Effect Of Buffer Type Research Articles

Reactions of hypoiodous acid with model compounds and the formation of iodoform in absence/presence of permanganate

The kinetics for the reactions of hypoiodous acid (HOI) with various phenols (phenol, 4-nitrophenol, 4-hydroxybenzoic acid), 3-oxopentanedioic acid (3-OPA) and flavone were investigated in the pH range of 6.0–11.0. The apparent second order rate constants for the reactions of HOI with phenolic compounds, 3-OPA, flavone and citric acid at pH 8.0 are 10–107 M−1s−1, (4.0 ± 0.3) × 103 M−1s−1, (2.5 ± 0.2) × 103 M−1s−1 and <1 M−1s−1, respectively. The effect of buffer type and concentration was investigated with acetate, phosphate and borate. All tested buffers promote the HOI reactions with phenols. The percentage of iodine incorporation for various (hydroxyl)phenolic compounds and two NOM extracts ranges from 5% to 98%, indicating that electrophilic aromatic substitution and/or electron transfer can occur. The extent of these reactions depends on the number and relative position of the hydroxyl moieties on the phenolic compounds. Iodoform formation rates increase with increasing pH and iodoform yields increase from 9% to 67% for pH 6.0–10.0 for the HOI/3-OPA reactions. In the permanganate/HOI/3-OPA and permanganate/iodide/3-OPA system at pH < 8.0, iodoform formation is elevated compared to the HOI/3-OPA system in absence of permanganate. For pH > 8.0, in presence of permanganate, iodoform formation is significantly inhibited and iodate formation enhanced, which is due to a faster permanganate-mediated HOI disproportionation to iodate compared to the iodination process. The production of reactive iodine in real waters containing iodide in contact with permanganate may lead to the formation of iodinated organic compounds.

Ferrous phosphate surface precipitates resulting from the reduction of intragrain 6-line ferrihydrite by Shewanella oneidensis MR-1

The reductive biotransformation of 6-line ferrihydrite located within porous silica (intragrain ferrihydrite) by Shewanella oneidensis MR-1 was investigated and compared to the behavior of 6-line ferrihydrite in suspension (free ferrihydrite). The effect of buffer type (PIPES and NaHCO3), phosphate (P), and an electron shuttle (AQDS) on the extent of reduction and formation of Fe(II) secondary phases was investigated under anoxic conditions. Electron microscopy and micro X-ray diffraction were applied to evaluate the morphology and mineralogy of the biogenic precipitates and to study the distribution of microorganisms on the surface of porous silica after bioreduction. Kinetic reduction experiments with free and intragrain ferrihydrite revealed contrasting behavior with respect to the buffer and presence of P. The overall amount of intragrain ferrihydrite reduction was less than that of free ferrihydrite [at 5 mmol L−1 Fe(III)T]. Reductive mineralization was not observed in the intragrain ferrihydrite incubations without P, and all biogenic Fe(II) concentrated in the aqueous phase. Irrespective of buffer and AQDS addition, rosettes of Fe(II) phosphate of approximate 20–30 μm size were observed on porous silica when P was present. The rosettes grew not only on the silica surface but also within it, forming a coherent spherical structure. These precipitates were well colonized by microorganisms and contained extracellular materials at the end of incubation. Microbial extracellular polymeric substances may have adsorbed Fe(II) promoting Fe(II) phosphate nucleation with subsequent crystal growth proceeding in different directions from a common center.

Separation of carboxylates by hydrophilic interaction liquid chromatography on titania

Hydrophilic interaction liquid chromatography (HILIC) can be performed on titania. To better understand the retention mechanisms on titania, a series of model carboxylates were used. Increasing acetonitrile above 60% dramatically increased the retention and efficiency for carboxylates. The effect of buffer type, buffer concentration, buffer pH and column temperature were also studied. Multiple retention mechanisms are operative on titania, and whether electrostatic repulsion, ligand exchange or HILIC dominates retention and separation depends on the eluent conditions. Guidelines for separations on titania are: (1) higher %ACN most improves retention and efficiency; (2) higher salt concentration increases retention; (3) elution strength is in the order acetate<<malate<methyl phosphonate<<phosphate; (4) electrostatic repulsion (ERLIC) is more operative at low %ACN than high %ACN. A bare titania column (150mmx4.6mm I.D., 5mum) was used for the separation of diphenylacetate, 4-nitrobenzoate, benzoate, 4-aminobenzoate, 4-hydroxybenzoate, phthalate, 3-aminophthalate, 1,3,5-benzenetricarboxylate, 1,2,4-benzenetricarboxylate, 1,2,4,5-benzenetetracarboxylate, benzenepentabenzoate and mellitate under HILIC conditions based on these guidelines, with efficiencies of 2800-55,000 plates/m.

Synthesis and examination of sulfated cyclofructans as a novel class of chiral selectors for CE

Cyclofructans (CFs) are a class of cyclic oligosaccharides with a crown ether skeleton. No enantioseparations have previously been reported using this class of chiral oligosaccharides in chromatography or electrophoresis. CFs and their sulfated derivatives were examined as chiral selectors using CE. The native CFs showed no enantioselectivity toward any tested compounds, while the sulfated CFs showed exceptional selectivity toward many cationic analytes, including primary, secondary, and tertiary amines and amino acids. Enantiomeric resolution factors as high as 15.4 were achieved within short analysis times (generally below 10 min). The effect of buffer type, buffer concentration, buffer pH, chiral selector concentration and organic modifier concentration was examined and optimized.

Study of a new chiral selector: Sodium arsenyl-( l)-(+) tartrate for capillary electrophoresis

Sodium arsenyl-( l)-(+) tartrate (Na 2[As 2(+)-tart 2]·3H 2O) was examined and evaluated as a chiral selector using capillary electrophoresis. This chiral selector showed enantioselective associations with many cationic analytes, including primary, secondary, and tertiary amines. Also, baseline separations of ruthenium(II) polypyridyl complexes were achieved within 10 min. The effect of buffer type, chiral selector concentration, voltage applied, buffer concentration, buffer pH and organic modifier concentration were examined and optimized.

Unusual retention behaviour of 4-substituted piperidines on polybutadiene and polystyrene coated zirconia by comparison to reverse phase silica

The retention properties of a range of N-methylated and N- des-methyl 4-substituted piperidines on polybutadiene (PBD) and polystyrene (PS) coated zirconia have been studied and compared to those of Xterra RP 18 and Genesis C 18 silica. The effect of buffer type and pH are investigated with regard to the elution order on all three stationary phases. The change in the elution order is linked to the degree of substitution of the piperidine nitrogen and appears to be independent of the rest of the structure, indicating that this moiety is most heavily involved in the separation mechanism on the zirconia phases.

The impact of buffers and surfactants from micellar electrokinetic chromatography on matrix-assisted laser desorption ionization (MALDI) mass spectrometry of peptides: Effect of buffer type and concentration on mass determination by MALDI-time-of-flight mass spectrometry

This paper describes the effect of various buffers, surfactants, and organic additives commonly encountered in capillary zone electrophoresis and micellar electrokinetic chromatography on the molecular weight determination of peptides by matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. Signal-to-noise ratio generally decreased with increasing buffer concentration without affecting mass accuracy, but the type of buffer was also important. Good spectra were obtained with an ammonium acetate buffer up to a concentration of 500 m M without impacting ionization of either peptides or other mobile phase constituents. Ionization of organic additives, such as anionic surfactants, non-ionic surfactants, and cyclodextrins was buffer dependent and presented a problem when the mass of the additive was in the range of the peptide mass. Brij ®-35, Tween ®-80, and cyclodextrins all produced prominent spectra of their own in the presence of sodium or potassium containing buffers, but not with ammonium acetate. Cationization of these neutral species with sodium or potassium ions allowed them to acquire a positive charge and produce spectra. In contrast, the ammonium ion appears to be a poor cationizating agent. Ionization of neutral surfactants was suppressed in ammonium acetate without impacting the spectra of peptides. Ammonium acetate buffers containing 30 m M sodium dodecyl phosphate also gave spectra with good signal intensity and no interference from the surfactant. Suppression of peptide ionization in MALDI was a problem when methanol, tetrabutyl amine, or poly(vinyl alcohol) were used with either ammonium acetate, sodium phosphate, and N-(2-hydroxyethyl)piperazine- N-(2-ethansulfonic acid).

Factors that Influence Mobility, Resolution, and Selectivity in Capillary Zone Electrophoresis. I. Sodium Phosphate vs. Potassium Phosphate

Abstract The effect of buffer type on mobility, selectivity and resolution in capillary zone electrophoresis (CZE) was studied. The results show that the sodium phosphate buffer gave shorter mobility times (tM) for a test dansyl amino acid mixture than the potassium phosphate buffer having the same concentration and pH. The resolution and selectivity were also better using the sodium phosphate buffer. A comparison of resolution, tM and selectivity using a monohydrogen and a dihydrogen sodium phosphate buffer (0. 1 M, pH 7. 0) showed no appreciable differences in selectivity and resolution, but the dihydrogen phosphate buffer gave tM which are almost 45% shorter than those obtained with the monohydrogen phosphate buffer. When monohydrogen and dihydrogen potassium phosphate (0. 1 M, pH 7) were used, differences in tM, selectivity and resolution were observed. Resolution improved with an increase in the buffer concentration (0. 2 M vs. 0. 1 M) but worsened and tM got considerably shorter when the concentration of the buffer was decreased from 0. 1 M to 0. 05 M.

Enzymic synthesis of peptide bonds. VIII. Activation phenomena in the papain-catalyzed synthesis of peptide bonds

The effect of cysteine hydrochloride concentration on the yield of the benzoylglycine-glycinanilide reaction as catalyzed by papain was studied. The results were interpreted as being in accord with the coenzyme theory of the activation process (5). In addition, the effect of buffer type and concentration on this same reaction and also on the benzoylglycine-aniline reaction was investigated. The results of these experiments indicated that metal chelation by the buffer was not its only effect on papain-catalyzed processes and that buffer-enzyme and buffer-substrate interactions were also occurring.