Comparison of Different Total Ionic Strength Adjustment Buffer Compositions for Determination of Low Level Fluoride in Environmental Water Samples with Fluoride Ion Selective Electrode

Background Fluoride content of environmental water samples collected from the vicinity of Pilanesberg National Park was determined using a fluoride ion selective electrode (F−ISE). Different total ionic strength adjustment buffers (TISABs) EDTA, CDTA, Citrate and Acetate buffers, were compared for their effectiveness in releasing fluorine into the solution in its ionic form, by adjusting the pH and ionic strength of the solution, as well as by chelating polyvalent cations present in the samples. Nine water samples were collected from different sites around the park, where there is a decommissioned fluorspar mine, and an extinct volcano; for fluoride content. Quantification was carried out by means of multipoint calibration covering the range of interest in all treatments. Result The fluoride concentration was calculated using the Nernest equation with values obtained from the calibration graph. It was found that CDTA and EDTA buffers were the best TISABs as they produced a better linearity, slope and recovery in that order, where as the other acetate also produced better parameters and results than the untreated water samples. Conclusion CDTA and EDTA TISAB solutions perform better than the others for fluoride content determination from environmental water samples.

Metal-Chelating Active Packaging Film Enhances Lysozyme Inhibition of Listeria monocytogenes

Several studies have demonstrated that metal chelators enhance the antimicrobial activity of lysozyme. This study examined the effect of metal-chelating active packaging film on the antimicrobial activity of lysozyme against Listeria monocytogenes. Polypropylene films were surface modified by photoinitiated graft polymerization of acrylic acid (PP-g-PAA) from the food contact surface of the films to impart chelating activity based on electrostatic interactions. PP-g-PAA exhibited a carboxylic acid density of 113 ± 5.4 nmol cm−2 and an iron chelating activity of 53.7 ± 9.8 nmol cm−2. The antimicrobial interaction of lysozyme and PP-g-PAA depended on growth media composition. PP-g-PAA hindered lysozyme activity at low ionic strength (2.48-log increase at 64.4 mM total ionic strength) and enhanced lysozyme activity at moderate ionic strength (5.22-log reduction at 120 mM total ionic strength). These data support the hypothesis that at neutral pH, synergy between carboxylate metal-chelating films (pKabulk 6.45) and lysozyme (pI 11.35) is optimal in solutions of moderate to high ionic strength to minimize undesirable charge interactions, such as lysozyme absorption onto film. These findings suggest that active packaging, which chelates metal ions based on ligand-specific interactions, in contrast to electrostatic interactions, may improve antimicrobial synergy. This work demonstrates the potential application of metal-chelating active packaging films to enhance the antimicrobial activity of membrane-disrupting antimicrobials, such as lysozyme.

Rate constants for reactions of horseradish peroxidase compounds I and II with 4-substituted arylboronic acids

The rate constants for the reactions of horseradish peroxidase compound I (k1) and compound II (k2) with three 4-substituted arylboronic acids, which enhance chemiluminescence in the horseradish peroxidase catalyzed oxidation of luminol by hydrogen peroxide, were determined at pH 8.6, total ionic strength 0.11 M, using stopped-flow kinetic measurements. For comparison, the rate constants of the reactions of 4-iodophenol with compounds I and II were also determined under the same experimental conditions. The three arylboronic acid derivatives and their rate constants are: 4-biphenylboronic acid, k1 = (1.21 ± 0.08) × 106 M−1 s−1, k2 = (4.6 ± 0.2) × 105 M−1 s−1; 4-bromophenylboronic acid, k1 = (5.5 ± 0.2) × 104 M−1 s−1, k2 = (3.6 ± 0.2) × 104 M−1 s−1; and 4-iodophenylboronic acid, k1 = (1.1 ± 0.2) × 105 M−1 s−1, k2 = (1.3 ± 0.1) × 104 M−1 s−1. 4-Biphenylboronic acid, which shows comparable luminescent enhancement to 4-iodophenol, has the highest reactivity in the reduction of both compounds I and II among the three arylboronic acid derivatives tested.

Activity coefficients of NaNO3 in (Mg, Ca, Sr, and Ba)(NO3)2 + H2O systems at 298 K by EMF methods

The activity coefficients of NaNO3 in Mg(NO3)2, Ca(NO3)2, Sr(NO3)2 and Ba (NO3)2 were determined at constant total ionic strength of 0.1, 0.5, 0.75, 1.0, 1.5, and 2.0 mol kg−1 at 298 K using EMF methods. The experimental activity coefficients were analyzed using four different formalisms, namely, Reilly–Wood–Robinson, Scatchard, Pitzer, and Harned equations, and the interaction parameters were evaluated. Excess Gibbs free energy of mixing and trace activity coefficients were calculated and the results are discussed.

Prediction of Viscosity for Partially Hydrolyzed Polyacrylamide Solutions in the Presence of Calcium and Magnesium Ions

Loss of solution viscosity in water of increasing ionic strength is a major problem encountered in the use of the partially hydrolyzed polyacrylamide polymers for improved oil recovery. It is recognized widely that the viscosity loss is more drastic in the presence of multivalent cations than is observed for sodium ions. There is, however, little information available on the relationships between total ionic strength, concentrations of multivalent cations, and solution viscosities.The purpose of this study is to establish relationships between total ionic strength, concentration of calcium or magnesium ions, polymer concentration, and the resulting viscosity for partially hydrolyzed polyacrylamides with varying degrees of hydrolysis. Solutions at constant ionic strength with varying ratios of calcium or magnesium to sodium ions are compared, and the loss of viscosity as a function of the fraction of divalent cations in the system is determined. For shear rates in the power-law region, the fractional loss in viscosity is a function of the fraction of multivalent cations and, in the range studied, is independent of the total ionic strength. A more complicated relationship is found at lower shear rates where the fractional viscosity loss does vary with total ionic strength.The relationship in the power-law region should prove valuable in predicting viscosities on the basis of the dependence of viscosity on ionic strength and on multivalent cation concentration at a single ionic strength, eliminating the need for many individual measurements of viscosity. More work is needed before useful predictions will be possible at lower shear rates. Introduction Partially hydrolyzed polyacrylamide (HPAM) polymers are currently the most widely used mobility control polymers for secondary and tertiary oil recovery. Small quantities of HPAM can increase the viscosity of water by two or more orders of magnitude in the absence of added electrolytes. This phenomenal increase in viscosity results from the extremely high molecular weight of these polymers and repulsion between the negative charges along the polymer chain, resulting in maximum chain extension. The latter mechanism leads to one of the greater disadvantages of using HPAM in an oil reservoir. In the presence of the electrolyte molecules in typical oilfield brines, negative charges along the polymer chain are screened from each other by association with cations from the solution. The polymer chains no longer are extended fully, and solution viscosity decreases. Mungan observed that divalent cations have a more pronounced effect on viscosity than univalent cations when compared on the basis of equal weights of the chloride salts.Viscosities have been reported for HPAM solutions in sodium chloride brines of varying strength as well as for solutions in brines containing CaCl2 or MgCl2. Some viscosities also have been reported for solutions in brines containing both sodium and calcium ions, but no systematic study of the viscosity trends in brines with more than one type of cation has been reported.The purpose of this study is to investigate HPAM solutions with varying ratios of univalent to divalent cations and to establish trends of the solution viscosities for different values of degree of polymer hydrolysis, polymer concentration, and total ionic strength. Such trends are useful for predicting a wide range of viscosities from a few basic measurements. SPEJ P. 623^