ATR-FTIR imaging for the analysis of organic materials in paint cross sections: case studies on paint samples from the National Gallery, London

The potential of attenuated total reflection Fourier transform infrared (ATR-FTIR) imaging for the characterisation of the chemical components of paint cross sections from old master paintings was investigated. Three cross sections were chosen to cover a variety of the analytical problems encountered in samples from paintings. The binding medium and degradation products in a green paint sample from a fifteenth-century Florentine painting were imaged, as well as a thin layer within a cross-section from a fifteenth-century German painting, and multiple thin surface coatings on a painting of the 1760s by Peter Romney. The application of chemometric methods for further analysis of the large data set generated for each sample was also explored. The study demonstrated the advantages of ATR-FTIR imaging, which allowed images to be obtained with high spatial resolution (ca. 3-4 microm) without the need to microtome the sample. The gain in sensitivity in detecting trace materials and the information derived from the location of these compounds in the sample was especially valuable, improving interpretation of the FTIR analysis and extending knowledge of the sample composition beyond that obtainable with other analytical techniques.     

High resolution auger electron spectroscopy for materials characterization

High resolution Auger microanalysis has become a widely applied technique in various fields of materials research. Its submicrometer spatial resolution is shown as being advantageous for surface, interface and thin film analysis. Limitations of the lateral resolution are outlined with respect to influences of electron backscattering, detection sensitivity, sample drift, beam heating and other electron induced processes. High in-depth resolution is linked with high spatial resolution for optimized depth profiling by sputtering. Crater edge profiling with scanning Auger microscopy is particularly useful for obtaining a three-dimensional microanalysis. Some examples demonstrate the capabilities and limitations in the analysis of precipitates, fracture surfaces and multilayer structures.     

Pitfalls in compound-specific isotope analysis of environmental samples

In the last decade compound-specific stable isotope analysis (CSIA) has evolved as a valuable technique in the field of environmental science, especially in contaminated site assessment. Instrumentation and methods exist for highly precise measurements of the isotopic composition of organic contaminants even in a very low concentration range. Nevertheless, the determination of precise and accurate isotope data of environmental samples can be a challenge. Since CSIA is gaining more and more popularity in the assessment of in situ biodegradation of organic contaminants, an increasing number of authorities and environmental consulting offices are interested in the application of the method for contaminated site remediation. Because of this, it is important to demonstrate the problems and limitations associated with compound-specific isotope measurements of environmental samples. In this review, potential pitfalls of the analytical procedure are critically discussed and strategies to avoid possible sources of error are provided. In order to maintain the analytical quality and to ensure the basis for reliable stable isotope data, recommendations on groundwater sampling, and sample preservation and storage are given. Important aspects of sample preparation and preconcentration techniques to improve sensitivity are highlighted. Problems related to chromatographic resolution and matrix interference are discussed that have to be considered in order to achieve accurate gas chromatography/isotope ratio mass spectrometry measurements. As a result, the need for a thorough investigation of compound-specific isotope fractionation effects introduced by any step of the overall analytical method by standards with known isotopic composition is emphasized. Finally, we address some important points that have to be considered when interpreting data from field investigations. Figure CSIA Principal (Carbon)     

Atomic Force Microscopy of technological and biological samples

Summary Atomic Force Microscopy (AFM) has been successfully used to characterize a variety of samples with different chemical composition. Polycrystalline sample preparation techniques, cleaving and careful adjustment of the imaging setup made it also possible to investigate materials with non-ideal geometry (small size, rough sample surface) down to the atomic scale. Pressed CaCO₃ powder samples of different origin have been imaged with atomic resolution. Multilayer systems of AlGaAs/GaAs and Si/GaAs on top of a GaAs substrate could be imaged readily. Single -layers of Si in GaAs could be resolved. The results demonstrate that simple sample preparation techniques and the implementation of chemical reactions can greatly enhance the analytical scope and applicability of AFM.     

A high-performance bio-tissue imaging method using air flow-assisted desorption electrospray ionization coupled with a high-resolution mass spectrometer

An air flow-assisted desorption electrospray ionization (AFADESI) MSI device was combined with a highresolution mass spectrometer to optimize the system parameters and achieve more accurate spatial distribution characteristics for compounds of interest while investigating bio-tissue sections. Finally, the parameter conditions that can provide optimal ionic intensity and enhanced resolution were confirmed.     

Recent developments in rapid multiplexed bioanalytical methods for foodborne pathogenic bacteria detection

Foodborne illnesses caused by pathogenic bacteria represent a widespread and growing problem to public health, and there is an obvious need for rapid detection of food pathogens. Traditional culture-based techniques require tedious sample workup and are time-consuming. It is expected that new and more rapid methods can replace current techniques. To enable large scale screening procedures, new multiplex analytical formats are being developed, and these allow the detection and/or identification of more than one pathogen in a single analytical run, thus cutting assay times and costs. We review here recent advancements in the field of rapid multiplex analytical methods for foodborne pathogenic bacteria. A variety of strategies, such as multiplex polymerase chain reaction assays, microarray- or multichannel-based immunoassays, biosensors, and fingerprint-based approaches (such as mass spectrometry, electronic nose, or vibrational spectroscopic analysis of whole bacterial cells), have been explored. In addition, various technological solutions have been adopted to improve detectability and to eliminate interferences, although in most cases a brief pre-enrichment step is still required. This review also covers the progress, limitations and future challenges of these approaches and emphasizes the advantages of new separative techniques to selectively fractionate bacteria, thus increasing multiplexing capabilities and simplifying sample preparation procedures.

Inductively coupled plasma-atomic emission spectrometry: Analytical assessment of the technique at the beginning of the 90's

The main application of the inductively coupled plasma (ICP) today is in atomic emission spectroscopy (AES), as an excitation spectrochemical source, although uses of an ICP for fluorescence as just an atomiser, and specially for mass spectrometry, as an ionization source, are rocketing in the last few years.Since its inception, only a quarter of a century ago, ICP-AES has rapidly evolved to one of the preferred routine analytical techniques for convenient determination of many elements with high speed, at low levels and in the most varied samples. Perhaps its comparatively high kinetic temperature (capable of atomising virtually every compound of any sample), its high excitation and ionisation temperatures, and its favourable spatial structure at the core of the ICP success.By now, the ICP-AES can be considered as having achieved maturity in that a huge amount of analytical problems can be tackled with this technique, while no major or fundamental changes have been adopted for several years. Despite this fact, important driving forces are still in operation to further improve the ICP-AES sensitivity, selectivity, precision, sample throughput, etc. Moreover, proposals to extend the scope of the technique to traditionally elusive fields (e.g. non-metals and organic compound analysis) are also appearing in the recent literature.In this paper the state of the art, the last developments and the expectations in trying to circumvent the limitations of the ICP-AES (on the light of literature data and personal experience) are reviewed.     

Toward high spatial resolution sampling and characterization of biological tissue surfaces using mass spectrometry

Mass spectrometry has emerged as a powerful tool for the bioanalytical sciences because of its ability to characterize small and large biomolecules in vanishingly small amounts. A recurring motif in mass spectrometry aims to decipher the chemical composition of biological samples at the molecular level, requiring drastic improvements in the ability to interrogate well defined and highly spatially resolved areas of a sample surface. With the growth of novel ionization methods, numerous advances have been made in sampling biological tissue surfaces. Here, current advancements in ambient, inlet, and vacuum ionization methods are discussed with respect to the potential improvements in the goal of achieving high spatial resolution and/or fast surface analysis. Of similar importance is the need for improvements in applicable characterization strategies using high performance fragmentation technologies such as electron transfer dissociation and electron capture dissociation directly from surfaces, and gas-phase separation through ion mobility spectrometry and high resolution mass spectrometry.

Surface charge spectroscopy and its applications

Surface Charge Spectroscopy (SCS) is a surface sensitive technique for measuring potential distributions across an ultrathin (<100Å) insulator/semiconductor structure. Although the applicability of the technique is rather narrowly confined to such a specific sample structure, SCS bears considerable industrial significance because insulator/semiconductor structures are the most commonly used functional elements in microelectronics, and because gate insulators used in the industry are indeed getting to a nanometer thickness scale. The basic SCS concept relies on the measurements of the potential energies of electronic states using the conventional photoemission spectroscopic method, energy data which bear the information of the electrical potential gradient across the probed surface region. Surface sensitivity of SCS is thus contained in the framework of photoemission spectroscopy. Unlike conventional photoemission studies, SCS always measures the potential gradients corresponding to a specific surface potential. In fact, its analytical power is only shown when the surface potential of a sample can be controlled, and coincidentally an insulator/semiconductor device structure in microelectronics is only functional when the potential gradient extending into the semiconductor region can be changed effectively by the surface potential of the insulator. When SCS data are examined beyond the simple space-charge model commonly employed by electrical characterisation techniques like capacitance-voltage measurements, they can give information other than the relationship between the insulator surface potential and semiconductor surface potential (and thus interface state distributions across the bandgap of the semiconductor). Rather, they also provide unique information on the depth distributions of various types of fixed charges in the sample structure at an atomic level, and on the insulator breakdown mechanisms.     

Populus nigra L. bud absolute: a case study for a strategy of analysis of natural complex substances

The new European regulations (e.g., REACH) require that Natural Complex Substances such as essential oils, absolutes, concretes, and resinoids are registered. This need implies that the chemical composition of these complex mixtures is characterized as exhaustively as possible in view of defining their toxicological risk. This study proposes an analysis strategy to be applied to the chemical characterization of poplar absolute as an example of Natural Complex Substances of vegetable origin. In the first part, the proposed strategy is described, and the advantages and the limitations related to the combination of conventional analytical techniques such as gas chromatography (GC) without and with sample derivatization and high-performance liquid chromatography (HPLC) are critically discussed. In the second part, the qualitative data obtained with GC and HPLC analysis of poplar bud absolute confirm the sample complexity which mainly consists of phenolic components. Fourteen compounds (i.e., phenolic acids, phenylpropanoids, and flavonoids) were then chosen as markers representative of the main classes of components characterizing poplar bud absolute. The marker quantitation carried out by GC-SIM-MS and HPLC-PDA analyses gives similar results confirming the reliability of both techniques. These results demonstrate that conventional analytical techniques can positively and effectively contribute to the study of the the composition of Natural Complex Substances, i.e., matrices for which highly effective separation is necessary, consisting mainly of isomers or homologous components. The combination of GC and HPLC techniques is ever more necessary for routine quality control when conventional instrumentations are used.

Recent developments in chemical characterization with MeV ion beams

A multitude of ion-atom interactions are induced with projectiles of E0.1 MeV/nucleon. Analytical techniques derived from these include particle induced X-ray emission (PIXE), charged particle activation analysis (CPAA), prompt nuclear reactions (PNR), and Rutherford backscattering spectrometry (RBS). Among their features are broad elemental coverage (PIXE), subnanogram sensitivity (PIXE, CPAA), isotopic specificity (CPAA, PNR), and depth resolution (RBS, PNR). A limiting requirement with each technique is the need for high intensity ion beams. Novel approaches seek now to obtain analytical information with very small numbers of bombarding ions. Sample integrity is then maintained; moreover, they can be delivered in a microbeam (diameter 5 mm). A phenomenon which under these conditions provides useful analytical information is the particle induced desorption of molecular fragments. Thus, microscopic chemical analysis can be achieved with a small number (<10,000) of heavy fast projectiles and identification of the species desorbed from the sample surface via time-of-flight mass spectrometry. Experimental work with 84 MeV kr ions indicates the following: (a) high desorption yields can be obtained (>50%); (b) mass spectrometry on microspots (diameter of a few m) is feasible; (c) < 10⁶ atoms can be detected. Further capabilities of ion beams for minute, detailed, and comprehensive chemical characterization remain to be explored.     

Laser-induced plasma spectrometry: truly a surface analytical tool

For a long period, analytical applications of laser induced plasma spectrometry (LIPS) have been mainly restricted to overall and quantitative determination of elemental composition in bulk, solid samples. However, introduction of new compact and reliable solid state lasers and technological development in multidimensional intensified detectors have made possible the seeking of new analytical niches for LIPS where its analytical advantages (direct sampling from any material irrespective of its conductive status without sample preparation and with sensitivity adequate for many elements in different matrices) could be fully exploited. In this sense, the field of surface analysis could take advantage from the cited advantages taking into account in addition, the capability of LIPS for spot analysis, line scan, depth-profiling, area analysis and compositional mapping with a single instrument in air at atmospheric pressure. This review paper outlines the fundamental principles of laser-induced plasma emission relevant to sample surface studies, discusses the experimental parameters governing the spatial (lateral and in-depth) resolution in LIPS analysis and presents the applications concerning surface examination.     

Design and initial characterization of a glow discharge atomic emission instrument for macro-scale elemental composition mapping of solid surfaces

An instrument intended for rapid, accurate, precise, macro-scale (i.e. up to many tens of square centimeters) elemental composition mapping of solid surfaces has been designed and constructed. The spatial resolution provided by the instrument, on the order of 1 mm at best, is coarse by today's standards but is appropriate for selected analytical problems. The instrument is based on a novel glow discharge atomic emission device capable of sustaining multiple discharges simultaneously. Each discharge exhibits atomic emission characteristic of the sample surface beneath it. Using Hadamard transform spatial imaging, the emissions are selectively multiplexed, and the individual emission intensities are recovered from the multiplexed data through matrix multiplication. In this publication, the instrument is described, and its performance for elemental composition mapping is demonstrated. The data indicate that internal standardization should be employed to reduce the likelihood of mapping errors.     

Recent progress of online sample preconcentration techniques in microchip electrophoresis

Microchip electrophoresis (MCE) has been advanced remarkably by the applications of several separation modes and the integration with several chemical operations on a single planer substrate. MCE shows superior analytical performance, e.g., high-speed analysis, high resolution, low consumption of reagents, and so on, whereas low-concentration sensitivity is still one of the major problems. To overcome this drawback, various online sample preconcentration techniques have been developed in MCE over the past 15 years, which have successfully enhanced the detection sensitivity in MCE. This review highlights recent developments in online sample preconcentration in MCE categorized on the basis of "dynamic" and "static" methods. The dynamic techniques including field amplified stacking, ITP, sweeping, and focusing have been easily applied to MCE, which provide effective enrichments of various analytes. The static techniques such as SPE and filtration have also been combined with MCE. In the static techniques, extremely high preconcentration efficiency can be obtained, compared to the dynamic methods. This review provides comprehensive tables listing the applications and sensitivity enhancement factors of these preconcentration techniques employed in MCE.     

Future in-fab applications of total reflection X-ray fluorescence spectrometry for the semiconductor industry

In-fab analytical methods are of increasing interest for wafer monitoring in advanced semiconductor device manufacturing. In particular, an analytical method which allows non-destructive measurements of implant dose and surface roughness would be very beneficial. We investigated the capabilities of total reflection X-ray fluorescence spectrometry (TXRF) to determine implant dose and surface roughness. These advanced applications of TXRF can be used to monitor processes like implantation, rapid thermal annealing, and chemical mechanical polish. As implants in Si at implant energies of 2 keV, 10 keV and 50 keV were studied. Angle resolved TXRF measurements were performed with a commercial Rigaku 3750 system. The TXRF results were compared to secondary ion mass spectrometry (SIMS) measurements.     

Online sample pre-concentration via dynamic pH junction in capillary and microchip electrophoresis

Various analytical techniques have been developed over the years to analyse a large diversity of biomolecules with a constant push towards ultra-sensitive detection. CE is at the forefront of the most powerful analytical tools available to date when considering its superior efficiency and resolution; however, the technique suffers from poor sensitivity as a result of the short path length at the detection site and small injection volumes (typically <1% capillary length). One of the approaches to abate the inherent problem is to employ clever chemistry using sample focusing techniques whereby a large sample plug can be injected, preconcentrated and separated, producing excellent sensitivity and efficiency at the detector. This particular review will focus on the use of dynamic pH junction as a means of improving sensitivity in CE and focuses on the use of a change in analyte ionisation due to different pHs between the sample and electrolyte. The review provides a fundamental discussion of the mechanisms, buffer and sample conditions required to concentrate various analytes and a comprehensive list of published works in tabular format for easy identification of suitable conditions for new applications. The review further encompasses the use of dynamic pH junction in CE and its involvement in combination with other preconcentrations techniques to produce high sensitivity enhancements recorded between the years 1990-2010.     

Development of individual semiconductor nanowire for bioelectrochemical device at low overpotential conditions

In this work we report the bioelectrochemical study using an individual indium tin oxide (ITO) nanowire (ITO-NW) electrode modified with glucose oxidase enzyme (GOx), in which the enzymatic activity and the biocatalytic activity was evaluated. The main objective is to show that at low overpotential condition, semiconductor NW can be used as an electron donor during biocatalytic process. We demonstrate the possibility of immobilizing an ITO-NW electrode on gold contacts deposited on top of a microchip (oxidized Si wafer). A protective polymer layer containing an aperture over the sample area was photolithographically deposited over the microchip to isolate the metallic contacts. For H₂O₂ reduction during the biocatalysis at ITO-NWs surface, with η  50 mV, normal linear behavior is not observed and an exponential current is evident, similar to n–p semiconductor junction behavior. These results can open new tools for studying redox enzymes at the single-molecule level, and the device described here is very promising as a candidate for further exploration in bioelectrochemical devices, such as biofuel cells and biosensors.     

Depth profiling with modified dc-Grimm and rf-Grimm-type glow discharges operated with high gas flow rates and coupled to a high-resolution mass spectrometer

The improved analytical capability of direct-current (dc) and radiofrequency (rf) fast flow glow discharges coupled to a sector field mass spectrometer (GD-SFMS) are presented. In particular, the effect of GD chamber design has been studied to obtain suitable crater shapes for depth-profile analysis of solid samples while maintaining the high sensitivity and stability of this source. In this study it was observed that the distance between the sample surface and the end of the flow tube is critical and so careful optimisation is needed. Under optimum conditions plane crater profiles, with high ion-signal sensitivity and sufficient stability, were obtained. The capability to determine qualitative and semi-quantitative depth profiles is presented here using, as model, a coated sample of certified thickness. Finally, the depth resolution achieved for qualitative depth profiles obtained by rf-GD-(SF)MS is compared with that for the well-established rf-GD optical emission spectroscopy (OES) technique.Dedicated to the memory of Wilhelm Fresenius