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Raman and laser-induced breakdown spectroscopy is integrated into a single system for molecular and elemental microanalyses. Both analyses are performed on the same ~ 0.002 mm² sample spot allowing the assessment of sample heterogeneity on a micrometric scale through mapping and scanning. The core of the spectrometer system is a novel high resolution dual arm Echelle spectrograph utilized for both techniques. In contrast to scanning Raman spectroscopy systems, the Echelle-Raman spectrograph provides a high resolution spectrum in a broad spectral range of 200-6000 cm- 1 without moving the dispersive element. The system displays comparable or better sensitivity and spectral resolution in comparison to a state-of-the-art scanning Raman microscope and allows short analysis times for both Raman and laser induced breakdown spectroscopy. The laser-induced breakdown spectroscopy performance of the system is characterized by ppm detection limits, high spectral resolving power (15,000), and broad spectral range (290-945 nm). The capability of the system is demonstrated with the mapping of heterogeneous mineral samples and layer by layer analysis of pigments revealing the advantages of combining the techniques in a single unified set-up.
Polyethylene (PE) frits were used to quantify sulphur in copper and its alloys by isotope dilution combined with LA-ICP-MS as an alternative approach to conventional sample preparation: the copper samples were spiked, the spiked samples were dissolved, the resulting solutions were absorbed in the PE frits and finally the PE frits were analysed by LA-ICP-MS. A prerequisite for such a support material is a low sulphur blank and thus PE was selected for this purpose. The absorption efficiency of the PE frits was studied for varying sulphur amounts ranging from 2 mg S to 80 mg S showing that more than 99.5% of the loaded sulphur was absorbed by the frit. The so prepared PE frits were measured by LA-ICP-MS and yielded a good linearity (R2 ¼ 0.999) for the sulphur ion intensities corresponding to sulphur amounts up to 40 mg S; the associated sensitivity is approximately 3.4 x 10⁴ cps μg⁻¹ for ³²S. For the validation of the developed procedure the reference materials BAM-M376a, BAM-228 and BAM-227 were applied such that 2 μg S, 5 μg S and 11 μg S were absorbed in the PE frits, respectively. These samples were pre-quantified for the adsorbed sulphur amount by external calibration LA-ICP-MS yielding sulphur amounts of 0.9 μg, 5.1 μg and 8.5 μg (quantified for ³²S only), respectively. Relative Standard deviations of the isotope ratios were below 5% in average (n ¼ 3 lines) in all cases (except for the pure spike solution). These samples were then analysed by LA-ICP-IDMS and the measurement results were validated by comparing them with the results obtained by conventional ICP-IDMS. The obtained relative expanded measurement uncertainties ranged between 10% and 26%. Pearson's coefficient was used to express the correlation between both techniques; the obtained value was 0.999 demonstrating a strong correlation. Contrary to most published LA-ICP-IDMS procedures, the developed procedure enables SI-traceability for the measurement results. The metrological traceability to the SI for the sulphur mass fractions in copper was established by an unbroken chain of comparisons, each accompanied by an uncertainty budget. Thus, the measurement results are considered reliable, acceptable and comparable within the stated measurement uncertainty. The metrological traceability chain from the kg down to mass fraction in the samples obtained by LA-ICP-IDMS is presented as well.
Triacetone triperoxide (TATP) is a primary explosive, which was used in various terrorist attacks in the past. For the development of biosensors, immunochemical µ-TAS, electronic noses, immunological test kits, or test strips, the availability of antibodies of high quality is crucial. Recently, we presented the successful immunization of mice, based on the design, synthesis, and conjugation of a novel TATP derivative. Here, the long-term immunization of rabbits is shown, which resulted in antibodies of extreme selectivity and more than 1,000 times better affinity in relation to the antibodies from mice. Detection limits below 10 ng L-1 (water) were achieved. The working range covers more than four decades, calculated from a precision profile. The cross-reactivity tests revealed an extraordinary selectivity of the antibodies—not a single compound could be identified as a relevant cross-reactant. The presented immunoreagent might be a major step for the development of highly sensitive and selective TATP detectors particularly for security applications.
An efficient solid phase extraction (SPE) method using bis-(2-ethylhexyl)-phosphate (HDEHP) coated reverse phase C18 support has been developed for the pre-concentration of Gadolinium (Gd) and Gd contrast agents widely used in magnetic resonance imaging (MRI). Enrichment of Gd in the ionic form has been compared with strong cation exchange material Chromabond SA (SCX), weak ion exchange material Chelex-100 and also with lanthanide specific HDEHP modified reverse phase C18. The determination of Gd and its complexes after enrichment were performed using inductively coupled plasma mass spectrometry (ICP-MS) and on the basis of 158Gd. Among the three SPE materials, HDEHP coated reverse phase C18 SPE has been found to be most efficient, yielding a hundredfold Gd enrichment with > 95% recovery for linear and cyclic contrast agents like Gd-DTPA (Magnevist), Gd-DOTA (Dotarem), Gd-BOPTA (Multihance), and Gd-BT-DO3A (Gadovist). The developed SPE method has been successfully applied to the surface water and waste water samples originated from different places in Berlin, Germany. The results were in good agreement with the results obtained with direct measurement with ICP-MS. The developed pre-concentration method can be efficiently used for the determination of trace levels of gadolinium in the environment even with less sensitive analytical techniques.
Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) has been proposed several years ago as an approach for quantitative analysis of Laser-Induced Breakdown Spectroscopy spectra. Recently developed refinement of the spectral processing method is described in the present work. Accurate quantitative results have been demonstrated for several metallic alloys. However, the degree of accuracy that can be achieved with Calibration-Free Laser-Induced Breakdown Spectroscopy analysis of generic samples still needs to be thoroughly investigated. The authors have undertaken a systematic study of errors and biasing factors affecting the calculation in the Calibration-Free Laser-Induced Breakdown Spectroscopy spectra processing. These factors may be classified in three main groups: 1) experimental aberrations (intensity fluctuations and inaccuracy in the correction for spectral efficiency of a detection system), 2) inaccuracy in theoretical parameters used for calculations (Stark broadening coefficients and partition functions) and 3) plasma non-ideality (departure from thermal equilibrium, spatial and temporal inhomogeneities, optical thickness, etc.). In this study, the effects of experimental aberrations and accuracy of spectral data were investigated, assuming that the analytical plasma is ideal. Departure of the plasma conditions from ideality will be the object of future work. The current study was based on numerical simulation. Two kinds of metallic alloys, iron-based and aluminum-based, were studied. The relative weight of the error contributions was found to depend on the sample composition. For the here-investigated samples, the experimental aberrations contribute to the overall uncertainty on the quantitative results more than theoretical parameters. The described simulation method can be applied to the Calibration-Free Laser-Induced Breakdown Spectroscopy analysis of any other kind of sample.
Particle-based assays are becoming versatile analytical tools due to their cost-effectiveness, speed, straightforward and diverse functionalization chemistries, especially when polystyrene particles are used. The introduction of functional groups (–COOH, –NH2, etc.) to the surface of such polystyrene particles promotes their application in bioanalytics. However, the traditional method to determine the amount of surface carboxylate groups is conductivity titration, which is usually time- and resources-consuming and discontinuous. Here, we synthesized polystyrene microparticles with different contents of carboxylate groups, and then investigated a simpler and potentially continuous approach to determine the amount of surface carboxylate groups by Zeta potential measurements. The results were compared to the traditional titration method and to actual coupling efficiencies of the functionalized particles with a model oligonucleotide probe as determined by flow cytometry. All quantification methods revealed good agreement.
The accurate knowledge of the properties of polycapillary X-ray semi-lenses has a significant influence on the quantitative results in a widespread field of applications involving microfocus X-ray beams. A routine procedure for the characterisation of a polycapillary X-ray semi-lens with a scanning electron microscope (SEM) having attached an energy dispersive spectrometer (EDS) is presented in this paper. A key issue of the procedure consists of fitting the semi-lens in front of the EDS for spectra acquisition. Relevant semi-lens parameters such as focal distance, full width at half maximum (FWHM) of the acceptance area, and transmission are determined in parallelising mode of the semi-lens. Special attention has been paid to the calculation of the transmission.
A simple metal staining procedure for identification and visualization of single cells by LA-ICP-MS
(2017)
High lateral resolution of metal detection in single cells by use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) demands powerful staining methods. In this work different staining procedures for the single cell analysis with LA-ICP-MS were optimized. An iridium intercalator was utilized to stain the cell nuclei whereas the whole cell was stained by the use of maleimido-mono-amide-DOTA (mDOTA) complexing lanthanide(III) ions. The content of the artificially introduced metals per cell was quantified using a matrix matched calibration approach based on cellulose membranes onto which standards were spotted by a microarray spotter. Absolute metal stain amounts in the range of 2.34 to 9.81 femtomole per cell were determined. The metal staining procedures allow direct identification and visualization of single cells and their cell compartments by element microscopy without the use of bright field images of the sample.
Acoustic levitation represents the physical background of trapping a sample in a standing acoustic wave with no contact to the wave generating device. For the last three decades, sample holders based on this effect have been commonly used for contact free handling of samples coupled with a number of analytical techniques. In this study, a wall-free climate unit is presented, which allows the control of the environmental conditions of suspended samples. The insulation is based on a continuous cold/hot gas flow around the sample and thus does not require any additional isolation material. This provides a direct access to the levitated sample and circumvents any influence of the climate unit material to the running analyses.
Abel inversion applied to a transient laser induced plasma: implications from plasma modeling
(2011)
We test the effects of non-uniformity, non-transparency, and non-stationarity of a laser-induced plasma on the results obtained by the Abel inversion method. The method is commonly used for obtaining spatially resolved emissivity of axially symmetric non-homogeneous radiating objects. Besides the axial symmetry, the plasma is assumed to be optically thin. As the method addresses a certain plasma state, the plasma is required to be stationary during measurements. It is difficult to satisfy the aforementioned conditions for transient laser induced plasmas. As such the plasmas are not stationary; they have steep gradients of thermodynamic parameters that rapidly vary during the plasma evolution. Therefore, any conclusion based on time-integrated measurements and the corresponding data processing should account for these effects. In this work, we use the collision-dominated plasma model to generate time- and spatially resolved synthetic spectra. The spectra are processed by executing the Abel inversion using two numerical algorithms. Thus obtained spatially resolved plasma parameters (emissivity, temperature, and number density) are compared with the exact parameters used to set up the model. In doing so, the accuracy of the Abel inversion method is assessed. Special attention is paid to the dynamic aspect of the expanding plasma and possible errors which result from time-integrated measurements.
Acoustic levitation is used as a newtool to study concentration-dependent processes influorescence
spectroscopy. With this technique, small amounts of liquid and solid samples can be measured
without the need for sample supports or containers, which often limits signal acquisition and
can even alter sample properties due to interactions with the support material. We demonstrate
that, because of the small sample volume, fluorescence measurements at high concentrations
of an organic dye are possible without the limitation of inner-filter effects, which hamper such
experiments in conventional, cuvette-based measurements. Furthermore, we show that acoustic
levitation of liquid samples provides an experimentally simple way to study distance-dependent
fluorescence modulations in semiconductor nanocrystals. The evaporation of the solvent during
levitation leads to a continuous increase of solute concentration and can easily be monitored by
laser-induced fluorescence.
The results of investigations on the emission of particulate matter from three outdoor firework displays are presented. During these events, possibly harmful and toxic aerosol emissions were measured. Aerosols in the size range from 30 to 450 nm were detected. The maxima in the observed particle size distribution were between 80 and 175 nm, and the highest value determined was ~1.3 · 106 particles per cm³, while the highest mass concentration was approximately 1.8 mg m–3. The time-averaged particle mass concentration did, however, not exceed 0.7 mg m–3 (over 15 min).
Hydrophilic interaction chromatography (HILIC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) were optimised for the direct determination of gadolinium-based contrast agents in tap water. In comparison to our previous work, a new developed zwitterionic HILIC column (ZIC-cHILIC) was used for speciation of Gd-containing contrast agents. The limit of quantification (LOQ) for the five contrast agents Gd-BOPTA, Gd-DPTA-BMA, Gd-BT-DO3A, Gd-DOTA and Gd-DTPA are in the range of 512 ng Gd per litre. Additionally, a new internal standard, Pr-DOTA, was investigated to correct intensity drifts, minor and major changes in the sample volumes and possible matrix effects. With the speciation method described, tap water samples from the area of Berlin were analysed and for the first time, three Gd species, Gd-BT-DO3A, Gd-DOTA and Gd-BOPTA, were found in tap water samples at concentrations of about 10–20 ng Gd per litre. These are the same Gd species which have been previously detected predominantly in surface waters of the Berlin area.
A micro-droplet generator (µDG) sample introduction system was coupled to a sector field ICP-MS instrument to investigate the analytical figures of merit with respect to single cell analysis. The sector field instrument was operated for the first time in a fast scanning mode (E-scan) with the shortest time resolution of 100 µs to measure the single droplet time resolved and using the original detector in a pulse counting mode without modification of the existing electronics. For reduction of the droplet diameter a triple pulse mode of the droplet generator was applied and a droplet diameter down to 23 µm has been achieved for this investigation with a 100% transport efficiency of droplets. Signal duration times of single droplets of less than 500 µs have been measured. Overall detection efficiencies in the range of 10-3 counts per atom have been achieved and absolute limits of detection range between 120 ag for Fe and 1.1 ag for Mg as a mean value from 1000 droplet events.
Gated detection with intensified detectors, e.g., ICCDs, is today the accepted approach for detection of plasma emission in laser-induced breakdown spectroscopy (LIBS). However, these systems are more cost-intensive and less robust than nonintensified CCDs. The objective of this paper is to compare, both theoretically and experimentally, the performance of an intensified (ICCD) and nonintensified (CCD) detectors for detection of plasma emission in LIBS. The CCD is used in combination with a mechanical chopper, which blocks the early continuum radiation from the plasma. The detectors are attached sequentially to an echelle spectrometer under the same experimental conditions. The laser plasma is induced on a series of steel samples under atmospheric conditions. Our results indicate that there is no substantial difference in the performance of the CCD and ICCD. Signal-to-noise ratios and limits of detection achieved with the CCD for Si, Ni, Cr, Mo, Cu, and V in steel are comparable or even better than those obtained with the ICCD. This result is further confirmed by simulation of the plasma emission signal and the corresponding response of the detectors in the limit of quantum (photon) noise.
Arraying of single cells for mass spectrometric analysis is a considerable bioanalytical challenge. In this study, we employ a novel single cell arraying technology for quantitative analysis and isotopic fingerprinting by laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS). The single cell arraying approach is based on a piezo-acoustic microarrayer with software for automated optical detection of cells within the piezo dispense capillary (PDC) prior to arraying. Using optimized parameters, single cell occupancy of >99%, high throughput (up to 550 cells per hour), and a high cell recovery of >66% is achieved. LA-ICP-TOF-MS is employed to detect naturally occurring isotopes in the whole mass range as fingerprints of individual cells. Moreover, precise quantitative determination of metal-containing cell dyes is possible down to contents of ∼100 ag using calibration standards which were produced using the same arrayer.
The potential of a diode pumped solid state (DPSS) laser for laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy was investigated. The DPSS laser operating at repetition rates of 1 Hz–200 kHz, pulse energy of ~1 mJ, and pulse duration of ~20 ns was added to a conventional LIBS system equipped with the flashlamp-pumped Nd:YAG laser (10 Hz, 400 mJ, 6 ns) to directly compare the two laser systems. Despite the lower mass ablated per laser pulse (~several nanograms) and a weaker plasma, the total mass ablated per measurement interval (~1 s) and total emission signal were significantly higher than those obtained with the flashlamp pumped Nd:YAG laser. This resulted in the improved signal-to-noise ratio and better limits of detection (LOD). The best LODs were obtained for Cu, Cr and Ni in ultrapure standard iron samples, 0.7 ppm, 1 ppm and 5 ppm, correspondingly. The plasma from the DPSS laser was characterized in terms of its radiative properties, temperature, and shockwave propagation speed. The suitability of this laser for LIBS-Raman was demonstrated by mapping the elemental and molecular composition of a mineral sample. The results strongly imply that DPSS lasers are the promising source for LIBS, Raman, or combined LIBS-Raman spectroscopy.
The stable carbon and nitrogen isotopic composition of urine and milk samples from cattle under different feeding regimes were analysed over a period of six months. The isotope ratios were measured with isotope ratio mass spectrometry (IRMS). The δ13C values of milk and urine were dependent on different feeding regimes based on C3 or C4 plants. The δ13C values are more negative under grass feeding than under maize feeding. The δ13C values of milk are more negative compared to urine and independent of the feeding regime. Under grass feeding the analysed milk and urine samples are enriched in 13C relative to the feed, whereas under maize feeding the 13C/12C ratio of urine is in the same range and milk is depleted in 13C relative to the diet. The difference between the 15N/14N ratios for the two feeding regimes is less pronounced than the 13C/12C ratios. The δ15N values in urine require more time to reach the new equilibrium, whereas the milk samples show no significant differences between the two feeding regimes.
Popular X-ray tube models available in the literature, i.e. 'Pella', 'Ebel', and 'Finkelshtein and Pavlova', are systematically evaluated with the focus on the estimation of the associated uncertainties. Also taken in consideration and compared is our recent semi-empirical own approach already employed in our lab. This has been working for the common target elements rhodium, molybdenum and tungsten and was further extended in the present work for the target elements copper, chromium and vanadium. By using a modern scanning electron microscope/energy dispersive spectroscopy (SEM/EDS) system this time, higher performances such as stability of the beam current and especially the better energy resolution of the EDS have enabled the reliable extension of our own X-ray tube spectrum approach into the low-energy range, due to increasing interest. Hence, also the more challenging X-ray lines of copper, chromium and vanadium L-series lying in the energy range below 12?keV are included into the model. Such low-energy L-lines or, e.g. M-lines of tungsten, are not treated explicitly by the other existing popular algorithms for the nowadays widely used geometries of side-window tubes, offering a unique virtue to our present, modern approach. With our own model, a measurement uncertainty of the X-ray tube spectra (considering the uncertainties associated with the SEM beam current, the detector acceptance solid angle and efficiency of the spectrometer) within 15% has been estimated. The validation of the approach is demonstrated with metrological measurements with a calibrated SEM/EDS system geometrically configured as a side-window X-ray tube.
Calibration of two commercially available glow discharge double focusing mass spectrometers, the VG 9000 and Element GD, is described using synthetic pin standards pressed from solution doped copper and zinc matrices. A special pressing die was developed for this purpose and optimal results were obtained with the highest possible pressures, i.e., 95 kN·cm- 2. This calibration approach permits the determination of trace element mass fractions down to µg·kg- 1 with small uncertainties and additionally provides traceability of the GD-MS results in the most direct manner to the SI (International System of Units). Results were validated by concurrent measurements of a number of compact copper and zinc certified reference materials. The impact of the sample pin cross-section (circular or square) was investigated with the use of a new pin-sample holder system for the Element GD. The pin-sample holder was designed by the manufacturer for pin-samples having circular cross-section; however, samples with square pin cross-section were also shown to provide acceptable results. Relative Sensitivity Factors for some 50 analytes in copper (VG 9000, Element GD) and zinc matrices (VG 9000) are presented. The field of applicability of GD-MS may be considerably extended via analysis of pin geometry samples based on their ease of preparation, especially with respect to the accuracy and traceability of the results and the enhanced number of analytes which can be reliably calibrated using such samples.
During the mineralisation of metal carbonates MCO3 (M = Ca, Sr, Ba, Mn, Cd, Pb) liquid-like amorphous intermediates emerge. These intermediates that form via a liquid/liquid phase separation behave like a classical emulsion and are stabilized electrostatically. The occurrence of these intermediates is attributed to the formation of highly hydrated networks whose stability is mainly based on weak interactions and the variability of the metal-containing pre-critical clusters. Their existence and compositional freedom are evidenced by electrospray ionization mass spectrometry (ESI-MS). Liquid intermediates in non-classical crystallisation pathways seem to be more common than assumed.
The catalytic efficiency of two magnetically responsive nanocatalysts was evaluated for the Degradation of Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84) azo dyes using hydrogen peroxide as oxidant undervery mild conditions (atmospheric pressure, room temperature). In order to obtain the nanocatalysts, thesurface of magnetite (Fe3O4) nanoparticles, prepared by a co-precipitation method, was further modified with ferrous oxalate, a highly sensitive non-hazardous reducing agent. The sensitized nanomaterials were characterized by X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy and vibrating sample magnetometry, and used in the catalytic wet hydrogen peroxideoxidation (CWHPO) of RB5 and RY84, in laboratory-scale experiments. The effect of important variables such as catalyst dosage, H2O2 concentration, and contact time was studied in the dye Degradation kinetics. The results showed that it was possible to remove up to 99.7% dye in the presence of 20 mM H2O2 after 240 min of oxidation for a catalyst concentration of 10 g L−1at 25◦C and initial pH value of 9.0.CWHPO of reactive dyes using sensitized magnetic nanocatalysts can be a suitable pre-treatment methodfor complete decolorization of effluents from textile dyeing and finishing processes, once the Optimum operating conditions are established.
High performance liquid chromatography (HPLC) was hyphenated with a previously reported carbamazepine-specific enzyme-linked immunosorbent assay (ELISA) as a screening approach to water analysis in order to identify possible interferences from transformation products. Treated wastewater was analysed and three substances were recognized by the antibody besides carbamazepine: the metabolites 10,11-dihydro-10,11-epoxycarbamazepine and 2-hydroxycarbamazepine plus the structurally not obviously related antihistamine cetirizine. The molar cross-reactivity against cetirizine was found to be pH-dependent and assessed to be 400% at pH 4.5 and 22% at pH 10.5. Performing the ELISA at pH 10.5 greatly improved the accuracy when carbamazepine was determined in surface and wastewater samples.
A commercially available airbrush gun as a new source for spray ionization is presented. It is best operated employing moderate stagnation pressures, resulting in a sonic gas flow. A mass spectrometric investigation on the amino acid lysine and several peptides reveals that this inexpensive approach results in reproducible mass spectra. The ion patterns strongly resemble the results from other studies obtained with custom made sonic spray vaporizers. The patterns as well resemble the mass spectra recorded with electrospray devices. For a better understanding of the vaporization process, the mass spectrometry experiments are accompanied by laser induced fluorescence experiments. Inverse Abel transform of the obtained fluorescence maps allows the determination of the full 3D distribution of the spray cone. Furthermore, via exploitation of the solvatochromism of the used dye the solvation state distribution can be visualized. In addition, expansion parameters like droplet size and velocity are obtained by laser stroboscopy. The experiments demonstrate that the analyte is hardly desolvated throughout the expansion. This indicates a subsequent vaporization of the residual solvent in the intermediate pressure region of the mass spectrometer.
The chemical characterization and discrimination of allergy-relevant pollen (common ragweed (Ambrosia artemisiifolia), white birch (Betula pendula), English oak (Quercus robur), and European linden (Tilia cordata)) has been studied by Raman microscopy. Spectra were obtained at different excitation wavelengths (514, 633, and 780 nm) and various methods were examined to minimize the strong fluorescence background. The use of a HeNe laser (633 nm) for excitation yields high-quality single pollen Raman spectra, which contain multiple bands due to pollen components such as carotenoids, proteins, nucleic acids, carbohydrates, and lipids. Multivariate classification, i.e. principal component analysis (PCA) and hierarchical cluster analysis, demonstrated the validity of the approach for discrimination between different pollen species.
An airborne laser plasma is suggested as an ambient ion source for mass spectrometry. Its fundamental physical properties, such as an excellent spatial and temporal definition, high electron and ion densities and a high effective cross section in maintaining the plasma, make it a promising candidate for future applications. For deeper insights into the plasma properties, the optical plasma emission is examined and compared to mass spectra. The results show a seemingly contradictory behavior, since the emitted light reports the plasma to almost entirely consist of hot elemental ions, while the corresponding mass spectra exhibit the formation of intact molecular species. Further experiments, including time- resolved shadowgraphy, spatially resolved mass spectrometry, as well as flow-dependent emission spectroscopy and mass spectrometry, suggest the analyte molecules to be formed in the cold plasma vicinity upon interaction with reactive species formed inside the hot plasma center. Spatial separation is maintained by concentrically expanding pressure waves, inducing a strong unidirectional diffusion. The accompanying rarefaction inside the plasma center can be compensated by a gas stream application. This replenishing results in a strong increase in emission brightness, in local reactive species concentration, and eventually in direct mass spectrometric sensitivity. To determine the analytical performance of the new technique, a comparison with an atmospheric pressure chemical ionization (APCI) source was conducted. Two kitchen herbs, namely, spearmint and basil, were analyzed without any sample pretreatment. The presented results demonstrate a considerably higher sensitivity of the presented laser-spark ionization technique.
Raman signatures of the carotenoid component are studied in individual pollen grains from different species of trees. The information is obtained as differences in the strong pre-resonant Raman spectra measured before and after photodepletion of the carotenoid molecules. The results provide the first in situ evidence of interspecies differences in pollen carotenoid content, structure, and/or assembly between plant species without prior purification. The analysis of carotenoids in situ is confirmed by high-performance thin-layer chromatography (HPTLC)-supported resonance Raman data measured directly on the HPTLC plates after separation of carotenoids in pollen extracts. Utilization of the in situ, extraction-free procedure in carotenoid analysis will improve sensitivity and structural selectivity and provides insight into carotenoid structure and composition in single pollen grains.
Asymmetrical flow field-flow fractionation (AF4) was applied to characterize aquatic colloids from biological sewage plants and to infer information of colloidal loads, sources, and sinks within the plants, resp. the colloidal interaction with the aqueous phase and the sewage sludge. To characterize the colloids further, especially the distributions of colloid associated heavy metals, the AF4 system was coupled to an inductively coupled plasma mass spectrometer (ICP-MS). The size distribution is determined by AF4 with UV absorbance and fluorescence detection after a calibration by monodisperse polystyrene sulfonate standards (PSS). Samples from different sewage plants and from different depths and locations within a plant were compared. The fulvic/humic acid fraction with a particle diameter dp < 10 nm appeared to be comparable in all samples and decreases only slightly along the plants, whereas larger colloids with dp > 10 nm almost completely passed into the sewage sludge. The concentrations of the initial colloidal heavy metals decreased along the plants.
Among the large number of new ambient ionization schemes in the last few years, dielectric barrier discharge (DBD) has witnessed special attention. In this contribution a versatile dual mode DBD is introduced and characterized by means of optical emission spectroscopy and time-of-flight mass spectrometry. A direct comparison of the individual results from spectroscopy, spectrometry and transient current/voltage consumption gives evidence for the existence of two individual operational mechanisms. The first is driven by rapid transient changes in the potential difference between the two electrodes over time (usually denoted as the homogeneous mode), while the second is caused at high static potential differences (leading to filamentary discharges). The transient versus steady-state characteristics of the individual discharge origin suggest the driving force for the current flow to be inductive and capacitive, respectively. In most cases of dielectric barrier plasmas both discharge types coexist as competitive ion formation channels, however, detailed plasma characteristics of DBDs operated under different conditions allow for a clear distinction of the individual contributions. In this way, two characteristic product channels for the ionization of ambient water could be observed resulting in the generation of either preferentially protonated water clusters or ammonium water clusters. Careful tuning of the operation parameters of the discharge device allows an operation predominated by either of the two modes. As a consequence, facile switching into the desired operational mode results in either protonated molecules or ammoniated molecules of the analyte. Plasma characteristics for both moieties were evaluated and cross-correlated on the basis of several factors including: the production of reagent ions, the individual appearance of current/voltage profiles, UV/Vis spectroscopy, voltage and flux dependence and the individual response to test compounds. Although the filamentary mode has been already discussed in the literature to induce fragmentation processes, no experimental evidence for analyte dissociation could be found in the case of the test compounds used
We report on the in situ characterization of tree pollen molecular composition based on Raman spectroscopy. Different from purification-based analysis, the nondestructive approach allows (i) to analyze various classes of molecules simultaneously at microscopic resolution and (ii) to acquire fingerprint-like chemical information that was used for the classification of pollen from different species. Hierarchical cluster analysis of spectra from fresh pollen samples of 15 species partly related at the genus level and family level indicates separation of species based on the complete Raman spectral signature and yields classification in accord with biological systematics. The results have implications for the further elucidation of pollen biochemistry and also for the development of chemistry-based online pollen identification methods.
For many analytical purposes, direct laser ionization of liquids is desirable. Several studies on supported droplets, free liquid jets, and ballistically dispensed microdroplets have been conducted, yet detailed knowledge of the underlying mechanistics in ion formation is still missing. This contribution introduces a simple combination of IR-MALDI mass spectrometry and an acoustical levitation device for contactless confinement of the liquid sample. The homebuilt ultrasonic levitator supports droplets of several millimeters in diameter. These droplets are vaporized by a carbon dioxide laser in the vicinity of the atmospheric pressure interface of a time of flight mass spectrometer. The evaporation process is studied by high repetition rate shadowgraphy experiments elucidating the ballistic evaporation of the sample and revealing strong confinement of the vapor by the ultrasonic field of the trap. Finally, typical mass spectra for pure glycerol/water matrix and lysine as an analyte are presented with and without the addition of trifluoracetic acid, and the ionization mechanism is briefly discussed. The technique is a promising candidate for a reproducible mass spectrometric detection scheme for the field of microfluidics.
Single particle ICP-MS (spICP-MS) has gained great influence in the analysis of engineered nanoparticles (NPs) due to its simplicity, speed and ability to obtain a particle number size distribution. Despite its many advantages, the method is hampered by matrix effects affecting the sensitivity of the instruments.
Consequently, over- or underestimated particle sizes might be obtained. To overcome these challenges, we present in this work the detection of both Ag isotopes with a quadrupole mass spectrometer for the application of isotopic dilution analysis (IDA) in combination with spICP-MS. Here, the isotopes are measured sequentially using the conventional spICP-MS integration time of 10 ms. Citrate stabilized Ag NPs of a spherical shape with the nominal diameters of 30, 40, 50 and 80 nm have been investigated.
The experimental concept of adding ¹⁰⁹Ag+ solutions to the NP suspensions resulted in the NP Spikes being only visible in the ¹⁰⁷Ag trace. Therefore, a maximum of 45% of the particles was detected compared to that by conventional spICP-MS. A modified mass flow equation was applied to determine the particle sizes, particle size distributions and particle number concentrations of various Ag NPs. The addition of different spike concentrations between 0.5 and 4 mg L⁻¹ ¹⁰⁹Ag resulted in similar particle diameters, suggesting that the calculated diameter might be independent of the spike concentration.
This would have the advantage that no size information would be needed before the analysis. By analyzing Ag NP suspensions in a simulated seawater matrix, we demonstrate its significant influence on the particle size determination using conventional spICP-MS. A lower transport efficiency of 6.1% was found in the matrix compared to 7.3% without the matrix. In our approach, the addition of the Matrix influenced the NP intensity stronger than the spike signal, resulting in slightly smaller diameters using IDA–spICP-MS with the matrix compared to the results without the matrix. On the other hand, the IDA–spICP-MS approach with the matrix can result in equivalent results for the particle sizes compared with
conventional spICP-MS using suspensions without the matrix. Due to the lower instrument sensitivity in the matrix, a diameter of 30 nm was found to be close to the detection limit of the instrument.
A combination of two analytical methods, time-resolved X-ray diffraction (XRD) and Raman spectroscopy, is presented as a novel tool for crystallization studies. An acoustic levitator was employed as sample environment. This setup enables the acquisition of XRD and Raman data in situ simultaneously within a 20 s period and hence permits investigation of polymorphic phase transitions during the crystallization process in different solvents (methanol, ethanol, acetone, dichloromethane, acetonitrile). These real time measurements allow the determination of the phase content from the onset of the first crystalline molecular assemblies to the stable system. To evaluate the capability of this approach, the setup was applied to elucidate the crystallization process of the polymorphic compound nifedipine. The results indicate the existence of solvent-dependent transient phases during the crystallization process. The quality of the data allowed the assignment of the lattice constants of the hitherto unknown crystal structure of the β-polymorph.
Synthetic pressed metal powder standards doped with standard solutions were used for the calibration of both commercially available high resolution GD-MS instruments Element GD and VG 9000 for zinc matrix. Different quantification procedures (IBR, Standard RSF, matrix matched RSF from the calibration with CRMs and use of doped synthetic standards) are compared using zinc matrix as an example, whereas the calibration with doped pellets turned out to be the best quantification technique for high-purity materials. The applicability of the Standard RSF concept is scrutinised. In this context, RSF values for several Matrices (Co, Cu, Fe, In and Zn) are reported additionally.
An immunoassay was developed for ochratoxin A (OTA) detection in wine and two completely different detection methods were compared: ICP-MS and photometry. For labelling, we applied secondary antibodies conjugated with gold nanoparticles for ICP-MS and with horseradish peroxidase for photometric detection, respectively. Detection limits of the assay were determined as 0.003 µg L-1 for both detection methods. OTA in wine was determined below the EU limit value of 2 µg kg-1. The measurement range was between 0.01 and 1 µg L-1 for ICP-MS and photometric detection. Assay precision detected by ICP-MS and photometry were similar showing that precision of the detection method has only a minor effect on total assay precision. By using BSA as a buffer additive to minimize nonspecific binding, we could also confirm that OTA strongly binds to BSA. In a comparison study of several additives, casein was found to be preferable.
Optical elemental analysis in the gas phase typically relies on electrically driven plasmas. As an alternative approach, laser-induced plasmas (LIPs) have been suggested but have so far been only scarcely used.
Here, a novel signal enhancement strategy for laser-based airborne plasma optical Emission spectroscopy for gas phase analytics is presented. In contrast to an electrically driven plasma, in the laser-induced analogue dynamic matter transport equilibrium builds up. The latter results in a rarefied density regime in the plasma core itself, surrounded by an area of compressed matter. The central rarefaction leads to a decrease in plasma intensity and analyte number density, both of which are detrimental for analytical purposes. Since the repetitive ignition of LIPs is a transient process, a restoration of the former gaseous medium by other dynamically equilibrated diffusion processes would be favourable. The presented combination of an airborne LIP and an ultrasonic acoustic resonator yields a fourfold signal enhancement while the Background contribution of ubiquitous air is at the same time effectively suppressed. Since the entire enhancement effect occurs without contact, no additional sources for abrasive sample contamination are introduced.
Considerations with regard to the calculation of key comparison reference values and uncertainties
(2009)
Much has been published over the last years on finding the best (consensus) reference value for a given set of key comparison data, and a suite of approaches proposed. In this paper, several aspects are highlighted which should be taken into account when deciding on key comparison strategies, protocols, and the best approach to reliable key comparison reference value and uncertainty. Some of these aspects are briefly discussed. The paper is intended to intensify discussions, and any comments and opinions are welcome.
Molecular masses and end groups of polystyrene (PS) formed in a novel container-less polymerization strategy, based on levitated droplets in an acoustic trap, were determined by Gel Permeation Chromatography (GPC) and Matrix-assisted Laser Desorption/Ionization Time of Flight Mass spectrometry (MALDI-TOF MS).
The meeting was organised by the European Commission’s Joint Research Centre and held at the JRC-Geel site on 22–23 February 2018. It was a follow-up of a similar meeting held in 2009. The objective of the meeting was to exchange information about ongoing publicly funded reference material (RM) production, identify areas of interest for future specific RMs, including certified reference material (CRM) developments, investigate potential areas of collaboration, and to identify areas which may be of a lower importance in the future for a specific RM producer. The benefit of exchanging such information is to avoid duplication of efforts in RM production, make better use of public funds by potentially matching competencies, and to address problems that are common to publicly funded RM producers.
Statistical ethylene oxide (EO) and propylene oxide (PO) copolymers of different monomer compositions and different average molar masses additionally containing two kinds of end groups (FTD) were investigated by ultra high pressure liquid chromatography under critical conditions (UP-LCCC) combined with electrospray ionization time-of flight mass spectrometry (ESI-TOFMS).
Theoretical predictions of the existence of a critical adsorption point (CPA) for statistical copolymers with a given chemical and sequence distribution1 could be studied and confirmed. A fundamentally new approach to determine these critical conditions in a copolymer, alongside the inevitable chemical composition distribution (CCD), with mass spectrometric detection, is described. The shift of the critical eluent composition with the monomer composition of the polymers was determined. Due to the broad molar mass distribution (MMD) and the presumed existence of different end group functionalities as well as monomer sequence distribution (MSD), Gradient separation only by CCD was not possible. Therefore, isocratic separation conditions at the CPA of definite CCD fractions were developed. Although the various present distributions partly superimposed the separation process, the goal of separation by end group functionality was still achieved on the basis of the additional dimension of ESI-TOF-MS. The existence of HO-H besides the desired allylO-H end group functionalities was confirmed and their amount estimated. Furthermore, indications for a MSD were found by UPLC/MS/MS measurements. This approach offers for the first time the possibility to obtain a fingerprint of a broad distributed statistical copolymer including MMD, FTD, CCD, and MSD.
Research on carbohydrate based interactions with proteins, nucleic acids or antibodies has gained increased interest in the last years especially in clinical diagnosis or drug development. The efficiency of diagnostic interfaces depends upon the number of probe molecules, e.g. carbohydrates. The control of surface parameters as density and distribution of immobilized carbohydrates is essential for a reliable interaction with protein analytes. A controlled production of biomolecular interfaces can be reached by a stepwise quality control during buildup of these biointerfaces.
Here, ß-amino-cyclodextrin molecules were attached to amine-reactive silicon oxide surfaces via click chemistry to construct a model biosensor surface. The amount of surface bound carbohydrates was determined indirectly after chemical derivatization with 4-(trifluoromethyl)-benzylamine (TFMBA). Moreover, these surfaces were used to form host-guest complexes of ferrocene (guest) and β-cyclodextrin (host) moieties to mimic the target binding (sensing) of the model biosensor. Surface chemical analysis of all steps during biosensor construction was performed using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Our approach widens the possibilities to generate switchable surfaces based on ß-Cyclodextrin surfaces for biosensor applications.
Deciphering the sulfate attack of cementitious materials by high-resolution micro-x-ray diffraction
(2011)
The durability of cementitious materials depends, among others, on their resistance against chemical attack during the service life of a building. Here, we present an approach to analyze changes in the phase composition due to chemical attack in the form of sulfate ingress within the microstructure. Micro-X-ray (µX-ray) diffraction using synchrotron radiation in Debye–Scherrer (transmission) geometry allowed a spatial resolution of 10 µm. Phase transformations in the wake of damaging processes were observed in a detailed high-resolution imaging study. In comparison, samples containing supplementary cementitious materials were investigated and used to reconstruct the influence of different degeneration processes in detail. Additionally, reaction fronts within the bulk were localized by micro-X-ray fluorescence analysis. The experimental setup provided the possibility for analyzing the phase assemblage of a given sample without destroying the microstructure. The specimens for phase analysis are thick sections of the primary material and can be used for further microscopic analysis of the microstructure and microchemistry, e.g., scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDX) or Raman spectroscopy.
Size-exclusion chromatography (SEC) was used to monitor changes of the molecular masses of thermoplastic polyether – and polyester urethane (TPU) exposed to thermal, hydrolytic, and photo-oxidative (UV) Degradation conditions for several days. The thermal treatment was performed at elevated temperatures (100–200 °C) under oxidative (air) as well as non-oxidative (nitrogen) conditions to evaluate the specific influence of oxygen on the degradation. At higher temperatures (≥175 °C) a fast decrease of the molecular masses of both PU accompanied by a high degree of crosslinking was found. At lower temperatures (≤150 °C) the polymers remained widely unaffected by thermal degradation within the investigated degradation interval of up to two weeks. Surprisingly, the influence of oxygen (air) was found to be less distinct. In contrast to that, UV treatment at 25 °C at less than 10% rel. humidity (RH) resulted in a fast crosslinking, whereas the molecular masses of both PU decreased slower than for thermal treatments. The depth of penetration of the UV radiation was estimated using 3D printed PU samples with different thicknesses. Hydrolysis based degradation effects were less significant. Only slight molecular mass changes were detected at temperatures ≤80 °C within a time span of 14 days, while no crosslinking could be measured. Considering the degradation results at the investigated exposure parameters, it could be shown that esterbased PU in general exhibits a significant higher stability compared to ether-based materials.
Methods for the determination of boron in various matrices described in the literature usually employ complexing agents like mannitol to retain the volatile boron species during matrix evaporation steps. However, also relatively high boron recoveries from silicon containing samples have been reported when no complexing agents were added to the digestion acids. The mechanism behind this matrix-dependant recovery has been investigated by studying the boron recovery in the analysis of solar grade silicon. It was found that the NH4+ ion formed by the reduction of nitric acid during sample digestion is responsible for the higher recovery of boron, which leads to a possible analysis method without the use of complexing agents if the sample preparation procedure is carefully optimized.
Boron isotope amount ratios n(10B)/n(11B) have been determined by monitoring the absorption spectrum of boron monohydride (BH) in a graphite furnace using high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Bands (0→0) and (1→1) for the electronic transition X1Σ+ → A1Π were evaluated around wavelengths 433.1 nm and 437.1 nm respectively. Clean and free of memory effect molecular spectra of BH were recorded. In order to eliminate the memory effect of boron, a combination of 2% (v/v) hydrogen gas in argon and 1% trifluoromethane in argon, an acid solution of calcium chloride and mannitol as chemical modifiers was used. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1 nm and 437.1 nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, for the evaluated region of 437 nm, an accuracy of 0.15‰ is obtained as the average deviation from the isotope reference materials. Expanded uncertainties with a coverage factor of k = 2 range between 0.15 and 0.44‰. This accuracy and precision are compatible with those obtained by mass spectrometry for boron isotope ratio measurements.