Donald E. Leyden

Characterization and application of silylated substrates for the preconcentration of cations

Abstract Chelating functional groups immobilized on silica and controlled pore glass beads are used to preconcentrate cations from aqueous solution in the concentration region of ng ml−1. The functional groups are chemically bonded to the substrates by silylation reagents which may be employed as received or further modified. For example, commercially available 1,2-diamines may be used or converted to the dithiocarbamate after immobilization. This report includes studies of ionic strength and sodium chloride effects on the recovery of transition metal ions. Batch extraction of transition metal ions is accomplished with silica as the substrate for solutions containing transition metal ions at μg ml−1 concentrations. Column extraction of solutions pumped at 50 ml min−1 is accomplished at concentrations of 25 ng ml−1. Recovery is good in both cases. The cations were determined directly on pelletized substrates by x-ray fluorescence. However, the ions may be eluted from the substrate and determined by other methods. Examples of determinations of several cations in lake water and high-purity industrial water are given.

Silica Gel with Immobilized Chelating Groups as an Analytical Sampling Tool

Abstract Chelating functional groups have been immobilized on chromatographic grade silica gel using silylation reactions. The recovery of trace metals from solution by these materials is illustrated. The pH and time dependence upon batch extractions was studied. These materials offer potential for variation of functional groups for specific tasks.

Distribution of total Al, Cd, Co, Cu, Ni and Zn in the tongue of the ocean and the northwestern Atlantic Ocean☆

Abstract The elements Al, Cd, Co, Cu, Ni and Zn were concentrated from seawater using tetraethylenepentamine resin and analysed by atomic absorption spectrophotometry. The spatial distribution of these elements in the northwest Atlantic Ocean is discussed with respect to possible riverine inputs to the area from Puerto Rico.

Preparation of Chemically Modified Cellulose Exchangers and their use for the Preconcentration of Trace Elements

I. INTRODUCTION Analytical chemistry at trace levels frequently requires special techniques and precautions to avoid systematic errors. Preconcentration of the analyte elements is one of these special steps that can be favorably applied to the sample prior to analysis.

pH dependence of the n.m.r. line broadening of water by paramagnetic EDTA chelates

Abstract The effect of pH and temperature upon the n.m.r. line width of solutions of the ethylenediaminetetraacetic acid (EDTA) chelates of copper(II), nickel(II) and iron(III) has been studied. The concentration of these chelates required to give a line width of 10 Hz is only a factor of about two greater than the hydrated metal ions. This result indicates rapid exchange of the solvent from a coordination site on the chelated metal ion. The temperature dependence of the n.m.r. spectra shows that in each case the line width is controlled by the relaxation time of the proton in the paramagnetic environment of the coordinated metal ion rather than the rate of solvent exchange. The pH dependence of the solvent line width is related to the formation of protonated and hydroxy complexes of the chelates as confirmed by potentiometric titration.

Nuclear magnetic resonance studies of the microscopic protonation of l-cysteine

Abstract The protonation scheme of L-cysteine has been investigated by nuclear magnetic resonance. Chemical shift data as a function of pH are given for L-cysteine, L-cysteine methyl ester and S-methyl-L-cysteine. Use of derivatives of L-cysteine permits determination of the effect of protonation of the amino, sulfhydryl and carboxylic sites on the chemical shift of the -CH and -CH 2 protons. On the basis of these results, a set of simultaneous equations was written whose solution yielded the fraction of protonation of each site upon the addition of n equivalents of acid to the initially completely deprotonated molecule.

Ligand-exchange chromatography of amino sugars and amino acids on copper-loaded silylated controlled-pore glass

Abstract The application of silylated controlled-pore glass (CPG) particles as a stationary phase for the liquid chromatographic separation of selected amino acids and amino hexoses is reported. Copper-loaded columns prepared from CPG particles whose surface was silylated to immobilize an ethylenediamine functional group were employed. Copper bleeding from the column occurred but was compensated by 10 -4 M copper in the ammoniacal eluent. Hydrolysis of the siloxane bonded to the surface limited the practical lifetime of a column to 50 h of continuous operation.

A STUDY OF EQUILIBRIUM ISOTOPE EFFECTS OF TERTIARY AMINES BY NMR AND POTENTIOMETRY.

Abstract A comparative study of solvent isotope effects on the dissociation constant of amine salts, by means of potentiometric and nuclear magnetic resonance techniques lias been performed. Agreement of the results of the two techniques was generally good. The magnetic resonance technique offers an advantage in cases in which the amine is insoluble in neutral or basic solutions. An observed correlation between the isotopic shift of N-methyl proton chemical shift and the spin coupling between the methyl protons and the N-H proton is mentioned.

An Esca Study of Intermediate Oxidation States in Cobalt-Mol Ybdenum-Alumina Catalysts

Abstract Changes in the oxidation states of molybdenum in a Co-Mo-alumina catalyst are reported as a function of reduction time. Mo(VI), Mo(V) and Mo(IV) were seen, but not Mo(III). Reduction of the catalyst is necessary for thiophene desulfurization. Sulfiding of the catalyst in H2S/H2 showed conversion to MoS2. Use of H2S/H2 also produced sulfiding of the cobalt.

Nuclear magnetic resonance studies of edta in the presence of excess calcium or strontium

Abstract The equilibria which exist between metal ions, ethylenediaminetetraacetic acid (EDTA), and the resulting chelates have been thoroughly investigated by many techniques, emphasis being placed on the study of complexes containing a 1:1 ratio of metal ion to ligand. The results presented here are concerned with the observation of the chemical shift of the nonlabile protons of EDTA when excess calcium or strontium ions are present. The results yield evidence for a 2:1 complex. Formation constants for the equilibria believed to be in effect are given and a possible structure of the 2:1 complex is discussed.