The response of the glass/calomel pH-cell in aqueous solutions containing dimethylsulphoxide at 25 and-12 degrees C.

The pH response of the glass/calomel electrochemical cell in aqueous solutions containing dimethylsulphoxide at 25 and ?12 °C has been assessed using buffer solutions whose standard pH values were assigned using the hydrogen-silver, silver chloride primary standardising cell. The glass/calomel pH cell was shown to function normally in 30% DMSO-H₂O at 25 and ?12 °C and its response, compared to the hydrogen electrode, was as good as its response in the standard aqueous system at room temperature.     

Isoelectric focusing of proteins using a pH gradient created by a concentration gradient of nonelectrolytes in solution.

A new method of producing a stable pH gradient in buffer solutions is suggested, obtained by the concentration gradient of a nonelectrolyte in buffer solutions as a result of the gradual change in the dielectric properties of the solution. The maximal concentrations of nonelectrolyte which do not influence the protein configuration allow a pH gradient with a range of two pH units to be produced. It is suggested that the properties of some polyols (i.e. glycerol or mannitol) be used to change the pH of the borate buffer for the production of greater pH gradient with a range of up to 4-5 pH units. Creating the gradient of concentration of polyols, one can obtain a pH gradient in borate buffer solutions. Though the polylydroxyl compound-borate complexes posses mobility in an electric field, a stable pH gradient can be achieved during 12 days of electrophoresis. The isoelectric focusing of haemoglobin, human serum albumin and immunoglobulins was carried out in both systems suggested. These findings were compared with isoelectric focusing in Ampholines. There was a good agreement between the methods compared. The possible differences are discussed.     

Biosensor for direct determination of organophosphate nerve agents. 1. Potentiometric enzyme electrode

A potentiometric enzyme electrode for the direct measurement of organophosphate (OP) nerve agents was developed. The basic element of this enzyme electrode was a pH electrode modified with an immobilized organophosphorus hydrolase (OPH) layer formed by cross-linking OPH with bovine serum albumin (BSA) and glutaradehyde. OPH catalyses the hydrolysis of organophosphorus pesticides to release protons, the concentration of which is proportional to the amount of hydrolysed substrate. The sensor signal and response time was optimized with respect to the buffer pH, ionic concentration of buffer, temperature, and units of OPH immobilized using paraoxon as substrate. The best sensitivity and response time were obtained using a sensor constructed with 500 IU of OPH and operating in pH 8.5, 1 mM HEPES buffer. Using these conditions, the biosensor was used to measure as low as 2 microM of paraoxon, ethyl parathion, methyl parathion and diazinon. The biosensor was completely stable for at least one month when stored in pH 8.5, 1 mM HEPES + 100 mM NaCl buffer at 4 degrees C.     

Electrogenerated chemiluminescence of luminol in neutral and alkaline aqueous solutions on a silver nanoparticle self-assembled gold electrode.

The electrochemiluminescence (ECL) behaviour of luminol on a silver nanoparticle self-assembled gold electrode in neutral and alkaline solutions was investigated using conventional cyclic voltammetry (CV). The silver nanoparticle self-assembled gold electrode exhibited excellent ECL properties for the luminol ECL system. In neutral solutions, four ECL peaks (ECL-1-ECL-4) were observed at 0.73, 1.15, -0.46 and -1.35 V (vs. SCE), respectively. The intensities of these peaks were enhanced significantly compared with those on a bulk gold electrode and a gold nanoparticle self-assembled gold electrode. It was found that ECL-1 and ECL-2 on a silver nanoparticle-modified electrode were about 1000 and 1770 times stronger than those on a bare Au electrode and were about 17 and 15 times stronger than those on a gold nanoparticle-modified electrode, respectively. In alkaline solutions, four ECL peaks were also observed that were much stronger than those in neutral solutions, and ECL-1 and ECL-2 were enhanced by about three orders and one order of magnitude compared with those on a bare Au electrode and on a gold nanoparticle self-assembled electrode, respectively. Moreover, the silver nanoparticle-modified electrode exhibited good stability and reproducibility for luminol ECL. These peaks were found to depend on a number of factors, including silver nanoparticles on the surface of the modified electrode, potential scan direction, scan rate, scan range, the presence of O2 or N2, pH values, the concentrations of NaBr and luminol, and buffer solutions. The emitter of the ECL was confirmed as 3-aminophthalate by analysing the CL spectra. The surface state of the silver nanoparticle self-assembled electrode was characterized by scanning electron microscopy (SEM) and the interface property of the electrode was studied by electrochemical impedance spectroscopy (EIS). A mechanism for the formation of these ECL peaks is proposed. The results demonstrate that luminol has excellent ECL properties, such as strong ECL intensity and good reproducibility on a silver nanoparticle-modified gold electrode, in both neutral and alkaline solutions, which is of great potential in analytical applications.     

Oxidation-reduction potential of the ferro-ferricyanide system in buffer solutions

The redox potential (E₀′) of the potassium ferrocyanide-potassium ferricyanide oxidation-reduction potential buffer was measured in four pH buffer solutions, acetate, Tris, phosphate, and borate, under specified conditions of pH, solution composition, and temperature. The potentials reported should be accurate, on the hydrogen electrode scale, to within about 2 mV and precise to within at least ±0.3 mV. Although the potential of the ferro-ferricyanide couple is sensitive to fairly small changes in experimental conditions, several methods are discussed by which this potential can be estimated with a reasonable degree of accuracy (about 2–10 mV) in solutions which differ somewhat from the particular solutions reported here. Attention is called to the need for greater care in specifying experimental conditions in the determination of redox potentials of various biological species.     

A comparison of methods using diaminobenzidine (DAB) to localize peroxidases in erythrocytes, neutrophils, and peroxidase-antiperoxidase complex.

Reactions using diaminobenzidine (DAB) to localize the enzyme peroxidase in neutrophils and peroxidase-antiperoxidase (PAP) complex during immunological staining are usually performed in Tris-HCl or phosphate buffer at pH 7.2-7.6. However, DAB solutions at pH 7.2-7.6 often demonstrate erythrocyte pseudoperoxidase as well. By lowering the pH of the DAB solutions, it is possible to selectively suppress the reactivity of pseudoperoxidase while maintaining optimal reactions in neutrophils and PAP complex. For this purpose we recommend ammonium acetate-citric acid buffer at pH 5.5 (pH 5.0-6.0) containing 44 mg DAB per 100 ml buffer and 0.003%-0.03% with respect to H2O2.     

Dye-coupled electrode system for the rapid determination of cell populations in polluted water.

We determined cell populations in polluted waters by using a fuel cell-type electrode. The electrode was constructed from a platinum anode, a silver peroxide cathode, and a membrane filter for retaining microorganisms. The principle of cell number determination is based on sensing a redox dye reduced by the microorganisms with the electrode. Sample solutions containing microorganisms were membrane filtered, and the resulting filter containing microbial cells was attached to the surface of a platinum anode. The electrode was immersed in phosphate buffer solution (0.05 M, pH 7) containing a redox dye (2,4-dichlorophenol-indophenol), and the current generated was measured. The response time of the electrode system was 10 to 20 min, and the current generated was proportional to cell populations above 10(4) cells/ml.     

A Comparison of Methods Using Diaminobenzidine (Dab) to Localize Peroxidases in Erythrocytes, Neutrophils, and Peroxidase-Antiperoxidase Complex

Reactions using diaminobenzidine (DAB) to localize the enzyme peroxidase in neutrophils and peroxidase-antiperoxidase (PAP) complex during immunological staining are usually performed in Tris-HCI or phosphate buffer at pH 7.2-7.6. However, DAB solutions at pH 7.2-7.6 often demonstrate erythrocyte pseudoperoxidase as well. By lowering the pH of the DAB solutions, it is possible to selectively suppress the reactivity of pseudoperoxidase while maintaining optimal reactions in neutrophils and PAP complex. For this purpose we recommend ammonium acetate—citric acid buffer at pH 5.5 (pH 5.0-6.0) containing 44 mg DAB per 100 ml buffer and 0.003V-0.03% with respect to H₂O₂.     

Electrochemically induced disintegration of layer-by-layer-assembled thin films composed of 2-iminobiotin-labeled poly(ethyleneimine) and avidin

A layer-by-layer assembly composed of avidin and 2-iminobiotin-labeled poly(ethyleneimine) (ib-PEI) was prepared on the surface of a platinum (Pt) film-coated quartz resonator, and an electrochemically induced disintegration of the avidin-ib-PEI assembly was studied using a quartz crystal microbalance. The resonance frequency of a five-bilayer (avidin-ib-PEI)5 film-coated quartz resonator was increased upon application of an electric potential to the Pt layer of the quartz resonator, suggesting that the mass on the quartz resonator was decreased as a result of disintegration of the (avidin-ib-PEI)5 film, due to a pH change in the vicinity of the surface of the Pt-coated quartz resonator. It may be that the (avidin-ib-PEI)5 film assembly was decomposed by acidification of the local pH on the surface of the Pt layer, which in turn was induced through electrolysis of water on Pt, because ib-PEI forms complexes with avidin only in basic media. In pH 9 solution, the (avidin-ib-PEI)5 film was decomposed under the influence of an applied potential of 0.6-1.0 V versus Ag/AgCl. The (avidin-ib-PEI)5 film was decomposed almost completely within a minute in a low concentration buffer (1 mM, pH 9), while the decomposition was slower in 10 and 100 mM buffer solutions at the same pH. The decomposition of the assembly was rapid when the electrode potential was applied in pH 9 solutions, while the response was relatively slow in pH 10 and 11 solutions. All the results are rationalized on the basis of an electrochemically induced acidification of the local environment around the (avidin-ib-PEI)5 film on the Pt layer.     

Nitrite protonation as a necessary stage in the generation of nitric oxide from nitrite in biological systems

The yields of nitric oxide from 1 mM and 10 mM sodium dithionite in 5 or 150 mM solutions of HEPES buffer (pH 7.4) differed by a factor of 200. Dithionite acted as both a strong reducing agent and an agent responsible for local acidification of the solutions without significant changes in pH. The concentration of nitric oxide was estimated by electron paramagnetic resonance (EPR) by monitoring its incorporation into water-soluble complexes of Fe with N-methyl-D-glucamine dithiocarbamate (MGD), which resulted in the formation of EPR-detectable mononitrosyl complexes of iron. Ten seconds after dithionite addition, the concentration of mononitrosyl iron complexes reached 2 μM, whereas it did not become greater than 0.01 μM in 5 mM HEPES buffer. It has been suggested that this difference results from a longer lifetime of a localized decrease in pH in a weaker buffer solution. This time could be long enough for the protonation of some nitrite molecules. Nitrous acid thus formed decomposed to nitric oxide. A difference in nitric oxide formation from nitrite in weak and strong buffer solutions was also observed in the presence of hemoglobin (0.3 mM) or serum albumin (0.5 mM). However, in the weak buffer the nitric oxide yield was only three-four times greater than in the strong buffer. An increase in the nitric oxide yield from nitrite was observed in solutions containing both proteins. A significant amount of nitric oxide from nitrite was formed in mouse liver preparation subjected to freezing and thawing procedure followed by slurrying in 150 mM HEPES buffer (pH 7.4) and dithionite addition (10 mM). We suggest that the presence of zones with lowered pH values in cells and tissues may be responsible for the predominance of the acidic mechanism of nitric oxide formation from nitrite. The contribution of nitric oxide formation from nitrite catalyzed by heme-containing proteins as nitrite reductases may be minor under these conditions.     

Alkali cation effect on carbonyl-hemoglobin's and -myoglobin's conformer populations when exposed to freeze-concentration of their phosphate-buffered aqueous solutions

Freeze-concentrated aqueous phosphate-buffered (pH 6.8) solutions of carbonyl-hemoglobin (HbCO) and -myoglobin (MbCO) were investigated by Fourier-transform infrared spectroscopy for the effect of alkali cation on the population of conformers. When using sodium phosphates as buffer components, HbCO was transformed from conformer III (at approximately 1951 cm-1) which is the dominant form at ambient temperatures, into conformer IV (at buffer concentration at a given temperature. The conformational changes started slightly below the temperature where ice began to crystallize and the remaining solution became freeze-concentrated, and they were reversible for HbCO. For MbCO in 0.5 M sodium phosphate buffer solution, however, they were irreversible and MbCO denatured completely. When potassium phosphate salts were used for preparing the buffer at the same pH of 6.8, little or no transformation of conformer III into conformer IV was observed. The conformational changes induced by sodium salts are attributed to a decrease in pH and it is shown by infrared spectroscopy that during freeze concentration drastic changes in composition of the two buffer components H2PO4-/HPO(2)4- occur, the acid component increasing strongly relative to the base component. Supersaturation is also important because change from conformer III to IV requires a minimum concentration of sodium salts: whereas 0.1 M sodium phosphate buffer concentration shows a strong effect, 0.03 M concentration does not and therefore behaves like a potassium phosphate buffer.     

A facile strategy for nonenzymatic glucose detection

Glassy carbon electrode modified with boron oxide nanoparticles supported on multiwall carbon nanotubes was obtained via a facile approach. The as-prepared modified electrode exhibits excellent electrocatalytic activity toward the redox of glucose in pH 7.0 phosphate buffer solution. The electrochemical response of the modified electrode to glucose shows a linear range of 1.5-260 μM with a correlation coefficient of 0.9986 and the calculated detection limit is 0.8 μM at a signal-to-noise ratio of 3, which makes it useful for developing the electrochemical determination of glucose concentrations without using glucose oxidase at physiological pH.     

pH and buffering in the bicinchoninic acid (4,4'-dicarboxy-2,2'-biquinoline) protein assay

The HCO3/CO3(2-) buffer used in the bicinchoninic acid (BCA) protein assay has only weak buffering capacity at the recommended pH (11.25). Consequently the assay is rather sensitive to interference from effectively acid or alkaline samples, particularly in the micro method. Adjustment of pH in these alkaline solutions of high [Na+] is complicated by Na+ errors on the pH electrode. Hence it is recommended to prepare the buffers from known amounts of NaHCO3 and Na2CO3, and to reduce the pH to around 10.7; this offers much better buffering capacity with only a limited reduction in color development.     

Use of pH 9.5 Tris-HCI Buffer Containing 5% Urea for Antigen Retrieval Immunohistochemistry

Successful antigen retrieval (AR) immunohistochemistry is dependent on the temperature, heating time, and pH value of the AR solutions. There is no single standardized AR solution, however, that is suitable for all antibodies “routinely” used in surgical pathology for immunostaining archival tissue sections. We tested a variety of AR solutions varying in pH value, chemical composition, and molarity. Based upon preliminary results, we compared three AR solutions: 0.1 M Tris-HCI buffer, pH 9.5, containing 5% urea, 0.1 M Tris-HCI buffer pH 9.5 without urea, and citrate buffer, pH 6.0. Each AR solution was tested with a panel of 34 antibodies using microwave heating for antigen retrieval. The heating conditions were standardized at 10 min and an automated stainer was used to standardize the immunostaining method. The Tris-HC1 containing urea was superior to pH 6.0 citrate buffer for 22 antibodies. In 12 cases, Tris-HC1 with urea was also superior to Tris-HC1 alone. In 12 cases, the intensity was similar for all three retrieval solutions. The staining obtained with Tris-HC1 with urea was equal to or better than with pH 6.0 citrate buffer in all cases. The Tris-HC1 with urea solution is satisfactory for AR of most antibodies employed in routine surgical pathology.     

Use of pH 9.5 Tris-HCI Buffer Containing 5% Urea for Antigen Retrieval Immunohistochemistry

Successful antigen retrieval (AR) immunohistochemistry is dependent on the temperature, heating time, and pH value of the AR solutions. There is no single standardized AR solution, however, that is suitable for all antibodies “routinely” used in surgical pathology for immunostaining archival tissue sections. We tested a variety of AR solutions varying in pH value, chemical composition, and molarity. Based upon preliminary results, we compared three AR solutions: 0.1 M Tris-HCI buffer, pH 9.5, containing 5% urea, 0.1 M Tris-HCI buffer pH 9.5 without urea, and citrate buffer, pH 6.0. Each AR solution was tested with a panel of 34 antibodies using microwave heating for antigen retrieval. The heating conditions were standardized at 10 min and an automated stainer was used to standardize the immunostaining method. The Tris-HC1 containing urea was superior to pH 6.0 citrate buffer for 22 antibodies. In 12 cases, Tris-HC1 with urea was also superior to Tris-HC1 alone. In 12 cases, the intensity was similar for all three retrieval solutions. The staining obtained with Tris-HC1 with urea was equal to or better than with pH 6.0 citrate buffer in all cases. The Tris-HC1 with urea solution is satisfactory for AR of most antibodies employed in routine surgical pathology.     

Nonisoelectric focusing in buffers.

Stable pH gradients were formed and focusing of proteins was carried out in polyacrylamide gels containing mixtures of simple, amphoteric buffers, replacing the Ampholine hitherto used in isoelectric focusing (IF). Stable pH gradients can also be formed between acid anolyte and basic catholyte if Ampholine is replaced by nonamphoteric buffers. The fact that focusing can be carried out with nonampholytes shows that focusing in this case is, and in all other cases may be, nonisoelectric. It is postulated that the pH gradient in IF forms by steady-state stacking (isotachophoresis) and forms within the stack. In distinction to ordinary steady-state stacking, however, the stack remains confined within the gel (or density gradient) since the strong acid and base in the electrolyte reservoirs bar by deprotonation or electrostatic repulsion migration into the electrode chambers.     

Urea sensor with single poly(propylene) membrane

Urease was immobilized on the plasma-aminated surface of a hyfrophobic poly(propylene) (PP) membrane. This membrane, with urease matrix on one side while maintaining its original hydrophobic property on the other, was used to construct the urea sensor. The new urea sensors had response sensitivities ranged from 19 mV/decade to 30 mV/decade depending on the conditions of the plasma reaction. The enzyme electrode using single membrane gave a shorter response time as compared to the corresponding conventional electrode employing two seperate PP membranes. The sensitivity of the enzyme electrode increased with increasing buffer pH and reached a maximal level (40 mV/decade) at pH 7.6. The response sensitivity of the electrode was not affected by the change of buffer strength. Deamination of the plasma-modified hydrophobic PP membrane did not occur in aqueous environment judging from the stability of the urea electrode up to 12 days of operation. (c) 1992 John Wiley & Sons. Inc.     

Standard electromotive force of the H2-AgCl;Ag cell in 30, 40, and 50 mass% glycerol/water from -20 to 25 degrees C: pK2 and pH values for a standard "mops" buffer in 50 mass% glycerol/water

Data are presented regarding the establishment of the pH (designated pH*) of a standard buffer solution suitable as a pH reference in 50 mass% glycerol/water mixtures at temperatures ranging from -20 to 25 degrees C. The buffer material selected was the ampholyte Mops [(3-N-morpholino)-propane sulfonic acid], and the reference standard consists of equal molal amounts of Mops and its sodium salt. The assignment of pH* values is based on measurements of the electromotive force (emf) of cells without liquid junction of the type: Pt;H2(g, 1 atm) / Mops, Na Mopsate, NaCl / AgCl;Ag and the pH* was derived from a determination of K2, the equilibrium constant for the dissociation process (Mops) +/- in equilibrium with (Mopsate)- + H+. The standard emf of the silver-silver chloride electrode in 30, 40, and 50 mass% glycerol/water mixtures was determined from emf measurements of the cell at subzero temperatures with HCl solutions replacing the buffer-chloride mixtures.     

Drug Potencies on Partially Purified Brain D2 Dopamine Receptors

To examine the sensitivities of partially purified dopamine receptors to various dopaminergic agonists and antagonists, canine brain striatum dopamine receptors were enriched by isoelectric focusing. The digitonin-solubilized receptors were prelabelled with [3H]spiperone and focused for two time periods. After 5 h (incomplete focusing), radioactive peaks were detected at pH 6 and 9-11. Only the pH 6 peak revealed drug sensitivities expected of D2 receptors. Receptor recovery of the pH 6 peak was 79% with purification being sevenfold. After focusing overnight to equilibrium, the pH 6 peak further separated into peaks at pH 4.6 and 6.8. The receptor was identified only in the pH 4.6 fraction. The recovery of receptors in the pH 4.6 peak was low (10%), indicating little enrichment of the receptor. The rank order of binding of neuroleptics and dopamine agonists to the purified material was similar to that of the original preparation of soluble receptors. Dopamine did not bind to the purified pH 4.6 fraction unless the phosphate buffer (used during focusing) was replaced with Tris buffer. The absence of receptors in the pH 6.8 and pH 10 fractions, although both contained prelabeled [3H]spiperone, indicates the importance of testing agonists and antagonists on each fraction at each step in purification.     

Rapid-growth responses of corn root segments: Effect of auxin on elongation

The effect of indole-3-acetic acid (IAA) on the elongation rates of 2 mm corn (Zea mays L.) root segments induced by citrate-phosphate buffer (or unbuffered) solutions of pH 4.0 and 7.0 was studied. At pH 7.0, auxin initially reduced the elongation rate in both buffered and unbuffered solutions. Only in buffer at pH 7.0 was auxin at a concentration of 0.1 M found to promote the elongation rate though briefly. THis promoted rate represented only ca. 20% of the rate achieved with only buffer at pH 4.0. Auxin in pH 4.0 buffered and unbuffered solutions only served to reduce the elongation rates of root segments. Some comparative experiments were done using 2 mm corn coleoptile segments. Auxin (pH 6.8) promoted the elongation rate of coleoptile segments to a level equal or greater than the maximal H ion-induced rate. The two responses of root segments to auxin are compared to auxin action in coleoptile growth.