A Simple Two-Membered Model for Retention in RP-IPC with Hydrophobic Counterions

Abstract

The retention behavior of some organic anions in the presence of tetralkyl ammonium ions in the mobile phase is analized under conditions where these hydrophobic counterions do adsorb on the surface of a reversed-phase packing. The study comprises the effects of the counterion concentration in the mobile and in the stationary phase, the salt concentration in the eluent and the salt type. Experimental results are discussed in view of previously proposed mechanisms and 2 simple two-member expression relating corrected capacity factor to adsorbed counterion concentration is deduced. The retention model indicates that solute is present in the stationary phase at two different levels; first into a diffuse ionic cloud associated electrically to the ionic surface and, second, at the surface of the packing where it forms ion pairs with the adsorbed counterions.     

Thermodynamic Studies of Interaction Between Cationic Surfactants and Lysozyme Using Potentiometric Techniques

Abstract

The interaction between a homologous series of nalkyl trimethyl ammonium bromides and lysozyme was studied by a potentiometric method using a surfactant-selective electrode. The binding isotherms the interaction between a homologous series of nalkyl trimethyl ammonium bromides were measured for different conditions and show a concentration dependence attributable to aggregation of the lysozyme-surfactanl complexes. The binding isotherms arc discussed in terms of the binding potential concept of Wyman and are used to calculate an apparent Gibbs energy of binding per surfactant cation. The binding isotherms show that the C₁ decreases with increasing chain length of surfactant.     

Sample Preparation Techniques Prior to HPLC Analysis of Serum Nucleosides and Their Bases

Abstract

Techniques for sample preparation and handling of serum prior to analysis for nucleoside and bases were evaluated. Efficiency data are reported for the trichloracetic acid (TCA), ammonium sulfate, ultrafiltration and pre-column concentration sample prep-atation techniques. Maximum recoveries for most of the compounds were obtained using the ultrafiltration, ammonium sulfate and pre-column concentration techniques. Poorer recovery was observed using the TCA/Freon-amine methods. Theophylline and tryptophan exhibited pH dependent recoveries using the ultrafiltration, ammonium sulfate and pre-column techniques.     

The solubility of cellulose in liquid ammonia/salt solutions

The dissolution of cellulose in solutions of liquid ammonia and ammonium thiocyanate is discussed. Viscosity measurements on dilute solutions of cellulose in this solvent over a range of shear rates and shear stresses are reported. A four-bulb Ubbelohde suspended level viscometer was used for the measurements. Plots of log [η] versus log M gave Mark-Houwink coefficients of a = 0.95 and K = 6.686 × 10^?5 at 25°C for [η] as dl/g. The Bloomfield equation was used to calculate effective bond lengths (b) from limiting viscosity numbers of cellulose in solutions of ammonia/ammonium thiocyanate and Cuene, respectively. Results indicate that cellulose may have similar configurations in both solvents and also that the ammonia solutions are true cellulose solutions. Miscibility of the cell- ulose/ammonia/ammonium thiocyanate solutions with organic solvents, such as glycerol, is also reported. Further, a few interesting characteristics of the liquid ammonia/ammonium salt solutions, discussed briefly, are the convenient boiling point, the rheological behavior, and the relatively high concentration of cellulose obtainable.     

Optimization of ammonium removal from waste water by natural zeolite using central composite design approach

The aims of the present study are to investigate removal of ammonium ion from wastewater using natural Western Azarbaijan zeolite and to optimize effective parameters by experimental design. In order to remove ammonium ions from aqueous solutions, experiments were carried out using column method as functions of the initial ammonium concentration, flow rate and pH of the solution. The results clearly confirmed that all mentioned parameters have vital affects on removing ammonium ions from wastewater and effluents, so got optimized. Central composite design with response surface methodology was applied for the optimization of main experiment parameters. The significance of the independent variables and their interactions were tested by the analysis of variance ANOVA and f-test statistics. Optimization of the variables for maximum removal efficiency by natural zeolite was performed using the quadratic model. The model predicted maximum removal efficiency under the optimum conditions including initial ammonium concentration of 30?mg?l^?1; flow rate of 1?ml?min^?1 and pH 6, which was very close to the experimental value determined in column experiment. The cation exchange capacity of natural Western Azarbaijan zeolite was found to be 1.79?meq?g^?1. Based on the experimental results, it can be concluded that the natural Western Azarbaijan zeolite has an excellent potential for removing ammonium ions from aqueous solutions and it is suggested as a suitable material for wastewater treatment.     

Understanding the Charge Issues in Mono and di-Quaternary Ammonium Compounds for Their Determination by LC/ESI-MS/MS

Chromatographers often develop problems while optimizing a method for the quantification of quaternary ammonium compounds in ESI-MS/MS. Intransigency observed in quaternary ammonium compounds to undergo the classical molecular adduct formation [M+H]⁺ in ESI-MS/MS reduces confidence among chromatographers while working with unit mass resolution. In this study, we provide the evidence for an exceptional rule followed by mono- and di-quaternary ammonium compounds in ESI-MS/MS in the precursor ion formation. Under ESI conditions mono- and di-quaternary ammonium compounds form molecular ions with the formula of m ^q / z ^q rather than ( m + z )/ z . Formation of m ^q / 2 is observed for di-quaternary ammonium compounds in precursor ion scan and m ^q / 1 in product ion scan, if loss of one of the quaternary charge occurs during CID. In di-quaternary ammonium compounds, this process can also result in the formation of fragment ions with higher mass as compared to precursor ion. Hydrophilic interaction liquid chromatographic separation has been used to demonstrate the elution of quaternary ammonium compounds in a single run in the ESI-MS/MS. This work concludes that the analyst must realize and consider these charge issues while dealing with positively charged compounds in LC/ESI-MS/MS.     

Comparison of ICP-AES and ICP-MS for the Analysis of Trace Elements in Soil Extracts

Abstract

The extraction of the chemical species Cr, Ni, Cu, Zn, Cd, and Pb, operationally defined, from a sewage sludge treated soil with various extractants (ammonium acetate, acetic acid and EDTA) has been studied by using two analytical techniques: inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). A comparison of the mean values measured by the two techniques with the t-criterion reveal that the differences are not significant in all the extractants mentioned above.

Results are also compared with data from a laboratory intercomparison exercise organized in the BCR-programme (Bureau Communautaire de Reference) and discussed. A fast screening of the concentration of other trace metals could be provided by ICP-MS with good precision and low detection limits.     

THE DISPLACEMENT OF BROMIDE ION BY DIMETHYL PHOSPHITE FROM THE OXOPENTABROMOMOLYBDATE(V) COMPLEX

Abstract

A study of the chemical behaviour of dimethyl phosphite, (CH₃O)₂PO(H), with ammonium oxopentabromo-molybdate(V), (NH₄)₂MoOBr₅, in the tetrahydrofuran was carried out. The stepwise substitution of the bromo ligand by dimethyl phosphite was observed by analysis of esr spectral changes. The relative concentration of each species in solutions of this reaction mixture was obtained as a function of time with the assistance of computer stimulated esr spectra by using a curvefitting program. Rate constants and activation parameters of each individual substitution step were obtained.     

Aromatization of aliphatic compounds—II: On the aromatization of some alkyl substituted cyclohexenones

2,3,5-Trimethyl-4-oxo-cyclohex-2-en acetic acid 5 treated with PyHCl aromatizes to the corresponding 2,3,5-trimethyl-benzene acetic acid 9 through a mechanism different from that leading to arylacetic acids from 2-oxo-cyclohex-3-en acetic acids 3. 2,3,4,6-Tetrakyl cyclohexenone 11, lacking the 2-carboxymethyl group, also aromatizes to tetralkyl benzene 13.     

The Determination of Trace Amounts of Tellurium and Selenium in Gallium Metal

Abstract

Analytical methods have been developed for the separation, concentration and determination of trace quantities of tellurium and selenium from primary and scrap gallium metal. A chloroform extraction is made of the tellurium diethyldithiocarbamate complex at a pH of 8.5. This extraction, in the presence of ammonium citrate, allows the satisfactory determination of tellurium by emission or atomic absorption spectrohcopy. The limit of sensitivity of the method is 0.5 pg of tellurium in 1.0 gram of gallium (0.5 ppm Te).     

A Solid Ammonium Ion Selective Electrode

Abstract

A new ammonium ion selective electrode has been developed and found to be capable of measuring ammonium ion in the presence of other cations. The electrode's selectivity over other cations is reported as well as its response time to step changes in ammonium ion activity. In addition, blood serum samples have been analyzed for urea content by treatment with urease with no special sample pre-treatment required.     

Arginine Determination with Ion-Selective Membrane Electrodes

Abstract

A new method for the determination of the amino acid arginine utilizes a dual enzyme catalyzed reaction monitored with an ammonium ion selective membrane electrode of the antibiotic type. The technique gives a linear correlation between arginine concentration and electrode response over the 3 × 10^?3 M to 3 × 10^?5 M range and a useful, but non-linear, response over a wider range. Major interferences are urea, K⁺, and NH₄ ⁺, but Na⁺ does not interfere in the physiological concentration range.     

High Performance Liquid Chromatography of Uroporphyrin Isomers

Abstract

The separation of uroporphyrin I and III isomers by reversed-phase high performance liquid chromatography on ODS-Hypersil with ammonium acetate buffer-acetonitrile solvent systems is described. The effects of buffer concentration, pH, organic modifier proportion and different organic modifiers on the resolution are studied. The optimum conditions for the separation were 12–13% acetonitrile in 1M ammonium acetate buffer pH 5.10–5.20. The method also separated uroporphyrin I and III from the II isomers but the resolution of uroporphyrin III and IV isomers was not achieved.     

The Combination of Pyrolytic Esterification and Ion Pair Extraction for the Analysis of Organic Acids

Abstract

Pyrolytic esterification and ion pair extraction were combined to furnish a rapid convenient method for analysis of organic acids. The extraction was not 100% efficient but the response of the gas chromatograph was linearly aroportional to the concentration of acid. However, it was necessary to have a large excess of the quaternary ammonium salt present.     

Graft copolymerization of 2-hydroxyethyl methacrylate and methyl methacrylate onto hide powder

Graft copolymerization of 2-hydroxyethyl methacrylate(HEMA) and mixtures of HEMA with methyl methacrylate (MMA) onto hide powder was attempted using ceric ammonium nitrate as initiator, with a view to optimize the conditions for graft copolymerization. Percent grafting and grafting efficiency were calculated for various variables such as monomer concentration, initator concentration and mole ratio of HEMA to MMA. R_p, R_g and R_h (rates of polymerization, grafting and homopolymerization respectively) were also evaluated. It was observed that R_p increased linearly with increasing concentration of MMA except at very low concentrations of the monomer. An explanation is given for the effect of variables on extent of grafting and grafting efficiency.     

Cationic Surfactants in Interfacial Synthesis of Linear Aromatic Polyester

Abstract

The polycondensation of terephthaloyl chloride and bisphenol A was used as a model reaction for the production of linear aromatic polyesters in stirred interfacial polymerization. The evaluation of several catalytic and surfactant additives to this system was based upon yields and intrinsic viscosities of the products obtained with both low and high concentrations of cationic surfactants of the quaternary ammonium type, of an anionic surfactant, and of a non-micelle forming quaternary ammonium salt. Although yields were similar in most cases, viscosity differences were marked. The highest intrinsic viscosities, hence highest degrees of polymerization, were found for preparations where cationic surfactant in excess of the critical micelle concentration was employed. Modes of action for such surfactants are suggested. The possibilities include, but are not limited to, solubilization of the product, solubilization of either or both monomers, emulsification of the liquid phases, catalytic phase transfer of one monomer, and micellar catalysis.     

Efficient and Convenient Pyridine Ring-E Formation of the Cytotoxic Marine Alkaloid Ascididemin and Related Analogues.

Conversion of tetracyclic quinone 1 to the cytotoxic pentacyclic alkaloid ascididemin (2) in 80% yield is achieved by reaction with paraformaldehyde and ammonium chloride in refluxing acetic acid. High yielding annelations are aiso observed for the related analogues N-8 deaza ascididemin (3) and kuanoniamine A (4).     

Application of factorial design to the study of xylitol production from eucalyptus hemicellulosic hydrolysate

This study deals with the bioconversion of xylose into xylitol by Candida guilliermondii FTI 20037 using eucalyptus hemicellulosic hydrolysate obtained by acid hydrolysis. The influence of various parameters (ammonium sulfate, rice bran, pH, and xylose concentration) on the production of xylitol was evaluated. The experiments were based on multivariate statistical concepts, with the application of factorial design techniques to identify the most important variables in the process. The levels of these variables were quantified by the response surface methodology, which permitted the establishment of a significant mathematical model with a coefficient determination of R ²=0.92. The best results (xylitol=10.0 g/L, yield factor=0.2 g/g, and productivity=0.1 g/[L·h]) were attained with hydrolysate containing ammonium sulfate (1.1 g/L), rice bran (5.0 g/L), and xylose (initial concentration of 60.0 g/L), after 72 h of fermentation. The pH of fermentation was adjusted to 8.0 and the inoculum level utilized was 3 g/L.     

Turbidimetric Determination of Ammonia Using 12-Molybdophosphoric Acid

Abstract

A turbidimetric method for the determination of ammonia was developed based on the co-precipitation of ammonium 12-molybdophosphate with thallium(I) 12-molybdophosphate. The analysis is carried out in strongly acidic solution which eliminates possible loss due to volatility and other interferences. Samples containing 0.1 to 3.0 mg of ammonia are conveniently analyzed in 30 minutes with a relative standard deviation 1.7%. A study of the effect of various diverse ions was conducted.     

Capillary zone electrophoresis of neutral organic molecules in organic – aqueous solution

Very good separations of non-ionic organic compounds have been achieved by capillary zone electrophoresis (CZE) using a tetrahep-tylammonium salt as an additive in aqueous acetonitrile as solvent. A systematic study was undertaken to determine the effect of experimental parameters on electroosmotic mobility and electro-phoretic mobility. It was found that pH, acetonitrile concentration, and the type and concentration of quaternary ammonium salt are important experimental variables. Under appropriate conditions, the separation window was enlarged and a broad range of electrically neutral organics, including very hydrophobic compounds (e. g. poly-cyclic aromatic hydrocarbons) and fairly hydrophilic compounds were separated in a relatively short time. By adjusting the separation conditions, high resolution CZE of a specific group of neutral organic compounds could be achieved. A method for calculation of capacity factor was proposed and capacity factors for a variety of non-lonic organic compounds were calculated.