Determination of nickel in the serum of occupationally exposed workers, by means of flame atomic-absorption spectroscopy

A flame atomic-absorption spectroscopy method for determination of nickel in the serum of occupationally exposed subjects has been developed. Trichloroacetic add is utilized for precipitating proteins and freeing bound nickel; sodium diethyldithiocarbamate is used as complexing agent and isopropyl acetate as the solvent for extraction. The method is characterized by good accuracy, precision and sensitivity, over a concentration range up to about 20 ng/ml. Calcium, which is present in serum in great excess with respect to typical nickel concentrations, does not interfere in the determination of the latter.     

Anodic chlorination of aromatic compounds in acetic acid part II

The anodic chlorination of aromatic compounds in anhydrous acetic acid has been further investigated. Evidence has been found for two different methods of electrochemical chlorination, in the systems Cl₂/aromatic compounds and Cl^?/aromatic compounds. These methods were also compared with the uncatalyzed chemical chlorination reaction. The yields of monochlorinated products and the related isometric distributions were taken into account. Since the isomeric distributions are equal with chemical and electrochemical chlorination methods, the formation of the same intermediate was proposed for both.     

Control charts in multi-element analysis of human urine

A plan for internal quality control (IQC) was designed to monitor the quality of analytical results obtained from the simultaneous determination by ICP-MS of nine trace elements (As, Cd, Mo, Ni, Pb, U, V, W and Zr) in 1350 samples of human urine collected as part of an epidemiological study. Analytical performances, assessed during the method validation, were as follows: limit of quantification ranging from 0.002 μg/L (U) to 0.9 μg/L (Ni); recovery rates varying between 82 % (As) and 110 % (W); intermediate precision as relative standard deviation ranging from 2.5 % (Mo) to 14.2 % (V). Only for Zr, a significantly higher relative standard deviation was obtained. Initially, two commercially certified reference materials (CRMs) based on freeze-dried human urine and containing the elements of interest at suitable levels of concentration were used as control materials. However, due to considerations of reliability, convenience and cost, a control material based on fresh human urine was prepared in-house, evaluated by comparison with the CRMs and implemented for the IQC. The IQC strategy was as follows: at least one control material was analysed in each analytical session and one more control material was analysed after every ten urine samples. The central lines of the control charts were based on the assigned concentration values; the warning and action limits were set on a statistical basis, as two-times and three-times the value of the uncertainty of certified values or the observed standard deviation. At the end of the study, the data collected for the in-house control material were re-evaluated and confirmed its suitability for the purpose. The use of an in-house control material had important advantages: it was more representative of the test samples; its preparation did not involve additional steps, therefore, reducing the risk of contamination; the cost of implementing the IQC was also reduced. Some issues concerning the control charts for As and Mo were addressed and will be discussed.     

Surface yellowing and fragmentation as warning signs of depolymerisation in Baltic amber

It is well known that the surrounding environment affects the initiation and rate of degradation of Baltic amber, causing changes in visual and mechanical properties. However, the mechanisms by which oxygen, the most important agent of degradation, causes those alterations are still unknown. Knowledge of such mechanisms would allow developing more efficient preventive conservation measures for amber artefacts in museums than those available today. In this study, an experiment using accelerated thermal ageing was conducted on representative Baltic amber samples. Changes in colour, topography and chemical properties were assessed regularly using non-destructive techniques, to identify the degradation phenomena which play a significant role during the discolouration and fragmentation processes of amber surfaces. The breakdown of the amber polymer chains, caused by oxidative radical reactions, was determined by means of FT-Raman spectroscopy and involved the formation of olefinic bonds in the terminal position. This depolymerisation process was correlated to modifications in colour, particularly yellowing, and in topographic features, analysed by spectrocolorimetry and confocal profilometry respectively. Thus, surface yellowing and fragmentation of amber objects in museum collections may act together as indicators of progressive depolymerisation.     

Identification of volatile degradation products from Baltic amber by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry

The aim of this study was to test and develop techniques for the detection and identification of volatile compounds released as degradation products by Baltic amber. During a preliminary investigation, the off-gassing of acidic volatiles was detected through the corrosion of lead coupons. The corrosive compounds released by the material were then identified as formic acid and acetic acid by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry. During an advanced investigation, based on the use of artificial ageing to initiate degradation of model amber samples in different microclimates, the detected formic acid and acetic acid off-gassing appeared to be more intense in a dry environment with normal oxygen concentration. The release of formic and acetic acids by the amber was likely the result of radical reactions which should be investigated in further studies.     

Characterisation of historic plastics using terahertz time-domain spectroscopy and pulsed imaging

Terahertz (THz) time-domain spectroscopy and 3D THz pulsed imaging have been explored with regard to polymer materials, both commodity and historic polymers. A systematic spectroscopic study of a wide range of different polymer materials showed significant differences in their spectra. Polyolefins and polystyrenes generally exhibit lower absorption than other examined polymers, various cellulose derivates, poly(vinyl chloride), poly(methyl methacrylate), polyamide, hard rubber and phenol formaldehyde resin, the last of these exhibiting the most intense absorption over the entire range, 0.15–4.2 THz. It was also examined how the presence of plasticisers in poly(vinyl chloride), the presence of fillers in polypropylene, and the degree of branching in polyethylene and polystyrene affect the spectra; inorganic fillers in polypropylene affected the absorption most. With 3D THz pulsed imaging, features in polymer objects were explored, appearing either as integral parts of the material (coatings and pores in foams) or as a consequence of physical deterioration (cracks, delamination). All of these features of various complexities can be successfully imaged in 3D. Terahertz technology is thus shown to have significant potential for both chemical and structural characterisation of polymers, which will be of interest to heritage science, but also to the polymer industry and development of analytical technologies in general.     

Preparation, mesomorphic properties and behaviour of 4,4'-biphenylenedibenzoates as stationary phases in gas chromatography

This paper describes the preparation, mesomorphic properties and behaviour as stationary phases of a series of biphenylenedibenzoates. These compounds exhibit broad mesomorphic ranges with high solid-crystal-liquid-crystal transition temperatures, and give relatively short retention times in the determination of polynuclear aromatic hydrocarbons. The chromatographic selectivity for linear and planar structures is confirmed.     

Determination of trace metals in sediment standard reference materials by graphite-furnace atomic absorption spectrometry with a stabilized temperature platform

Trace elements (As, Be, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, V, Zn) in NBS 1645 (river sediments), NBS 1646 (estuarine sediment), MESS-1 and BCSS-1 (marine sediments), IAEA SL-1 (Lake Sediment) and IAEA Soil-5, are determined by graphite furnace atomic absorption spectrometry with the L'vov platform. The samples (ca. 0.25 g) are dissolved in a mixture of nitric, perchloric and hydrofluoric acids in a PTFE bomb. Results based on direct calibration with simple aqueous solutions are in good agreement with those obtained by the method of standard additions and with recommended values. The relative standard deviations are generally 5–10%. Chromium determinations are also evaluated by inductively-coupled plasma/atomic emission spectrometry.     

A Model of Contact Forces in Pneumatic Motor Vanes

The paper presents an investigation on the dynamic equilibrium of a pneumatic motor vane. The investigation was based on an analysis of the vane's free body diagram. In particular, a model was formulated for determining the contact forces between vane, rotor and stator and the contact configuration from the known motor geometry, friction coefficients and chamber pressures. In addition, the paper presents experimental measurements of friction coefficients in vane-rotor and vane-stator contact together with a validation of the model through comparison with a FEM model.     

Static and Dynamic Experimental Investigation of a Pneumatic Open Loop Proportional Valve

Experimental Techniques - Fluid power regulation elements play a fundamental role in determining the characteristics of a servosystem. Valve is a critical component when deciding the overall...