Concentrated Buffer Solutions Research Articles

Drug Crystal Precipitation in Biorelevant Bicarbonate Buffer: A Well-Controlled Comparative Study with Phosphate Buffer.

The purpose of the present study was to clarify whether the precipitation profile of a drug in bicarbonate buffer (BCB) may differ from that in phosphate buffer (PPB) by a well-controlled comparative study. The precipitation profiles of structurally diverse poorly soluble drugs in BCB and PPB were evaluated by a pH-shift precipitation test or a solvent-shift precipitation test (seven weak acid drugs (pKa: 4.2 to 7.5), six weak base drugs (pKa: 4.8 to 8.4), one unionizable drug, and one zwitterionic drug). To focus on crystal precipitation processes, each ionizable drug was first completely dissolved in an HCl (pH 3.0) or NaOH (pH 11.0) aqueous solution (450 mL, 50 rpm, 37 °C). A 10-fold concentrated buffer solution (50 mL) was then added to shift the pH value to 6.5 to initiate precipitation (final volume: 500 mL, buffer capacity (β): 4.4 mM/ΔpH (BCB: 10 mM or PPB: 8 mM), ionic strength (I): 0.14 M (adjusted by NaCl)). The pH, β, and I values were set to be relevant to the physiology of the small intestine. For an unionizable drug, a solvent-shift method was used (1/100 dilution). To maintain the pH value of BCB, a floating lid was used to avoid the loss of CO2. The floating lid was applied also to PPB to precisely align the experimental conditions between BCB and PPB. The solid form of the precipitants was identified by powder X-ray diffraction and differential scanning microscopy. The precipitation of weak acids (pKa ≤ 5.1) and weak bases (pKa ≥ 7.3) was found to be slower in BCB than in PPB. In contrast, the precipitation profiles in BCB and PPB were similar for less ionizable or nonionizable drugs at pH 6.5. The final pH values of the bulk phase were pH 6.5 ± 0.1 after the precipitation tests in all cases. All precipitates were in their respective free forms. The precipitation of ionizable weak acids and bases was slower in BCB than in PPB. The surface pH of precipitating particles may have differed between BCB and PPB due to the slow hydration process of CO2 specific to BCB. Since BCB is a physiological buffer in the small intestine, it should be considered as an option for precipitation studies of ionizable weak acids and bases.

Nonlinear electrophoresis of nonspherical particles in a rectangular microchannel.

Nonlinear electrophoresis offers advantageous prospects in microfluidic manipulation of particles over linear electrophoresis. Existing theories established for this phenomenon are entirely based on spherical particle models, some of which have been experimentally verified. However, there is no knowledge on if and how the particle shape may affect the nonlinear electrophoretic behavior. This work presents an experimental study of the nonlinear electrophoretic velocities of rigid peanut- and pear-shaped particles in a rectangular microchannel, which are compared with rigid spherical particles of similar diameter and surface charge in terms of the particle slenderness. We observe a decrease in the nonlinear electrophoretic mobility, whereas an increase in the nonlinear index of electric field when the particle slenderness increases from the peanut- to pear-shaped and spherical particles. The values of the nonlinear index for the nonspherical particles are, however, still within the theoretically predicted range for spherical particles. We also observe an enhanced nonlinear electrophoretic behavior in a lower concentration buffer solution regardless of the particle shape.

Comparison of injection pain in pediatric population; original versus generic rocuronium.

Background:Rocuronium-induced injection pain causes withdrawal movements. These movements may cause accidental disruption of indwelling needles. Generic rocuronium contains low-acid concentration buffer solution compared with original rocuronium. In animal experiments, it has been suggested that the difference of the buffer solution may alleviate injection pain. The purpose of this study was to identify the difference of injection pain between original and generic rocuronium in pediatric population.Material and Methods:Patients ranging in age from 1 to 15 years, American Society of Anesthesiologists physical status I or II, undergoing elective surgeries were randomly allocated to two groups; generic rocuronium group (Group R) and original rocuronium (Eslax®) group (Group E). Following anesthetic induction with oxygen, nitrous oxide, and sevoflurane, original or generic rocuronium (1 mg/kg) was administered via intravenous catheter. The difference of vital signs and withdrawal movement associated with rocuronium injection were evaluated.Results:A total of 64 patients were included in the study. Three patients were excluded. Twenty-nine patients were assigned to Group E and 32 patients to Group R. There was no significant difference in mean arterial pressure and heart rate. No withdrawal movements were observed in both groups.Conclusion:There was no significant difference in injection pain between original and generic rocuronium under inhalational induction.

Estimating Detection Limits of Potentiometric DNA Sensors Using Surface Plasmon Resonance Analyses.

As the signals of potentiometric-based DNA ion-selective field effect transistor (ISFET) sensors differ largely from report to report, a systematic revisit to this method is needed. Herein, the hybridization of the target and the probe DNA on the sensor surface and its dependence on the surface probe DNA coverage and the ionic strength were systematically investigated by surface plasmon resonance (SPR). The maximum potentiometric DNA hybridization signal that could be registered by an ISFET sensor was estimated based on the SPR measurements, without considering buffering effects from any side interaction on the sensing electrode. We found that under physiological solutions (200 to 300 mM ionic strength), the ISFET sensor could not register the DNA hybridization events on the sensor surface due to Debye screening. Lowering the salt concentration to enlarge the Debye length would at the same time reduce the surface hybridization efficiency, thus suppressing the signal. This adverse effect of low salt concentration on the hybridization efficiency was also found to be more significant on the surface with higher probe coverage due to steric hindrance. With the method of diluting buffer, the maximum potentiometric signal generated by the DNA hybridization was estimated to be only around 120 mV with the lowest detection limit of 30 nM, occurring on a surface with optimized probe coverage and in the tris buffer with 10 mM NaCl. An alternative method would be to achieve high-efficiency hybridization in the buffer with high salt concentration (1 M NaCl) and then to perform potentiometric measurements in the buffer with low salt concentration (1 mM NaCl). Based on the characterization of the stability of the hybridized DNA duplexes on the sensor surface in low salt concentration buffer solutions, the estimated maximum potentiometric signal could be significantly higher using the alternative method. The lowest detection limit for this alternative method was estimated to be around 0.6 nM. This work can serve as an important quantitative reference for potentiometric DNA sensors.

Measurement of Ion-Pairing Interactions in Buffer Solutions With Microwave Microfluidics

Microwave microfluidic spectroscopy is an emerging technique for quantifying the frequency-dependent electrical response of fluids. This technique can access important physical properties, including ion mobility and hydration, which are directly applicable to biochemistry. One critical step toward quantifying these effects is to develop accurate models for the behavior of buffer solutions containing mobile ions. Here, we show that ions in buffer solutions produce a weak ion-pairing response. We used microfluidic channels integrated with coplanar waveguides in combination with a hybrid microwave calibration protocol to extract the broadband microwave admittance spectra of a standard TAE-Mg2+ buffer solution between 100 kHz and 67 GHz. To characterize the ion-pairing response, we fit the calibrated admittance data with two models: a conventional model without ion-pairing and with a water relaxation described by a “Cole-Cole” function, to our alternative model that includes ion-pairing and a single Debye-type water relaxation. Including ion-pairing improved the goodness of fit across the entire frequency range. In the higher concentration buffer solution, we saw a reduction in the max systematic error in the fit residuals from 10% to less than 4%. The measurement and fitting techniques are widely applicable, providing critical information about the behavior of solvated ions.

Qualitative and quantitative measurement of cannabinoids in cannabis using modified HPLC/DAD method

This study presents an accurate and high throughput method for the quantitative determination of various cannabinoids in cannabis plant material using high pressure liquid chromatography (HPLC) with a diode array detector (DAD). Sample extraction and chromatographic analysis conditions for the measurement of cannabinoids in the complex cannabis plant material matrix were optimized. The Agilent Poroshell 120 SB-C18 column provided high resolution for all target analytes with a short run time (10minutes) given the core shell technology. The aqueous buffer mobile phase was optimized with ammonium acetate at pH 4.75. The change in the mobile phase and the new column ensured a separation between cannabidiol (CBD and cannabigerol (CBG) along with cannabigerol and tetrahydrocannabinolic acid (THCA), which were not well separated by previous publications, improved buffering capacity, and provided analytical performance stability. Moreover, baseline drifting was significantly minimized by the use of a low concentration buffer solution (25mM ammonium acetate). In addition, evaporation and reconstitution of the sample residue with a methanol-organic pure (OP) water solution (65:35) significantly reduced the matrix interference. The modified extraction produced good recoveries (>91%) for each of the eight cannabinoids.The optimized method was validated for specificity, linearity, sensitivity, precision, accuracy, and stability. The combined relative standard deviation (%RSD) for intra-day and inter-day precision for all eight analytes varied from 2.5% to 5.2% and 0.28% to 5.5%, respectively. The %RSD for the repeatability study varied from 1.1% to 5.5%. The recoveries from spiked cannabis matrix samples were greater than 90% for all analytes, except delta-8-tetrahydrocannabinol (Δ8-THC), which was 80%. The recoveries varied from 81% to 107% with a precision of 0.7-8.1%RSD. Delta-9-tetrahydrocannabinol (Δ9-THC) in all of the cannabis samples (n=635) was less than 10%, which is in compliance with the NJ Medicinal Marijuana regulation. Analysis of samples from two cultivars, which included ten individual samples, four composite samples, seven calibration standards, and four quality control standards, can be performed within 24hours by this high throughput method.

27 - Redox Behavior of 2,2-Diphenyl-1-Picrylhydrazyl Radical (DPPH∙) Solubilized in Water by β-Cyclodextrin

2,2-Diphenyl-1-picrylhydrazyl radical (DPPH ● ) is a relatively stable radical and frequently used as a reactivity model of reactive oxygen species. However, its insolubility in water precludes the investigation of the redox behavior of DPPH ● in aqueous media, especially in concentrated buffer solutions. We have recently reported that DPPH ● can be successfully solubilized in water by β -cyclodextrin ( β -CD). The as-obtained β -CD-solubilized DPPH ● (DPPH ● / β -CD) was demonstrated to be a powerful tool for evaluating the antioxidative activity of water-soluble antioxidants, such as ascorbic acid, Trolox, and caffeic acid, in concentrated buffer solutions. In this study, the redox behavior of DPPH ● / β -CD was investigated by cyclic voltammetry. A well-defined reversible redox wave was observed for one-electron reduction of DPPH ● / β -CD in phosphate buffer (0.1 M, pH 7.4). On the other hand, one-electron oxidation of DPPH ● / β -CD showed a quasi-reversible redox wave, which suggests that DPPH cations (DPPH + ) generated by the electrochemical one-electron oxidation may undergo a follow-up chemical reaction, such as an addition of a water molecule.

Efficient solar hydrogen production from neutral electrolytes using surface-modified Cu(In,Ga)Se2photocathodes

Surface thin conductor layers enhance sunlight driven hydrogen evolution from water using Cu(In,Ga)Se2photocathodes in a concentrated phosphate buffer solution.

Surface grafted chitosan gels. Part II. Gel formation and characterization.

Responsive biomaterial hydrogels attract significant attention due to their biocompatibility and degradability. In order to make chitosan based gels, we first graft one layer of chitosan to silica, and then build a chitosan/poly(acrylic acid) multilayer using the layer-by-layer approach. After cross-linking the chitosan present in the polyelectrolyte multilayer, poly(acrylic acid) is partly removed by exposing the multilayer structure to a concentrated carbonate buffer solution at a high pH, leaving a surface-grafted cross-linked gel. Chemical cross-linking enhances the gel stability against detachment and decomposition. The chemical reaction between gluteraldehyde, the cross-linking agent, and chitosan was followed in situ using total internal reflection Raman (TIRR) spectroscopy, which provided a molecular insight into the complex reaction mechanism, as well as the means to quantify the cross-linking density. The amount of poly(acrylic acid) trapped inside the surface grafted films was found to decrease with decreasing cross-linking density, as confirmed in situ using TIRR, and ex situ by Fourier transform infrared (FTIR) measurements on dried films. The responsiveness of the chitosan-based gels with respect to pH changes was probed by quartz crystal microbalance with dissipation (QCM-D) and TIRR. Highly cross-linked gels show a small and fully reversible behavior when the solution pH is switched between pH 2.7 and 5.7. In contrast, low cross-linked gels are more responsive to pH changes, but the response is fully reversible only after the first exposure to the acidic solution, once an internal restructuring of the gel has taken place. Two distinct pKa's for both chitosan and poly(acrylic acid), were determined for the cross-linked structure using TIRR. They are associated with populations of chargeable groups displaying either a bulk like dissociation behavior or forming ionic complexes inside the hydrogel film.

Development of a square wave voltammetric method for dopamine determination using a biosensor based on multiwall carbon nanotubes paste and crude extract of Cucurbita pepo L.

The development of an enzymatic biosensor for dopamine (DA) determination based on functionalized multiwall carbon nanotubes (MWCNTs) and horseradish peroxidase (HRP) obtained from the crude extract of zucchini (Cucurbita pepo L.) is proposed. The biosensor was developed by means of the immobilization of the enzyme by covalent bonding to carrier MWCNTs functionalized. In the presence of hydrogen peroxide, HRP catalyzes the oxidation of DA to o-dopaquinone and the reduction of o-dopaquinone, which requires a low potential difference. The influence on the response of analytical parameters of biosensor such as enzyme concentration, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) concentration, H2O2 concentration, pH and phosphate buffer solution concentration, as well as the electroanalytical technique, cyclic voltammetry, square wave voltammetry and differential pulse voltammetry were investigated. The analytical parameters obtained including the sensitivity, linearity, precision, accuracy, and stability were investigated and were within the recommended guidelines. The validated method proved to be efficient for DA determination in pharmaceutical formulation and presented good selectivity even in the presence of uric acid and ascorbic acid.

Investigation of processes of chlorination of thorium-containing rare-metal concentrates, deactivation of solutions, purification of scandium from impurities to obtain marketable scandium oxide

The possibility and conditions of the inversion voltammetric estimation of antimony on the basis of different in nature and concentration background electrolytes or buffer solutions are shown and optimized. It is established that the elaborated method can be applied in the analysis of modeled binary, triple, and more complex mixtures as well as of real natural objects and industrial materials. In all cases the elaborated inversion voltammetric method is evaluated by metrological procedure, and the relative standard deviation (S r) is no more 0.129.

Analytical abilities of the inversion voltammetry in setermination of antimony in industrial materials

The possibility and conditions of the inversion voltammetric estimation of antimony on the basis of different in nature and concentration background electrolytes or buffer solutions are shown and optimized. It is established that the elaborated method can be applied in the analysis of modeled binary, triple, and more complex mixtures as well as of real natural objects and industrial materials. In all cases the elaborated inversion voltammetric method is evaluated by metrological procedure, and the relative standard deviation (Sr) is no more 0.129.

Structure variations of the grafted functional polymer brush enhance membrane adsorber performance

A new method to prepare membrane adsorbers with structure variations of functional polymer brush, the initiator entrapping method via photo-initiated surface-selective graft-copolymerization was used in this work. Functional polymer brush structures on polypropylene (PP) microfiltration membrane pore surfaces were obtained by using acrylic acid (AA) as functional monomer. Copolymerization of AA with ‘‘diluent’’ monomer acryl amide (AAm) and ‘‘crosslinker’’ methylene bisacrylamide (MBAA) was done for variations of the grafted layer. Characterization had been done by measurements of reversible protein binding (lysozyme, Lys), stepwise change of a high concentration buffer solution to a low one having the same pH value (inadvertent pH transient) and breakthrough curves for Lys. Membrane adsorber grafted with functional monomer AA was used as reference, membrane adsorber grafted with the mixture of functional and diluent monomers (AA/AAm) show low amount of protein binding and low inadvertent pH transient value as well as early and broad breakthrough curve, while membrane adsorber grafted with a mixture of functional and crosslinker monomer (AA/MBAA) show high amount of protein binding and high inadvertent pH transient value as well as late and sharp breakthrough curve. Structure variations of the grafted functional polymer brush membrane adsorber with crosslinker monomer (AA/MBAA) show the lowest axial dispersion and thus also increase the efficiency of adsorbent utilization.

Synthesis and properties of electrically‐sensitive poly(acrylic acid‐co‐acetoacetoxy ethyl methacrylate) gels

AbstractA series of electric field sensitive copolymer P(AA‐co‐AAEM) gels of acrylic acid (AA) with acetoacetoxy ethyl methacrylate (AAEM) were prepared by free‐radical copolymerization, with N,N′‐methylene bisacrylamide (MBAAm) and ammounium persulfate (APS) as crosslinking agent and initiator, respectively. The structures and properties of the gels were tunable by changing the monomer feed weighty ratio (R) (R = WAAEM/(WAAEM + WAA) of AAEM and AA. The influences of the NaCl concentration and pH buffer solutions on the equilibrium swelling ratios of the gels were studied in detail. It is shown that both NaCl concentration and pH value of the buffer solution affect the swelling properties of the P(AA‐co‐AAEM) gels greatly. Moreover, the gel deswelling behavior induced by a direct current electric field was investigated and an excellent electric‐sensitivity was found. Among all the samples, the gel with monomer feed weighty ratio (R) = 0.1479 showed the best electrical contraction properties. On the basis of the experimental results, the mechanism of the electricity‐induced deswelling behavior was presented. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of Joule heating on electrokinetic transport

The Joule heating (JH) is a ubiquitous phenomenon in electrokinetic flow due to the presence of electrical potential gradient and electrical current. JH may become pronounced for applications with high electrical potential gradients or with high ionic concentration buffer solutions. In this review, an in-depth look at the effect of JH on electrokinetic processes is provided. Theoretical modeling of EOF and electrophoresis (EP) with the presence of JH is presented and the important findings from the previous studies are examined. A numerical study of a fused-silica capillary PCR reactor powered by JH is also presented to extend the discussion of favorable usage of JH.

An online field-amplification sample stacking method for the determination of diuretics in urine by capillary electrophoresis-amperometric detection

A simple and sensitive online field-amplification sample stacking (FASS) pre-enrichment method following by capillary electrophoresis with amperometric detection has been developed for the determination of diuretics, such as indapamide (IDP), hydrochlorothiazide (HCT) and bumetanide (BMTN) in urine. Under the optimum conditions, it was found that the low concentration buffer solution could be used as the diluents for simultaneous field-amplification injection of three diuretics after electrokinetically injecting a short water plug (15 kV, 3 s). Three analytes could be well separated within 10 min in an uncoated fused-silica capillary with H 3BO 3–Na 2B 4O 7 (BB) buffer solution (pH 8.98). The detection limits (S/N = 3) were 9.0 ng/mL for IDP, 20 ng/mL for HCT and 1.5 ng/mL for BMTN, respectively. The detection limits of three diuretics were much lower by FASS than that by conventional sample injection, of which the detection limits were 340, 890 and 330 ng/mL for IDP, HCT and BMTN, respectively. Especially, for bumetanide the detection limit was 220-time lower by FASS. The linear ranges of three diuretics were all over three orders of magnitude. The proposed method has been successfully applied to analyze the diuretics in human urine samples without off-column sample pre-concentration.

Electrochemical sensing of silver tags labelled DNA immobilized onto disposable graphite electrodes

An electrochemical approach for the improved electrochemical sensing of DNA was developed in this study based on the oxidation signals of silver and DNA base, guanine by using disposable pencil graphite electrode (PGE) electrodes. The easy surface modification of disposable electrodes PGEs with nucleic acids was performed by passive adsorption using amino linked DNA oligonucleotide attached onto the surface of silver nanoparticles (Ag-NPs). Firstly, the microscopic characterization of silver nanoparticles was investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and the electrochemical behaviour of these NPs was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Then, the overall performance of this novel electrochemical DNA sensing method based on these nanoparticles is studied and discussed in terms of optimum analytical conditions, such as; the effect of DNA concentration, NPs concentration and different buffer solutions, etc. in order to obtain silver and guanine oxidation signals in higher sensitivity and selectivity. The main features related with this electrochemical assay based on silver nanoparticles are discussed and compared with other assays reported in the literatures.

μAg particle-based molecular sensing/recognition via surface-enhanced Raman spectroscopy

In this study, we demonstrate that powders of commercially available 2-microm-sized Ag (microAg) can be used as a core material for constructing molecular sensing/recognition units operating via surface-enhanced Raman scattering (SERS). This is possible because microAg powders are very efficient substrates for both the infrared and Raman-spectroscopic characterization of molecular adsorbates prepared in a similar manner on silver surfaces. The Raman spectrum of organic monolayers on powdered silver is a SERS spectrum. The agglomeration of microAg particles in a highly concentrated buffer solution could be prevented by the deposition of polar molecules like 1,4-phenylenediisocyanide (1,4-PDI), and mixed self-assembled monolayers of 1,4-PDI and N-(+)-biotinyl-6-aminocaproic acid on microAg particles were then confirmed via the SERS of 1,4-PDI to selectively recognize the avidin arrays formed on a separate biotinylated substrate. According to a dose response curve, avidin at >10(-6)g/mL could be easily identified by the present method. In addition, the non-specific adsorption of microAg particles was found to be negligibly small, probably because the Ag particles were too heavy to be retained on organic substrates solely by non-specific interaction.

Silver-Particle-Based Surface-Enhanced Raman Scattering Spectroscopy for Biomolecular Sensing and Recognition

In this study, we demonstrate that 2-microm-sized Ag (microAg) powders can be used as a core material for constructing molecular sensing/recognition units operating via surface-enhanced Raman scattering (SERS). This is possible because microAg powders are very efficient substrates for both the infrared and Raman-spectroscopic characterization of molecular adsorbates prepared in a similar manner on silver surfaces; we can obtain an infrared spectrum of organic molecules adsorbed on microAg particles with a very high signal-to-noise ratio by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and the Raman spectrum of organic monolayers on powdered silver is an SERS spectrum. The agglomeration of microAg particles in a highly concentrated buffer solution could be prevented by the layer-by-layer deposition of cationic and anionic polyelectrolytes such as poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). In fact, prior to depositing PAA and PAH, 4-aminobenzenethiol (4-ABT) was assembled on the surfaces of the microAg particles as SERS markers. Because of the presence of amine groups of 4-ABT, PAA could be readily deposited on the microAg particles. On the other hand, the outermost PAA layer could also be derivatized with biotin-derivatized poly(L-lysine). The nonspecific interaction of poly(L-lysine) with proteins could be suppressed by grafting poly(ethylene glycol) into the biotin-derivatized poly(L-lysine) molecules. On the basis of the nature of the SERS peaks of 4-ABT, it was confirmed that these biotinylated microAg powders were effective in selectively recognizing the streptavidin arrays. Because a number of different molecules can be used as SERS-marker molecules, such as probable 4-ABT, commercially available microAg powders must be a prospective material in molecular sensing/recognition, particularly via SERS.

Comment on “On the use of anion exchange chromatography for the characterization of water soluble organic carbon” by H. Chang et al.

Comment on “On the use of anion exchange chromatography for the characterization of water soluble organic carbon” by H. Chang et al.