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pH Difference (ph + difference)
Selected AbstractsDirect chiral analysis of primary amine drugs in human urine by single drop microextraction in-line coupled to CEELECTROPHORESIS, Issue 16 2009Kihwan Choi Abstract Three-phase single drop microextraction (SDME) was in-line coupled to chiral CE of weakly basic amine compounds including amphetamine. SDME was used for the matrix isolation and sample preconcentration in order to directly analyze urine samples with the minimal pretreatment of adding NaOH. A small drop of an acidic aqueous acceptor phase covered with a thin layer of octanol was formed at the tip of a capillary by simple manipulation of the liquid handling functions of a commercial CE instrument. While the saline matrix of the urine sample was blocked by the octanol layer, the basic analytes in a basic aqueous donor phase were concentrated into the acidic acceptor drop through the octanol layer by the driving force of the pH difference between the two aqueous phases. The enantiomers of the enriched amines were resolved by using (+)-(18-crown-6)-tetracarboxylic acid as a chiral selector for the subsequent CE separation. From 10,min SDME with the agitation of the donor phase by a small stirrer retrofit to the CE instrument, enrichment factors were about a 1000-fold, yielding the LOD of 0.5,ng/mL for amphetamine. This low LOD value as well as the convenience of in-line coupled SDME make the proposed scheme well suited for the demanding chiral analysis of amphetamine-type stimulants. [source] pH transients during salt removal in isoelectric trapping separations: A curse revisitedELECTROPHORESIS, Issue 4 2007Evan Shave Abstract The pH transients that occur during isoelectric trapping separations as a result of the removal of nonampholytic ionic components have been re-examined. Salts containing strong electrolyte anions and cations, both with equal and dissimilar mobilities, have been studied using anodic and cathodic buffering membranes whose pH values were both equidistant and nonequidistant from pH,7. The direction and magnitude of the pH transient (acidic or basic) was found to depend on both the mobilities of the anion and cation (,anion/,cation) and the pH difference between pH,7 and the pH of the buffering membranes (|pHmembanodic,,,7|/|7,,,pHmembcathodic|). When |pHmembanodic,,,7|/|7,,,pHmembcathodic|,=,1, ,anion/,cation<1 leads to an acidic pH transient, ,anion/,cation,=,1 eliminates the pH transient and ,anion/,cation>1 leads to a basic pH transient. When ,anion/,cation,=,1, |pHmembanodic ,,7|/|7,,,pHmembcathodic|<1 leads to a basic pH transient, |pHmembanodic,,,7|/|7,,,pHmembcathodic|,=,1 eliminates the pH transient and |pHmembanodic,,,7|/|7,,,pHmembcathodic|>1 leads to an acidic pH transient. By selecting appropriate anodic and cathodic buffering membranes to adjust the |pHmembanodic,,,7|/|7,,,pHmembcathodic| value, pH transients caused by dissimilar anion and cation mobilities can be avoided. [source] Linear Expression of the Mathematical Relationship between Electroosmotic Mobility and Buffer ConcentrationCHINESE JOURNAL OF CHEMISTRY, Issue 1 2006Xu Xu Abstract It was believed that electroosmotic mobility ,eo is inversely proportional to the square root of the ionic strength I. But the linear relationship for regression analysis was expressed differently in different papers. The paper studied the linear expression of the mathematical relationship between ,eo and c (background buffer concentration) by mathematical transform and real experimental data. ,eo values of fused silica capillary were determined in four buffer systems. Their experimental conditions were controlled carefully for decreasing temperature difference ,T and pH difference ,pH in 50 µm ID capillary, in which no double layer overlap existed. The linear relationship between the reciprocal of electroosmotic mobility and the square root of concentration (or ionic strength) was derived by mathematical method. The regression analysis of experimental data was shown to well correspond to the relationship. The constants in regression equation could be well defined and the calculated results were acceptable. [source] Intracellular pH homeostasis in the filamentous fungus Aspergillus nigerFEBS JOURNAL, Issue 14 2002Stephan J. A. Hesse Intracellular pH homeostasis in the filamentous fungus Aspergillus niger was measured in real time by 31P NMR during perfusion in the NMR tube of fungal biomass immobilized in Ca2+ -alginate beads. The fungus maintained constant cytoplasmic pH (pHcyt) and vacuolar pH (pHvac) values of 7.6 and 6.2, respectively, when the extracellular pH (pHex) was varied between 1.5 and 7.0 in the presence of citrate. Intracellular metabolism did not collapse until a ,pH over the cytoplasmic membrane of 6.6,6.7 was reached (pHex 0.7,0.8). Maintenance of these large pH differences was possible without increased respiration compared to pHex 5.8. Perfusion in the presence of various hexoses and pentoses (pHex 5.8) revealed that the magnitude of ,pH values over the cytoplasmic and vacuolar membrane could be linked to the carbon catabolite repressing properties of the carbon source. Also, larger ,pH values coincided with a higher degree of respiration and increased accumulation of polyphosphate. Addition of protonophore (carbonyl cyanide m -chlorophenylhydrazone, CCCP) to the perfusion buffer led to decreased ATP levels, increased respiration and a partial (1 µm CCCP), transient (2 µm CCCP) or permanent (10 µm CCCP) collapse of the vacuolar membrane ,pH. Nonlethal levels of the metabolic inhibitor azide (N3,, 0.1 mm) caused a transient decrease in pHcyt that was closely paralleled by a transient vacuolar acidification. Vacuolar H+ influx in response to cytoplasmic acidification, also observed during extreme medium acidification, indicates a role in pH homeostasis for this organelle. Finally, 31P NMR spectra of citric acid producing A. niger mycelium showed that despite a combination of low pHex (1.8) and a high acid-secreting capacity, pHcyt and pHvac values were still well maintained (pH 7.5 and 6.4, respectively). [source] Exhaled breath condensate pH in infants and children with acute and recurrent wheezy bronchitisPEDIATRIC PULMONOLOGY, Issue 12 2007Christian Vogelberg MD Abstract The analysis of exhaled breath condensate (EBC) is a promising new method to measure airway inflammation. So far only limited data exist about methodological issues of EBC sampling in infants and young children. We evaluated 18 children with acute wheezy bronchitis (median age 24.3 months (min,max: 4,89.9)), 54 children with recurrent wheezy bronchitis (median age 52.5 months (7.2,94.8)), and 32 healthy controls (median age 49.6 months (25.3,67.8)). EBC was sampled with a modified commercially available EBC-sampler, pH was measured after deaeration. EBC volume was significantly correlated to age (r,=,0.56, P,<,0.001). EBC pH was significantly decreased in all patients compared to the healthy controls (acute wheezy bronchitis 7.87 (7.16,8.19), P,=,0.003, recurrent wheezy bronchitis 7.86 (6.95,8.39), P,=,0.002, and healthy controls 8.04 (7.81,8.87), respectively). There were no significant differences of the EBC pH between the disease groups. When divided into different subgroups, an influence of inhaled steroid treatment was found with steroid-naive recurrent wheezers having significantly lower EBC pH levels compared to healthy controls (7.80 (6.95,8.37), P,=,0.018), but not so steroid treated (7.94 (7.24,8.39), P,=,0.055). Both, recurrent wheezers with or without a positive allergy test had significantly lower EBC pH compared to healthy controls (7.91 (6.95,8.37), P,=,0.007 and 7.82 (7.32,8.39), P,=, 0.005, respectively). This study indicates that EBC can be collected with a modified commercially available EBC sampler in infants and young children. Further studies need to be performed to evaluate the relevance and meaning of pH differences of EBC in this age group. Pediatr Pulmonol. 2007; 42:1166,1172. © 2007 Wiley-Liss, Inc. [source] Antibody variable region interactions with Protein A: Implications for the development of generic purification processesBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2005Sanchayita Ghose Abstract In this paper, a wide range of antibodies from various subclasses and subfamilies are employed to evaluate the creation of generic separation processes using Protein A chromatography. The reasons for elution pH differences amongst several IgG1s, IgG2s, antibody fragments, and Fc-fusion proteins during Protein A chromatography are investigated using several complimentary techniques. The results indicate that variable region interactions play a major role in determining elution pH for VH3 subfamily antibodies while using traditional protein A chromatographic materials. On the other hand, experiments with a resin which employs a ligand consisting solely of B domain of Protein A indicate that variable region interactions can be mitigated, enabling the use of a single elution pH for a range of antibodies. Finally, the moderation of elution conditions associated with this engineered ligand are shown to minimize problems associated with low pH induced aggregation. It is expected that the findings reported in this paper will facilitate faster process development cycle times for this important class of human therapeutics. © 2005 Wiley Periodicals, Inc. [source] | |||||||||||||