A multivariate spot filtering model for two-dimensional gel electrophoresis

Image segmentation plays an important role in the automatic analysis of protein spots in 2-DE. Using image segments representing protein spots, the amount of protein in each segment can be quantified, and corresponding segments can be matched and compared for multiple gels. However, the common presence of image segments caused by noise and unwanted artefacts highly disturb the analysis and comparison of the gels. Common sources of such artefacts are cracks in the gel surface, fingerprints, dust and other pollutions. It would be advantageous to remove these unwanted artefacts during or after the segmentation procedure. To achieve this task a multivariate spot filtering model is developed using image segments from a gel segmentation. Parameters in the model are based on texture, shape and intensity measurements of the image segments. The model successfully managed to separate segments caused by noise, artefacts and cracks from image segments representing true protein spots. The classification method used is discriminant partial least squares regression.     

Comparative investigation on copper oxides by depth profiling using XPS,RBS and GDOES

Depth profiling has been performed by using X-ray photoelectron spectrometry (XPS) in combination with Ar-ion sputtering, Rutherford backscattering spectrometry (RBS) and glow discharge optical emission spectrometry (GDOES). The data obtained by XPS have been subjected to factor analysis in order to determine the compositional layering of the copper oxides. This leads to two or three relevant components within the oxide layers consisting of Cu(2)O or CuO dependent on the sample preparation. GDOES measurements show sputtering profiles which are seriously influenced by a varying sputter rate. To ensure the results obtained so far, RBS measurements of the oxide layers have been carried out in order to discover artefacts of the other methods used and to demonstrate the excellent suitability of RBS for quantitative analysis of these layers. Chemical analysis consisting of (1) carrier-gas fusion analysis (CGFA) and (2) selective dissolution of Cu(2)O/CuO allows the determination of the total amount of oxygen and copper, respectively, and can serve as a cornerstone of quantitative analysis.     

Multiple exciton generation in nanocrystal quantum dots--controversy, current status and future prospects

Multiple exciton generation is a process that can occur in quantum dots by which the energy of an absorbed photon in excess of the bandgap can be used to create one or more additional excitons instead of being wasted as heat. This effect has received considerable interest because it has the potential to significantly enhance the performance of solar cells, nanocrystal lasers, high speed electronic devices and photocatalysts. However, measuring the efficiency of multiple exciton generation is experimentally challenging and the results of these measurements have been the subject of some controversy. This Perspective describes the techniques used to determine the quantum yield of multiexcitons in nanocrystals and also details the experimental artefacts that can confuse these measurements and have been the source of much of the recent debate. The greater understanding of these artefacts that has emerged recently and the experimental techniques developed to eliminate their effects on quantum yield measurements will also be described. The efficiency of multiple exciton generation currently obtainable from nanocrystals and its potential impact on solar cell performance is assessed in the light of this improved experimental understanding. Whilst it is found the quantum yields thus far reported are insufficient to result in more than a modest increase in solar cell efficiency, an analysis of the expected performance of a nanocrystal engineered to maximise multiple exciton generation indicates that a significant improvement in solar cell performance is possible. Moreover, a nanocrystal design is proposed for optimised efficiency of multiple exciton generation which would allow its potential benefit to solar power production to be realised.     

The accuracy and precision of the advanced Poisson dead‐time correction and its importance for multivariate analysis of high mass resolution ToF‐SIMS data

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) data collected in single ion counting mode suffers from dead‐time effects that lead to potentially confusing artefacts when common multivariate analysis (MVA) methods are applied to the data. These artefacts can be eliminated by applying an advanced Poisson dead‐time correction that accounts for the signal intensity in the dead‐time window preceding each time channel. Because this correction is nonlinear, it changes the noise distribution in the data. In this work, the accuracy of this dead‐time correction and the noise characteristics of the corrected data have been analysed for spectra with small numbers of primary ion pulses. A simple but accurate equation for estimating the standard deviation in the advanced dead‐time corrected data has been developed. Based on these results, a scaling procedure to enable successful MVA of advanced dead‐time corrected ToF‐SIMS data has been developed. The improvements made possible by using the advanced dead‐time correction and our recommended scaling are presented for principal components analysis of a ToF‐SIMS image of aerosol particles on polytetrafluoroethylene. Recommendations are made for using the advanced dead time correction and scaling ToF‐SIMS data in order optimize the outcomes of MVA. Copyright © 2014 John Wiley & Sons, Ltd.     

Investigation of inherent degradation in cellulose nitrate museum artefacts

Cellulose nitrate was one of the first semi-synthetic plastics to be commercially exploited and as such many museums contain a large number of artefacts illustrating the versatility of this plastic for the creation of a wide variety of functional and aesthetic artefacts. Conservators find themselves faced with the challenge of preserving these ageing artefacts which are showing evidence of significant degradation. The challenge is enhanced by artefacts of similar age and type exhibiting different degrees of degradation. This paper reports the analytical study of selected historical artefacts to explore the origins of these differences. A connection between the durability of the artefacts and the quality of the original synthetic process is identified, indicating the influence of inherent chemical factors on stability. The major contributory factors determining degradation appear to be the sulphate content remaining from the stabilization process and the rate of loss of the camphor plasticizer. A simple swab test is proposed to aid the identification of artefacts which are potentially susceptible to degradation. The test involves analysis of swab extracts by ion chromatography to reveal the presence of oxalate, which is indicative of cellulose nitrate chain scission.     

Comparative investigation on copper oxides by depth profiling using XPS, RBS and GDOES

Depth profiling has been performed by using X-ray photoelectron spectrometry (XPS) in combination with Ar-ion sputtering, Rutherford backscattering spectrometry (RBS) and glow discharge optical emission spectrometry (GDOES). The data obtained by XPS have been subjected to factor analysis in order to determine the compositional layering of the copper oxides. This leads to two or three relevant components within the oxide layers consisting of Cu₂O or CuO dependent on the sample preparation. GDOES measurements show sputtering profiles which are seriously influenced by a varying sputter rate. To ensure the results obtained so far, RBS measurements of the oxide layers have been carried out in order to discover artefacts of the other methods used and to demonstrate the excellent suitability of RBS for quantitative analysis of these layers. Chemical analysis consisting of (1) carrier-gas fusion analysis (CGFA) and (2) selective dissolution of Cu₂O/CuO allows the determination of the total amount of oxygen and copper, respectively, and can serve as a cornerstone of quantitative analysis.     

Identification of ancient gilding technology and Late Bronze Age metallurgy by EDXRF, Micro-EDXRF, SEM-EDS and metallographic techniques

A combination of analytical techniques capable of elemental and microstructural characterisation was used for the identification of ancient gilding technology and bronze metallurgy. EDXRF, micro-EDXRF, SEM-EDS analysis and metallographic examinations were applied in the study of artefacts dating to the end of the second millennium BC from Crasto de São Romão in Central Portugal. Results report to the finding of an exceptional gilded copper nail among bronze artefacts with 9 wt.% to15 wt.% tin and minute other metallic impurities. Additionally, analysis of a crucible fragment points out for bronze production at the archaeological site. EDXRF and micro-EDXRF analysis made on the copper nail showed that it was gilded only on the front side of the head, and that the gold layer has been lost in the most exposed areas. SEM-EDS analysis showed that the gold layer has 5–8 µm in thickness and is covered with a thick corrosion layer. The gilding technique is discussed based on the gold layer composition and gold/copper substrate interface. So far, this object seems to be the first diffusion gilded artefact identified in the Portuguese territory dated to Late Bronze Age.     

Active infrared thermography applied to the investigation of art and historic artefacts

Infrared thermography (IRT) is a non-destructive technique that has recently been extensively applied to the investigation of cultural heritage. It provides information on the surface and subsurface structure of the artefacts by the analysis of the heat diffusion process within the sample. IRT has been successfully applied to the study of historic large structures and buildings most of the time by means of the so-called passive approach, where only the naturally occurring temperature changes in the sample are analysed. On the other hand, IRT has also been applied to the study of other art and historic artefact by applying the so-called active method where the thermal stimulation of the sample is required. In this article, an overview of the applications of active thermography to the investigation of art and historic artefacts will be presented and discussed.     

A new instrument adapted to in situ Raman analysis of objects of art

The analysis of precious artefacts and antiquities demands care in order to minimise the risk of accidental damage during measurement. Mobile fibre-optic-based Raman instruments offer a means to avoid destructive sampling and eliminate the need to transport artefacts for spectrochemical analysis. In this work we present a new mobile instrument developed and optimised for the in situ Raman investigation of objects of art and antiquities. The instrument is controlled by a portable computer. Selected mounts cover many types of artefacts. Newly written software routines organise spectra together with measurement parameters and facilitate calibration of the instrument. The present paper describes this new Raman instrument and discusses some challenges in the transition from a laboratory environment to in situ investigations in museums.     

Raman spectroscopic and structural studies of indigo and its four 6,6'-dihalogeno analogues

The Raman and electron impact mass spectra of synthetic indigo and its four 6,6'-dihalogeno analogues are reported and discussed. The influence of varying the halogen on these Raman spectra is considered. Particular emphasis is laid on distinguishing indigo from 6,6'-dibromoindigo and differentiating between the dihalogenocompounds, so as to develop protocols for determining whether artefacts are coloured with dyes of marine or terrestrial origin and whether such artefacts are dyed with genuine "Tyrian Purple" or with dihalogenoindigo substitutes that do not contain bromine. The value of even low resolution electron impact mass spectrometry in a forensic context as a means of identifying authentic 6,6'-dibromoindigo and distinguishing it from its dihalogenoanalogues is emphasised     

Multi-analytical study of patination methods on steel substrates: a full insight into surface chemistry and morphology

Patination of metals has been used for decorative or protective purposes, and several methods aimed to create coloured films on metal surfaces have been developed. This work describes a multi-analytical approach to characterize artificial blue patinas created on mild steel substrates by means of traditional recipes and methods for colouring ancient objects and artefacts. We suggest the combined use of secondary ion mass spectrometry, focused ion beam, X-ray diffraction spectroscopy, white light interferometry and reflectance spectroscopy to characterize blue patinas on steel substrates and to investigate the relationship between the developed colour and the patina layer microstructure and composition. Therefore, the analysis of the oxide films produced by either thermal or chemical colouring methods has been successfully performed, providing information about the film morphology, the surface composition and in-depth elemental distribution within the coloured layers, and the origin of the colour developed on the surface.     

Correction of the influence of baseline artefacts and electrode polarisation on dielectric spectra

The deconvolution of biological dielectric spectra can be difficult enough with artefact-free spectra but is more problematic when machine baseline artefacts and electrode polarisation are present as well. In addition, these two sources of anomalies can be responsible for significant interference with dielectric biomass measurements made using one- or two-spot frequencies. The aim of this paper is to develop mathematical models of baseline artefacts and electrode polarisation which can be used to remove these anomalies from dielectric spectra in a way that can be easily implemented on-line and in real-time on the Biomass Monitor (BM). We show that both artefacts can be successfully removed in solutions of organic and inorganic ions; in animal cell and microbial culture media; and in yeast suspensions of varying biomass. The high quality of the compensations achieved were independent of whether gold and platinum electrodes were used; the electrode geometry; electrode fouling; current density; the type of BM; and of whether electrolytic cleaning pulses had been applied. In addition, the calibration experiments required could be done off-line using a simple aqueous KCl dilution series with the calibration constants being automatically calculated by a computer without the need for user intervention. The calibration values remained valid for a minimum of 3 months for the baseline model and indefinitely for the electrode polarisation one. Importantly, application of baseline correction prior to polarisation correction allowed the latter's application to the whole conductance range of the BM. These techniques are therefore exceptionally convenient to use under practical conditions.     

Ultra-low-angle microtomy and static secondary ion mass spectrometry for molecular depth profiling of UV-curable acrylate multilayers at the nanoscale

Development of sustainable materials requires methods capable of probing the molecular composition of samples not only at the surface but also in depth. Static secondary ion mass spectrometry (S-SIMS) characterises the distribution of organic and inorganic compounds at the surface. Ultra-low-angle microtomy (ULAM) has been studied as an alternative or complementing method to the molecular depth profiling with, e.g. C₆₀⁺ projectiles. Acrylate-based multilayers relevant to industrial inkjet printing have been sectioned at a cutting angle below 1°. In this way, analysis of the section over a distance of 1 μm allows a depth range in the order of a few nm in the original sample to be achieved. Adequate procedures to optimise the ULAM step and minimise or control the cutting artefacts have been developed. The combination of ULAM with S-SIMS has allowed a depth resolution of 10 nm to be obtained for components at a distance of 35 μm from the surface.     

Using FTIR spectroscopy to detect sericin on historic silk

Silks represent some of the most precious ancient and historic textile artefacts in collections worldwide.Their optimum preservation demands an appreciation of their characteristics.One important concern,especially with regard to ancient Chinese silks,is whether the fabrics have been degummed.Silks with remnant sericin gum coating the fibroin fibres would require different conservation protocol.In previous research on aged silks,the presence of sericin has been inferred from amino acid analysis of hydrolysa...     

Use of electrochemical techniques for the conservation of metal artefacts: a review

Electrochemical techniques like mechanical and chemical ones should be among the panoply of techniques conservators normally use when they conserve metal artefacts. Often though, they are discarded because they are considered as too complicated and dangerous. As a consequence, not much development in the use of these techniques in conservation was observed before the 1990s when their application to marine artefacts once again drew the attention of conservation professionals. More recently, the latter have recognised the importance of these techniques in the understanding of corrosion processes as well as their monitoring and in the solving of specific conservation issues. Furthermore, instruments that were previously only used by corrosion scientists are today entering the conservation field. Portable tools have even been designed so that treatments can be carried out in situ. The current trend is to cluster electrochemical and analytical techniques in parallel in order to fully understand the behaviour of metal artefacts when conserved.     

THE STRUCTURE OF CHLOROPHYLL RC I, A CHROMOPHORE OF THE REACTION CENTER OF PHOTOSYSTEM I

Abstract— Chlorophyll RC I is a particular chlorophyll of photosystem I common to all organisms with oxygenic photosynthesis. Its structure could be revealed by'H-NMR, FTIR, neutron activation analysis, complemented by plasma desorption mass spectrometry data. It has been identified as 13'-hydroxy-20-chloro-Chl a . Two stereoisomers of Chl RC I have also been isolated and identified. Evidence is presented that chlorination of the pigment does not occur during extraction and that artefacts due to impurities are ruled out.     

Non-destructive analysis of museum objects by fibre-optic Raman spectroscopy

Raman spectroscopy is a versatile technique that has frequently been applied for the investigation of art objects. By using mobile Raman instrumentation it is possible to investigate the artworks without the need for sampling. This work evaluates the use of a dedicated mobile spectrometer for the investigation of a range of museum objects in museums in Scotland, including antique Egyptian sarcophagi, a panel painting, painted surfaces on paper and textile, and the painted lid and soundboard of an early keyboard instrument. The investigations of these artefacts illustrate some analytical challenges that arise when analysing museum objects, including fluorescing varnish layers, ambient sunlight, large dimensions of artefacts and the need to handle fragile objects with care. Analysis of the musical instrument (the Mar virginals) was undertaken in the exhibition gallery, while on display, which meant that interaction with the public and health and safety issues had to be taken into account. Experimental set-up for the non-destructive Raman spectroscopic investigation of a textile banner in the National Museums of Scotland     

Quantitative spectrophotometry using integrating cavities

Absorption spectrophotometry, a standard tool for quantitative analysis, suffers from two major drawbacks: lack of sensitivity and vulnerability to scattering. It has been pointed out earlier that the solution to these problems lies in using a reflecting cavity as a sample holder. Due to multiple reflections at the cavity wall, the effective pathlength becomes considerably larger than the diameter of the cavity, and scattering losses are eliminated because scattered light is prevented from escaping the detector. Though much effort has been spent in analysing and improving the performance of such a device, often called an integrating cavity absorption meter (ICAM), a simple strategy for deducing the absorbance of the sample is still lacking. It is shown here that the absorbance A' measured by using an ICAM exhibits a sublinear increase with the solute concentration C. The physical reason for this departure from linearity is explained, and a straightforward procedure for converting A' to the true absorbance A (proportional to C) is established. The reliability of the procedure is demonstrated by comparing the ICAM absorption spectrum of dilute dye solutions with the spectra of more concentrated solutions recorded in a conventional spectrophotometer. The ability of the device to cope with scattering was tested by filling the ICAM with a suspension of chloroplasts, and the spectrum was found, as expected, to be free from scattering artefacts.     

Evading the Illusions: Identification of False Peaks in Micro-Raman Spectroscopy and Guidelines for Scientific Best Practice

Micro-Raman spectroscopy is an important analytical tool in a large variety of science disciplines. The technique is suitable for both identification of chemical bonds and studying more detailed phenomena like molecular interactions, material strain, crystallinity, defects, and bond formations. Raman scattering has one major weakness however: it is a very low probability process. The weak signals require very sensitive detection systems, which leads to a high probability of picking up signals from origins other than the sample. This complicates the analysis of the results and increases the risk of misinterpreting data. This work provides an overview of the sources of spurious signals occurring in Raman spectra, including photoluminescence, cosmic rays, stray light, artefacts caused by spectrometer components, and signals from other compounds in or surrounding the sample. The origins of these false Raman peaks are explained and means to identify and counteract them are provided.     

The two-terminal equivalent network of a three-terminal electrochemical cell

The two-terminal equivalent network of a three-terminal electrochemical cell is derived. This reveals, in a particularly clear way, how various artefacts arise from the layout of the cell. It is found that the working electrode response appears in series with an inductive artefact, and both appear in parallel with a capacitive artefact. Advice is given on how to diminish the size of these artefacts.