new gaps are close to zero and the buffers suggested are more in line with the countercyclical capital buffer ratios that were in place in 2018.

Inkjet-printed paper-based sensor array for highly accurate pH sensing

In this work, a novel paper-based colorimetric sensor array was developed by inkjet printing method with polyethylene glycol (PEG) immobilization system. Eight commercially available pH indicators with sequential pH segments in nearly whole pH range were dissolved in nine mixed inks to fabricate the 3 × 3 sensor array on mixed cellulose ester (MCE) paper. Based on homogeneous deposition of inkjet printing, the eight pH indicators were sufficiently immobilized on MCE paper with the assistance of PEG-400, which guaranteed pH detection of aqueous samples on sensor array without hydrophobic barriers. Besides, the indicating range of each indicator obtained an extension through the addition of PEG 400, which remarkably enriched the distinguishable capability of sensor array and benefited for high resolution of pH detection. As such, the as-fabricated paper-based sensor array exhibited an excellent discrimination ability in pH range of 1.00–13.60 with a high resolution of 0.20 pH unit, not only for standard pH buffer solutions but for real aqueous samples.

PHAIR: a biosensor for pH measurement in air\u2013liquid interface cell culture

In many biological systems, pH can be used as a parameter to understand and study cell dynamics. However, measuring pH in live cell culture is limited by the sensor ion specificity, proximity to the cell surface, and scalability. Commercially available pH sensors are difficult to integrate into a small-scale cell culture system due to their size and are not cost-effective for disposable use. We made PHAIR—a new pH sensor that uses a micro-wire format to measure pH in vitro human airway cell culture. Tungsten micro-wires were used as the working electrodes, and silver micro-wires with a silver/silver chloride coating were used as a pseudo reference electrode. pH sensitivity, in a wide and narrow range, and stability of these sensors were tested in common standard buffer solutions as well as in culture media of human airway epithelial cells grown at the air–liquid interface in a 24 well cell culture plate. When measuring the pH of cells grown under basal and challenge conditions using PHAIR, cell viability and cytokine responses were not affected. Our results confirm that micro-wire-based sensors have the capacity for miniaturization and detection of diverse ions while maintaining sensitivity. This suggests the broad application of PHAIR in various biological experimental settings.

Phosphatidylcholine and L-acetyl-carnitine-based freezing medium can replace egg yolk and preserves human sperm function.

BackgroundConventional cryopreservation methods induce chemical and mechanical damage to the sperm membranes. The cryoprotectant potential of phospholipids of vegetal origin as soybean lecithin has been investigated as a substitute for egg yolk in diluents used for the cryopreservation of human spermatozoa. Therefore, the objective of this study was comparing the efficacy of a synthetic cryoprotectant supplemented with L-α-phosphatidylcholine (PC) and L-acetyl-carnitine (ANTIOX-PC) and the standard egg-based TEST-yolk buffer (TYB) in preserving sperm motility and chromatin quality in cryopreserved semen samples.MethodsProspective experimental study in which semen samples from 63 men with normal sperm motility and 58 men with low sperm motility were included and analyzed both before and after cryopreservation using ANTIOX-PC or TYB freezing media. Sperm quality was evaluated by routine semen analysis and DNA fragmentation index using the Terminal deoxynucleotidyl transferase dUTP nick end labeling assay.ResultsDifferences in the post-thaw progressive motility and DNA fragmentation index were not detected between TYB and ANTIOX-PC cryoprotectants in both normal and low sperm motility groups (P>0.05). However, ANTIOX-PC medium retained higher non-progressive motility and lower percentage of immotile sperm when compared to TYB medium, resulting in a greater total motile sperm count (P<0.05), regardless baseline values of motility characteristic of the normospermic or asthenozoospermic samples.ConclusionsANTIOX-PC medium was effective to protect human sperm during a freeze-thaw cycle compared to the TYB medium. A clinically relevant advantage in better preserving kinetic parameters as higher total motility and lower immotile post-thawed sperm from ANTIOX-PC, in normal and low motility semen samples, demonstrated the positive impact of phospholipid and antioxidant treatment on sperm cryotolerance with high potential for egg yolk lipids replacement and biosafety.

Are wide but selectively logged buffer strips better than narrow ones?

ABSTRACT The microclimate of streamside habitats are protected from the effects of logging with buffer strips of retained trees. However, these buffer strips are often narrow due to their financial loss. Wider, selectively logged buffers might protect the microclimate while providing the same economic return. This study investigates the effects of logging on the microclimate and the growth of the bryophyte Hylocomium splendens on two streamside buffers: a standard unlogged narrow buffer (∼15 m) and a wider buffer (∼30 m) selectively logged with decreasing intensity towards the stream. The study was conducted in Central Finland on eight sites where the two buffers were logged next to each other. The near-stream change in air temperature and relative humidity was measured from pre-logging to post-logging. Additionally, post-logging microclimate gradients and the growth of H. splendens was measured on a 30 m transect away from the stream. The results showed no significant differences in the ability of the two kinds of buffers in maintaining streamside microclimate, and neither buffer seems to protect the microclimate from the negative effects of logging. The growth of H. splendens also decreased in both buffers. We conclude that wider, unlogged buffer strips are required to protect riparian forest microclimate.

Use of Ionic Liquids in Protein and DNA Chemistry.

Ionic liquids (ILs) have been receiving much attention as solvents in various areas of biochemistry because of their various beneficial properties over the volatile solvents and ILs availability in myriad variants (perhaps as many as 108) owing to the possibility of paring one cation with several anions and vice-versa as well as formulations as zwitterions. Their potential as solvents lies in their tendency to offer both directional and non-directional forces toward a solute molecule. Because of these forces, ionic liquids easily undergo intermolecular interactions with a range of polar/non-polar solutes, including biomolecules such as proteins and DNA. The interaction of genomic species in aqueous/non-aqueous states assists in unraveling their structure and functioning, which have implications in various biomedical applications. The charge density of ionic liquids renders them hydrophilic and hydrophobic, which retain intact over long-range of temperatures. Their ability in stabilizing or destabilizing the 3D-structure of a protein or the double-helical structure of DNA has been assessed superior to the water and volatile organic solvents. The aptitude of an ion in influencing the structure and stability of a native protein depends on their ranking in the Hofmeister series. However, at several instances, a reverse Hofmeister ordering of ions and specific ion-solute interaction has been observed. The capability of an ionic liquid in terms of the tendency to promote the coiling/uncoiling of DNA structure is noted to rely on the basicity, electrostatic interaction, and hydrophobicity of the ionic liquid in question. Any change in the DNA's double-helical structure reflects a change in its melting temperature (Tm), compared to a standard buffer solution. These changes in DNA structure have implications in biosensor design and targeted drug-delivery in biomedical applications. In the current review, we have attempted to highlight various aspects of ionic liquids that influence the structure and properties of proteins and DNA. In short, the review will address the issues related to the origin and strength of intermolecular interactions, the effect of structural components, their nature, and the influence of temperature, pH, and additives on them.

Performance of Source Follower Buffers Implemented with Standard and Strained Triple-Gate nFinFETs

In this work the application of standard and strained triple-gate FinFETs in unity-gain source-follower configuration is compared. The analysis is performed by evaluating the buffer voltage gain with respect to the fin width and channel length as well as the total harmonic distortion. It is demonstrated that the application of strained material in narrow FinFETs, when the devices are operating in double-gate mode, can be beneficial for the performance of buffers in any channel length. On the other hand, for triple-gate FinFETs or quasi-planar ones the degradation of the output conductance overcomes the transconductance improvements from strained material and the performance of standard buffers is better than of strained ones. Narrow strained buffers also offer better harmonic distortion.

Multifactor colorimetric analysis on pH-indicator papers: an optimized approach for direct determination of ambient aerosol pH

Abstract. Direct measurement of the acidity (pH) of ambient aerosol particles/droplets has long been a challenge for atmospheric scientists. A novel and facile method was introduced recently by Craig et al. (2018), where the pH of size-resolved aerosol droplets was directly measured by two types of pH-indicator papers (pH ranges: 0–2.5 and 2.5–4.5) combined with RGB-based colorimetric analyses using a model of G−B (G minus B) vs. pH2. Given the wide pH range of ambient aerosols, we optimize the RGB-based colorimetric analysis on pH papers with a wider detection range (pH ∼ 0 to 6). Here, we propose a new model to establish the linear relationship between RGB values and pH: pHpredict = a⋅Rnormal+b⋅Gnormal+c⋅Bnormal. This model shows a wider applicability and higher accuracy than those in previous studies and is thus recommended in future RGB-based colorimetric analyses on pH papers. Moreover, we identify one type of pH paper (Hydrion® Brilliant pH dip stiks, lot no. 3110, Sigma-Aldrich) that is more applicable for ambient aerosols in terms of its wide pH detection range (0 to 6) and strong anti-interference capacity. Custom-made impactors are used to collect lab-generated aerosols on this type of pH paper. Preliminary tests show that, with a collected particle size range of ∼ 0.4–2.2 µm, the pH paper method can be used to predict aerosol pH with an overall uncertainty ≤ 0.5 units. Based on laboratory tests, a relatively short sampling time (∼ 1 to 4 h) is speculated for pH prediction of ambient aerosols. More importantly, our design of the impactors minimizes potential influences of changed environmental conditions during pH paper photographing processes on the predicted aerosol pH. We further show that the routinely adopted way of using pH color charts to predict aerosol pH may be biased by the mismatch between the standard colors on the color charts and the real colors of investigated samples. Thus, instead of using the producer-provided color charts, we suggest an in situ calibration of pH papers with standard pH buffers.

Glass electrode half-cells for measuring unified pH in ethanol–water mixtures

Abstract. The acidities of any given solvent or mixtures thereof can be compared by pH measurements on a unified scale, so-called pHabsH2O measurements. The method is quite new and has not been characterized with respect to metrological criteria to date. Metal solid-contact glass electrode half-cells, three commercial, conventional glass electrode half-cells with inner liquid filling and one pair of combined electrodes were used to investigate the stability of the measurement and the reproducibility of pHabsH2O results of ethanol mixtures with water. All electrodes are suitable for unified acidity measurements in standard aqueous buffers. In ethanol mixtures, the combined electrodes were found to be unsuitable. The half-cell electrodes can be reasonably used only in buffered solutions.