Analytical Setups Research Articles

Micro X-ray Fluorescence Imaging in a Tabletop Full Field-X-ray Fluorescence Instrument and in a Full Field-Particle Induced X-ray Emission End Station.

A full field-X-ray camera (FF-XRC) was developed for performing the simultaneous mapping of chemical elements with a high lateral resolution. The device is based on a conventional CCD detector coupled to a straight shaped polycapillary. Samples are illuminated at once with a broad primary beam that can consist of X-rays or charged particles in two different analytical setups. The characteristic photons induced in the samples are guided by the polycapillary to the detector allowing the elemental imaging without the need for scanning. A single photon counting detection operated in a multiframe acquisition mode and a processing algorithm developed for event hitting reconstruction have enabled one to use the CCD as a high energy resolution X-ray detector. A novel software with a graphical user interface (GUI) programmed in Matlab allows full control of the device and the real-time imaging with a region-of-interest (ROI) method. At the end of the measurement, the software produces spectra for each of the pixels in the detector allowing the application of a least-squares fitting with external analytical tools. The FF-XRC is very compact and can be installed in different experimental setups. This work shows the potentialities of the instrument in both a full field-micro X-ray fluorescence (FF-MXRF) tabletop device and in a full field-micro particle induced X-ray emission (FF-MPIXE) end-station operated with an external proton beam. Some examples of applications are given as well.

Biomarkers defining the metabolic age of red blood cells during cold storage

AbstractMetabolomic investigations of packed red blood cells (RBCs) stored under refrigerated conditions in saline adenine glucose mannitol (SAGM) additives have revealed the presence of 3 distinct metabolic phases, occurring on days 0-10, 10-18, and after day 18 of storage. Here we used receiving operating characteristics curve analysis to identify biomarkers that can differentiate between the 3 metabolic states. We first recruited 24 donors and analyzed 308 samples coming from RBC concentrates stored in SAGM and additive solution 3. We found that 8 extracellular compounds (lactic acid, nicotinamide, 5-oxoproline, xanthine, hypoxanthine, glucose, malic acid, and adenine) form the basis for an accurate classification/regression model and are able to differentiate among the metabolic phases. This model was then validated by analyzing an additional 49 samples obtained by preparing 7 new RBC concentrates in SAGM. Despite the technical variability associated with RBC processing strategies, verification of these markers was independently confirmed in 2 separate laboratories with different analytical setups and different sample sets. The 8 compounds proposed here highly correlate with the metabolic age of packed RBCs, and can be prospectively validated as biomarkers of the RBC metabolic lesion.

In silico validation procedure for cell volume fraction estimation through dielectric spectroscopy

Dielectric spectroscopy has proved to be a good tool for analyzing the passive electrical properties of biological tissues as well as those of inhomogeneous materials. This technique promises to be a valid alternative to the classical ones based on metabolites to monitor the growth and cell volume fraction of cell cultures in a simple and minimally invasive way. In order to obtain an accurate estimation of the cell volume fraction as a function of the permittivity of the suspension, a simple in silico procedure is proposed. The procedure is designed to perform homogenization from the micro-scale to the macro-scale using simple analytical models and simulation setups hypothesizing the properties of diluted suspension (cell volume fraction less than 0.2). Results obtained show the possibility to overcome some trouble involving the analytical treatment of the cellular shape by considering a sphere with the same permittivity in the quantitative analysis of the cell volume fraction. The entire study is based on computer simulations performed in order to verify the correctness of the procedure. Obtained data are used in a cell volume fraction estimation scenario to show the effectiveness of the procedure.

Harnessing the complexity of metabolomic data with chemometrics

Because of the ever-increasing number of signals that can be measured within a single run by modern platforms in analytical chemistry, life sciences datasets become not only gradually larger but also more intricate in their structures. Challenges related to making use of this wealth of data include extracting relevant elements within massive amounts of signals possibly spread across different tables, reducing dimensionality, summarising dynamic information in a comprehensible way and displaying it for interpretation purposes. Metabolomics constitutes a representative example of fast-moving research fields taking advantage of recent technological advances to provide extensive sample monitoring. Because of the wide chemical diversity of metabolites, several analytical setups are required to provide a broad coverage of complex samples. The integration and visualisation of multiple highly multivariate datasets constitute key issues for effective analysis leading to valuable biological or chemical knowledge. Additionally, high-order data structures arise from experimental setups involving time-resolved measurements. These data are intrinsically multiway, and classical statistical tools cannot be applied without altering their organisation with the risk of information loss. Dedicated modelling algorithms, able to cope with the inherent properties of these metabolomic datasets, are therefore mandatory for harnessing their complexity and provide relevant information. In that perspective, chemometrics has a central role to play. Copyright © 2013 John Wiley & Sons, Ltd.

Harnessing the complexity of metabolomic data with chemometrics

Because of the ever‐increasing number of signals that can be measured within a single run by modern platforms in analytical chemistry, life sciences datasets become not only gradually larger but also more intricate in their structures. Challenges related to making use of this wealth of data include extracting relevant elements within massive amounts of signals possibly spread across different tables, reducing dimensionality, summarising dynamic information in a comprehensible way and displaying it for interpretation purposes. Metabolomics constitutes a representative example of fast‐moving research fields taking advantage of recent technological advances to provide extensive sample monitoring. Because of the wide chemical diversity of metabolites, several analytical setups are required to provide a broad coverage of complex samples. The integration and visualisation of multiple highly multivariate datasets constitute key issues for effective analysis leading to valuable biological or chemical knowledge. Additionally, high‐order data structures arise from experimental setups involving time‐resolved measurements. These data are intrinsically multiway, and classical statistical tools cannot be applied without altering their organisation with the risk of information loss. Dedicated modelling algorithms, able to cope with the inherent properties of these metabolomic datasets, are therefore mandatory for harnessing their complexity and provide relevant information. In that perspective, chemometrics has a central role to play. Copyright © 2013 John Wiley & Sons, Ltd.

Characterization and Modeling of the Interactions between Coffee Storage Proteins and Phenolic Compounds

This study addresses the interactions of coffee storage proteins with coffee-specific phenolic compounds. Protein profiles of Coffea arabica and Coffea canephora (var. robusta) were compared. Major phenolic compounds were extracted and analyzed with appropriate methods. The polyphenol-protein interactions during protein extraction have been addressed by different analytical setups [reversed-phase high-performance liquid chromatography (RP-HPLC), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS), and Trolox equivalent antioxidant capacity (TEAC) assays], with focus directed toward identification of covalent adduct formation. The results indicate that C. arabica proteins are more susceptible to these interactions and the polyphenol oxidase activity seems to be a crucial factor for the formation of these addition products. A tentative allocation of the modification type and site in the protein has been attempted. Thus, the first available in silico modeling of modified coffee proteins is reported. The extent of these modifications may contribute to the structure and function of "coffee melanoidins" and are discussed in the context of coffee flavor formation.

Nitrogen and triple oxygen isotopes in near‐road air samples using chemical conversion and thermal decomposition

The determination of triple oxygen (δ(18)O and δ(17)O) and nitrogen isotopes (δ(15)N) is important when investigating the sources and atmospheric paths of nitrate and nitrite. To fully understand the atmospheric contribution into the terrestrial nitrogen cycle, it is crucial to determine the δ(15)N values of oxidised and reduced nitrogen species in precipitation and dry deposition. In an attempt to further develop non-biotic methods and avoid expensive modifications of the gas-equilibration system, we have combined and modified sample preparation procedures and analytical setups used by other researchers. We first chemically converted NO(3)(-) and NH(4)(+) into NO(2)(-) and then into N(2)O. Subsequently, the resulting gas was decomposed into N(2) and O(2) and analyzed by isotope ratio mass spectrometry (IRMS) using a pre-concentration system equipped with a gold reduction furnace. The δ(17)O, δ(18)O and δ(15)N values of nitrate and nitrite samples were acquired simultaneously in one run using a single analytical system. Most importantly, the entire spectrum of δ(17)O, δ(18)O and/or δ(15)N values was determined from atmospheric nitrate, nitric oxide, ammonia and ammonium. The obtained isotopic values for air and precipitation samples were in good agreement with those from previous studies. We have further advanced chemical approaches to sample preparation and isotope analyses of nitrogen-bearing compounds. The proposed methods are inexpensive and easily adaptable to a wide range of laboratory conditions. This will substantially contribute to further studies on sources and pathways of nitrate, nitrite and ammonium in terrestrial nitrogen cycling.

Th-U-PbT dating by electron probe microanalysis, part I. monazite: analytical procedures and data treatment

A metodologia de datação de minerais portadores de Th e/ou U com microssonda eletrônica (EPMA), com ênfase em monazita, adquiriu enorme importância em literatura, devido a sua alta resolução espacial e versatilidade, que permitem correlacionar processos petrológicos, por vezes registrados apenas em microescala em minerais e rocha, com idades absolutas. Embora a acurácia seja até uma ordem de grandeza inferior à alcançada com os métodos isotópicos convencionais, o EPMA é o equipamento que resulta na melhor resolução espacial, alcançando alguns poucos µm³ sob algumas condições. A quantificação de elementos menores e em traços com precisão e acurácia adequadas envolve estratégias instrumentais, analíticas e de tratamento de dados específicas e significativamente mais rigorosas quando comparadas com as empregadas em análises convencionais. A datação Th-U-PbT é um exemplo destes casos. Cada EPMA é um aparelho único em função de suas características instrumentais e sistema de automação e, desta forma, os procedimentos analíticos devem ser ajustados para as especificidades de cada laboratório. As estratégias analíticas e de tratamento de dados adotadas no Laboratório de Microssonda Eletrônica do Instituto de Geociências da Universidade de São Paulo, Brasil, com um equipamento JEOL JXA8600S e sistema de automação ThermoNoran-Voyager 4.3 são apresentadas e comparadas com similares aplicadas em outros laboratórios. A influência de fatores instrumentais e das interferências espectrais para a quantificação de Th, U e Pb é discutida. Os procedimentos para correções de interferências, propagação de erros, tratamento e apresentação dos resultados finais de idades químicas, bem como de amostragem e análise são enfatizados. Alguns exemplos típicos de aplicação são discutidos, ressaltando os aspectos mais relevantes associados à datação com microssonda eletrônica.

Measuring Hg Isotopes in Bio‐Geo‐Environmental Reference Materials

With the emergence of new analytical techniques and the expansion of scientific fields explored by using mercury isotopes, the community needs reference materials (RM) to validate and assure the accuracy of the results. The present work investigates (1) the characterisation of secondary RM in order to validate analytical systems, (2) the effects of two complex matrices on isotopic determination using stannous chloride cold vapour generation coupled to MC‐ICP‐MS (CV‐MC‐ICP‐MS), (3) the effects of multiple digestion techniques for total Hg extraction and (4) the characterisation of nine geo‐bio‐environmental RM. Two secondary mono‐elemental RMs analysed using two different analytical setups yielded isotopic compositions on δ202Hg of −3.54 ± 0.27‰ (CRPG‐F65A, 2SD, n = 38) and +2.59 ± 0.19‰ (CRPG‐RL24H, 2SD, n = 30) relative to the CRM NIST SRM 3133. These two RMs cover the whole range of Hg isotopic fractionation in natural samples and are made available to the scientific community. Complex fly ash and hydroxysulfate green rust matrices were synthesised, spiked with NIST SRM 3133, then digested and finally analysed versus the mono‐elemental NIST SRM 3133 to show potential effect of these complex matrices during CV‐MC‐ICP‐MS. Three digestions techniques, including traditional acid digestion, microwave digestion and high pressure‐high temperature digestion, were applied to the lichen RM BCR‐482 in order to compare advantages and drawbacks of these methods. Finally, the isotopic compositions of nine RMs including soils (NIST SRM 2711; GXR‐2; GSS‐4), sediment (GSD‐10), jasperoid (GXR‐1), ore deposit (GXR‐3), fly ashes (BCR‐176; BCR‐176R) and lichen (BCR‐482) are reported. These selected materials have δ202Hg values ranging from −1.75‰ to +0.11‰. Some RMs also presented mass‐independent fractionation with Δ199Hg and Δ201Hg of up to −0.6‰.

A Critical Investigation of Hydride Generation-Based Arsenic Speciation in Sulfidic Waters

In sulfidic environments, hydride generation-based approaches are not suitable for arsenic determination because thioarsenates which can constitute the predominant arsenic species under these conditions (> 80% of total arsenic) are completely ignored. Sample acidification for preservation or during hydride generation leads to loss of total inorganic arsenic due to precipitation of arsenic-sulfur phases. Total concentrations can be determined correctly using 1% potassium iodide as prereducing agent while with L-cysteine (0.16 mol L(-1)), transformation of tetra-, tri-, and dithioarsenate to arsenite remains incomplete. By decreasing the original sample pH, hydride generation destroys thioarsenate species distribution because only monothioarsenate is stable over the whole pH range. Dithioarsenate transforms to arsenite below pH 4. Tetrathioarsenate transforms to trithioarsenate (pH 11.9) which subsequently transforms to arsenite (pH 5.6), followed by precipitation of arsenic-sulfur phases below pH 5. It is thus impossible to determine thioarsenates by hydride generation. The "As(III)"--fraction contains tetra-, tri-, and some dithioarsenate as well as arsenite, while monothioarsenate is determined with arsenate as "As(V)". Different analytical setups have substantial impact on thioarsenate hydride-generation behavior, thus provide little comparability and render reinterpretation of existing arsenic hydride-generation speciation data from sulfidic environments impossible. In natural geothermal water samples from Yellowstone National Park, total arsenic concentrations determined by ICP-MS and by HG-AFS with prereductant agreed well (< 6% relative difference). Speciation results deviated from the behavior predicted for thioarsenates from laboratory experiments, probably due to matrix effects.

Determination of the composition of Co–Pt thin films with quantitative electron-probe microanalysis

Quantitative electron-probe microanalysis (EPMA) with energy-dispersive (EDS) and wavelength-dispersive (WDS) X-ray spectroscopy was performed to determine the chemical composition of Co–Pt ferromagnetic thin films. The conventional “bulk” EPMA approach was applied and tested in detail by using several analytical set-ups with different combinations of Co and Pt spectral lines, beam energies and quantitative matrix-correction programs. The analyses with dedicated, thin-film EPMA programs were also made for comparison. The results were critically examined in order to assess their reliability and accuracy. The commonly used EDS analyses showed significant scatter between the set-ups and generally suffered from a poor analytical sensitivity. In contrast, the quantitative WDS analyses were fully consistent and practically independent of the analytical set-up. With the optimized WDS a high analytical precision, an improved sensitivity and an ultimate quantitative accuracy of better than 1% relative were achieved. The results confirmed that by using WDS microanalysis at low beam energies and by measuring the low-energy Co–Lα and Pt–Mα X-rays we were able to obtain the most accurate and reliable, quantitative, compositional analyses of Co–Pt thin films with thicknesses down to ≈ 100 nm.

High‐frequency, accurate measurement of dimethylsulfide in surface marine environments using a microporous membrane contactor

An automated sampling and analysis system for the shipboard measurement of dissolved dimethylsulfide (DMS) in surface marine waters is described. The system includes DMS extraction and trapping devices, a gas chromatograph (GC) equipped with a flame photometric detector (FPD), and a data acquisition system based on Visual Basic 6.0/C 6.0. The DMS is continuously and rapidly extracted from a seawater stream flowing at 100 mL min−1 across the hydrophobic wall pores of a membrane contactor. The stripping gas stream containing DMS flows at a rate of 300 mL min−1 for 1 min through an 8 cm Tenax‐TA‐filled glass tube controlled at −10°C by a thermoelectric cooler, within which DMS is selectively trapped. The trapped DMS is released by heating the trap to 160°C and is quantified by the GC‐FPD. The detection limit of the proposed automated system is 0.2 nM of S (DMS), and the analytical precision is better than 3%. A complete analytical cycle takes 7 min from the extraction of DMS from the seawater stream to measurement of the DMS peak area, which is 3–4 times shorter than has been achieved using sparge‐trap analytical setups. In field operations, the system runs on a daily cycle during which three DMS standards are measured at the beginning of the cycle and DMS derived from the seawater stream is subsequently analyzed throughout the day. The successful application of this analysis system to coastal waters suggests that the proposed DMS detection method will greatly facilitate data collection in future biogeochemical studies of the marine environment.

Electro-chemiluminescent biosensing

The present review draws a general picture of the bioanalytical applications of electro-chemiluminescent reactions (ECL). Only the two main ECL reactions-i.e. the luminol-based and Ru(bpy)(3)(2+)-based reactions-are considered for application in the fields of enzyme biosensors, immunochemical biosensors, DNA biosensors, and biochips. The mechanism, principle, and experimental conditions of these two reactions are described. Then, for each category of analytical tools, experimental set-ups and performances are presented and discussed.

Spectroscopic analysis using a hybrid LIBS-Raman system

A novel setup, combining two spectroscopic techniques, laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy in a hybrid unit, is described. The work presented herein is part of a broader project that aims to demonstrate the applicability of the hybrid LIBS-Raman unit as an analytical tool for the investigation of samples and objects of cultural heritage. The system utilizes a nanosecond pulsed Nd:YAG laser (532 nm) for both LIBS and Raman analysis. In the Raman mode, a low intensity beam from the laser probes the sample surface and the scattering signal is collected into a grating spectrograph coupled to an intensified charge-coupled device (ICCD) detector, which records the Raman spectrum. In the LIBS mode a single high intensity pulse from the laser irradiates the sample surface and the time- and spectrally-resolved emission from the resulting laser ablation plume yields the LIBS spectrum. The use of a non-gated CCD detector was found to produce similar quality data (in terms of S/N ratio and fluorescence background) in the Raman mode, while in the LIBS mode spectral features were clearly broader but did not prevent identification of prominent atomic emission lines. Several model pigment samples were examined and the data obtained show the ability of the hybrid unit to record both Raman and LIBS spectra from the same point on the sample, a clear advantage over the use of different analytical setups.

Standardisation of elemental analytical techniques applied to provenance studies of archaeological ceramics: an inter laboratory calibration study.

Chemical analysis is a well-established procedure for the provenancing of archaeological ceramics. Various analytical techniques are routinely used and large amounts of data have been accumulated so far in data banks. However, in order to exchange results obtained by different laboratories, the respective analytical procedures need to be tested in terms of their inter-comparability. In this study, the schemes of analysis used in four laboratories that are involved in archaeological pottery studies on a routine basis were compared. The techniques investigated were neutron activation analysis (NAA), X-ray fluorescence analysis (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). For this comparison series of measurements on different geological standard reference materials (SRM) were carried out and the results were statistically evaluated. An attempt was also made towards the establishment of calibration factors between pairs of analytical setups in order to smooth the systematic differences among the results.

Theoretical and experimental investigations of the optical waveguiding properties of on-chip microfabricated capillaries

An on-chip capillary system with potential applications in miniaturized analytical chemistry and spectroscopy setups has been microfabricated using photolithographic, etching, and aligned bonding techniques. The optical waveguiding properties of the capillary are investigated theoretically and experimentally. Chip insertion losses as low as 3 dB at 0.514 μm wavelength have been measured for a 15-mm-long water-filled capillary waveguide with 63 μm internal diameter.