Instrumental neutron activation analysis: A valuable link in chemical metrology

Summary Prompt gamma activation analysis (PGAA) is a common technique for the identification of hydrogen and the measurement of hydrogen concentrations within a material. Carbon fiber reinforced epoxy matrix composites are materials that are known to absorb water. The experiments described herein demonstrate the feasibility of using PGAA to detect water absorption and desorption and show that PGAA measurements of hydrogen concentration are more sensitive to water absorption than gravimetric measurements. Hydrogen concentration measurements are made using PGAA after calibration with a boric acid solution sample. Relative changes in PGAA measurements generally agree with values expected based on gravimetric measurements.     

Accuracy of single measurements

Single measurements are widely used in industry, trade and science, yet the problem of the estimation of the accuracy of this type of measurements is neither addressed nor even recognized in traditional Metrology. In particular, the Guide to the Expression of Uncertainty in Measurement is devoted to multiple measurements only and does not mention single measurements. This paper studies the problem of estimating the inaccuracy of single measurements and describes solutions to this problem. The proposed methods are based on metrological characteristics of measuring instruments rated in accordance with Recommendation R34 of International Organization of Legal Metrology (OIML). These characteristics are usually given in manufacturer certificates or provided by calibration laboratories. This paper treats single measurements as the basic type of measurement and multiple measurements as sets of successive single measurements. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

Traceable measurements in clinical laboratories

 Reliable, traceable and comparable measurements provide the rational basis for evaluation of the quality of a result and the starting point for recognized laboratory accreditation in any national area. Modern medical diagnostics and treatment involve rapidly rising numbers and types of clinical laboratory measurements, that are reliable. Therefore, the basic principles to be followed to assure the traceability of clinical measurements as required by the Romanian Laws of Metrology are reviewed. Main sources affecting the quality of the unbroken chain of calibrations that relate the measurements back to appropriate measurement standards are discussed. Examples of how to achieve traceable measurements in clinical laboratories are presented. Details of specific uses of reference materials, measuring instruments and standard measurement methods are also discussed. Received: 8 January 1998 · Accepted: 21 April 1998     

New method for vapor pressure measurement applicable to potassium over coal slag

A constant-temperature graphite furnace for vapor pressure measurements at high temperatures is described. The capability of the furnace for measurements of potassium vapor pressures over coal slags is evaluated, and a series of measurements are presented and analyzed. Vapor loss mechanisms which are of general interest for graphite furnace spectroscopy are discussed.     

How to determine high growth speeds in polymer crystallization

With the fast crystallizing polymers HDPE and i-PP it is extremely difficult to extend the range of measurements of the growth speed of spherulites to temperatures as low as 80 °C. So far the lower limit for these measurements has been about 120 °C for both polymers. Several possibilities for this kind of measurements are explored in the present paper. It appears that none of these measurements is without uncertainties. So, only the comparison of results, as obtained with several independent measurements and with theory furnishes a sufficient credibility. Optical measurements, from light scattering to visual inspection, all under very special conditions of heat transfer, are described.Dedicated to Prof. Dr. D.W. van Krevelen, Arnhem     

Intersystem crossing from singlet states of molecular dimers and monomers in mixed molecular crystals: picosecond stimulated photon echo experiments

An experimental study of the excited-state dynamics of pentacene dimers and monomers in p-terphenyl host crystals is presented. Picosecond stimulated photon echoes, picosecond photon echoes, and fluorescence lifetime measurements are used to study intersystem crossing and homogeneous dephasing of delocalized dimers and monomers at 1.8 K. It is found that the dimer states can have intersystem crossing rate constants which are orders of magnitude greater than the corresponding monomers. Three mechanisms are considered to explain the differences between dimer and monomer intersystem crossing. Fluorescence lifetime measurements and photon echo measurements demonstrate that the only source of homogeneous line broadening at 1.8 K is population relaxation. These measurements combined with the stimulated echo measurements show that differences in lifetimes exhibited by the various dimer and various monomer sites are due solely to differences in intersystem crossing rate constants.     

无酶葡萄糖检测的研究进展

本文主要介绍了各种无酶葡萄糖的检测方法。 相对于酶法,该方法克服了由于酶本身固有的属性而导致的在固定化过程中不稳定易失活的缺点,具有较好的重现性、稳定性以及抗干扰能力。     

Measurement and standardisation of food colour

Summary Techniques for the measurement of colour are required widely by the food industry. Where such measurements are used only locally then few problems arise from non standard measurement methods or calibrations. If however, such measurements are to be used as quality criteria or to meet specifications set by an exterior customer, problems can result from disagreement over colour measurements. There is a clear need for standardisation to improve the transferability of measurements. A good example of this problem and its solution is seen in the tomato industry. Further studies on other colours have shown the limits within which a calibrant is useful.     

Laboratory assessment of protein energy status.

Protein energy malnutrition (PEM) is widespread throughout the world in both community and hospital settings. Assessment of PEM in an individual consists of good dietary and clinical assessment, followed by laboratory measurements. Recent changes in body weight and simple anthropometric measurements are also useful. Laboratory measurements have the advantage in that they are independent of body size, they can be made precisely, and allow monitoring of progress. However, laboratory measurements must be interpreted with caution, especially in seriously ill patients in the hospital.     

STANDARDS FOR UV INSTRUMENTS AND RISK OF EXISTING DEVICES

Abstract— Different methods for measurements of UV-radiation of various light sources are quantitatively compared: direct measurements, based on detectors of known responsivity, as well as indirect measurements, based on a spectral irradiance calibration. The optical arrangement of an accurate spectroradiometric equipment, and the structure and parameters for a new type of cosine corrected detector for the measurement of actinic radiation are described, too. The measurements of actinic radiation with commercial devices are affected by great relative errors.
A standard for natural irradiance will allow a comparison of weighted irradiances and threshold irradiations with natural insolation and with artificial UV radiation. The risk of existing irradiation apparatuses will be calculable by this comparison.     

Some NDA Techniques Applied to International Safeguards Projects

Recent attention to international safeguards has stimulated interest in nondestructive analysis techniques. These NDA techniques include high- and low-resolution gamma-ray spectrometry, active and passive neutron counting, and physical measurements. Often, the NDA measurements are made abroad under field conditions, and in these cases, portability is important. In other cases, the measurements are made under laboratory conditions but no calibration materials are available. This paper describes several NDA applications in support of international safeguards projects, all involving international cooperation.     

Evaluation of a single-monochromator diode array spectroradiometer for sunbed UV-radiation measurements

The suitability of a new technology single-monochromator diode array spectroradiometer for UV-radiation safety measurements, in particular for sunbed measurements, was evaluated. The linearity, cosine response, temperature response, wavelength scale, stray-light and slit function of the spectroradiometer were determined and their effects on the measurement accuracy evaluated. The main error sources were stray-light and nonideal cosine response, for which correction methods are presented. Without correction, the stray-light may reduce the accuracy of the measurement excessively, particularly in the UV-B range. The expanded uncertainty of the corrected UV measurements is estimated to be 14%, which is confirmed with the comparative measurements carried out with a well-characterized double-monochromator spectroradiometer. The measurement accuracy is sufficient for sunbed measurements, provided that all corrections described above have been done and the user of the instrument has a good understanding of the instrument's operating principles and potential error sources. If these requirements are met, the tested spectroradiometer improves and facilitates market surveillance field measurements of sunbeds.     

Determination of potential landscapes using video microscopy

Colloidal particles are used to characterize microscopic potential landscapes, which are defined on a sample surface and arise in ensembles of particles. The positions of the particles are recorded using video microscopy. Analysis of the positions, which the particles occupy during their Brownian motion, yields the exact shape of the surface potential, in which the particles move. The underlying principle of our measurements is well-known from measurements using total internal reflection microscopy; in contrast to these measurements, our scheme can be expanded to measurements of inter-particle interactions. As an example, we demonstrate the measurement of interactions between two magnetic particles, sedimenting towards a potential barrier in a tilted geometry.     

Solvent‐Polymeric ISEs Tailored for Measurements in Solutions Containing Tetrabutylammonium,Cesium, and Calcium Ions

Ion‐selective electrodes are described, with membranes tailored for measurements of tetrabutylammonium ions in aqueous and formamide solutions, and for measurements of cesium and calcium ions in the presence of tetrabutylammonium. It is shown that reliable measurements of cesium ions are possible when a correction is introduced for interference from tetrabutylammonium, using Nikolsky selectivity coefficient. A novel membrane composition is described which ensures high selectivity to calcium ions over tetrabutylammonium.     

PQ型显影体系的电化学研究

通过改变PQ型系列显影液的组分和浓度,使该系列显影液的显影特性从Lith型逐渐演变到超加合型。用循环伏安法对系列显影液中的对苯二酚氧化还原过程进行测量。证明了该系列显影过程所遵循的机理从Yule提出的Lith机理转变到Levenson的再生机理。电化学测量结果与Van Veelen的照相性能测定结果相一致。     

Measurement uncertainty and its meaning in legal metrology of environmental chemistry and public health

 The need for reliability of measurements supporting legal decisions in environmental policy or medical diagnosis and treatment is well known and widely accepted. This prerequisite can be met only by ensuring that legal measurements are accurate and traceable to national or international standards. Consequently, an outline of the organizational structure of the Romanian National Institute of Metrology (INM) for ensuring uniformity, consistency and accuracy of all measurements including legal measurements performed in chemical laboratories is presented. Since reliable measurements can only be accomplished within an appropriate traceability chain, the experience of the INM in identification and evaluation of measurement uncertainty in legal activities concerning the environment and health is reviewed. Practical examples of measurement uncertainty evaluation in spectrophotometric determination of five analytes, commonly determined in environmental and clinical chemistry are described. The implications of measurement uncertainty for interpretation of regulatory compliance are discussed. Received: 3 January 1998 · Accepted: 9 June 1998     

Direct Quantitative Photometry on Thin Layer Chromatograms

The principal methods for the direct photometric evaluation of thin layer chromatograms are discussed with the aid of examples. Since light is strongly scattered by TLC adsorbents, absorption measurements in reflection are preferable to transmission measurements. In the reflection measurements, an approximation method for the Kubelka-Munk function leads to satisfactory straight calibration lines. The working range for quantitative reflection measurements is in the μg range, and the detection limit is of the order of 10^?8g. The standard deviation for spots of equal concentration is less than ±1%. The signal-to-background ratio is improved by simultaneous measurement of reflection and transmission. The measurement of diminution in fluorescence (“fluorescence quenching”) is found to be less sensitive than the reflection at the absorption maximum. However, combined measurement of the reflection and the diminution of fluorescence gives an increase in sensitivity as compared to pure reflection measurements. As in solution photometry, fluorescence measurements are generally much more sensitive than absorption measurements. The working range is normally in the ng region, and the detection limit is around 10^?11g. All the investigations described in this paper were carried out on the Zeiss chromatogram spectrophotometer.     

Problems connected with the analysis of halocarbons and hydrocarbons in the non-urban atmosphere

The problems connected with the measurement of hydrocarbons outside urban areas are considerable: The atmospheric mixing ratios of most of the hydrocarbons are very low--from a few ppb down to some ppt; the mixture of hydrocarbons is extremely complex, ranging from light n-alkanes to alkyl benzenes and terpenes; for measurements in remote areas the logistic conditions often restrict the instrumentation which can be used for sample collection or in situ measurements (such as lack of electric power supply, weight restrictions etc.). Nevertheless, sensitive and sufficiently reliable measurements of hydrocarbons in the non-urban atmosphere are important. Hydrocarbons are important factors in the tropospheric photochemistry (e.g. ozone formation) and can be used as valuable tracers for man-made atmospheric pollutants etc. Other useful tracers for anthropogenic emission are halocarbons such as dichlormethane, tri- and tetrachloroethen etc. The impact of man-made hydrocarbons on the chemistry of the troposphere can only be understood if the extent of natural (biogenic) contributions is known. From measurements of a large variety of hydrocarbons and halocarbons it is often possible to obtain information about the sources of the most important atmospheric hydrocarbon species, even for trace gases with both significant anthropogenic and biogenic sources. In this presentation some of the problems and their solutions connected with such measurements of atmospheric hydrocarbons and halocarbons are presented and discussed. Some of the results obtained by several series of measurements are described, indicating that man-made as well as biogenic hydrocarbons can be important factors for the chemistry of the atmosphere.     

FTIR-ATR study of self-assembled thiol monolayers on gold

Self-assembled monolayers of 1-teradecanethiol on gold were characterized by means of FTIR-ATR measurements, XPS and contact angle measurements. Linear dichroism measurements using FTIR-ATR are used to estimate the orientation of the alkyl chains. An equation for calculating the orientation angles of the alkyls chains was deduced.