Measured pH Values Research Articles

Electrochemical sensors and sensor module for studying biological systems in space vehicles

A sensor module has been developed for carrying out scientific experiments on biological systems under microgravity conditions. It contains miniaturized electrochemical sensors for measuring pH values and dissolved oxygen concentrations, a temperature sensor and the analogue electronic measuring assembly for the sensors. The sensor module has been successfully tested in 1 g laboratory experiments.

Effect of pH changes in cerebrospinal fluid specimens on bacterial survival and antigen test results.

To determine the effect of pH changes occurring in cerebrospinal fluid (CSF) after sampling on the viability of meningitis causing bacteria, and on the performance of agglutination assays used for the rapid detection of bacterial antigens. The pH of CSF collected via lumbar puncture was measured by various methods, and the effects of the following different incubation conditions on subsequent changes were determined: air at 4 degrees C; air at room temperature (22 degrees C); air at 37 degrees C; and air with 5% CO2 at 37 degrees C. The growth/survival in pooled CSF of 15 bacterial isolates collected from 74 patients with meningitis was assessed in these incubation conditions over 24 hours. The effects of pH changes in the CSF on the sensitivity of two latex agglutination and one co-agglutination kits for detecting Haemophilus influenzae, Neisseria meningitidis groups B and C, and Streptococcus pneumoniae were determined. The measured pH of CSF was highly affected by the method used and particularly the time delay between patient sampling and assay. Measured pH values at the time of sampling (mean 7.5) increased rapidly within 60 seconds by about one unit. CSF pH continued to increase during incubation in all tested conditions (up to approximately pH 10), with the exception of in air with 5% CO2 at 37 degrees C where pH changes were reversible and near physiological values were attained. Bacterial survival for all species tested was poorest in CSF incubated in air at 37 degrees C and best following exposure to air with 5% CO2 at 37 degrees C. Agglutination in rapid antigen detection kits with CSF incubated in air as opposed to air with 5% CO2 generally took longer to occur and in some instances was less prominent. In one case a false negative result was obtained with CSF seeded with N meningitidis group B incubated in the former but not the latter conditions. CSF pH increases after patient sampling are minimised and/or mostly reversed by incubation in an atmosphere containing 5% CO2. CSF samples should ideally be placed in such an atmosphere as soon as possible after collection, and left there until laboratory processing occurs, to reduce the detrimental effects of pH stress on bacterial survival. pH increases may also reduce the likelihood of obtaining a positive result in rapid antigen detection assays.

Hydration and pH Behavior of the Cement Prepared from the Mixture of Haüyne-Containing Clinker, Anhydrite and Blastfurnace Slag

Four types of cement were prepared by mixing haüyne-containing clinker, anhydrite and blastfurnace slag (HAS cement), and their hydration reaction and pH behavior were investigated. HAS cement pastes cured for 3-180 d contained ettringite, calcium silicate hydrate (C-S-H) and Al(OH)3 gel as hydrates, but neither Ca(OH)2 nor monosulfate hydrate. Measured pH values of the liquid phases coexisting with hardened HAS cement pastes were in the range of 11.3-12.3, and each of them agreed well with the pH value calculated from ionic concentrations in the liquid phase. Final hydrate of each cement paste was estimated from chemical composition of cement, and then a final pH of liquid phase was presumed from CaO/SiO2 ratio of estimated C-S-H. Measured pH showed similar tendency to the estimated final pH, but the former grew relatively higher than the latter especially in the range of lower pH. It was considered that coexisting alkali ions remarkably influenced liquid phase in that pH range. The compressive strengths of HAS cement mortars cured for 28 d were about 37-39N/mm2.

31P-MRS measurements of extracellular pH of tumors using 3-aminopropylphosphonate.

The extracellular pH (pHex) of tumors is generally acidic. However, it is only recently that noninvasive magnetic resonance spectroscopic (MRS) measurements have determined that the intracellular pH (pHin) of tumor cells in situ is neutral or slightly alkaline compared with that of normal tissues. Thus cells in tumors maintain larger pH gradients than do cells in nontumor tissues. To date, measurements of pHex in tumors have been made using microelectrodes, which preclude measurement of pHex and pHin within the same preparation. In addition, microelectrodes are invasive and have the potential to alter the measured pH values. The present communication describes simultaneous measurement of pHex and pHin in vitro in bioreactor culture and in vivo using 31P-MRS analyses of 3-aminopropylphosphonate (3-APP) and inorganic phosphate. In vitro results indicate that 3-APP is not toxic and that its resonant frequency is sensitive to pH and not significantly affected by temperature or ionic strength. Bioreactor experiments indicate that this compound is neither internalized nor metabolized by cells. Experiments in vivo indicate that 3-APP can be administered intraperitoneally and that RIF-1 tumors maintain a steady-state pHin of 7.25 and a pHex of 6.66. These data have significance to basic tumor cell physiology and to the design of approaches to cancer chemotherapy and hyperthermic therapy, because both of these modalities exhibit pH sensitivity. It is also likely that these techniques will be applicable to localized MRS of other organ systems in vivo.

Development of a patient-dedicated, on-demand, blood gas monitor.

A new monitor (CDI 2000) that brings blood gas measurements to the patient's bedside has been developed. To measure blood gases, blood is drawn into the patient's arterial pressure-monitoring line past in-line fluorescent-based sensors. After measurement, the blood is returned to the patient, avoiding blood loss and delays in sample turnaround and reducing the risk of infection to both patient and operator. We assessed this system's performance in vitro with tonometered bovine blood. Bias (mean difference between monitor and tonometered gas or measured pH values) +/- the standard deviation (SD) were 0.01 +/- 0.02 at pH = 7.39; 0.0 +/- 0.7 mm Hg at Pco2 = 39 mm Hg; and 2.4 +/- 3.2 mm Hg at a Po2 = 100 mm Hg (n = 54). Changes in hematocrit, blood temperature, or serum sodium concentration did not have clinically significant effects on system performance. Studies in normal volunteers, in whom large changes in blood gases were induced, showed a bias (mean difference between monitor and IL 1306 values) +/- SD of 0.00 +/- 0.02 for pH, -0.4 +/- 2.0 mm Hg for Pco2, and -3.6 +/- 7.7 mm Hg for Po2 (n = 69). We conclude from the present study that the performance of this system is comparable to that of conventional blood gas analyzers.

PIXE analysis of rain water collected in Montgomery, Alabama for a five-year period

Concentrations of trace elements in 297 rain samples were determined using PIXE. These rain samples were collected at every rainfall occurrence in Montgomery, Alabama over a period of almost five years between January 1985 and November 1989. The measured pH values indicated that, with only a few exceptions, the northern rains were more acidic than the southern rains. Also, a slight decrease in the pH value was found during this period, suggesting a corresponding increase in the rainfall acidity. Graphs showing the five-year databases for frequently occurring elements are given in terms of their average seasonal concentrations. Also, the characteristics of the elemental distributions in rain are discussed.

Prediction of pH in Model Systems Pressurized with Carbon Dioxide

AbstractMathematical models were developed to predict the pH of model liquid food systems (pure water, ascorbic acid‐water, citric acid‐water, and ascorbic acid‐citric acid‐water) pressurized with carbon dioxide, as functions of pressure (0–34.50 MPa), temperature (32,37, and 42° C), and component concentrations [(0–1.107) X10−3 M for ascorbic acid, (0 to 6.080) × 10−4 M for citric acid]. For all simulation systems, predicted pH values closely followed experimentally measured pH values. In the pure water‐CO2 systems, pH was a strong function of pressure but a weak function of temperature. In ascorbic acid‐water‐CO2, citric acid‐water‐CO2, and ascorbic acid‐citric acid‐water‐CO2 systems, pH was relatively insensitive to CO2 pressure and was a strong function of acid concentrations. This method could be a first step toward predicting the pH of orange juice and other liquid food systems under pressurized CO2.

Inorganic nutrients in precipitation over the Magdalen Islands area (Quebec, Canada) and their impact on the primary productivity of the lagoons

Concentrations of nitrate, ammonium and phosphate have been monitored from June to October 1989 in rain water collected at the Magdalen Islands (Gulf of St. Lawrence, Québec, Canada). Nitrate was the main dissolved organic nitrogen (DIN) compound with concentrations ranging from 2.2 to 95 μM. Ammonium was occasionally dominant and varied between 0.7 and 41 μM. Phosphate concentrations were low and extremely variable with values ranging from 0.2 μM to 2 μM. All three inorganic nutrients were positively correlated and the relationships best described by a non-linear regression model. NH 4 +:NO 3 − atomic ratios fell within the range of those previously measured, i.e. the northeast part of North America, and suggest a continental origin for both DIN and phosphate. Measured pH values failed to show high levels of acidity (pH=4.8 ±0.4). For the lagoonal system of the Magdalen Islands, atmospheric deposition is the major source of nitrate during the summer period we surveyed. In such an ecosystem the atmospheric inputs of DIN are greater than those from the sediment and may at times contribute up to 70% of the phytoplankton primary production requirements. In contrast, phosphate of rain origin was only of marginal importance relative to sediment inputs.

Chemical and physical processes occurring in the Fushime geothermal system, Kyushu, Japan.

The chemical and physical features of the deeper part of the Fushime geothermal system (about 1000–2000 m depth), where temperatures exceed 300°C, have been revealed in the course of its exploration. The fluids discharged from wells are saline, and the maximum Cl concentrations of the reservoir waters are similar to that of seawater. The waters are depleted in Mg and SO4 but are enriched in K, Ca, Fe, Mn, Zn, Pb, SiO2, etc., over those of seawater, suggesting that the geothermal fluid originates from high temperature seawater-rock interaction. Relatively long term discharge testing shows that excess enthalpy conditions (i.e. two-phase feed) commonly develop, and that isothermal boiling has also occurred in the high temperature reservoir. The fluid chemical compositions that are the least disturbed by these physical processes caused by testing were selected from the data base for study. They indicate that boiling and dilution predominate in the undisturbed reservoir. Variations in the K and Ca concentrations of the waters suggest that the precipitation of K-bearing minerals and the dissolution of Ca-bearing minerals occur in the reservoir. Fluid-mineral equilibria for the Fushime reservoir waters were calculated without allowing for redox reactions for dissolved gases (CH4-CO2, H2-H2O and N2-NH3), because allowing for these reactions results in an extreme discrepancy between analytical CH4, H2 and SO4 concentrations and those calculated. Calculations show that the fluids are close to anhydrite saturation and are close to equilibrium with both Na/K-feldspars. However, apparent undersaturation with respect to calcite is indicated. Higher pH values are calculated for the reservoir waters in relatively lower temperature wells (the measured pH values are also higher than those of the higher temperature wells). They are approximately in equilibrium with K-feldspar and K-mica at reservoir conditions. In contrast, the lower pH waters in wells with higher temperature are not calculated to be in equilibrium with this pair. The latter is inconsistent with the observation that these two minerals are common as alteration products. The numerical back titration into the fluids of sphalerite and galena, which are observed in scale deposited in the wells and surface equipment, results in a pH increase in the high temperature reservoir water. This reconciles the disagreement between the observed presence of these minerals and fluid composition of high-temperature wells. Thus, the precipitation of sphalerite and galena is the most likely source of the acidity.

PH in physiological salt solutions: direct measurements

Calculations of pH in modified Krebs solutions by inserting PCO2 and total-CO2 in the Henderson-Hasselbalch (H.-H.) equation are obvious as the equation originally served for this purpose. An exact calculation of the relation between pH and PCO2 is complicated as the concentration of bicarbonate, the dissociation constant and the solubility of CO2 change. Furthermore, the dissociation constant in the H.-H. equation is constant only if activities are used in the equation instead of stoichiometric concentrations. We therefore investigated the influence of different carbon dioxide tensions and bicarbonate concentrations on directly measured pH of organ baths aerated with mass-spectrometric analyzed O2-CO2 gases. For reference precision buffers were used. The measured pH values differed distinctly from calculated pH values in the acidic and alkaline parts of the pH interval investigated (6.57-8.15). Measurements of actual pH with proper calibration standards therefore seem mandatory.

Estimation and measurements of pH in high temperature and high pressure sour environments.

A new technique for estimating the pH of concentrated aqueous solutions in equilibrium with high pressure H2S and CO2 at elevated temperature was proposed. Based on the thermodynamic investigation for solution properties, the following equation was obtained.pH=-logγH+{(K1, H, KH, H, PH2S/γ2±H2S)1/2+(K1, C, KH, C, PCO2/γ2±CO2)1/2}The physico-chemical parameters in the equation were calculated by PBILC (Principle of Balance of Identical-Like Charges) proposed by Cobble et al. or assumed to be identical with those for HCl+NaCl aqueous solutions. The calculation of the pH of high temperature and high pressure sour environments was facilitated by the of this equation.A Nb-doped TiO2 semiconductor electrode of n-type was found to be suitable for the measurement of the pH of the environments; no interference from NaCl, H2S and CO2 occurred. The measured pH values agreed well with those estimated by the newly proposed technique at the temperatures up to 473 K and at partial pressures of H2S and CO2 up to 4 MPa. It was ascertained by pH measurements for HCl+NaCl aqueous solutions at elevated temperatures that the assumption made for physico-chemical parameters in the pH estimation was valid.

31P NMR measurements of myocardial pH [formula omitted

A 31P NMR magnetization transfer method for measuring myocardial pH in vivo is demonstrated in the lamb, dog and cat. The method involves measuring the difference in chemical shift between the resonances of phosphocreatine and inorganic phosphate in magnetization transfer difference spectra in which the γ-phosphate resonance of ATP has been saturated. The method has been verified by measuring the chemical shift difference between the resonances of 2-deoxyglucose 6-phosphate and phosphocreatine following infusion of the animals with 2-deoxyglucose. The measured pH values are significantly lower than those obtained in previous studies on the heart in vivo .

Intercellular pH of Peach and Apricot Mesocarp

Intercellular pH of developing peach (Prunus persica (L.) Batsch) and apricot (Prunus armeniaca L.) mesocarp was estimated from the pH of small volumes of water in contact with washed cut surfaces. In both fruits, the pH changed from neutral to acidic as the rate of growth changed from slow and declining to rapid. In peaches, the changes in intercellular pH and growth rate occurred gradually over a 4-week period, while in apricots these changes were more rapid. Studies on the mechanism of the pH change showed the measured pH values to be a reasonable and adequate estimate of intercellular pH in vivo. We propose that intercellular acidity influences mesocarp development in at least two ways. It allows high rates of assimilate utilisation by inducing activity in existing intercellular invertase, and it predisposes the tissue to ripening.

Aerosol and cloudwater properties at whiteface mountain, New York

A field program for the measurement of the physical and chemical properties of aerosols and clouds was conducted at Whiteface Mountain, N.Y., during an 8-week period in June, July, and August 1983. Analysis of two-stage Nuclepore filter samples by proton-induced X-ray emission (PIXE) spectroscopy showed that most (85 to 90%) of the aerosol sulfate was in the accumulation mode (modal radius r - 0.1 μm) and that ≅90% of total sulfate originated southwest of the Whiteface Mountain site. During a typical pollution episode originating in the Midwest, the total aerosol sulfate concentration was 19 pg m −3, or 63 of total dry aerosol, which was - 30 gg m− s. Scavenging of sulfate aerosol by clouds was found to be greater than 95% efficient in clouds of 0.5gm−3 liquid water content. Measured pH values when the air mass trajectories were from the southwest were systematically lower than when the trajectories were from the northwest or northeast, i.e., 3.4 vs 4.4 and 4.8. In the southwest sector water samples, S04−2 and N03− were highly correlated to each other and to free H+, Ca2−, Cl−, Pb, and Ba.

The Second Dissociation Constant of H 2 S

A recent method demonstrated for glass pH electrode measurement in concentrated alkaline solutions is employed to measure the aqueous second acid dissociation constant, , of . At 25°C, we find to be <10−17.3. Values up to 5 orders of magnitude larger than this are commonly applied. Uncertainties arising in previous studies, from attempts to access small amounts of available free sulfide, are minimized by using recently characterized, extremely concentrated electrolytes. Measured pH values, for (i) and (ii) titrated by , are compared to simulated curves which are computed with measured water activities and cation selective electrode measured potassium ion activities. The concentration dependent dissociation parameter, , where imposes a unit ratio of the HS− to S= activity coefficients, is found to be , consistent with recent spectroscopic studies.

Prediction of pH Errors in Soil‐water Extractors Due to Degassing

AbstractMoisture samples taken from the unsaturated zone with soil water extractors undergo degassing and an upward shift in pH. The measured pH values from commercially available extractors are usually sufficiently in error that they cannot be used in a quantitative manner. A model has been developed that predicts the extent of CO2 degassing and the resulting pH error. Using this model measured pH values can be corrected back to in situ soil water pH provided that precipitation has not occurred in the extractor. Extractors are classified into two groups—single chamber and multichambered. The extractors are evaluated for both operation under constant vacuum (open to the source) and decreasing vacuum (evacuated and then sealed). Analysis of the data and model predictions indicates that the major factor controlling the pH error is the ratio of liquid volume to total extractor volume. Additional factors exerting major influence are the initial extractor gas composition and the total pressure in the extractor when sampled. Variations in soil solution composition and differences in soil CO2 concentrations in carbonate buffered systems had a major effect on pH values but a negligible effect on the extractor induced pH error. Under typical field conditions the multichambered extractor is predicted to give the most satisfactory results; the pH errors were sufficiently small that no corrections for degassing were necessary.

PH measurements in ultranarrow immobilized pH gradients

It is possible to measure pH values in immobilized pH gradients (IPG) when the polyacrylamide matrix is made to contain an additional, carrier ampholyte-generated pH gradient. After an IPG run, 5 mm gel segments, along the separation axis, are cut and eluted in 300 μl of 10 mM KCl and the pH read with a standard pH meter. When using ultranarrow pH gradients, larger gel segments (ca. 265 μl) are eluted in 900 μl of 100 mM KCl and the pH assessed with a differential pHmeter. In the latter case, either internal or external standards are used as a reference, or starting point, to convert Δ pH values into an actual pH curve. The reproducibility of the system is better than ±0.05 pH units, with a ca. 15% error over a 0.3 pH unit span. In ultranarrow pH gradients, it is imperative to use mixtures of all commercially available carrier ampholytes, so as to smoothen conductivity and buffering capacity gaps. By the present method, it is also possible to convert a wide (2–3 pH unit) carrier ampholyte interval into a narrow (0.2–0.3 pH unit) one.

A Soil Water Extractor That Minimizes CO2 Degassing and pH Errors

Soil water extractors that are presently used to sample the unsaturated zone cause substantial CO2 degassing within the sampler. The resultant pH errors are sufficiently large that the measured pH values are unacceptable for determining specific mineralogic controls on solution composition. The pH increases can also result in oxide and carbonate precipitation within the extractor thereby altering solution composition. The soil water samplers described here reduce CO2 degassing by minimizing the gas‐liquid ratio in the extractor and by flushing several volumes of solution through the liquid‐filled sampling container before a sample is removed. The construction of both shallow and deep samplers is described.

PH measurements after isoelectric focusing in immobilized pH gradients

It is impossible to measure pH values in immobilized pH gradients either with a surface electrode or by cutting gel slices and eluting in 10 m M potassium chloride solution. The use of reversible gels, cross-linked with bisacrylylcistamine, improves the measurements in the acidic region, but gives false values in the alkaline region, owing to the buffering power of added 2-mercaptoethanol or dithiothreitol. By using mixed-type gels, containing Immobilines and 1% carrier ampholytes, accurate and reliable pH measurements can be obtained. The discrepancy between the theoretical slope of the immobilized pH gradient and the actual pH values obtained by reading the pH of eluted Ampholine focusing in the same gel fragment is less than 0.1 pH unit over a 1 pH unit span. The effects of temperature and of carbon dioxide absorptionbnd on pH readings are demonstrated and evaluated.

Conductivity, buffering capacity, concentration and pH profiles of carrier ampholytes focused in narrow-range immobilized pH gradients

It is possible to measure pH values in ultra-narrow immobilized pH gradients (IPGs) when the polyacrylamide matrix contains a secondary, carrier ampholyte generated pH gradient. After an IPG run, the buffering ampholytes, contained in 5 mm gel segments, along the focusing axis, are eluted and the following measurements are made: pH, conductivity, buffering capacity and concentration profiles of carrier ampholytes. Local concentration maxima of buffering ampholytes correspond to maximum conductivity and buffering capacity. The same relationship applies to local minima of the same parameters. No single commercial carrier ampholyte mixture ensures smooth conductivity and buffering capacity profiles and even pH gradients over very narrow pH intervals (0.3 pH unit spans). The best profiles are obtained only with mixtures of different commercial carrier ampholytes. Across neutrality, ca. 10% total buffering ampholytes should be added to an ultra-narrow IPG gradient to ensure an average buffering power (β av.) of ca. 3 mequiv./1 · pH and an average conductivity (λ av.) of 20–30 μS, while in acidic (around pH 4 and below) and alkaline (above pH 9) pH intervals only one third of this concentration is needed, as the carrier ampholytes exhibit substantially higher λ and β values and the hydrolytic products of water begin to contribute to the buffering capacity and conductivity of the system.