Measurement of perchlorate in water by use of an 18O-enriched isotopic standard and ion chromatography with mass spectrometric detection

A novel analytical method has been developed for the determination of 4-tert.-octylphenol (OP) and 4-nonylphenol (NP) in laboratory animal feed samples, which involves stir bar sorptive extraction (SBSE) followed by liquid desorption (LD) and column-switching liquid chromatography-mass spectrometry (CS-LC-MS) with solid-phase extraction (SPE). The method required correction by stable isotopically labeled surrogate standards, deuterium 4-tert.-octylphenol (OP-d) and [2H5] 4-(1-methyl)octylphenol (m-OP-d5). A feed sample was homogenized with methanol by ultrasonication. After centrifugation, the supernatant was subjected to extraction for 120 min at room temperature (25 degrees C) using a stir bar coated with polydimethylsiloxane. After the extraction, the analyte was desorbed from the stir bar by LD using acetonitrile. Then, the liquid sample was analyzed by CS-LC-MS with SPE. The average recoveries from laboratory feed samples spiked with OP and NP at 20 ng g(-1) were 99.5 and 103.8%, respectively, with correction using the added surrogate standards. The limits of quantification were 1 ng g(-1) for OP and 5 ng g(-1) for NP in feed sample. The measurement of OP and NP in commercial laboratory animal feed samples resulted in the detection of sub ng g(-1) NP     

Application of the anomeric samarium route for the convergent synthesis of the C-linked trisaccharide alpha-D-Man-(1-->3)-[alpha-D-Man-(1-->6)]-D-Man and the disaccharides alpha-D-Man-(1-->3)-D-Man and alpha-D-Man-(1-->6)-D-Man

Studies are reported on the assembly of the branched C-trisaccharide, alpha-D-Man-(1-->3)-[alpha-D-Man-(1-->6)]-D-Man, representing the core region of the asparagine-linked oligosaccharides. The key step in this synthesis uses a SmI(2)-mediated coupling of two mannosylpyridyl sulfones to a C3,C6-diformyl branched monosaccharide unit, thereby assembling all three sugar units in one reaction and with complete stereocontrol at the two anomeric carbon centers. Subsequent tin hydride-based deoxygenation followed by a deprotection step produces the target C-trimer. In contrast to many of the other C-glycosylation methods, this approach employes intact carbohydrate units as C-glycosyl donors and acceptors, which in many instances parallels the well-studied O-glycosylation reactions. The synthesis of the C-disaccharides alpha-D-Man-(1-->3)-D-Man and alpha-D-Man-(1-->6)-D-Man is also described, they being necessary for the following conformational studies of all three carbohydrate analogues both in solution and bound to several mannose-binding proteins.     

Aqueous solution properties of polyampholytes: Effect of the net charge distribution

Viscometric and light scattering studies have been performed on aqueous solutions of polyampholyte terpolymers based on sodium-2-acrylamido-2-methylpropanesulfonate (Na-AMPS), 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT), and acrylamide (AM), prepared by an inverse microemulsion polymerization technique. The distribution of net charges among the chains was varied by adjusting the initial monomer composition and the degree of conversion. The effect of this distribution on the solubility of the samples and on the chain conformation was studied. It was found that samples with a narrow distribution of net charges were soluble in pure water even if the average net charge is small. Addition of salt induces a transition from an extended conformation to a more compact one, in qualitative agreement with theoretical predictions. A practically alternated NaAMPS-MADQUAT copolymer prepared by polymerization in homogeneous solution and with a small average net charge shows a behavior quite similar to that of the terpolymers. © 1996 John Wiley & Sons, Inc.     

Dynamic light scattering by weakly ionized gels: Effects of inhomogeneities and non-ergodicity

Small angle neutron scattering and light scattering experiments have been performed on partially neutralized poly(acrylic acid) solutions and gels. The structure factor obtained from small angle scattering and static light scattering reveals the absence of significant contribution from large scale inhomogeneities in the gels as soon as the ionization degree exceeds 9·10⁻³. The comparison of the time and ensemble averages of the autocorrelation function of scattered light intensity shows that the gels behave with respect to that experiment as ergodic media.     

Review of the methods of the US Environmental Protection Agency for bromate determination and validation of Method 317.0 for disinfection by-product anions and low-level bromate

In recent years several methods have been published by the United States Environmental Protection Agency (EPA) which specify bromate as a target analyte. The first of these was EPA Method 300.0. As technological improvements in ion chromatographic hardware have evolved and new detection techniques have been designed, method detection limits for bromate have been reduced and additional procedures have been written, including EPA Method 300.1, 321.8 and, most recently, EPA Method 317.0. An overview of the evolution of these bromate methods since 1989 is presented. The focus is specific to each of these respective procedures, highlighting method strengths, weaknesses, and addressing how these methods fit into EPA’s regulatory agenda. In addition, performance data are presented detailing the joint EPA/American Society for Testing and Materials multilaboratory validation of EPA Method 317.0 for disinfection by-product anions and low-level bromate.