Retention of ionizable compounds on HPLC. 4. Mobile-phase pH measurement in methanol/water

The different procedures used in HPLC to measure the pH of a mobile phase are evaluated in terms of the rigorous IUPAC definition of pH. The three procedures evaluated are as follows: measurement of the pH of the aqueous HPLC buffer before mixing it with the organic modifier, measurement of the pH of the HPLC buffer after mixing it with the organic modifier using a pH electrode system calibrated with aqueous buffers, and measurement of the pH of the HPLC buffer after mixing it with the organic modifier but calibrating the electrode system with reference buffers prepared in the same mixed solvent used as mobile phase. Following IUPAC definitions and recommendations, the three pH values can be related with the pH scales: w(w)pH, s(w)pH, and s(s)pH, respectively. The relationships between these three pH scales are also presented. The retention of several compounds with acid/base behavior in a C-18 and a polymeric column with buffered methanol/water as mobile phase is related to the mobile phase pH value measured in the three pH scales. It is demonstrated that the s(w)pH and s(s)pH scales give better relationships than the w(w)pH scale (pH measured in the aqueous buffer before mixing it with the organic modifier), commonly used on HPLC. The s(w)pH scale is specially recommended because of its simplicity of measurement: the pH is measured after mixing the aqueous buffer with the organic modifier, but the pH calibration is performed with the common aqueous reference buffers.     

Optical Replacement of pH Electrode

The development of a noninvasive, self-contained optical pH sensor probe intended as a direct replacement for a pH electrode is presented. It uses a fluorescent excitation-ratiometric pH sensing dye in a patch. The patch is excited by light emitting diodes of differing wavelengths which are controlled by a microcontroller (MCU). The emission levels are measured by analog circuitry and their ratio is converted by the MCU into a linear output which mirrors that of a conventional pH electrode. The optical sensor readings were consistent with readings from a glass pH electrode with average difference .061 pH. This sensor allows noninvasive, low-cost optical pH sensing with the ability to interface with existing pH monitoring equipment.      

国产管线钢的环境开裂性能研究

采用电化学测试和慢应变速率实验(SSRT)研究了国产X70管线钢在近中性pH和高pH溶液中的应力腐蚀破裂(SCC)行为.结果表明,X70钢在高pH溶液和近中性pH溶液中的阳极极化曲线表现出明显的差异:在高pH溶液中有明显的活化-钝化转变而在近中性pH溶液中则无;在近中性pH溶液中,X70管线钢的开裂模式是穿晶型的,具有准解理特征,并且随着外加阴极电位的降低,SCC敏感性增加,氢致破裂占主导;随温度的下降以及溶液中CO2含量的增加,溶液pH值降低,SCC敏感性增加.在高pH溶液中,在阴极极化时,X70钢表现出与在近中性pH溶液中类似的破裂行为和特征,即SCC敏感性随电位降低而增大,裂纹数目少而大,裂纹易扩展;但在阳极极化时,裂纹数目多而小,易萌生但难扩展.在2种溶液中阳极极化时,均存在SCC敏感电位区.     

Synthesis of piperazinylalkyl ester prodrugs of ketorolac and their in vitro evaluation for transdermal delivery

Ketorolac, an NSAID, has low intrinsic permeation capacity through the skin. In this work, seven piperazinylalkyl ester prodrugs of ketorolac were synthesized to enhance its skin permeation. The chemical hydrolysis and the stability in human serum at 37 degrees C were investigated in buffer solutions (pH 5.0 and 7.4) and in 80% human serum (pH 7.4), respectively. The prodrugs were chemically more stable at pH 5.0 than at pH 7.4 with prodrug 8 being the most stable (t(1/2) = 119.75 h and 11.97 h at pH 5 and 7.4, respectively). The prodrugs' t(1/2) in human serum ranged from 0.79 to 3.92 min. The prodrugs' aqueous solubility was measured in buffer solution at pH 5.0 and 7.4 and Log P(app) was measured by partitioning between buffer solution (pH 5.0 and 7.4) and n-octanol. The prodrugs were more lipophilic than ketorolac at pH 7.4. Skin permeation of ketorolac and prodrug 8, the most stable chemically, through rat skin was studied at pH 5.0 and 7.4. Prodrug 8 enhanced permeation by 1.56- and 11.39-fold at pH 5 and 7.4, respectively. This is attributed to higher lipophilicity at pH 7.4 and higher aqueous solubility at pH 5 compared to ketorolac.     

Influence of pH on performance of sodium phosphinate for decreasing the particle size

To clarify the influence of pH on performance of sodium phosphinate (NaPH₂O₂) for decreasing particle size of Pt nanoparticles, carbon-supported Pt nanoparticles that contained phosphorus (P–Pt/C) were synthesised by an electron-beam irradiation reduction method (EBIRM) under four different pH conditions (pH = 3, 6, 9, and 12) and under five different NaPH₂O₂ concentrations (0.0, 0.5, 1.0, 3.0, and 5.0 mM). The relationship among pH, NaPH₂O₂ concentration, average particle size of Pt nanoparticle, and Pt loading weight was investigated in this study. The average particle size of Pt nanoparticles was in the range of 0.8–3.4 nm and lower in the order; pH12 > pH3 > pH6 > pH9; for example, under the same NaPH₂O₂ concentrations of 3.0 mM, the particle size of P–Pt/C prepared at pH = 12 and pH = 9 was 1.5 and 0.8 nm, respectively. In addition, Pt loading weight was also lower in the order; pH12 > pH3 > pH6 > pH9. In summary, these results indicated that the pH in the precursor solution affected the performance of NaPH₂O₂. These findings would be useful for controlling the particle size of monometallic Pt and Pt-based bimetallic nanoparticles supported on carbon particles for fuel cell applications.     

Effect of pH on surface energy of glass and Teflon and theoretical prediction of Staphylococcus aureus adhesion

The surface energy of glass and Teflon at various pH values was examined. Contact angle was used to determine physico-chemical substratum properties. The surface energy of both substratums including, hydrophobicity, and electron donor/electron acceptor (Lewis acid–base properties) were found to depend on pH of contact solution. The maximum of hydrophobicity (higher negative value of ΔG_iwi) was obtained at pH 11 and pH 6.5 for glass and Teflon respectively. The electron donor property was higher at pH 5 and pH 3 for glass and Teflon respectively. Moreover, prediction of Staphylococcus aureus adhesion on both substratums was estimated by calculating the total interaction free energy (ΔG^Tot). Based on the value of ΔG^Tot, S. aureus should adhere to glass at pH 2, pH 3 and pH 11 with the maximal adhesion obtained at pH 3 and pH 11. For Teflon, regardless of pH values, S. aureus should be able to attach on this substratum with the high adhesion level at pH 5. The relation between surface energy of substratum and the total interaction free energy was also examined. Based on this relation and the value of the components of total interaction free energy, we show that adhesion to glass could be governed by both short range forces (Lewis acid–bases forces) and by long range forces (van der Waals forces) and the adhesion to Teflon could be mediated only by the short range forces.     

纺织品水萃取液pH值测定影响因素的探讨

本文从pH计的选择、测试用水、剪碎后试样大小、取样部位、振荡时间、萃取液静置时间六个方面,较全面地探讨了纺织品pH值测试的影响因素。结果表明：pH计的选择、pH值相差较大的三级水以及不同取样部位对pH值测定结果的影响很大;而其它三个因素往往对于pH值偏高的试样影响较大,而对于大多数pH值较低的试样影响较小。但是有些布样比较特殊,其测试值的影响因素不存在上述规律,这可能与面料的整理工艺有关。     

Removal of soluble organics from water by a hybrid process of clay adsorption and membrane filtration

The removal of phenol and o-cresol from water by a hybrid process of clay adsorption and ultrafiltration (clay-UF) was studied. Batch adsorption equilibrium experiments showed that the amount of adsorption for phenol and o-cresol decreased in the order kaolin>montmorillonite at an equilibrium pH (pH(e)) of 9.1. The clay-UF experiments were performed as a function of clay dose, solution pH, and transmembrane pressure. The role of pH in clay-UF process mainly depended on the acid-base nature of phenols and clays, and the charge of UF membrane. The rejection of phenol increased with increasing pH, and had a maximum at pH(e)=8.2 with kaolin but at pH(e)=9.1 with montmorillonite. The rejection of o-cresol also increased with increasing pH, and had a maximum at pH(e)=9.2 with kaolin but at pH(e)=10.2 with montmorillonite. Such differences between solute rejections depended on the pK(a) of the solutes, zeta potential of the clays, and surface charge of the membrane. The amount of soluble organics adsorbed onto the surface of membrane was negligible and the flux slightly decreased with increasing transmembrane pressure.     

pH值在胶印中的应用研究

胶印中使用的各种材料,它们的性质或多或少都会影响到印刷质量.其中,纸张和润湿液的pH值对印刷也有显著的影响.因此,本文就纸张和润湿液的pH值对印刷质量的影响,和印刷中所需的最佳pH值,以及纸张pH值和润湿液pH值之间的相互关系加以探讨.     

Sorption of selenium(IV) and selenium(VI) to mackinawite (FeS): effect of contact time, extent of removal, sorption envelopes

Higher concentrations (127, 253 μM) of Se(IV) at pH 8 were completely removed by 0.5 g/L FeS within 120 min. Removal of Se(VI) by FeS at pH 8 was less extensive than removal of Se(IV). Only 10% of the Se(VI) was removed by 1 g/L FeS within 1h. Removal patterns for Se by FeS depend on pH. Removal patterns of Se at pH 7 and pH 8 were best described by BET models for Se(IV) and Freundlich models for Se(VI), while removal patterns of both at pH 9 and 10 were best described by Langmuir models. Sulfate at 1 and 10 mM had negligible effect on removal of Se(IV) by FeS, while sulfate had little effect on removal of Se(VI) by FeS, but there was some indication that sulfate promoted removal of Se(VI) at intermediate concentrations. The test for the effect of pH on sorption of Se(IV) by FeS showed nearly complete removal at all but the high initial pH. When pH was raised back to initial value, greater removals were observed than initially. Mixtures of Se(VI) and FeS showed moderate removal at low pH, a minimum removal near pH 6 and nearly complete removal at high pH. Very high stability was observed with negligible release as pH decreased.     

Degradation Kinetics of Diltiazem

The kinetics of degradation of diltiazem hydrochloride in aqueous buffered solutions (pH 1-7) were studied. Diltiazem was found to undergo hydrolysis to desacetyldiltiazem. The decomposition of diltiazem followed pseudo-first order kinetics under the experimental conditions. The drug was relatively stable over the pH range 3-6 with optimum stability at pH 5. The extrapolated shelf-life at this pH was 42.0 days compared to 15.8 day at pH 2.     

Real-Time Imaging of Microscopic pH Distribution with a Two-Dimensional pH-Imaging Apparatus

Real-time two-dimensional pH imaging has become possible with the development of a new type of potentiometry, by which the pH distribution can be visualized as pH images with submillimeter spatial resolution. The measurement time for one image is short enough for practical use. The transient change of pH distribution generated by the protons released from a single cation-exchange resin was observed and visualized as the pH images. From the pH images, the evaluation of the resin performance was also carried out.     

Retention of ionizable compounds on HPLC. 8. Influence of mobile-phase pH change on the chromatographic retention of acids and bases during gradient elution.

The relationships between retention and mobile-phase pH in gradient elution are studied for acids and bases. The apparent pH shift caused by the increasing amount of acetonitrile and methanol has been determined starting from a wide range of pH values. It is shown that good relationships between the retention of ionizable compounds and the pH of the aqueous buffer can be established if the same type of buffer (ammonium acetate in this work) is used for all pH points. Equations are proposed to fit the gradient retention data to the pH of the aqueous buffer. The proposed equation gives an account of the relative variation of the pKa of the compound in the reference to the variation of the pH of the buffer as both parameters change during gradient elution.     

Extended-range spectroscopic pH measurement using optimized mixtures of dyes

The spectroscopic technique for pH measurement is a well-established laboratory technique that can give high-accuracy pH values. Recent studies have shown the advantage of this technique over standard potentiometric methods for pH measurements in fresh water and seawater and also at high temperatures and pressures. However, a limitation of the spectroscopic technique is that a single pH dye is sensitive only over a narrow pH range. We have developed optimized dye mixtures that are both sensitive and accurate over a broad pH range. The measurement is robust and simple, requires a minimum of two wavelengths, and is independent of the volume of the dye mixture added. Optimization of the dye mixture formulation to maximize accuracy in a broad range of pH involves varying both the dye type and its mole fraction and also accounting for spectral noise. This technique has been successfully applied for in situ pH measurements of oilfield formation waters.     

Synthesis of Piperazinylalkyl Ester Prodrugs of Ketorolac and their In Vitro Evaluation for Transdermal Delivery

Ketorolac, an NSAID, has low intrinsic permeation capacity through the skin. In this work, seven piperazinylalkyl ester prodrugs of ketorolac were synthesized to enhance its skin permeation. The chemical hydrolysis and the stability in human serum at 37°C were investigated in buffer solutions (pH 5.0 and 7.4) and in 80% human serum (pH 7.4), respectively. The prodrugs were chemically more stable at pH 5.0 than at pH 7.4 with prodrug 8 being the most stable (t_1/2 = 119.75 h and 11.97 h at pH 5 and 7.4, respectively). The prodrugs' t_1/2 in human serum ranged from 0.79 to 3.92 min. The prodrugs' aqueous solubility was measured in buffer solution at pH 5.0 and 7.4 and Log P_app was measured by partitioning between buffer solution (pH 5.0 and 7.4) and n-octanol. The prodrugs were more lipophilic than ketorolac at pH 7.4. Skin permeation of ketorolac and prodrug 8, the most stable chemically, through rat skin was studied at pH 5.0 and 7.4. Prodrug 8 enhanced permeation by 1.56- and 11.39-fold at pH 5 and 7.4, respectively. This is attributed to higher lipophilicity at pH 7.4 and higher aqueous solubility at pH 5 compared to ketorolac.     

Synthesis and application of submicrometer fluorescence sensing particles for lysosomal pH measurements in murine macrophages

Phagocytosis of bioparticles such as bacteria and viruses by macrophages is a critical component of the immune response against infections. In this paper we describe the synthesis of submicrometer fluorescent particles with pH sensing capability. The particles are used to measure the pH and to monitor the effect of chloroquine, an antimalarial drug, on the pH in the lysosome, the cellular organelle involved in the phagocytosis process. The synthesis of the pH sensing particles is realized by the covalent attachment of amine reactive forms of Oregon Green (pH sensitive dye) and Texas Red (pH insensitive dye) to the surface of amino-modified submicrometer polystyrene particles. The particles are absorbed by J774 Murine Macrophages through phagocytosis and directed to lysosomes. Despite the high lysosomal levels of digestive enzymes and acidity, the absorbed particles remain stable for 12 h in the cells when they are stored in a PBS buffer solution at pH 7.4. The pH dynamic range of the sensing particles is between pH 4.5 and 7 with a sensitivity of 0.1 pH units. Exposure of the cells to chloroquine increases the lysosomal pH from 4.8 to 6.5. The effect is concentration-dependent.     

Effects of pH on dechlorination of trichloroethylene by zero-valent iron

The surface normalized reaction rate constants (k(sa)) of trichloroethylene (TCE) and zero-valent iron (ZVI) were quantified in batch reactors at pH values between 1.7 and 10. The k(sa) of TCE linearly decreased from 0.044 to 0.009l/hm(2) between pH 3.8 and 8.0, whereas the k(sa) at pH 1.7 was more than an order higher than that at pH 3.8. The degradation of TCE was not observed at pH values of 9 and 10. The k(sa) of iron corrosion linearly decreased from 0.092 to 0.018l/hm(2) between pH 4.9 and 9.8, whereas it is significantly higher at pH 1.7 and 3.8. The k(sa) of TCE was 30-300 times higher than those reported in literature. The difference can be attributed to the pH effects and precipitation of iron hydroxide. The k(sa) of TCE degradation and iron corrosion at a head space of 6 and 10ml were about twice of those at zero head space. The effect was attributed to the formation of hydrogen bubbles on ZVI, which hindered the transport the TCE between the solution and reaction sites on ZVI. The optimal TCE degradation rate was achieved at a pH of 4.9. This suggests that lowering solution pH might not expedite the degradation rate of TCE by ZVI as it also caused faster disappearance of ZVI, and hence decreased the ZVI surface concentration.     

The pH sensing characteristics of the extended-gate field-effect transistors of multi-walled carbon-nanotube thin film using low-temperature ultrasonic spray method

A novel, simple and low-temperature ultrasonic spray method was developed to fabricate the multi-walled carbon-nanotubes (MWCNTs) based extended-gate field-effect transistors (EGFETs) as the pH sensor. With an acid-treated process, the chemically functionalized two-dimensional MWCNT network could provide plenty of functional groups which exhibit hydrophilic property and serve as hydrogen sensing sites. For the first time, the EGFET using a MWCNT structure could achieve a wide sensing rage from pH = 1 to pH = 13. Furthermore, the pH sensitivity and linearity values of the CNT pH-EGFET devices were enhanced to 51.74 mV/pH and 0.9948 from pH = 1 to pH = 13 while the sprayed deposition reached 50 times. The sensing properties of hydrogen and hydroxyl ions show significantly dependent on the sprayed deposition times, morphologies, crystalline and chemical bonding of acid-treated MWCNT. These results demonstrate that the MWCNT-EGFETs are very promising for the applications in the pH and biomedical sensors.     

Retention of ionizable compounds on HPLC. 5. pH scales and the retention of acids and bases with acetonitrile-water mobile phases

The pH calibration procedures that lead to the different pH scales in acetonitrile-water mixtures used as mobile phases in reversed-phase liquid chromatography are discussed. Appropriate buffers of known pH value in acetonitrile-water mixtures are selected and used to establish the relationship (delta values) between the two rigorous acetonitrile-water pH scales: sspH and wspH (pH measured in acetonitrile-water mixtures and referred to acetonitrile-water or water, respectively, as standard state). These delta values allow one to convert pH values measured in acetonitrile-water with electrode systems calibrated with aqueous buffers (wspH scale) to sspH values, which are directly related to the thermodynamic acid-base constants. This offers an easy way to measure the pH of acetonitrile-water mobile phases and to relate this pH to the chromatographic retention of acids and bases through the thermodynamic acid-base constants. The relationships are tested for the variation of the retention of acids and bases with the pH of the mobile phase at several mobile-phase compositions and favorably compared with the relationships obtained with the common wwpH scale (pH measured in the aqueous buffer before mixing it with the organic modifier). The use of the rigorous sspH and wspH scales allows one to explain the retention behavior of bases, which in many instances cannot be justified from the pH measurement in the ill-founded wwpH scale.     

Microscopic measurement of pH with iridium oxide microelectrodes

Microscopic pH electrodes were produced by deposition of hydrous iridium oxide onto carbon fiber microelectrodes. The electrodes exhibit two linear regions of potentiometric response between pH 2-6 and pH 6-12. The electrodes respond to pH changes within 50 ms, and an equilibrium value is reached within 30 s. By using these electrodes as probes in the scanning electrochemical microscope, dynamic pH changes occurring at or near a surface can be measured and pH maps of the surface can be generated. Vertical pH profiles and images of pH were obtained at substrates where electrochemical (oxidation and reduction of H2O2, hydrogen evolution) or enzymatic (glucose oxidase) reactions involving proton transfers occur.