Comparison of laser ablation-inductively coupled plasma-mass spectrometry and micro-X-ray fluorescence spectrometry for elemental imaging in Daphnia magna

Visualization of elemental distributions in thin sections of biological tissue is gaining importance in many disciplines of biological and medical research. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and scanning micro-X-ray fluorescence spectrometry (micro-XRF) are two widely used microanalytical techniques for elemental mapping. This article compares the capabilities of the two techniques for imaging the distribution of selected elements in the model organism Daphnia magna in terms of detection power and spatial resolution. Sections with a thickness of 10 and 20 μm of the fresh water crustacean Daphnia magna were subjected to LA-ICP-MS and micro-XRF analysis. The elemental distributions obtained for Ca, P, S and Zn allow element-to-tissue correlation. LA-ICP-MS and micro-XRF offer similar limits of detection for the elements Ca and P and thus, allow a cross-validation of the imaging results. LA-ICP-MS was particularly sensitive for determining Zn (LOD 20 μg g⁻¹, 15 μm spot size) in Daphnia magna, while the detection power of micro-XRF was insufficient in this context. However, LA-ICP-MS was inadequate for the measurement of the S distributions, which could be better visualized with micro-XRF (LOD 160 μg g⁻¹, 5 s live time). Both techniques are thus complementary in providing an exhaustive chemical profiling of tissue samples.     

Biomonitoring of metal contamination in a marine prosobranch snail (Nassarius reticulatus) by imaging laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

An imaging mass spectrometric method using laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) was developed to determine Cu, Zn, Cd, Hg and Pb and metal distribution in longitudinal tissue sections of the marine snail Nassarius reticulatus (Gastropoda, Prosobranchia). Snails were sampled in northern Brittany (France) at three stations with different contamination levels.The quantification of metal distribution (imaging or mapping) in a thin slice of the snail tissue was carried out using different strategies: by one-point calibration and via matrix-matched laboratory standards using different biological materials (BCR 278, snail tissue, and rat brain). Together with the imaging of metals the distribution of two non-metals (carbon and sulfur) was analyzed. The imaging LA-ICP-MS analysis yielded an inhomogeneous distribution for all elements investigated. The detection limits for the distribution analysis of Cu, Zn, Cd, Hg and Pb measured by LA-ICP-MS were in the low μg g⁻¹ range.     

DBD Surface Modification of Polymers in Relation to the Spatial Distribution of Reactive Oxygen Species

The homogeneity of a helium dielectric barrier discharge, working at atmospheric pressure and containing oxygen as contaminant, is assessed by mapping the spatial distribution of oxygen metastable atoms in relation to the uniformity of surface properties. Tunable diode laser absorption spectroscopy is used to monitor the time evolution of the absorption coefficient corresponding to the oxygen metastable atoms on the 3⁵S₂ level, as a function of the laser absorbing path, whereas bi-dimensional Abel transform is used to obtain local information on the space distribution of the metastable atoms in the discharge. The radial distribution of the surface properties is investigated using atomic force microscopy, contact angle measurement and X-ray photoelectron spectroscopy. The results show that the oxygen metastables density has complex space–time behavior, and the spatial distribution of the reactive species yields specific radial profile of the surface properties of a polymer film depending on the treatment time.     

Elemental imaging of MRI contrast agents: benchmarking of LA-ICP-MS to MRI

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been used to map the spatial distribution of magnetic resonance imaging (MRI) contrast agents (Gd-based) in histological sections in order to explore synergies with in vivo MRI. Images from respective techniques are presented for two separate studies namely (1) convection enhanced delivery of a Gd nanocomplex (developmental therapeutic) into rat brain and (2) convection enhanced delivery, with co-infusion of Magnevist (commercial Gd contrast agent) and Carboplatin (chemotherapy drug), into pig brain. The LA technique was shown to be a powerful compliment to MRI not only in offering improved sensitivity, spatial resolution and signal quantitation but also in giving added value regarding the fate of administered agents (Gd and Pt agents). Furthermore simultaneous measurement of Fe enabled assignment of an anomalous contrast enhancement region in rat brain to haemorrhage at the infusion site.     

Discrepancy between the spin distribution and the magnetic ground state for a triaminoxyl substituted triphenylphosphine oxide derivative

The magnetic interaction and spin transfer via phosphorus have been investigated for the tri-tert-butylaminoxyl para-substituted triphenylphosphine oxide. For this radical unit, the conjugation existing between the pi* orbital of the NO group and the phenyl pi orbitals leads to an efficient delocalization of the spin from the radical to the neighboring aromatic ring. This has been confirmed by using fluid solution high-resolution EPR and solid state MAS NMR spectroscopy. The spin densities located on the atoms of the molecule could be probed since (1)H, (13)C, (14)N, and (31)P are nuclei active in NMR and EPR, and lead to a precise spin distribution map for the triradical. The experimental investigations were completed by a DFT computational study. These techniques established in particular that spin density is located at the phosphorus (rho=-15x10(-3) au), that its sign is in line with the sign alternation principle and that its magnitude is in the order of that found on the aromatic C atoms of the molecule. Surprisingly, whereas the spin distribution scheme supports ferromagnetic interactions among the radical units, the magnetic behavior found for this molecule revealed a low-spin ground state characterized by an intramolecular exchange parameter of J=-7.55 cm(-1) as revealed by solid state susceptibility studies and low temperature EPR. The X-ray crystal structures solved at 293 and 30 K show the occurrence of a crystallographic transition resulting in an ordering of the molecular units at low temperature.     

Laser ablation inductively coupled plasma mass spectrometry for direct analysis of the spatial distribution of trace elements in metallurgical-grade silicon

The spatial distribution and concentration of impurities in metallurgical-grade silicon (MG-Si) samples (97–99% w/w Si) were investigated by use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The spatial resolution (120 μm) and low limits of detection (mg kg⁻¹) for quality assurance of such materials were studied in detail. The volume-dependent precision and accuracy of non-matrix-matched calibration for quantification of minor elements, using NIST SRM 610 (silicate standard), indicates that LA-ICP-MS is well suited to rapid process control of such materials. Quantitative results from LA-ICP-MS were compared with previously reported literature data obtained by use of ICP-OES and rf-GD-OES. In particular, the distribution of element impurities and their relationship to their different segregation coefficients in silicon is demonstrated. Dedicated to Professor Klaus G. Heumann     

Preparation, characterization and surface study of poly-epsilon caprolactone magnetic microparticles

Magnetic microparticles (MMP) have shown to be applied in increasing applications in various fields of biotechnology and medicine. One of their most promising utilization is the magnetic resonance imaging (MRI) in which superparamagnetic substances as magnetite are used in a nanometric size (less than 30 nm) and encapsulated within locally injected biodegradable microparticles. In this paper, magnetite has been encapsulated in polymer-based microparticles. The MMP have been prepared by an emulsion evaporation method. The different parameters influencing the particles size were investigated. The size was found to decrease as the stirring speed or the stabilizer amount (to certain limit) increases. The encapsulation efficacy was more than 90% yielding a magnetite loading of up to 30%, w/w. The X-ray photoelectron spectroscopy (XPS) showed less than 2% of iron atoms at the microparticles surface. The zeta potential response of MMP towards pH variation was very similar to that of magnetite-free microparticles confirming the encapsulation of magnetite within the microparticles. X-ray diffraction assays showed that magnetite crystalline structure was conserved after emulsification and MMP formation. Vibration simple magnetometer (VSM) showed a superparamagnetic profile of the MMP with a magnetic saturation increasing with the increased magnetite amount in the microparticles. These magnetic microparticles can enable clinicians to control microparticles distribution after a local administration in tumors by MRI. They can also be administered to target a defined tumor area by focusing a magnetic field on the surfaces covering the cancerous tissue.     

Imaging mass spectrometry in biological tissues by laser ablation inductively coupled plasma mass spectrometry

Of all the inorganic mass spectrometric techniques, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) plays a key role as a powerful and sensitive microanalytical technique enabling multi- element trace analysis and isotope ratio measurements at trace and ultratrace level. LA-ICP-MS was used to produce images of detailed regionally-specific element distribution in 20 microm thin sections of different parts of the human brain. The quantitative determination of copper, zinc, lead and uranium distribution in thin slices of human brain samples was performed using matrix-matched laboratory standards via external calibration procedures. Imaging mass spectrometry provides new information on the spatially inhomogeneous element distribution in thin sections of human tissues, for example, of different brain regions (the insular region) or brain tumor tissues. The detection limits obtained for Cu, Zn, Pb and U were in the ng g(-1) range. Possible strategies of LA-ICP-MS in brain research and life sciences include the elemental imaging of thin slices of brain tissue or applications in proteome analysis by combination with matrix-assisted laser desorption/ionization MS to study phospho- and metal- containing proteins will be discussed.     

Study of plasma parameters influencing fractionation in laser ablation-inductively coupled plasma-mass spectrometry

Methods permitting to test the influence of the matrix as well as of its local and temporal distribution on the plasma conditions in laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) are developed. For this purpose, the MS interface is used as plasma probe allowing to investigate the average plasma condition within the ICP zone observed in terms of temporal and spatial distribution of the matrix.     

Imaging of uranium on rat brain sections using laser ablation inductively coupled plasma mass spectrometry: a new tool for the study of critical substructures affined to heavy metals in tissues

The specific toxicity of trace metals and compounds largely depends on their bioavailability in different organs or compartments of the organism considered. Imaging mass spectrometry (IMS) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with a spatial resolution in the 100 microm range was developed and employed to study heavy metal distribution in brain tissues for toxicological screening. Rat brain post-mortem tissues were stained in an aqueous solution of either uranium or neodymium (metal concentration 100 microg g(-1)) for 3 h. The incubation of heavy metal in thin slices of brain tissue is followed by an imaging mass spectrometric LA-ICP-MS technique. Stained rat brain tissue (thickness 30 microm) were scanned with a focused laser beam (wavelength 266 nm, diameter of laser crater 100 microm and laser power density 3 x 10(9) W cm(-2)). The ion intensities of (235)U(+), (238)U(+), (145)Nd(+) and (146)Nd(+) were measured by LA-ICP-MS within the ablated area. For quantification purposes, matrix-matched laboratory standards were prepared by dosing each analyte to the pieces of homogenized brain tissue. Imaging LA-ICP-MS allows structures of interest to be identified and the relevant dose range to be estimated. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Reaction-path switching induced by spatial-distribution change of reactants: CO oxidation on Pt(111)

We studied the mechanism of CO oxidation on O-covered Pt(111) surfaces during CO exposure by means of time-resolved near edge x-ray absorption fine structure spectroscopy. Two distinct reaction processes were found to occur sequentially; isolated O atoms and island-periphery O atoms contribute to each process. Combination of in situ monitoring of the reaction kinetics and Monte Carlo simulations revealed that CO coadsorption plays a role of inducing the dynamic change in spatial distribution of O atoms, which switches over the two reaction paths.     

Application of elemental bioimaging using laser ablation ICP-MS in forest pathology: distribution of elements in the bark of Picea sitchensis following wounding

Element distribution in the bark of two 20-year-old clones of Picea sitchensis following wounding was studied using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Bark was sampled at 0, 3, and 43 days after wounding and analysed using a focused Nd:YAG laser (266 nm). Intensities of ¹³ C, ²⁵Mg, ²⁷Al, ³¹P, ³²S, ³⁹K, ⁴⁸Ca, ⁵⁵Mn, ⁵⁷Fe, ⁶³Cu and ⁶⁴Zn were measured by ICP-MS to study elemental distribution across the bark samples during the wound repair process. A clear accumulation of Mg, P and K at the boundary zone between the lesion and healthy tissue was detected in the wounded samples and was more distinctive at 43 than at 3 days after treatment. This zone of accumulation mapped onto the position of formation of the ligno-suberised boundary zone and differentiation of the wound periderm. These accumulations suggest major roles for Mg, P and K in the non-specific response of Sitka spruce both to wounding, possibly as co-factors to enzymes and energy utilisation. The LA-ICP-MS method developed in this work proved useful to study spatial element distribution across bark samples and has great potential for applications in other areas of plant pathology research.     

Biomonitoring of essential and toxic metals in single hair using on-line solution-based calibration in laser ablation inductively coupled plasma mass spectrometry

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been established as a powerful and sensitive surface analytical technique for the determination of concentration and distribution of trace metals within biological systems at micrometer spatial resolution. LA-ICP-MS allows easy quantification procedures if suitable standard references materials (SRM) are available. In this work a new SRM-free approach of solution-based calibration method in LA-ICP-MS for element quantification in hair is described. A dual argon flow of the carrier gas and nebulizer gas is used. A dry aerosol produced by laser ablation (LA) of biological sample and a desolvated aerosol generated by pneumatic nebulization (PN) of standard solutions are carried by two different flows of argon as carrier or nebulizer gas, respectively and introduced separately in the injector tube of a special ICP torch, through two separated apertures. Both argon flows are mixed directly in the ICP torch. External calibration via defined standard solutions before analysis of single hair was employed as calibration strategy. A correction factor, calculated using hair with known analyte concentration (measured by ICP-MS), is applied to correct the different elemental sensitivities of ICP-MS and LA-ICP-MS. Calibration curves are obtained by plotting the ratio of analyte ion M⁺/³⁴S⁺ ion intensities measured using LA-ICP-MS in dependence of analyte concentration in calibration solutions. Matrix-matched on-line calibration in LA-ICP-MS is carried out by ablating of human hair strands (mounted on a sticky tape in the LA chamber) using a focused laser beam in parallel with conventional nebulization of calibration solutions. Calibrations curves of Li, Na, Mg, Al, K, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Mo, Ag, Cd, I, Hg, Pb, Tl, Bi and U are presented. The linear correlation coefficients (R) of calibration curves for analytes were typically between 0.97 and 0.999. The limits of detection (LODs) of Li, V, Mn, Ni, Co, Cu, Sr, Mo, Ag, Ba, Cd, I, Hg, Pb, Bi and U in a single hair strand were in the range of 0.001-0.90 μg g⁻¹, whereas those of Cr and Zn were 3.4 and 5.1 μg g⁻¹, respectively. The proposed quantification strategy using on-line solution-based calibration in LA-ICP-MS was applied for biomonitoring (the spatial resolved distribution analysis) of essential and toxic metals and iodine in human hair and mouse hair.     

Mapping of lead,magnesium and copper accumulation in plant tissues by laser-induced breakdown spectroscopy and laser-ablation inductively coupled plasma mass spectrometry

Laser-Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) were utilized for mapping the accumulation of Pb, Mg and Cu with a resolution up to 200 μm in a up to cm × cm area of sunflower (Helianthus annuus L.) leaves. The results obtained by LIBS and LA-ICP-MS are compared with the outcomes from Atomic Absorption Spectrometry (AAS) and Thin-Layer Chromatography (TLC). It is shown that laser-ablation based analytical methods can substitute or supplement these techniques mainly in the cases when a fast multi-elemental mapping of a large sample area is needed.     

Neutron powder diffraction and difference maximum entropy method analysis of protium- and deuterium-dissolved BaSn0.5In0.5O2.75+α

We propose a new method, a difference maximum entropy method (MEM) analysis of the neutron diffraction data, for revealing the detailed structure around hydrogen atoms in proton-conducting oxides. This MEM analysis uses the differences between the structure factors of protium- and deuterium-dissolved crystals. Simulations demonstrate that it not only provides the distribution of hydrogen atoms alone, but also improves the spatial resolution of MEM mapping around hydrogen atoms. Applied to actual diffraction data of protium- and deuterium-dissolved BaSn_0.5In_0.5O_2.75+α at 9 K, difference MEM analysis reveals that O-D bonds mostly tilt towards the second nearest oxygen atoms, and that the distributions of deuterium and oxygen atoms are probably insignificant in interstitial regions.     

Mechanism of the CO oxidation reaction on O-precovered Pt(111) surfaces studied with near-edge x-ray absorption fine structure spectroscopy

The mechanism of CO oxidation reaction on oxygen-precovered Pt(111) surfaces has been studied by using time-resolved near-edge x-ray absorption fine structure spectroscopy. The whole reaction process is composed of two distinct paths: (1) a reaction of isolated oxygen atoms with adsorbed CO, and (2) a reaction of island-periphery oxygen atoms after the CO saturation. CO coadsorption plays a role to induce the dynamic change in spatial distribution of O atoms, which switches over the two reaction paths. These mechanisms were confirmed by kinetic Monte Carlo simulations. The effect of coadsorbed water in the reaction mechanism was also examined.     

IN VIVO 31P NMR STUDY OF COMBINED HYPERTHERMIA and PHOTODYNAMIC THERAPIES OF MAMMARY CARCINOMA IN THE MOUSE

Although the sequence and time interval effects of combined photodynamic therapy (PDT) and hyperthermia tumor treatments have been studied using survival curves, tumor regrowth, and cloning assays, the metabolic response to combined treatment measured by nuclear magnetic resonance (NMR) spectroscopy has not yet been clarified. In this study, mammary carcinoma in the flank of C3H mice was subjected to PDT (12.5 mg/kg Photofrin II, 632 +/- 1 nm at 200 J/cm2) and water bath hyperthermia (43.5 degrees C, 30 min) with no delay or 4 h delay between treatments. In vivo 31P-NMR spectroscopy was employed to measure energy metabolism and pH of the tumors before and serially after treatment for up to 1 week. The data revealed significant differences in the time course of high energy phosphate levels between treatment combinations, which may reflect the biological effectiveness of the combined treatments. Our observations indicate that 31P-NMR spectroscopy can be used to evaluate the metabolic response of tumors to treatment with combined PDT and hyperthermia.     

High-resolution laser ablation-inductively coupled plasma-mass spectrometry imaging of cisplatin-induced nephrotoxic side effects

Two-dimensional elemental mapping (bioimaging) via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was performed on 5 μm thick formalin-fixed, paraffin-embedded kidney tissue sections from Cynomolgus monkeys administered with increasing pharmacological doses of cisplatin. Laterally resolved pixels of 1 μm were achieved, enabling elemental analysis on a (sub-)cellular level. Zones of high Pt response were observed in the renal cortex, where proximal tubules are present, the epithelium of which is responsible for partial reabsorption of cisplatin. Histopathological evaluation, of hematoxylin and eosin-stained serial sections, adjacent to the sections probed via LA-ICP-MS, revealed minimal to mild cisplatin-related lesions (<100 μm) in the renal cortex. Necrotic proximal tubules with sloughed epithelial cells in their lumen could be linked directly to the areas with the highest accumulation of cisplatin, indicating a direct link between cellular concentration and toxicity, thereby providing more insight into the mechanisms through which renal damage occurs.     

Discrepancy between the Spin Distribution and the Magnetic Ground State for a Triaminoxyl Substituted Triphenylphosphine Oxide Derivative

The magnetic interaction and spin transfer via phosphorus have been investigated for the tri‐tert‐butylaminoxyl para‐substituted triphenylphosphine oxide. For this radical unit, the conjugation existing between the π* orbital of the NO group and the phenyl π orbitals leads to an efficient delocalization of the spin from the radical to the neighboring aromatic ring. This has been confirmed by using fluid solution high‐resolution EPR and solid state MAS NMR spectroscopy. The spin densities located on the atoms of the molecule could be probed since ¹H, ¹³C, ¹⁴N, and ³¹P are nuclei active in NMR and EPR, and lead to a precise spin distribution map for the triradical. The experimental investigations were completed by a DFT computational study. These techniques established in particular that spin density is located at the phosphorus (ρ=?15×10^?3 au), that its sign is in line with the sign alternation principle and that its magnitude is in the order of that found on the aromatic C atoms of the molecule. Surprisingly, whereas the spin distribution scheme supports ferromagnetic interactions among the radical units, the magnetic behavior found for this molecule revealed a low‐spin ground state characterized by an intramolecular exchange parameter of J=?7.55 cm^?1 as revealed by solid state susceptibility studies and low temperature EPR. The X‐ray crystal structures solved at 293 and 30 K show the occurrence of a crystallographic transition resulting in an ordering of the molecular units at low temperature.     

Simultaneous Determination of Moxifloxacin Hydrochloride and Dexamethasone Sodium Phosphate in Rabbit Ocular Tissues and Plasma by LC-MS/MS: Application for Pharmacokinetics Studies

Treatment of ocular infection involves pharmacotherapy with steroids and antibiotic drops, such as moxifloxacin hydrochloride (MFH) and dexamethasone sodium phosphate (DSP). To characterize the pharmacokinetics of these two compounds, we performed and validated a liquid chromatography-mass spectrometry (LC-MS/MS) method to quantify them in rabbit ocular tissues and plasma. We used protein precipitation to extract the compounds. The analyte and internal standard (IS) were separated using a Shim-pack Scepter C₁₈ column. The mobile phase was composed of 0.1% formic acid water (A) and methanol (B). MFH and DSP were detected using positive ion electrostatic ionization (ESI) in multiple reaction monitoring mode (MRM). The calibration curves for both compounds showed good linearity over concentrations ranging from 0.5 to 200 ng/mL in rabbit ocular tissues and plasma. The lower limit of quantification for both MFH and DSP was 0.5 ng/mL. We validated this method for selectivity, linearity (r2 > 0.99), precision, accuracy, matrix effects, and stability. Thus, we used this method to assess the pharmacokinetic (PK) characteristics of MFH and DSP in rabbit ocular tissues and plasma after single doses. Our results indicate that this method can be used for the simultaneous analysis of moxifloxacin hydrochloride and dexamethasone sodium phosphate in clinical samples.