Donald J. Pietrzyk

Anion−cation separations on a mixed bed alumina−silica column

Mixed bed ion-exchange (MBIE) columns containing alumina and silica were evaluated for the simultaneous separation of anion and cation analytes. At the mobile phase pH used alumina provides anion exchange sites while silica provides cation exchange sites. Since alumina and silica exhibit weak acid and base properties, their anion and/or cation exchange properties are pH dependent. Ion exchange capacities, rates of exchange and analyte ion exchange selectivities are also pH dependent. The major mobile phase parameters affecting analyte anion and cation resolution and elution order are pH and type and concentration of counter anion and counter cation, respectively. The weight ratio of the two exchangers and/or the exchange capacities of the two in the column can also be used to alter resolution and elution order. Several examples of the simultaneous separation of inorganic mono- and divalent anions and cations using a single sample injection, a single column and a single detector (conductivity) illustrate the parameters and scope of the alumina-silica MBIE column.

Ion-exchange resins in non-aqueous solvents-III Solvent-uptake properties of ion-exchange resins and related adsorbents.

Solvent-uptake properties for several synthetic resins and common adsorbents were determined by the centrifugation method. Data are reported for eighteen different solvents, which include water and the common polar and non-polar organic solvents. The cation-exchange resins are of two varieties: the microreticular or gel type and the macroreticular or porous type. The latter resin being rigid and porous takes up all types of solvents, whereas the former resin, which relies on swelling of the resin matrix, does not take up the nonpolar solvents. Data for the H(+) form and Na(+) form macroreticular resin are compared. Unsulphonated polystyrene-divinylbenzene polymers which possess similar micro- and macroreticular properties to the cation-exchange resins were also studied in the same solvents. The swelling properties of these non-polar resins are compared with each other and with the polar cation resins. Other adsorbents, which are frequently used as supports in chromatography were also examined in the same solvents. Several of these have large average pore diameters and surface areas like the macroreticular resin.

Anion-cation separations on a mixed-bed ion-exchange column with indirect photometric detection

Abstract Inorganic cations and anions are separated simultaneously on a mixed bed of anion and cation exchangers. Columns studied are mixtures of polymer based and silica based anion and cation exchangers and stationary phases that contain both chemically bonded anion and cation ionogenic groups. The major parameters that influence retention and resolution are the mobile phase counterions, their concentration, and the ion-exchange capacities. Because electrolyte solutions are required for elution, detection by conductivity is limited. Using a electrolyte that is composed of a chromophoric cation and anion not only satisfies elution requirements but also permits analyte cations and anions to be detected by an indirect photometric detection strategy.

Comparison of Reversed Stationary Phases for the Chromatographic Separation of Inorganic Analytes Using Hydrophobic Ion Mobile Phase Additives

Abstract Alkyl-modified silica (RSi) and polystyrenedivinylbenzene (PRP-1) stationary phases are compared for the chromatographic separation of inorganic analyte anions and cations using hydro-phobic ions of opposite charge as mobile phase additives. Tetra-alkylammonium salts were used for anion separations and alkyl sulfonate salts for cation separations. Two major equilibria influence the retention of analyte ions on PRP-1. These are: retention of the hydrophobic ion on PRP-1 and an ion exchange selectivity between the hydrophobic counterion and the analyte ion. When using RSi retention is also influenced by ion exchange at residual silanol groups, which act as weak cation exchange sites. Mobile and stationary phase variables that influence analyte retention are identified. Optimization of these provides favorable eluting conditions for the separation of inorganic ionic analytes. Of particular interest is the potential use of PRP-1 and RSi columns for the separation of inorganic cations; conditions for ...

Liquid chromatography and postcolumn indirect detection of glyphosate

Glyphosate [N-(phosphonomethyl)glycine] and its metabolite aminomethylphosphonic acid (AMPA) were separated and detected by a postcolumn indirect detection strategy. Separation can be done on a cation-exchange column, where glyphosate elutes before AMPA, or on an anion-exchange column, where the elution order is reversed. Detection was achieved by using a fluorescent Al(3+)-morin postcolumn reagent. When the postcolumn reagent combines with the column effluent in a mixing tee, the fluorescence decreases in the presence of both analytes. Variables affecting the postcolumn indirect fluorescence detection were established and optimized; the major factors were postcolumn pH and volume and temperature of the postcolumn reaction coil. Detection limits, defined as three times the background noise, for glyphosate and AMPA separated on an anion-exchange column were 14 and 40 ng, respectively.

Investigation of the Influence of Hydrophobic Ions as Mobile Phase Additives on the Liquid Chromatographic Separation of Amino Acids and Peptides

Abstract Tetraalkylammonium, R4N+, and alkylsulfonate, RSO3 −, salts were evaluated as mobile phase additives for the separation of amino acids and peptides. The former were used in a basic mobile phase and the latter in an acidic one, conditions which convert the terminal carboxyl or amine groups in amino acids and peptides and the acidic or basic side chains if present into anionic or cationic forms, respectively. Because of the required strongly basic or acidic mobile phase pH, a polystyrene-divinylbenzene copolymer, PRP-1, was used as the reversed stationary phase. The retention is suggested to follow a dynamic interaction involving two major equilibria, namely retention of the hydrophobic ion and an ion exchange between the co-ion accompanying the hydrophobic ion and the amino acid or peptide ion of opposite charge. The effect of amino acid and peptide structure on retention is discussed. Key mobile phase variables are identified; a major one is the optimization of the hydrophobic ion concentration-m...

Ion-exchange resins in non-aqueous solvents—I: Sorption rates of p-nitroaniline and the effects of small amounts of water

The rates of sorption of p-nitroaniline onto three hydrogenform resins in methanol, ethanol, n-propanol, isopropanol, n-butanol, acetonitrile, benzene, acetic acid and dioxan are reported. Two of the resins are typical gel-type, microreticular, sulphonated resins and the third is a new, highly porous and rigid, macroreticular, sulphonated resin, Amberlyst 15. There appears to be a correlation between viscosity or dielectric constant and the time for maximum sorption or maximum distribution coefficient when the alcohols are used, but no correlation for all the solvents is apparent. The macroreticular resin still functions when dry, even in the presence of non-polar solvents, but the microreticular resin does not. Small amounts of water present in the solvent or resin aid the sorption of the amine onto both types of resin. The effect of mesh size and cross-linkage are examined.

Enhanced capillary zone electrophoretic separation of dinitrophenyl-amino acid derivatives through control of electroosmotic flow by the buffer cation

Abstract The effect of Mg2+, Cd2+ and Zn2+ are evaluated as buffer additives to reduce electroosmotic flow (EOF) to facilitate the capillary zone electrophoretic (CZE) separation of 2,4-dinitrophenyl (DNP) derivatives of amino acids. As the divalent cation concentration increases EOF decreases and reduction of EOF follows the order Zn2+>Cd2+>Mg2+. The electrophoretic mobility of the DNP-amino acid derivatives remains constant for a given buffer and pH over a change in divalent cation concentration. The effect of the divalent cation buffer additive is consistent with cation-exchange at the silanol sites on the fused-silica wall. Higher buffer pH favors greater cation-exchange and reduced EOF. Separation of multicomponent mixtures of DNP- l -amino acid derivatives in the presence of Mg2+, Cd2+ and Zn2+ are compared at pH 7.00. Derivative migration time, resolution and peak shape are enhanced and are best for Mg2+ as the buffer additive although Mg2+ must be used at a higher concentration than either Cd2+ or Zn2+. Raising the buffer pH to 9.25 in the presence of Mg2+ increases migration time and resolution but analysis time is also increased.

Preparation, stability and acidity of difluoromethylene bis phosphonic acid

Abstract Hydrolysis of difluoromethylene phosphonate esters quantitatively yields difluoromethylene bis phosphonic acid as a dihydrate. In vacuo drying leads to either the monohydrate or the anhydrous acid. Titration of either the free acid or its disodium salt and computer fit of the data gives all four pKas. The disodium salt and the free acid are thermally stable, and the disodium salt is extremely stable even to strong base.

Relationship between bisphosphonate concentration and osteoclast activity and viability.

SummaryDifluoromethylidene bisphosphonate (F2MBP) is one of the many bisphosphonates known to inhibit bone resorption in vitro and in vivo. We have developed an analytical method, employing anion exchange and postcolumn indirect fluorescence detection, by which F2MBP can be quantified in bone samples. The objective of this study was to relate the concentration of F2MBP in embryonic bones treated in organ culture to the physiological effects of the compound, such as bone resorption (i.e., the amount of 45Ca released into the medium from prelabeled bones) and viability of the osteoclast population (i.e., the incidence of abnormal osteoclasts). Osteoclasts in bones treated with F2MBP exhibited morphological features of apoptosis, such as nuclear fragmentation. Both the number and percentage of these abnormal cells increased with dose of F2MBP and duration of incubation. The decrease in normal osteoclasts was correlated with the decreased amount of 45Ca released into the medium. Bones treated with F2MBP for only the first 5 min of the 48-h incubation period had similar numbers of abnormal osteoclasts and amounts of 45Ca released, as had bones incubated with F2MBP continuously for 48 h. The uptake of F2MBP into the bone was rapid. Bones treated with F2MBP for 6 h were similar to bones treated with F2MBP for the entire 48-h incubation period, both in F2MBP concentration and the 45Ca release ratios. These relationships between concentrations of F2MBP within bone and osteoclast activity and viability implicate apoptosis in the mechanism by which this bisphosphonate inhibits bone resorption.