Outline for the revision of ISO Guide 35

The production of reference materials (RMs) is a key activity for the improvement and maintenance of a worldwide coherent measurement system. As detailed in ISO Guide 33, RMs with different characteristics are used in measurements, such as calibration, quality control and method validation, as well as for the assignment of values to other materials. Currently, ISO Guide 35 is in its third edition after it was revised in 2006. The Guide was developed to support best practices in the value assignment to specified properties of Certified Reference Materials (CRMs). This Guide gives general guidance and explains concepts to assist the understanding and development of valid methods to assign values to the properties of a reference material, including the evaluation of their associated measurement uncertainties, and the establishment of their metrological traceability. From the outcome of a systematic review of ISO Guide 35 among the members of ISO/REMCO, the ISO Committee on Reference Materials, it followed that there is a need for revising the current edition of ISO Guide 35. The mandate for the revision is focused on editorial updates to explain the concepts in more detail. It is not envisaged that major technical changes will be introduced. This paper explains the approach and rationale for the revision of ISO Guide 35 and invites comments from the users of the current edition of ISO Guide 35.     

Improving the Rate of Silver Nanoparticle Adhesion to ‘Sticky Electrodes’: Stick and Strip Experiments at a DMSA‐Modified Gold Electrode

The immobilisation of nanoparticles from solution at a solid surface followed by anodic stripping voltammetry is a simple technique allowing the analysis of nanoparticle concentrations and identity. We report that the modification of gold electrodes with meso‐2,3‐dimercaptosuccinic acid (DMSA) shows a useful increase in the adsorption rate of silver nanoparticles on a gold substrate showing that the chemical modification of the electrode is analytically advantageous.     

A review of interference effects and their correction in chemical analysis with special reference to uncertainty

This paper reviews matrix effects and interference in chemical analysis and the methods by which analytical chemists reduce their effects to either negligible or minimal magnitude. The aim is to provide a framework for estimating the contribution to uncertainty due to these effects in analysis, with or without the application of procedures for correcting them. The general characteristics of matrix effects and interference are discussed, and general principles for the estimation of uncertainty associated with matrix effects are introduced. The principal techniques available to minimise matrix effects are described, together with methods of uncertainty estimation where appropriate.The Analytical Methods Committee of the Royal Society of Chemistry has received and approved for publication the following report from its Matrix Effects Working Group. The constitution of the working group was Dr. S. Ellison (Chairman), Prof. M. Thompson, Dr. D. Bullock, Dr. J. Dean, Prof. T. Fearn, W. Hardcastle, Dr. T. Lynch, Dr. N. Reid, Dr. S. Scott, Dr. Thompson.

---

Electron trapping in polar-solvated zeolites

Of current interest in our laboratory is the nature of photoinduced processes in the cavities of zeolites completely submerged in polar solvents, or polar-solvated zeolites (PSZ). The present study addresses the nature of electron trapping in PSZ with emphasis on the zeolites NaX and NaY. Free electrons were generated by two-photon, pulsed-laser excitation of either pyrene or naphthalene included in zeolite cavities. Trapped electrons were monitored by diffuse transmittance, transient absorption spectroscopy at visible wavelengths. In anhydrous alcohols, electron trapping by Na(4)(4+) ion clusters was observed in both NaX and NaY. The resulting trapped electrons decayed over the course of tens of milliseconds. No evidence for alcohol-solvated electrons was found. More varied results were observed in solvents containing water. In NaX submerged in CH(3)OH containing 5% or higher water, species having microsecond lifetimes characteristic of solvated electrons were observed. By contrast, a 2 h exposure of NaY to 95/5 CH(3)OH/H(2)O had no effect on electron trapping relative to anhydrous CH(3)OH. The difference between NaX and NaY was explained by how fast water migrates into the sodalite cage. Prolonged exposure to water at room temperature or exposure to water at elevated temperatures was necessary to place water in the sodalite cages of NaY and deactivate Na(4)(4+) as an electron trap. Additional studies in NaY revealed that solvent clusters eventually become lower energy traps than Na(4)(4+) as the water content in methanol increases. In acetonitrile-water mixtures, electron trapping by Na(4)(4+) was eliminated and no equivalent species characteristic of solvated electrons in methanol-water mixtures was observed. This result was explained by the formation of low energy solvated electrons which cannot be observed in the visible region of the spectrum. Measurements of the rate of O(2) quenching in anhydrous solvents revealed rate constants for the quenching of ion cluster trapped electrons that were 2-4 times higher than that for pyrene triplets. In NaX, the rate constant in methanol was 10(4) times smaller than that in cyclohexane, showing greater inhibition of O(2) reactivity in the medium of PSZ. The results of this study point out the conditions under which Na(4)(4+) is active as an electron trap in PSZ and that water must be present in the sodalite cage to produce solvated electrons in the supercage.     

Ring-opened metathesis polymers from cyclohexenylnorbornene and related Diels-Alder adducts of cyclopentadiene with vinyl and divinyl cyclohydrocarbons

5-(3-Cyclohexen-1-yl)-2-norbornene [CHNB] has been shown to form a very lightly crosslinked polymer (T_g = 127°C) with good elongation via ring-opening metathesis polymerization (ROMP). Based on swelling behavior with added norbornadiene dimer, the low crosslink density is ascribed to ≪0.5% participation by the cyclohexenyl ring. Compared to dicyclopentadiene (DCPD), CHNB polymerizations were less exothermic, required less catalyst, and exhibited greater molding latitude, which are advantageous for Reaction Injection Molding (RIM). Styrene-isoprene and styrene-ethylene/butylene block copolymers were effective impact modifiers for polyCHNB, forming large particle morphologies. Small rubber particles formed from styrene-butadiene block copolymers were not effective for impact enhancement of polyCHNB, in contrast to polyDCPD. Rubber-modified polyCHNB retained impact resistance four to six times longer than polyDCPD samples when aged in air at 50–70°C. Related RIM-ROMP of liquid monomer mixtures prepared by cyclopentadiene cycloadditions with 4-vinyl-1-cyclohexene, cis-1,3-divinylcyclopentane, 3,5-divinylcyclopentene or cis-2,4-divinylbicyclo[3.3.0]oct-6-ene formed highly crosslinked, less ductile copolymers with T_gs as high as 206°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3049–3063, 1997