Isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS) for the certification of lead and cadmium in environmental standard reference materials

Lead (Pb) and cadmium (Cd) have been determined in six new environmental standard reference materials (SRMs) using isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). The SRMs are the following: SRM 1944, New York-New Jersey Waterway Sediment, SRMs 2583 and 2584, Trace Elements in Indoor Dust, Nominal 90 mg/kg and 10,000 mg/kg Lead, respectively, SRMs 2586 and 2587, Trace Elements in Soil Containing Lead from Paint, Nominal 500 mg/kg and 3,000 mg/kg Lead, respectively, and SRM 2782, Industrial Sludge. The capabilities of ID ICP-MS for the certification of Pb and Cd in these materials are assessed. Sample preparation and ratio measurement uncertainties have been evaluated. Reproducibility and accuracy of the established procedures are demonstrated by determination of gravimetrically prepared primary standard solutions and by comparison with isotope dilution thermal ionization mass spectrometry (ID TIMS). Material heterogeneity was readily demonstrated to be the dominant source of uncertainty in the certified values.     

Precise synthesis of poly(macromonomer)s containing sugars by repetitive ring-opening metathesis polymerisation

Various poly(macromonomer)s containing sugars have been prepared by ROMP of norbornene macromonomers substituted with ROMP block copolymers containing acetal-protected sugars as the side chain, which upon removal of the protecting group affords a novel amphiphilic architecture.     

The electrooxidation of methanol and related compounds at ruthenium dioxide-coated electrodes

The underlying metal was observed to corrode when a ruthenium dioxide-coated titanium electrode was anodized in an aqueous methanol solution. With a similarly coated platinum electrode peaks were observed on the voltammogram below 1.0 V which were attributed to methanol oxidation on the underlying metal. This effect was more pronounced when the electrode was subjected during cycling to potentials close to 0 V. Rapid oxidation of methanol on RuO₂ was observed at potentials above 1.0 V, the rate at a given potential increasing in an approximately linear manner with increasing alcohol concentration. The rate of reaction also increased with increasing temperature and increasing surface roughness. Tafel slope values were rather high (>100 mV decade^?1) and a mechanism involving anodically generated species such as OH_ads was proposed to account for these results. The variation of activity with pH was similar to that reported earlier for oxygen evolution at these anodes and this was again explained in terms of partial deactivation of the surface due to a combination of proton loss and phosphate ion adsorption at intermediate pH values. The release of carbon dioxide from aqueous solutions of higher alcohols at 25°C confirmed the high oxidizing power of RuO₂ anodes.     

Measurement of total fructan in foods by enzymatic/spectrophotometric method: collaborative study

An AOAC collaborative study was conducted to evaluate the accuracy and reliability of an enzyme assay kit procedure for measuring oligofructans and fructan polysaccharide (inulins) in mixed materials and food products. The sample is extracted with hot water, and an aliquot is treated with a mixture of sucrase (a specific sucrose-degrading enzyme), alpha-amylase, pullulanase, and maltase to hydrolyze sucrose to glucose and fructose, and starch to glucose. These reducing sugars are then reduced to sugar alcohols by treatment with alkaline borohydride solution. The solution is neutralized, and excess borohydride is removed with dilute acetic acid. The fructan is hydrolyzed to fructose and glucose using a mixture of purified exo- and endo-inulinanases (fructanase mixture). The reducing sugars produced (fructose and glucose) are measured with a spectrophotometer after reaction with para-hydroxybenzoic acid hydrazide. The samples analyzed included pure fructan, chocolate, low-fat spread, milk powder, vitamin tablets, onion powder, Jerusalem artichoke flour, wheat stalks, and a sucrose/cellulose control flour. Repeatability relative standard deviations ranged from 2.3 to 7.3%; reproducibility relative standard deviations ranged from 5.0 to 10.8%.     

Hybridization and Melting Behavior of Peptide Nucleic Acid (PNA) Oligonucleotide Chimeras Conjugated to Gold Nanoparticles

Peptide nucleic acids (PNA) and PNA–DNA chimeras carrying thiol groups were used for surface functionalization of Au nanoparticles. Conjugation of PNA to citrate‐stabilized Au nanoparticles destabilized the nanoparticles causing them to precipitate. Addition of a tail of glutamic acid to the PNA prevented destabilization of the nanoparticles but resulted in loss of interaction with complementary sequences. Importantly, PNA–DNA chimeras gave stable conjugates with Au nanoparticles. The hybridization and melting properties of complexes formed from chimera–nanoparticle conjugates and oligonucleotide–nanoparticle conjugates are described for the first time. Similar to oligonucleotide–nanoparticle conjugates, conjugates with PNA–DNA chimeras gave sharper and more‐defined melting profiles than those obtained with unmodified oligonucleotides. In addition, mismatch discrimination was found to be more efficient than with unmodified oligonucleotides.     

Detection of DNA adducts of benzo[a]pyrene using immunoelectrophoresis with laser-induced fluorescence. Analysis of A549 cells

Detection of benzo[a]pyrene diol epoxide (BPDE)-damaged DNA in a human lung carcinoma cell line (A549) has been performed using free zone affinity capillary electrophoresis with laser-induced fluorescence (LIF). Using BPDE as a model carcinogenic compound, the speed, sensitivity and specificity of this technique was demonstrated. Under free zone conditions, an antibody bound adduct was baseline-resolved from an unbound adduct in less than 2 min. The efficiencies of separation were in excess of 6 x 10(5) and 1 x 10(6) plates per meter for the antibody-bound and unbound adducts, respectively. Separation using a low ionic strength buffer permitted the use of a high electric field (830 V/cm) without the loss of resolving power. Using LIF detection, a concentration detection limit of roughly 3 x 10(-10) M was achieved for a 90-mer oligonuleotide containing a single BDPE. The use of formamide in the incubation buffer to enhance denaturing of DNA did not affect the stability of the complex between the antibody and the adducts. Using a fluorescently labeled BPDE-modified DNA adduct probe, a competitive assay was established to determine the levels of BPDE-DNA adducts in A549 cells.     

Fluorenyl-containing sulfonated poly(aryl ether ether ketone ketone)s (SPFEEKK) for fuel cell applications

A series of fluorenyl-containing sulfonated poly(aryl ether ether ketone ketone)s (SPFEEKK) were synthesized via aromatic nucleophilic substitution polymerization. The sulfonation content (SC) was controlled by the feed ratios of sulfonated and nonsulfonated monomers. Flexible and strong membranes in the sulfonic acid form were obtained from cast membranes in the sodium salt forms by treatment with acid. The thermal properties, water uptake, swelling ratio, water state, oxidative stability, proton conductivity and methanol permeability were investigated. All the polymers had proton conductivities greater than 1 × 10⁻² S/cm at room temperature, and the conductivity values of m-SPFEEKK-80 and p-SPFEEKK-80 were up to 1.86 × 10⁻¹ and 1.78 × 10⁻¹ S/cm at 100 °C. This series of polymers also possessed good dimensional stability in water and low methanol crossover.     

Et3SiH + KOtBu provide multiple reactive intermediates that compete in the reactions and rearrangements of benzylnitriles and indolenines

The combination of potassium tert-butoxide and triethylsilane is unusual because it generates multiple different types of reactive intermediates simultaneously that provide access to (i) silyl radical reactions, (ii) hydrogen atom transfer reactions to closed shell molecules and to radicals, (iii) electron transfer reductions and (iv) hydride ion chemistry, giving scope for unprecedented outcomes. Until now, reactions with this reagent pair have generally been explained by reference to one of the intermediates, but we now highlight the interplay and competition between them.

The combination of potassium tert-butoxide and triethylsilane provides simultaneous access to multiple reactive intermediates, radicals, H-atom donors, hydride donors and electron donors, giving scope for unprecedented reaction outcomes.