Background Electrolyte Solution Research Articles

Beyond monopole electrostatics in regulating conformations of intrinsically disordered proteins.

Conformations and dynamics of an intrinsically disordered protein (IDP) depend on its composition of charged and uncharged amino acids, and their specific placement in the protein sequence. In general, the charge (positive or negative) on an amino acid residue in the protein is not a fixed quantity. Each of the ionizable groups can exist in an equilibrated distribution of fully ionized state (monopole) and an ion-pair (dipole) state formed between the ionizing group and its counterion from the background electrolyte solution. The dipole formation (counterion condensation) depends on the protein conformation, which in turn depends on the distribution of charges and dipoles on the molecule. Consequently, effective charges of ionizable groups in the IDP backbone may differ from their chemical charges in isolation-a phenomenon termed charge-regulation. Accounting for the inevitable dipolar interactions, that have so far been ignored, and using a self-consistent procedure, we present a theory of charge-regulation as a function of sequence, temperature, and ionic strength. The theory quantitatively agrees with both charge reduction and salt-dependent conformation data of Prothymosin-alpha and makes several testable predictions. We predict charged groups are less ionized in sequences where opposite charges are well mixed compared to sequences where they are strongly segregated. Emergence of dipolar interactions from charge-regulation allows spontaneous coexistence of two phases having different conformations and charge states, sensitively depending on the charge patterning. These findings highlight sequence dependent charge-regulation and its potential exploitation by biological regulators such as phosphorylation and mutations in controlling protein conformation and function.

Automated analyses of dried blood spots collected by volumetric microsampling devices

BackgroundDried blood spot (DBS) sampling on cellulose cards suffers from varying blood haematocrit levels and from chromatographic effects, which have a direct impact on quantitative DBS analyses. Commercial volumetric microsampling devices were, therefore, introduced to mitigate these effects, however, these devices are not compatible with automated DBS processing systems and must be processed manually. ResultsCapillary electrophoresis (CE) instruments use fused-silica (FS) capillaries for precise and accurate liquid handling as well as for injection, separation, and quantitative analyses of liquid samples. These inherent features of an Agilent 7100 CE instrument were employed for the automated processing (elution and homogenization) of DBSs collected by hemaPEN® volumetric devices (2.74 μL of capillary blood per spot). The hemaPEN® samples were processed directly in CE vials by consecutive transfers of 56 μL of methanol and 14 μL of deionized water through the FS capillary in a sequence of 39 DBSs with repeatability of the liquid transfers better than 1.4 %. The resulting DBS eluates were homogenized by a quick air flush through the capillary and analyzed by the same capillary and CE instrument. Creatinine was selected as a clinically relevant model analyte and its endogenous concentrations in DBSs were determined by CE with capacitively coupled contactless conductivity detection (CE-C4D) in a background electrolyte solution consisting of 50 mM acetic acid and 0.1 % (v/v) Tween 20 (pH 3.0). The overall repeatability of the automated DBS processing and CE-C4D analyses of 39 DBSs was ≤7.1 % (peak areas) and ≤0.6 % (migration times), the calibration curve was linear in the 25–500 μM range (R2 = 0.9993) and covered all endogenous blood creatinine levels, the limit of detection was 5.0 μM, and sample throughput was >12 DBSs per hour. DBS ageing for 60 days and varying blood haematocrit levels (20–70 %) did not affect creatinine quantitative results (≤6.9 % for peak areas). Inter-capillary and inter-instrument repeatability was ≤7.7 % (peak areas) and ≤3.4 % (migration times) and demonstrated an excellent transferability of the proposed analytical concept among laboratories. Significance and noveltyThis contribution is the first-ever report on the use of a single off-the-shelf analytical instrument for fully automated analyses of DBSs collected by commercial volumetric microsampling devices and holds great promise for future unmanned quantitative DBS analyses.

Development of an eco-friendly capillary electrophoresis method for the simultaneous determination of piperacillin, tazobactam and ibuprofen in plasma samples: application to a pharmacokinetic study in rats.

Piperacillin (PIP) and tazobactam (TAZ) are broad-spectrum beta-lactam antimicrobial agents, which are frequently co-prescribed in intensive care units (ICUs) worldwide. Ibuprofen (IBU) is a potent pain killer which is commonly co-prescribed with PIP and TAZ postoperatively. The combination therapy of PIP, TAZ, and IBU has been administered commonly after surgical procedures to combat aerobic and anaerobic microbes and exert anti-inflammatory and analgesic effects. This study describes, for the first time, the development of a new capillary electrophoresis (CE) method with a photodiode array detector for the simultaneous determination of PIP, TAZ, and IBU in plasma samples. The experimental factors affecting the elution of analytes were carefully optimized. The final analysis was achieved using a fused silica capillary (58 cm effective length and 75 μm ID) and a background electrolyte solution containing a methanol/borax buffer solution (15 mM and pH 9.3) in a ratio of (10 : 90 v/v) with a driving voltage of 30 kV and detection at 210 nm. The relationship between the peak area and concentration was linear from 1 to 200 μg mL-1 for both PIP and TAZ and from 3 to 200 μg mL-1 for TAZ. The method used was thoroughly validated in accordance with the validation requirements set out by the Food and Drug Administration (FDA) for bio-analytical processes. The proposed CE method was employed to conduct pharmacokinetic and bioavailability studies of the drugs in rat models. The pharmacokinetic results revealed that there is a significant impact upon prescribing this combination concurrently when compared to their single administration. To illustrate, the time required to reach their maximum concentrations (T max) was increased by 0.25 h for both PIP and TAZ, whereas it was increased by 0.5 for IBU. When it comes to their maximum concentration (C max), it was increased by 13.7%, 55.5%, and 44% for PIP, TAZ, and IBU, respectively. Furthermore, the bioavailabilities of PIP, TAZ, and IBU were significantly increased by 55.4%, 19.7%, and 35.6%, respectively. These findings require caution when these drugs are co-prescribed as there is a noticeable augmentation in their therapeutic impacts. Additionally, the greenness of the proposed method was assessed by three metric tools. In conclusion, the method is a valuable tool for further studies on drug-drug interaction in humans.

Effect of biosolid-derived dissolved organic matter on orthophosphate sorption to soils depends on clay mineralogy and solution composition.

Dissolved organic matter (DOM) from biosolids can alter the sorption of orthophosphate (inorganic phosphorus (IP)) to soils and, therefore, affect the bioavailability of IP. It is not clear how clay mineralogy and solution composition interfere with DOM effects on IP sorption by soils. Hence, we studied the effect of DOM on IP sorption to five semi-arid soils dominated by either illite/smectite (I/S) or kaolinite clays. IP sorption isotherms were constructed in either NaCl or CaCl2 background solution, with and without the addition of DOM. The IP sorption capacity maxima (SMAX, Langmuir model) of the I/S soils were 33-102% higher in the presence of CaCl2, as compared to NaCl. Although DOM had no effect on the IP-SMAX in the presence of CaCl2, it increased the IP-SMAX by 35-59% in the presence of the NaCl solution. Surprisingly, DOM sorption to the I/S soils was 30-90% greater in the presence of a Na+-dominated solution, as compared to a Ca2+-dominated solution. In contrast to the I/S soils, the SMAX of the kaolinitic soil was not affected by the background electrolyte (Na+, Ca2+) or the addition of DOM. Furthermore, the addition of IP reduced the sorption of DOM to the kaolinitic soil (by up to 50%) in both background electrolyte solutions. These results highlight the contrasting roles of divalent and monovalent cations in conjunction with DOM in IP sorption to semi-arid I/S soils. We propose a new approach based on two conceptual mechanisms to explain the DOM's enhancement of IP sorption to I/S soils. (1) Under dispersion conditions in the Na+-dominated solutions, Ca2+-mediated DOM-IP complexes bind to the clay's negative planar surfaces. (2) Under flocculation conditions in the Ca+-dominated solutions, the distance between adjacent platelets decreases, reducing both the electronegative charge spillover and Ca2+ bridge-mediated DOM sorption. In contrast, the addition of DOM to kaolinite, a multi-platelet clay with a low isomorphic negative charge, reduces IP sorption due to competitive sorption on the clay's broken edges.

Unraveling the role of polysaccharide-goethite associations on glyphosate’ adsorption–desorption dynamics and binding mechanisms

HypothesisGlyphosate retention at environmental interfaces is strongly governed by adsorption and desorption processes. In particular, glyphosate can react with organo-mineral associations (OMAs) in soils, sediments, and aquatic environments. We hypothesize mineral-adsorbed biomacromolecules modulate the extent and rate of glyphosate adsorption and desorption where electrostatic and noncovalent interactions with organo-mineral surfaces are favored. ExperimentsHere we use in-situ attenuated total reflectance Fourier-transform infrared, X-ray photoelectron spectroscopy, and batch experiments to characterize glyphosate’ adsorption and desorption mechanisms and kinetics at an organo-mineral interface. Model polysaccharide-goethite OMAs are prepared with a range of organic (polysaccharide, PS) surface loadings. Sequential adsorption–desorption studies are conducted by introducing glyphosate and background electrolyte solutions, respectively, to PS-goethite OMAs. FindingsWe find the extent of glyphosate adsorption at PS-goethite interfaces was reduced compared to that at the goethite interface. However, increased polysaccharide surface loading resulted in lower relative glyphosate desorption. At the same time, increased PS surface loading yielded slower glyphosate adsorption and desorption kinetics compared to corresponding processes at the goethite interface. We highlight that adsorbed PS promotes the formation of weak noncovalent interactions between glyphosate and PS-goethite OMAs, including the evolution of hydrogen bonds between (i) the amino group of glyphosate and PS and (ii) the phosphonate group of glyphosate and goethite. It is also observed that glyphosate’ phosphonate group preferentially forms inner-sphere monodentate complexes with goethite in PS-goethite whereas bidentate configurations are favored on goethite.

Fractionation and transport of compost‐derived dissolved organic matter fractions in saturated red soil and black soil columns

AbstractThe fractionation and transport of compost‐derived dissolved organic matter (DOMC) could affect the transport and fate of nutrients and DOM‐associated pollutants in the soil environment. In this study, the humic acid fraction of DOMC (HAC) and fulvic acid fraction of DOMC (FAC) were selected to investigate the fractionation and transport of DOMC in repacked soil columns of a red soil and a black soil under different KCl concentrations. The effluent DOMC fractions were monitored by ultraviolet (UV)‐visible (Vis) light and fluorescence spectroscopy. The results showed that the molecular weight (MW) of the effluent DOM approached that of the influent DOMC fractions with the injection of DOMC fractions. Three‐dimensional fluorescence excitation emission matrices (3D‐EEMs) coupled with parallel factor analysis resolved three fluorescent components, that is, low MW UV humic‐like substances (C1), high MW UV humic‐like substances (C2), and protein‐like substances (C3). The mobility of HAC and FAC decreased with increasing KCl concentrations (1 mM–50 mM), implying that electrostatic interaction was an important mechanism for the retention of DOMC in soil columns. The fact that the mobility of DOMC fractions in the black soil was greater than that in the red soil could be attributed to the high free Fe oxide content in the red soil. The retained DOMC fractions did not entirely desorb by the background electrolyte solution, suggesting that a part of the DOMC fractions retained in soil columns was strongly bound. These results are helpful in understanding the fractionation and transport of DOMC in soil environments.

Validated green high performance liquid chromatographic and capillary electrophoretic methods for estimation of dinitolmide in presence of its acid-degradation product

This study describes two new, green, fast, specific and highly sensitive stability-indicating techniques for determination of Dinitolmide (DM) in presence of its acid induced degradation product without prior separation; Acid degradation was carried out by hydrolysis with 0.1 N HCl; and the acidic degradation pathway was established by IR, and MS techniques. The first is a HPLC-Diode Array detector was performed by isocratic mode on BDS Hypersil C18 column (150 mm × 4.6 mm × 5 μm particle size) at ambient temperature with a mobile phase consisting of 5 mM sodium acetate buffer (pH 5.5): acetonitrile (40:60, v/v), flow rate of 1 mL/min and detection at 210 nm. DM and its acid degradant were eluted at 4.3 and 2.8 min, respectively offering quick analysis. Linearity of the calibration curves confirm good correlation in range of 1–15 μg/mL with recovery % of 100.02 ± 0.460. The LOD and LOQ were 0.243 and 0.737, respectively. The second method is CE -Diode Array detector was carried out at 25 °C using borate buffer (30 mM, pH 9) as background electrolyte solution and detection at 225 nm. The migration times were 2.26 and 2.97 min for DM and its acid degradant, respectively. The linearity range was 5–50 μg/mL with recovery % of 99.55 ± 0.910, LOD and LOQ were 1.010 and 3.050, respectively. The small LOD and LOQ values for both methods confirm high sensitivity of the methods The developed methods were validated according to the ICH guidelines demonstrating good accuracy and precision. The results were statistically compared with those obtained by a reported method in terms of accuracy, precision, and no significant difference was found. Both methods were successfully applied for estimating DM and its acid degradant in pure and pharmaceutical dosage forms. In addition, the methods were assessed for their greenness profile and CE was greener owing to using safer solvents and less energy consumption.

Autonomous capillary electrophoresis processing and analysis of dried blood spots for high-throughput determination of uric acid

A new set-up for fully autonomous and high-throughput capillary electrophoresis (CE) analyses of dried blood spot (DBS) samples is presented. The DBS samples were prepared by collecting exactly 5 μL of capillary blood from a finger-prick onto a pre-punched DBS disc in a disposable plastic CE vial and by in-vial blood drying. The vials with the DBS samples were then loaded into a commercial CE instrument for a fully unmanned sample processing and analysis. A fused-silica capillary of the CE instrument was first used for the transfer of 100 μL of elution solvent to each vial, in-vial DBS elution, and in-vial eluate homogenization. The same capillary was also used for at-line injection, separation, and selective analysis of the resulting eluates. Novel CE sequences were tailor-programmed for consecutive processing and analyses of multiple DBSs, which facilitated a fully autonomous determination of uric acid with a throughput of 240 DBS samples per day (24 h). The presented analytical protocol (using 100 μm i. d./30 cm capillary; 30 mM 2-(N-morpholino)-ethanesulfonic acid, 30 mM l-histidine, and 30 μM cetyltrimethylammonium bromide background electrolyte solution; and UV detection at 292 nm) provided excellent precision at endogenous and spiked uric acid concentrations with RSD values of peak areas below 3.2%. Calibration curves were linear over the 33.3 − 1200 μM range (R2 better than 0.998), limits of detection and quantification in the original capillary blood were 10 and 33.3 μM, respectively, and were well below the uric acid clinical range (140–420 μM). The stability of uric acid in DBS samples stored at laboratory temperature for up to 2 months was also excellent demonstrating less than a 4.2% decrease in uric acid concentrations. The actual set-up might thus be highly attractive for clinical subjects and laboratories because it is minimally invasive and requires minimum intervention from laboratory staff.

Chiral separation by capillary electrokinetic chromatography with hydrophobic deep eutectic solvents as pseudo-stationary phases

This study demonstrated for the first time that hydrophobic deep eutectic solvents (HDESs) can be used in capillary electrophoresis (CE) for chiral separations. We found that the an HDES methyltrioctylammonium chloride:octanoic acid (N8881Cl:OctA) can exist in the form of nano-sized microdroplets in CE background electrolyte solutions, and show hydrophobic effects as a new type of pseudo-stationary phase (PSP) during CE separation. When used in combination with various cyclodextrin (CD)-type chiral selectors, the presence of N8881Cl:OctA significantly improved the enantioresolutions of several model drugs. Moreover, the migration time of the enantiomers can also be reduced when an anionic CD (e.g., carboxymethyl-β-cyclodextrin (CM-β-CD)) was used. Critical factors influencing the chiral separations were systematically investigated including the HDES concentration, hydrogen-bond acceptor (HBA)/hydrogen-bond donor (HBD) ratio, CD concentration, buffer pH, and applied voltage, etc. An insight into chiral recognition mechanism with HDES is provided for reference. A comparison of the chiral CE performance of HDESs with traditional surfactants was also performed to demonstrate their superiority as a new type of PSP.

Voltammetric Determination of Hg2+, Zn2+, and Pb2+ Ions Using a PEDOT/NTA-Modified Electrode.

A novel electrochemical sensor for determining trace levels of Hg2+, Pb2+, and Zn2+ ions in water using square wave voltammetry (SWV) is reported. The sensor is based on a platinum electrode (Pt) modified by poly(3,4-ethylenedioxythiophene) and Nα,Nα-bis-(carboxymethyl)-l-lysine hydrate (NTA lysine) PEDOT/NTA. The modified electrode surface (PEDOT/NTA) was prepared via the introduction of the lysine-NTA group to a PEDOT/N-hydroxyphthalimide NHP electrode. The (PEDOT/NTA) was characterized via cyclic voltammetry (CV), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The effects of scan rates on the electrochemical properties of the polymer electrode were also investigated. The electrochemical results were used to estimate the coverage of the electrode polymer surface and its electrostability in background electrolyte solutions. Several analytical parameters, such as polymer film thickness, metal deposition time, and pH of the electrolyte, were examined. Linear responses to Hg2+, Pb2+, and Zn2+ ions in the concentration range of 5–100 μg L–1 were obtained. The limits of detection (LODs) for the determination of Hg2+, Pb2+, and Zn2+ ions were 1.73, 2.33, and 1.99 μg L–1, respectively. These promising results revealed that modified PEDOT/NTA films might well represent an important addition to existing electrochemical sensor technologies.

Sustainable quantitative determination of allopurinol in fixed dose combinations with benzbromarone and thioctic acid by capillary zone electrophoresis and spectrophotometry: Validation, greenness and whiteness studies

The design of novel validated methodologies targeting many goals such as simplicity, greenness, analytical efficiency and sustainability, has gained great concern in quality control units. In this sense, fast, white and sustainable analytical procedures were optimized and validated for estimation of Allopurinol (ALP) with either Benzbromarone (BZB) or Thioctic acid (TIO) in their fixed dose combinations. In procedure I, capillary zone electrophoresis (CZE) was performed using fused silica capillary (50 cm, 50 μm id), a background electrolyte solution of 50 mM borate buffer (pH 8.5) with 17 s injection time and 30 kV voltage. The diode array detector was operated at 210 nm for the three drugs. Separation occurred in 4 min with migration times 2.9, 3.3 and 3.6 min for ALP, BZB and TIO respectively. Linearity range was 10–200 μg/mL for the three drugs. Additionally, simple spectrophotometric methods were designed for simultaneous estimation of the two binary mixtures. Method I was direct absorbance measurement for determination of ALP and TIO simultaneously at 250 and 330 nm respectively. Similarly, direct Amax measurement at 356 nm was implemented for estimation of BZB in mixture with ALP. Methods II and III were based on the ratio difference and ratio spectra derivative measurements for the quantitation of ALP using BZB as divisor. The developed methods were validated conforming to the ICH guidelines and assessed for greenness and sustainability using AGREE model and the hexagon tool. On studying the whiteness features, the suggested methods were compared with 7 reported methods using the recently introduced RGB12 model.

Impact of microporous structures of esterified cellulose filter papers on Co (II) rejection in cross-flow microfiltration

• Ion rejection by a low-pressure filtration is possible by Donnan exclusion effect. • A microporous structure is important for establishing Donnan exclusion effect. • This phenomenon could be explained by the Gouy-Chapman-Stern (GCS) model. • Highly overlapped EDLs are responsible for developing Donnan exclusion effect. The Donnan exclusion effect is a unique phenomenon in which ions are electrostatically repelled by a surface bearing an identical charge. In this study, cellulose filter papers were esterified by ten different organic acids to systematically evaluate how surface properties regulate the development of the Donnan exclusion effect and subsequent Co(II) rejection. Among the esterified cellulose filter papers, those exhibiting high Co(II) rejection (>80% in 1.0 mg/L Co(II) in 1.0 mM NaCl background electrolyte solution) were noted to simultaneously possess positive zeta potential when in contact with Co(II), low adsorption affinity, and a relatively high microporous environment. This behavior could be explained by the Gouy–Chapman–Stern (GCS) model, in which the ion retention in the overlapped electrical double layers (EDLs) regulates the zeta potential development and consequently the Co(II) rejection. In addition to introducing reactive carbonyl and carboxyl groups, we suggest that the creation of a relatively microporous environment is essential for high Co(II) rejection. Our results are valuable for developing low-energy filtration systems for environmentally friendly water and wastewater treatment.

Capillary electrophoresis with capacitively coupled contactless conductivity detection: Recent applications in food control

Food quality control has become much more important during the last decade and demanded the development of robust, efficient, sensitive, and cost-effective analytical techniques. Capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) is a powerful separation method based on the different migration time rate of components in the background electrolyte solution, and it is suitable for all charged ions. There is a large number of compound groups in food that can be determined by the CE-C4D method, such as amino acids, biogenic amines, fatty acids, food additives, sweeteners, and nutrients. This paper provides an overview of recent applications of the CE-C4D in food analysis over the last decade. General conclusions and future prospects of applicability of the CE-C4D method in food analysis are presented.

Impact of solute charge and diffusion coefficient on electromigration and mixing in porous media

The application of electrokinetic techniques in porous media has great potential to enhance mass transfer rates and, thus, to mobilize contaminants and effectively deliver reactants and amendments. However, the transport mechanisms induced by the application of an external electric field are complex and entail the coupling of physical, chemical and electrostatic processes. In this study we focus on electromigration and we provide experimental evidence of the impact of compound-specific properties, such as the aqueous diffusivity and the valence of charged species, on the macroscopic electrokinetic transport. We performed a series of multidimensional experiments considering the displacement of three different tracer plumes (i.e., permanganate, allura red and new coccine) in different background electrolyte solutions. The outcomes of the experiments clearly show that both the compound-specific diffusivity and the charge of the injected and resident ions impact the transport of the selected color tracer plumes, whose evolution was monitored with image analysis. The investigated experimental scenarios led to distinct plume behavior characterized by different mass distribution, average displacement velocities, longitudinal and lateral plume spreading, shape of the invading and receding fronts, as well as dilution of the injected solutes. A numerical simulator, based on the Nernst-Planck-Poisson equations and on aqueous speciation reactions in the pore water, allowed us to quantitatively interpret the experimental results, to capture the observed patterns of plume evolution, and to illuminate the coupling between the governing physico-chemical mechanisms and the controlling role of small scale compound-specific and electrostatic properties. Finally, the model was also extended to a typical configuration of in situ electrokinetic remediation of contaminated groundwater to show the impact of such mechanisms at larger scale.

Study on development of an analytical procedure to quantify glyphosate by capillary electrophoresis method and its application for beverage

Nowadays, the issue of fresh food, drinks, and residue analysis of toxic compounds in food and drinks is increasingly interested in society. In this study, an analytical procedure for quantitative analysis of the glyphosate residue in beverages such as tea infusion and beer was developed based on the capillary electrophoresis method with capacitively-coupled contactless conductivity detector combined with sample preparation using solid phase extraction technique. The analytical conditions optimised for capillary electrophoresis equipment included: histidine/acetic acid background electrolyte solution with histidine concentration of 1 mM and pH value was adjusted to 2.75 by acetic acid; a separation voltage was 20 kV was applied and a high voltage injection at 20 kV for 10 seconds was chosen. The optimised analytical procedure has resulted in a low detection limit of glyphosate (0.42 μg/l), the repeatability and reproducibility expressed by the relative standard deviation of the peak area and migration time were both less than 10%, a wide linear range, and the obtained recovery efficiency of glyphosate on different drinks were achieved to values ranging from 88.7 to 96.3%.

Capillary Electrophoresis-based Hydrogen/Deuterium Exchange for Conformational Characterization of Proteins with Top-down Mass Spectrometry.

Resolving conformational heterogeneity of multiple protein states that coexist in solution remains one of the main obstacles in the characterization of protein therapeutics and the determination of the conformational transition pathways critical for biological functions, ranging from molecular recognition to enzymatic catalysis. Hydrogen/deuterium exchange (HDX) reaction coupled with top-down mass spectrometric (MS) analysis provides a means to characterize protein higher-order structures and dynamics in a conformer-specific manner. The conformational resolving power of this technique is highly dependent on the efficiencies of separating protein states at the intact protein level and minimizing the residual non-deuterated protic content during the HDX reactions. Here we describe a capillary electrophoresis (CE)-based variant of the HDX MS approach that aims to improve the conformational resolution. In this approach, proteins undergo HDX reactions while migrating through a deuterated background electrolyte solution (BGE) during the capillary electrophoretic separation. Different protein states or proteoforms that coexist in solution can be efficiently separated based on their differing charge-to-size ratios. The difference in electrophoretic mobility between proteins and protic solvent molecules minimizes the residual non-deuterated solvent, resulting in a nearly complete deuterating environment during the HDX process. The flow-through microvial CE-MS interface allows efficient electrospray ionization of the eluted protein species following a rapid mixing with the quenching and denaturing modifier solution at the outlet of the sprayer. The online top-down MS analysis measures the global deuteration level of the eluted intact protein species, and subsequently, the deuteration of their gas-phase fragments. This paper demonstrates this approach in differential HDX for systems, including the natural protein variants coexisting in milk.

Tuning microscopic structure of Al-based metal-organic frameworks by changing organic linkers for efficient phosphorus removal

In this study, five aluminum-based metal-organic frameworks ( i.e. Al-BDC, Al-BDC-NH 2 , Al-BHTA, Al-PMA and Al-BPDC) were synthesized by changing the organic linker. Among the five Al-MOFs, Al-BDC, which used 1,4-benzenedicarboxylate as a linker, showed the highest phosphorus adsorption capacity (97.50 mg P/g), while Al-PMA, which used 1,2,4,5-benzenetetracarboxylic acid as a linker, exhibited the lowest phosphorous adsorption capacity (42.25 mg P/g). The adsorption capacity was higher than most adsorbents reported in the literature. In addition, Al-PMA and Al-BPDC are more cost-effective for removing low concentrations of phosphorous from water. When the aqueous phosphorus concentration was less than 1.0 mg P/L, and the dosage of the five Al-MOFs was only 0.10 g/L, more than 90% of phosphorus was removed. The Al-MOFs are suitable for phosphorus removal from water over a wide pH range (5.0–9.0). In this pH range, almost no Al was detected in water after phosphorus removal, indicating that the Al-MOFs can remove phosphorus from water without causing secondary pollution. Moreover, in a NaCl (0.01 mol/L) background electrolyte solution, the Al-MOFs showed high phosphorus removal stability. The Al-MOFs have the potential to remove phosphorus from natural water. Furthermore, the mechanism study shows that electrostatic interaction and ligand exchange were defined as the main phosphorus removal pathways using the prepared Al-MOFs. These findings demonstrate that the synthesized Al-MOFs are promising candidates for removal of phosphorus from eutrophic water. • The microscopic structures of Al-MOFs were tuned with different organic linkers. • Surface area and pore structure of MOFs significantly affect the phosphorus adsorption performance. • Al-BDC shows high adsorption capacity of 97.50 mg P/g for phosphorus. • Excellent phosphorus removal efficiency was obtained in real water. • Electrostatic interaction and ligand exchange are responsible for the adsorption mechanism.

Evaluation of Enantioselective Capillary Electrophoretic Approach for the Enantiomeric Separation of Abscisic Acid

Background: The application of enantioselective capillary electrophoresis approach for the assessment of the enantiomeric purity of chiral molecules is receiving increased attention. Abscisic acid is one of the chiral sesquiterpenic plant growth regulators that regulate various ecological and physiological roles in higher plants. Enantiomeric determination of ABA is of great concern because of the different biological activity of its enantiomers. Materials and Methods: In this study, we investigated the enantioseparation selectivity of ABA by incorporating native β-cyclodextrins (β-CD) and its derivatives as chiral modifiers in the background electrolyte of an enantioselective capillary zone electrophoresis system. Electrophoretic aspects that affect the enantiomeric separation, such as pH, types of β-CD and its concentration, applied voltage, injection pressure and time, were studied and optimised. Results and Discussions: An enhancement in enantioseparation was achieved in a bare fused-silica capillary (64.5 cm × 50 mm i.d.) using a background electrolyte solution consisting of (2-hydroxypropyl)- β-CD (80 mM) solubilised in 100 mM phosphate buffer adjusted to pH 5.9 with NaOH, operated under normal polarity mode (25 kV) at 25°C, and using hydrodynamic injection (75 mbar for 10s). Relative standard deviations of (intra- and inter-day) ≤ 3.23% and ≤ 1.39% for migration times and enantiomeric fractions (EF) were achieved using the proposed method. Conclusion: The proposed chiral capillary electrophoretic method offers advantages in terms of enantioselectivity and analysis times, which can serve as a reliable platform for the stereoisomeric analysis of ABA.

Determination of sulfa antibiotic residues in river and particulate matter by field-amplified sample injection-capillary zone electrophoresis.

In the present research, field-amplified sample injection-CZE (FASI-CZE) coupled with a diode array detector was established to determine trace level sulfa antibiotic. Sulfathiazole, sulfadiazine, sulfamethazine, sulfadimethoxine, sulfamethoxazole, and sulfisoxazole were selected as analytes for the experiments. The background electrolyte solution consisted of 70.0mmol/L borax and 60.0mmol/L boric acid (including 10% methanol, pH 9.1). The plug was 2.5mmol/L borax, which was injected into the capillary at a pressure of 0.5psi for 5s. Then the sample was injected into the capillary at an injection voltage of -10kV for 20s. The electrophoretic separation was carried out under a voltage of +19kV. The capillary temperature was maintained at 20˚C throughout the analysis, and six sulfonamides were completely separated within 35min. Compared with pressure injection-CZE, the sensitivity of FASI-CZE was increased by 6.25-10.0 times, and the LODs were reduced from 0.2-0.5 to 0.02-0.05μg/mL. The method was applied to the determination of sulfonamides in river water and particulate matter samples. The recoveries were 78.59-106.59%. The intraday and interday precisions were 2.89-7.35% and 2.77-7.09%, respectively. This provides a simpler and faster method for the analysis of sulfa antibiotic residues in environmental samples.

Adsorption of Pb(II) by tourmaline-montmorillonite composite in aqueous phase

In this study, a tourmaline-montmorillonite composite (TMMs) was synthesized by vacuum sintering to adsorb Pb(II) from aqueous phase. Different sintering temperature and proportion of tourmaline (TM) were first investigated by evaluating the adsorption capacity for Pb(II). The results indicated that the proper sintering temperature of the synthesis process and proportion of TM were 800 °C and 30.7% respectively. Batch experiments indicated Pseudo-second-order kinetic model and Freundlich adsorption isotherms fitted well with the adsorption characteristics of Pb(II) on TMMs, indicating that the adsorption progress of Pb(II) on TMMs related to chemical absorption and the maximum adsorption capacity was 303.21 mg/g. The background electrolyte concentration and solution pH have little effect on the adsorption behavior of TMMs. Adsorption mechanism of Pb(II) on TMMs might attribute to the electrostatic and complexation processes such as dissociation of metal ion bonds on the surface, hydroxylation on the surface of minerals, and self-polarization. The structure of TMMs was tested by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). This work provided a good reference for the application of tourmaline on treatment of heavy metals pollution in water.