Markéta Holá

Quantitative analysis of Fe-based samples using ultraviolet nanosecond and femtosecond laser ablation-ICP-MS

The quantification capabilities of iron-based samples were investigated using three commercially available ultraviolet (UV) nanosecond (ns) and femtosecond (fs) laser ablation systems coupled to inductively coupled plasma mass spectrometry (LA-ICP-MS). A comparison of three pulsed laser ablation systems (ArF* excimer, Nd:YAG and Ti-sapphire) with different wavelengths and pulse time durations (15 ns, 4 ns and 150 fs, respectively) was performed. Minor and trace elements were determined using 57Fe as internal standard element. Using similar spatial resolution for all laser systems and commonly applied operating conditions for each system, higher ion-signals (25–30%) and more stable elemental ratios (10% TRSD) were obtained for UV-fs-LA-ICP-MS. Scanning electron microscope images and particle size distributions measured for UV-ns-LA systems showed a bimodal distribution formed by nano-sized agglomerates and micro-sized molten spherical particles. In contrast, due to reduced thermal effects achieved using ultra-short pulses, the particle size distribution measured using UV-fs-LA showed a broad monomodal distribution (nano-sized agglomerates in the range of 50–250 nm). Matrix-matched (within metallic samples) and non-matrix matched calibrations were applied for the analysis of Fe-based samples, using a silicate glass (SRM NIST 610) as non-matrix matched calibration sample (glass-metals). Improved analytical results in terms of precision and accuracy were obtained using femtosecond laser ablation when using similar matrices for calibration. Moreover, non-matrix matched calibration used for quantification provides more accurate results (5–15%) in comparison with both UV-ns-LA-ICP-MS (5–30% using Nd:YAG laser and 15–60% using ArF* laser).

The SYRMEP Beamline of Elettra: Clinical Mammography and Bio‐medical Applications

At the SYnchrotron Radiation for MEdical Physics (SYRMEP) beamline of Elettra Synchrotron Light Laboratory in Trieste (Italy), an extensive research program in bio‐medical imaging has been developed since 1997. The core program carried out by the SYRMEP collaboration concerns the use of Synchrotron Radiation (SR) for clinical mammography with the aim of improving the diagnostic performance of the conventional technique. The first protocol with patients, started in 2006 has been completed at the end of 2009 and the data analysis is now in progress.Regarding applications different from clinical imaging, synchrotron X‐ray computed microtomography (micro‐CT) is the most used technique, both in absorption and phase contrast. A new software tool, Pore3D, has been developed to perform a quantitative morphological analysis on the reconstructed slices and to access textural information of the sample under study.

Investigation of the microstructure and mineralogical composition of urinary calculi fragments by synchrotron radiation X-ray microtomography: a feasibility study

The outcomes from the feasibility study on utilization of synchrotron radiation X-ray microtomography (SR-μCT) to investigate the texture and the quantitative mineralogical composition of selected calcium oxalate-based urinary calculi fragments are presented. The comparison of the results obtained by SR-μCT analysis with those derived from current standard analytical approaches is provided. SR-μCT is proved as a potential effective technique for determination of texture, 3D microstructure, and composition of kidney stones.

Examination of sol-gel technique applicability for preparation of pellets for soil analysis by laser ablation inductively coupled plasma optical emission spectrometry

Silica sol–gel matter was examined as a binder assisting the preparation of agricultural soil sample pellets for elemental analysis by laser ablation inductively coupled plasma optical emission spectrometry. The sol–gel method, allowing homogenous dispersion of internal standard (Sc) and analytes in calibration pellets, was applied to the determination of Cr, Ni, Cu, Zn and Pb in four types of soils. A Q-switched Nd:YAG laser (1064 nm) was employed for ablation of pellets prepared by pressing of a ground and homogenized blend of soil and silica gel. Calibration curves exhibited correlation coefficients greater than 0.997. The repeatability of determination for elements of interest did not exceed 7% RSD. Accuracy of determination was proved by X-ray fluorescence analysis of soil pellets prepared with a wax binder and by solution analysis after total decomposition of samples by a mixture of HF and HClO4. The pellet homogeneity was checked by electron probe X-ray microanalysis, measuring element distribution, and the ablation craters were studied using optical microscopy. The depths of the ablation craters exhibited different ablation rates for samples with diverse matrices. Analytical results obtained for CRM by the method presented exhibit bias in the range from 6 to 15% rel. (α = 0.05) depending on the element.

Study of aerosols generated by 213 nm laser ablation of cobalt-cemented hard metals

Cobalt-cemented hard metals present an example of samples with a complicated matrix consisting of components differing in chemical and physical properties and with extremely low volatility of all components. The purpose of this study was to compare particle formation of a set of real samples with similar matrices but different content of major components. The laser ablation process was studied using a Q-switched quintupled (213 nm) nanosecond Nd:YAG laser. Five samples of Co-cemented tungsten carbides, actually WC-TiC-(Ta,Nb)C-Co with a varied content of main constituents, were selected as representatives of a family of 15 miscellaneous tungsten carbide hard metal products. Physical and chemical properties vary over this specimen selection and therefore the effect on particle size formation and distribution was expected. The size distributions by number of ablated particles in different size ranges were measured using an optical aerosol spectrometer. The results proved the relationship between particle formation and sample composition. The structure of laser generated particles and the properties of ablation-craters were additionally studied by scanning electron microscopy (SEM). Spherical particles in the diameter range of 0.25–2 μm and μm-sized agglomerates composed of primary nano-particles were observed. The W and Co content in the aerosol particles was determined by energy dispersive X-ray spectroscopy (EDS). The volumes of ablation craters were measured by an optical profilometer. The laser ablation study of selected Co-cemented tungsten carbide hard metals indicates a similar total volume of formed particles with composition-dependent particle-size distributions.

UV and IR laser ablation study of natural organic powdered materials—an example: ICP-OES with laser ablation of spiked infant formula cast pellets

Laser ablation (LA) sample introduction into inductively coupled plasma optical emission spectrometry (ICP-OES) was used for powdered infant food formula being representative of samples with an organic matrix. Milk samples enriched with eight naturally occurring elements were presented for LA-ICP-OES experiments as cast epoxy resin disks. For Ca, Cu, Fe, Mg and Zn, a performance of IR (1064 nm) and UV (266 nm) ablation was compared in a fixed spot mode (UV) and in a scanning mode (both UV and IR). Signal vs. content dependences proved to be linear both with and w/o the internal standard Ca (IS). Using the IS the linear regression parameters for the scanning mode were improved for both UV and IR ablation. The UV fixed spot ablation provided the closest correlation and so, except for Cu (low content), repeatability for all elements of interest did not exceed 10% RSD. Lowest determinable quantities were 0.06% Ca, 0.008% Mg, 0.0005% Cu, 0.001% Fe and 0.0008% Zn. Condensation of Zn on ejected particles was observed at the UV ablation.

Tungsten carbide precursors as an example for influence of a binder on the particle formation in the nanosecond laser ablation of powdered materials

A study of LA-ICP-MS analysis of pressed powdered tungsten carbide precursors was performed to show the advantages and problems of nanosecond laser ablation of matrix-unified samples. Five samples with different compositions were pressed into pellets both with silver powder as a binder serving to keep the matrix unified, and without any binder. The laser ablation was performed by nanosecond Nd:YAG laser working at 213 nm. The particle formation during ablation of both sets of pellets was studied using an optical aerosol spectrometer allowing the measurement of particle concentration in two size ranges (10-250 nm and 0.25-17 microm) and particle size distribution in the range of 0.25-17 microm. Additionally, the structure of the laser-generated particles was studied after their collection on a filter using a scanning electron microscope (SEM) and the particle chemical composition was determined by an energy dispersive X-ray spectroscope (EDS). The matrix effect was proved to be reduced using the same silver powdered binder for pellet preparation in the case of the laser ablation of powdered materials. The LA-ICP-MS signal dependence on the element content present in the material showed an improved correlation for Co, Ti, Ta and Nb of the matrix-unified samples compared to the non-matrix-unified pellets. In the case of W, the ICP-MS signal of matrix-unified pellets was influenced by the changes in the particle formation.

Comparison of inductively coupled plasma optical emission spectrometry, energy dispersive X-ray fluorescence spectrometry and laser ablation inductively coupled plasma mass spectrometry in the elemental analysis of agricultural soils

A silica sol–gel technique was applied to the preparation of pellets of agricultural soils for determination of trace elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). For the purpose of evaluation of feasibility of the LA-ICP-MS technique for quantitative determination, elemental contents in twenty two spiked archive agricultural soils and three CRMs (GBW07405, GBW07406, and GBW07407) were determined by independent analytical techniques, namely by inductively coupled plasma optical emission spectrometry with pneumatic nebulization (PN-ICP-OES) after total decomposition with a mixture of acids, and by energy dispersive X-ray fluorescence (ED-XRF) spectrometry analysis of pellets prepared with a wax binder. Ablation was carried out with a Nd:YAG laser at 213 nm. Possible matrix interferences associated with ablation of the multiphase soil material were anticipated and therefore, the sequential extraction procedure was employed for fractionation analysis to determine elemental concentrations, in particular soil constituents, for explaining potential deviations of LA-ICP-MS analyses. Methods were compared based on the determination of ordinarily monitored trace elements Cu, Cr, Ni, Pb and Zn in archive soils and certified reference materials. The PN-ICP-OES, ED-XRF and LA-ICP-MS methods were compared by means of linear regression analysis to search for a possible systematic proportional or constant error. Besides the ordinary least-squares linear regression method, also weighted least squares, orthogonal, Deming, maximum likelihood and Passing–Bablok regressions were employed. The Bland–Altman plot and score plot based on principal component analysis (PCA) were used for visual comparison.