Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Buffers”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed1998

Copper(II) complexation properties and surfactant activity of 3-[N, N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid and N-(2-Hydroxyethyl)piperazine-N'-2-hydroxypropanesulfonic acid pH buffers which may affect trace metal speciation in in vitro studies.

Disadvantages of the some zwitterionic pH buffers are (i) that they can interact with metal ions as well as protons, and (ii) that they may have a surfactant effect in chemical or in vitro biological or biochemical studies. This has to be taken into account when a buffer is selected. Here, the copper-complexing capacity and the surfactant activity of three compounds, 3-[N,N-bis (2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO), N-(2-hydroxyethyl)piperazine-N'-(2-hydroxypropanesulfonic acid) (HEPPSO), and piperazine-N,N'-bis(2-ethanesulfonic acid) (Pipes), were investigated. Global stability constants (log betaabc) of copper(II)-buffer complexes were determined, at 25 degrees C, 0.5 M ionic strength, and at 0.8 mM buffer concentration, by pH and pCu ion-selective electrode measurements. Here, betaabc corresponds to the equilibrium: aCu2+ + bL- + cH+ left and right arrow (CuaLbHc)(2a-b+c); HL = DIPSO or HEPPSO; c: +1 = proton; -1 = hydroxide. Using SUPERQUAD constants were calculated, giving: DIPSO: log beta110 = 5.02, log beta120 = 8.99, log beta130 = 13.0, log beta140 = 16.3, log beta14-1 = 9.26, log beta14-2 = 0.645, log beta150 = 20.5, log beta160 = 24.3, log beta16-1 = 16.1, log beta16-2 = 8.98; HEPPSO: log beta110 = 4.29, log beta120 = 8.35, log beta130 = 12.1, log beta140 = 15.9, log beta150 = 19.6, log beta160 = 23.4, log beta16-1 = 14.9. The pKa values were determined at higher buffer concentrations, giving a value 7.33 for DIPSO and 7.84 for HEPPSO at 2.0 mM buffer concentration. Effects of buffer concentration on stability and acidity constants were investigated and compared with measurements using voltammetric and potentiometric stripping analysis, confirming no copper(II) complexation by Pipes. Surfactant activities were determined using alternating current polarography, confirming marked surface activity of 10 mM of DIPSO or HEPPSO.

Buffers↗
PubMed1994

[The effect of buffers in liver preservation solutions on hepatocytes in a model of in vitro preservation and reoxygenation].

In order to answer the question of whether there is an optimal buffer system for the preservation and reoxygenation period in liver transplantation, sodium/potassium phosphate, HEPES, TRIS (THAM), MOPS and histidine/His-HCl buffers were investigated. The buffers were added to an "extracellular" electrolyte composition of preservation solution. The solutions were incubated with in vitro cultures of pig hepatocytes in two different models. I: during cold hypoxia (4 degrees C, PO2 < 0.1 mmHg) for 24 h, and II. during the reoxygenation period of 3 h after preservation in UW solution. Cell viability, cell detachment rate, and LDH and GOT liberation were used as parameters of cell alteration. The lowest amount of enzyme release during the preservation period and reoxygenation was obtained using sodium or potassium phosphate buffer. Rising LDH and GOT liberation rates during preservation and reoxygenation were observed with HEPES and TRIS buffer. The enzyme release induced by these three buffer systems correlated with their pKa values. Higher pH of the preservation solution resulted in higher enzyme leakage from the cells. In contrast, the Histidine/HCl buffer system with low pH led to striking cell damage during preservation as well as during reoxygenation. MOPS, a weak acid with the lowest pH in solution, led to the lowest enzyme release during the preservation period, but to high enzyme release after reoxygenation with standard medium. Incubation of the cultures with MOPS after UW preservation resulted in lower enzyme levels in comparison to the controls. In summary, PBS had the best results in our study.

Acid-Base Equilibrium↗
PubMed1979

Rapid demineralization in acidic buffers.

The demineralization of routine histological specimens in buffers of weakly ionized organic acids, unbuffered formic acid, and EDTA was investigated. The rate of demineralization was measured by a chemical method and from radiographs. Lactate-containing buffers and buffers of formic acid with its potassium salt were more rapid in effect than any other agent. Acidic buffers and unbuffered formic acid produced rapid diffuse demineralization with secondary precipitation of calcium salts. Preservation of dental enamel in such buffers resulted from the significantly slower rate of enamel demineralization than that for bone and dentine. In rapid demineralizing agents the secondary salts were quickly redissolved while in slow buffers these salts persisted. Multivalent ions such as citrate and maleate slowed the rate of demineralization, and a citrate-containing buffer was the slowest of all the agents tested. Demineralization in EDTA exhibited a different pattern with the establishment of a well-defined front of demineralization without apparent reprecipitation. EDTA attacked enamel, bone and dentine at the same rate. An attempt was made to relate the observed rates of demineralization to current theories of the demineralization process.

Animals↗
PubMed1976

Influence of 2,3-diphosphoglycerate on the buffering properties of human blood: role of the red cell membrane.

The effect of the concentration of red cell 2,3-diphosphoglycerate (2,3-DPG, 0.5-21 mumoles/g cells) on the buffering properties and on the slope of the relation between the extracellular and intracellular pH (deltapHi/deltapHe) of human blood was studied. The results were evaluated in connection with previous findings concerning the effect of 2,3-DPG on the Donnan ratio rH+ = H+e/H+i. deltapHi/deltapHe decreases with rising red cell 2,3-DPG content as well as with rising extracellular pH. deltapHi/deltapHe and rH+ can be related to each other by the empirical equation deltapHi/deltapHe = 1 + log rH+ = 1 + pHi - pHe. The validity of this equation appears to be restricted to conditions where the Donnan ratio rH+ is altered between 0.3 and 1 either by changes of the red cell concentration of buffering anions such as 2,3-DPG or by changes of the extracellular pH. As determined in suspensions of red cells with intact membranes, the 2,3-DPG-and pH-induced changes of deltapHi/deltapHe lead to proportional changes in the buffering power of the non-bicarbonate buffers of erythrocytes. Due to this effect the buffering power of suspensions of cells containing 5 times the normal concentration of the buffer 2,3-DPG is lower than that of cells with normal 2,3-DPG content (at extracellular pH values above 7). These findings demonstrate that the action of intracellular non-bicarbonate buffers in blood is effectively modulated by the physico-chemical properties of the red cell membrane.

Biological Transport↗
PubMed2006

Comparison of buffered and unbuffered local anaesthesia for inguinal hernia repair: a prospective study.

Bicarbonate buffered local anaesthetic solutions are known to reduce the pain of infiltration. However, its efficacy in reducing the pain of infiltration in patients undergoing inguinal hernia repair has never been tested. This study aims to test the efficacy of bicarbonate buffered solution in reducing the pain of infiltration and pain for the total surgical procedure in a series of patients undergoing elective inguinal hernia repair. Forty consecutive male patients with unilateral, reducible inguinal hernias were studied prospectively. All patients underwent surgery under local anaesthesia, the first 20 with unbuffered solution and the next 20 using buffered solution. Pain scores were obtained for the infiltration in the anaesthetic room and for the total surgical procedure. In addition, satisfaction scores were obtained at the end of the procedure. The mean pain score for the initial infiltration of unbuffered anaesthetic was 3.00 (range 0-5), and for the buffered anaesthetic it was 1.45 (range 0-4), P=0.02. The mean pain score for the entire procedure for the unbuffered group was 3.05 (range 0-6), and for the buffered group it was 1.45 (range 0-5), P=0.02. The patient satisfaction rate was higher with the buffered solution compared to unbuffered solution (P<0.05). There were no complications reported with either solution. Buffered local anaesthetic solution significantly reduces the perceived pain of inguinal hernia repair, both during the infiltration and during the procedure itself. It is safe to administer and it results in a high rate of patient satisfaction.

Adult↗
PubMed1991

Binding of antibodies and other proteins to nitrocellulose in acidic, basic, and chaotropic buffers.

This report compares the binding of proteins to nitrocellulose membranes in acidic buffers (pH 2 and 3) with binding in neutral buffer (pH 7), basic buffers (pH 12 and 13), 8 M urea (pH 2, 3, and 7), and 6 M guanidine hydrochloride (pH unadjusted). Initially, similar amounts of antibodies and other proteins bound to the nitrocellulose membrane in all of these buffers and solvents. However, the susceptibility of individual proteins to displacement (stripping) from the membrane by the milk blocking agent depended on both the pH and the type of buffer or solvent used to bind the proteins to the membrane. Most proteins that were bound to nitrocellulose in acidic buffers were relatively resistant to milk stripping compared to proteins bound in pH 7 buffer. After correction for the amount of antibody remaining on the membrane after the milk block, it was found that acid-bound antibodies were unchanged in biological activity when compared with the same antibodies bound at neutral pH. These results suggest that acid binding of proteins could increase the sensitivity of nitrocellulose membrane assays using a milk block.

Animals↗
PubMed1988

The buffer capacity of single-site, resting, human dental-plaque fluid.

A carbonate equilibration method was used to measure the buffer capacity of resting plaque fluid collected from single buccal or interproximal sites of upper and lower first molars or anterior teeth. The maximum buffer capacity was 26 m-equiv./l at pH 7.1. The buffer contribution from the measured concentrations of phosphate and carbonate was calculated for each sample. These values were compared with the buffering actually measured and with that expected from organic acids, proteins, and amino acids at average values, as taken from reports in the literature. Relative contributions of buffer species at the average pH of the samples (6.86) were: 35 per cent phosphate, 10 per cent carbonate, 10 per cent protein, 10 per cent organic acids, 2 per cent amino acids, 30 per cent unidentified. There were no significant differences in the buffer capacities of samples originating from sites that differ in their accessibility to saliva. Buffering in resting plaque fluid is more than twice that in saliva and did not show differences correlated with the intra-oral location of the samples.

Buffers↗
PubMed1986

Buffer dependence of retinal glycolysis and ERG potentials.

Using the isolated rat retina, the present experiments have examined the effects of varying the type and concentration of buffer system with and without changes in external pH on lactic acid production and ERG potentials. The buffers chosen for study included bicarbonate/CO2, HEPES, Tris+ and phosphate. High rates of retinal glycolysis were observed with either 25 mM bicarbonate and 5% CO2 (control condition) or with 30 mM quantities of the other buffers at an external pH of 7.4. Significantly lower rates of retinal glycolysis were obtained when the concentration of each buffer was reduced to 10, 5 or 3 mM without a change in external pH. Lactic acid production was also decreased when the external pH was lowered regardless of the buffer system employed. The a- and b-waves were well maintained in the presence of 25 mM bicarbonate and 5% CO2. Lowering the bicarbonate concentration at constant external pH led to a decrease in their amplitudes. With either Hepes, Tris+ or phosphate employed at concentrations between 3 and 30 mM the amplitude of the a-wave was reduced and the b-wave was lost. These results show that the nature and concentration of the buffer system used in in vitro retinal studies influences metabolic and electrical activities in this tissue and emphasize the importance of the buffer as a constituent of the incubation medium.

Animals↗
PubMed1981

Non-bicarbonate buffering of ascites tumor cells in the rat as titrated by strong acids.

Buffer equations originally derived for blood were applied to the in vitro system "ascites tumor cells and ascitic fluid'. Non-bicarbonate buffer values beta(mmol x pH(-1) x 1(-1)) were determined experimentally by titration of ascites, cell free ascitic fluid and cell homogenates with NaOH in the absence of CO2. beta in ascitic fluid, in native ascites and in cell homogenate were beta (F) = 5.9, beta (A) = 16.4 and beta (H) = 24.9, respectively. Intracellular beta value beta (C) calculated from buffer equations depended on the ratio delta pHi/delta pHe. With delta pHi/delta pHe = 1, beta (C) was 38.8. The difference between beta (C) and beta (H) could be partly accounted for by differences in the cellular protein content. With delta pHi/delta pHe = 0.62 as in the presence of CO2, beta (C) becomes 62.6. In the presence of CO2 (see Albers et al., 1981), the extracellular buffering was higher and the intracellular buffering lower than the values titrated in the absence of CO2. It is concluded that in the presence of CO2 and/or HCO3- the apparent intracellular buffering of intact tumor cells results from non-bicarbonate buffering by cell proteins as well as from active or passive ionic exchanges with the extracellular fluid.

Acid-Base Equilibrium↗
PubMed1992

Buffering of calcium in the vicinity of a channel pore.

The function of calcium entry or release channels is often modulated by the cytosolic free calcium concentration. When such channels are studied in isolation, calcium buffer solutions are usually used to control the free calcium at the cytosolic face of the channel. Such solutions are generally formulated on the basis of equilibrium considerations. We calculate the gradient of [Ca2+] in the vicinity of a channel pore, in the presence of such buffers. We find that the effective degree of buffering near the pore is markedly affected by kinetic considerations. Commonly used EGTA solutions are completely ineffective in buffering [Ca2+] within macromolecular distances of the pore. In order to achieve useful buffering, the fastest buffers (e.g. BAPTA derivatives) must be used, in concentrations very much higher than those conventionally employed. Because of the diffusion limit on the maximum rate of binding of calcium to the buffer ligand, it is physically impossible to achieve good control of [Ca2+] at cytosolic levels at distances of less than a few nm from a pore conducting pico-ampere calcium current.

Buffers↗
PubMed1992

Buffer dependence of CO2 hydration catalyzed by human carbonic anhydrase I.

The steady-state kinetics of CO2 hydration catalyzed by human carbonic anhydrase I (carbonate hydro-lyase, EC 4.2.1.1) has been investigated at three pH values corresponding to different parts of the pH-rate profile. Two buffer systems with similar pKa values were used at each pH. The results show that the catalyzed rates depend on the buffer concentration but also on the chemical nature of the buffer. For example, at pH 8.8 the buffer 1,2-dimethylimidazole behaves formally as a second substrate in a 'ping-pong' mechanism yielding a maximal kcat value of 2.2 x 10(5) s-1, whereas much lower rates were obtained with Taps buffers. Similarly, at pH 7.3 1-methylimidazole yields higher rates than Mops and at pH 6.3 3,5-lutidine is more efficient than Mes. Non-Michaelis-Menten kinetics were observed with all buffers except 1,2-dimethylimidazole. In addition, while the apparent buffer activation by 1,2-dimethylimidazole can be described by a single Km value of 26 mM, the Mes concentration dependence is consistent with the presence of two components of similar magnitudes with Km values of 45 mM and 0.15 mM. These results are interpreted within the framework of the 'zinc-hydroxide' mechanism in terms of multiple pathways for the rate-contributing transfer of a proton from the zinc-bound water molecule, formed during CO2/HCO3- interconversion, to the reaction medium, thus, regenerating zinc-bound OH-.

Buffers↗
PubMed1994

'Organic phase buffers' control biocatalyst activity independent of initial aqueous pH.

Combinations of triisooctylamine with its hydrochloride, or of triphenylacetic acid with its Na+ salt, can function as buffers for use during biocatalysis in organic media. They can control the pH of an adjacent aqueous phase, even though both forms of each buffer remain in the organic phase. With 0.1 M aqueous NaCl, the mid-point pH values obtained with the two buffer systems are around pH 4.5 and 7.0, respectively. The activity of an immobilized subtilisin Carlsberg shows a strong dependence on the ratio of the two forms of the triphenylacetic acid buffer system. Without the buffer, the rate shows the normal dependence on the pH of the aqueous solution before drying; however, this is almost eliminated if the buffer is used. The amine buffer system can similarly affect the activity of an immobilized Rhizomucor miehei lipase.

Buffers↗
PubMed1992

Bicarbonate and other buffer systems can enhance the rate of H+ diffusion through mucus in vitro.

The effect of various diffusible buffers on mucus H+ permeability, and in particular the potency of the HCO3-/CO2 buffer system relative to other selected buffers is reported here. The diffusional resistance of mucus and water was demonstrated to be dependent on buffer concentration, and the contrast between the two types of layer was most pronounced for low DH+ values near neutrality. This concentration dependence was most marked with mucus layers in the buffer systems investigated. Furthermore, the nature and pKa values of the diffusible buffer systems used in this study had a profound effect on measured DH+. The effect was particularly striking in the case of HCO3- buffer with mucus. Possible implications of these in vitro findings in mucosal protection from acid are discussed.

Bicarbonates↗
PubMed1992

Reduction of pain and local complications when buffered lidocaine solution is used as a local anesthetic in conjunction with hyperthermia treatments: results of a randomized trial.

Unbuffered lidocaine (pH = 6.5) is commonly employed as a local anesthetic prior to transcutaneous placement of catheters for use in temperature monitoring during hyperthermia treatments. The most frequent complaint associated with this procedure is stinging or burning pain at the injection site. Tender firm subcutaneous nodules at sites of lidocaine infiltration for catheter placement have also been noted in fields treated with radiation and hyperthermia. A reduction in the pain associated with lidocaine infiltration has been reported by the use of alkalinized (buffered) local anesthetic solutions. To confirm this finding in patients treated with hyperthermia for superficially-located tumors, a randomized prospective double blind trial comparing unbuffered (pH 6.5) and buffered (pH 7.3) 2% lidocaine (without epinephrine) was undertaken. Between March and October 1990, a total of 54 hyperthermia treatment fields were each randomized to buffered or unbuffered lidocaine to be used at the time of all catheter placements (146 placements). Patients were scored both for the pain noted during the infiltration of lidocaine and the pain noted with subsequent catheter placement. In addition, the development of subcutaneous nodules at the sites of catheter placement was monitored at the time of 3-week follow-up. Follow-up was available for all but two fields. Treatment fields that received the buffered anesthetic had a statistically significant reduction in the pain associated with infiltration of lidocaine (p less than 0.05) without any compromise in its therapeutic efficacy as observed on a linear Visual Analog Scale. Furthermore, the incidence of subcutaneous nodules was lower in the fields treated with the buffered solution (1/23 vs 7/29, p = 0.05 for buffered and unbuffered solutions, respectively). The results of this trial support the use of buffered lidocaine prior to catheter placement for hyperthermia treatments as a method of reducing pain at infiltration and the subsequent development of subcutaneous nodules.

Buffers↗
PubMed1993

Electrical field stimulation causes oxidation of exogenous histamine in Krebs-Henseleit buffer: a potential source of error in studies of isolated airways.

Electric field stimulation (EFS) relaxes human histamine-precontracted airways in vitro. This relaxation is only partly neurally mediated. Nonneural relaxation has been also shown in blood vessels and is due to the generation of oxygen radicals by EFS. In isolated airways the origin of the nonneural component of the relaxation is not clear. Because exogenous catecholamines are oxidized during EFS of carbogenated Krebs-Henseleit (K-H) buffer, we questioned whether this is also the case for exogenous histamine. Human airways precontracted with histamine or methacholine were exposed to either EFS-stimulated carbogenated K-H buffer that also contained histamine or methacholine or unstimulated buffer. Airways exposed to EFS-stimulated buffer that contained histamine relaxed, whereas airways exposed to buffer containing methacholine or exposed to unstimulated buffer did not. It appeared that the histamine concentrations in the organ baths decreased during 30 min of EFS. This decrease was significantly reduced in the presence of ascorbic acid. We conclude that EFS causes oxidation of histamine in carbogenated K-H buffer, and this may at least partly explain the nonneural component of EFS-induced relaxations of precontracted human isolated airways. Therefore, histamine should not be used to induce precontraction in EFS experiments.

Aged↗
PubMed2004

Retention of ionisable compounds on high-performance liquid chromatography. XV. Estimation of the pH variation of aqueous buffers with the change of the acetonitrile fraction of the mobile phase.

The most commonly used mobile phases in reversed-phase high-performance liquid chromatography (RP-HPLC) are hydro-organic mixtures of an aqueous buffer and an organic modifier. The addition of this organic solvent to buffered aqueous solutions involves a variation of the buffer properties (pH and buffer capacity). In this paper, the pH variation is studied for acetic acid-acetate, phosphoric acid-dihydrogenphosphate-hydrogenphosphate, citric acid-dihydrogencitrate-citrate, and ammonium-ammonia buffers. The proposed equations allow pH estimation of acetonitrile-water buffered mobile phases up to 60% (v/v) of organic modifier and initial aqueous buffer concentrations between 0.001 and 0.1 mol L(-1), from the initial aqueous pH. The estimated pH variation of the mobile phase and the pKa variation of the analytes allow us to predict the degree of ionisation of the analytes and from this and analyte hydrophobicities, to interpret the relative retention and separation of analyte mixtures.

Acetonitriles↗
PubMed2006

Use of a medium buffered with N-hydroxyethylpiperazine-N-ethanesulfonate (HEPES) in intracytoplasmic sperm injection procedures is detrimental to the outcome of in vitro fertilization.

OBJECTIVE: This study was conducted to determine whether N-hydroxyethylpiperazine-N-ethanesulfonate (HEPES)-buffered medium used for the microinjection of sperm into oocytes may be detrimental for the embryo. DESIGN: Controlled randomized study. SETTING: Private IVF center. PATIENT(S): Women (n = 708) undergoing ICSI. INTERVENTION(S): The women were randomized into two study groups: 2,204 oocytes from 357 women were treated using a medium buffered with bicarbonate without HEPES during the ICSI procedure, and 2,168 oocytes from 351 women were treated using a medium buffered with HEPES during the ICSI procedure. MAIN OUTCOME MEASURE(S): Fertilization rate, degeneration rate, triploid rate, cleavage rate, embryo quality, pregnancy rate, implantation rate, and abortion rate. RESULT(S): Oocytes treated with a HEPES-buffered medium showed a statistically significant higher rate of triploid and degenerated oocytes after fertilization with ICSI compared with oocytes treated with a medium without HEPES. The embryos obtained from oocytes microinjected with a HEPES-buffered medium showed a statistically significant higher rate of highly fragmented embryos compared with the controls. Pregnancy rate and implantation rate were statistically significantly lower in the patient group with oocytes treated with the HEPES-buffered medium. The other parameters evaluated did not show any statistically significant differences. CONCLUSION(S): Our study showed that the use of media buffered with HEPES, during the microinjection of sperm into the oocytes, is detrimental for IVF outcome and should be avoided.

Adult↗
PubMed2006

Decreasing the pain of local anesthesia: a prospective, double-blind comparison of buffered, premixed 1% lidocaine with epinephrine versus 1% lidocaine freshly mixed with epinephrine.

BACKGROUND: Local anesthetics are acidic and cause pain on infiltration into the skin. Two methods are commonly used by dermatologists to raise the pH of lidocaine with epinephrine: buffering with sodium bicarbonate or freshly mixing lidocaine with epinephrine on the day of use. OBJECTIVE: Our purpose was to compare the pain induced by infiltration of the skin with 1% lidocaine with epinephrine 1:100,000 buffered with sodium bicarbonate (buffered) versus 1% lidocaine freshly mixed with epinephrine (fresh). METHODS: Sixty volunteers were recruited for this prospective, double-blind study. Each subject received an intradermal injection of the buffered solution and the fresh solution. Immediately after each injection subjects rated the pain of infiltration on a 100-mm visual analog scale. The pain scores for the anesthetic solutions were compared using the paired t test. RESULTS: The pain score for the buffered solution was 18.3 +/- 20.3, and the pain score for the fresh solution was 23.5 +/- 19.1 (P = .0543). Sixty-five percent of subjects felt the fresh solution was more painful than the buffered solution. LIMITATIONS: The results did not reach statistical significance. CONCLUSION: In this small study, buffered lidocaine with epinephrine caused less pain on infiltration into the skin than lidocaine freshly mixed with epinephrine, but the results were not statistically significant.

Anesthetics, Local↗