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Novel approach to constructing laser ionization elemental time-of-flight mass spectrometer

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Abstract

The main advantages of laser sampling are associated with following features: sample preparations as well as consumables are not needed, low risk of sample contamination, good spatial resolution. In mass spectrometry, high laser irradiance can be used for both ablation and ionization processes. The method is especially profitable in time-of-flight mass spectrometry. A new principle of constructing laser ionization time-of-flight mass spectrometer based on wedge-shaped ion mirrors and the absence of electrostatic ion acceleration before mass analysis is discussed. Among advantages of the analyzer there are ability to provide temporal focusing of ions in a wide energy range (±20%), compactness of the analyzer, and minimization of the requirements for power supplies. The approach is expected to be profitable for standardless elemental analysis of solid samples, which should be possible at laser irradiation power density more than 3 × 109 W/cm² that ensures complete ionization of all elements in a laser plasma. The analytical signal of each element is formed as the sum of the signals for all charge states and the energy scan of the mass spectra is provided.

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Two methods were used to analyse fly ash for trace elements using laser ablation inductively coupled plasma-mass spectrometry. Individual particles in polished blocks proved difficult to analyse because of the fine grain size of the particles. Identification of particles was one problem and another was loss of sensitivity for key trace elements with a very small diameter (10 μm) laser beam. Analysis using transects covering many particles mounted on slides proved more successful. Statistical analysis of the data using major elements to measure the variation in key components in the ash showed: (1) that the glass is an important location for V, Cr, Cu and Zn; (2) Cr and V are thought to be concentrated in magnetite, although the major source in the ash is the glass; and (3) As, U, Pb, Tl, Mo, Se and probably Ge and Ga to a lesser extent, have a major association with the surfaces of the ash particles.
Article
A laser ionization time-of-flight mass spectrometer with an ion guide collision cell has been developed for the elemental analysis of solids. The system has successfully solved the contradiction between resolution and ions with large kinetic energy generated in the ion source (with 109–1010 W cm−2 laser irradiation flux). It demonstrates near-uniform sensitivity coefficients for different elements. There are very few interferences from the gas species and doubly charged species in the spectra, and their intensities are so low that they can be ignored. With these achievements, semi-quantitative multielemental analysis is possible with no standard required. Furthermore, unlike other laser ablation and ionization mass spectrometry techniques, no mathematical adjustment is needed in this technique. The ratios of the individual elemental signals to the summed signal from all detected elements could be used to produce percent composition values directly.
Book
Laser induced breakdown spectroscopy (LIBS) is basically an emission spectroscopy technique where atoms and ions are primarily formed in their excited states as a result of interaction between a tightly focused laser beam and the material sample. The interaction between matter and high-density photons generates a plasma plume, which evolves with time and may eventually acquire thermodynamic equilibrium. One of the important features of this technique is that it does not require any sample preparation, unlike conventional spectroscopic analytical techniques. Samples in the form of solids, liquids, gels, gases, plasmas and biological materials (like teeth, leaf or blood) can be studied with almost equal ease. LIBS has rapidly developed into a major analytical technology with the capability of detecting all chemical elements in a sample, of real- time response, and of close-contact or stand-off analysis of targets. The present book has been written by active specialists in this field, it includes the basic principles, the latest developments in instrumentation and the applications of LIBS . It will be useful to analytical chemists and spectroscopists as an important source of information and also to graduate students and researchers engaged in the fields of combustion, environmental science, and planetary and space exploration. * Recent research work * Possible future applications * LIBS Principles.
Article
A small high irradiance laser ablation and ionization time-of-flight mass spectrometer with orthogonal sample introduction was described. Nearly uniform relative sensitivity coeffs. as well as satisfactory resolving power (.apprx.2200) were achieved for most of metal elements. Fairly good signal stability was obtained by automated step moving of the sample stage in short time intervals. Interferences of multiply charged ions and polyat. ions were nearly eliminated in the spectrum by utilizing helium as the buffer gas in the ion source, which resulted in a relative clean background. Standardless semi-quant. anal. of steel was realized and the limits of detection are about 10-6 g/g for most of metal elements. [on SciFinder (R)]
Article
The evolution of high-irradiance laser-ionization time-of-flight mass spec-trometry (LI-TOF-MS) mainly progressed following significant improvements in the laser source, the TOF mass analyzer and construction geometries. We summarize the main developments in LI-TOF-MS, including the instrumen-tation and the applications. We also present particular instruments that our group developed recently.
Chapter
A review. Laser ionization mass spectrometry was widely employed for direct solid anal. in the past decades. It uses high laser irradiance focusing onto the sample surface for atomization and ionization. Such direct solid anal. technique requires no or little sample prepn. which can be used for the anal. of almost all types of materials including conductors, insulates, and biol. samples. In this chapter, laser ionization mass spectrometry using different mass analyzers, such as time-of-flight mass spectrometers, quadrupole mass spectrometers, double focusing mass spectrometers, and Fourier Transform mass spectrometers, as well as some new developments about these techniques are described. Representative applications for each technique are generalized. [on SciFinder (R)]
Article
A femtosecond laser system was used in combination with a time-of-flight mass spectrometer (TOF-MS) for in-depth profiling of semiconductor and metal samples. The semiconductor sample was a Co-implanted (10(17) ions/cm3) silicon wafer that had been carefully characterized by other established techniques. The total depth of the shallow implanted layer was 150 nm. As a second sample, a thin film metal standard had been used (NIST 2135c). This standard consisted of a silicon wafer with nine alternating Cr and Ni layers, each having a thickness of 56 and 57 nm, respectively. An orthogonal TOF-MS setup was implemented. This configuration was optimized until a sufficient mass resolution of 300 (m/delta m) and sensitivity was achieved. The experiments revealed that femtosecond-laser ablation TOF-MS is capable of resolving the depth profiles of these demanding samples. The poor precision of the measurements is discussed, and it is shown that this is due to pulse-to-pulse stability of the current laser system. Femtosecond-laser ablation TOF-MS is shown to be a promising technique for rapid in-depth profiling with a good lateral resolution of various multilayer thin film samples.
Article
XRF and TXRF were established as useful techniques for multi-element analysis of whole blood and human head hair samples. Direct-XRF with different collimation units and different X-ray excitation modes was successfully used for the determination of S, P, K, Ca, Fe, and Br elements in blood samples and K, Ca, Mn, Fe elements in human hair samples. Direct analysis by TXRF was used for the determination of Rb and Sr in digested blood and human hair samples, respectively, while, the co-precipitation method using APDC for TXRF analysis was used for the determination of Ni, Cu, Zn, and Pb elements in both matrices. As a result, the improved XRF and TXRF methods were applied for multi-element determination of elements in whole blood and human hair samples in non-occupational exposed population living in Damascus city. The mean concentrations of analyzed elements in both matrices were on the reported range values for non-occupational population in other countries.
Chapter
The paper is related generally to the problematic of environmental analysis. Presented are laboratory results, obtained in the process of adaptation for earth application of a miniature laser time-of-flight analyzer, originally created for the purposes of space research on board of a lander. The earth-based version of the instrument is intended to serve as a core analyzer of a universal and multi-purpose transportable mass spectrometric complex for express environmental analysis. The general conclusions about the environmental applicability of the instrument, which analytical performance is qualitative and semi-quantitative, is that the laser spectrometer is acceptable to perform an express mass analysis of environmental samples.
Article
A novel laser ablation and ionization time-of-flight mass spectrometer has been used for direct elemental analysis of alloys. The system was incorporated with an ion guide cooling cell to reduce the kinetic energy distribution for the purpose of better resolution. Parametric studies have been conducted on the system with respect to the buffer gas pressure and the distance from sample to the nozzle to obtain the maximal signal intensities. In order to obtain satisfactory relative sensitivity coefficients (RSC) for different elements, the influence of the laser irradiance, nozzle voltage, rf frequency and voltage of the hexapole were also investigated. Under the optimized conditions, the RSC of different elements were available for direct semi-quantitative analysis. The mass resolving power (FWHM) of the spectrometer was approximately 7000 (m/Δm) and the limit of detection (LOD) was 10− 6 g/g.
Article
We describe a laser ablation and ionization time-of-flight mass spectrometer with orthogonal sample introduction and axial field rf-only quadrupole cooling device. Experimental results have shown the fairly uniform sensitivities for different metal elements, and a satisfactory resolving power. Little interference is shown in the spectrum. The detection limits are about 10− 7–10− 8 g/g for most of the metal elements.
Article
Laser ablation coupled to inductively coupled plasma mass spectrometry has become a versatile and powerful analytical method for direct solid analysis. The applicability has been demonstrated on a wide variety of samples, where major, minor, and trace element concentrations or isotope ratio determinations have been of interest. The pros and cons of UV-nsec laser ablation have been studied in detail, and indicate that aerosol generation, aerosol transport, and aerosol excitation-ionization within the ICP contribute to fractionation effects, which prevent this method from a more universal application to all matrices and all elements. Recent progresses in IR-fs and UV-fs laser ablation coupled to ICP-MS have been reported, which increase the inter-matrix and multi-element quantification capabilities of this method. These fundamental improvements in LA-ICP-MS are of significant importance for entering new applications in material science and related research fields. In particular, because coatings (conducting and non-conducting) consist of single or multilayers of various elemental composition and of different thickness (nm-mm range), significant progress in the field of depth profiling with fs-laser ablation can be expected. Therefore, in-depth profile analysis of polymers, semiconductors, and metal sample investigations, using ultra-fast laser ablation for sampling and the currently achievable figures of merit, are discussed. In this review manuscript, the enhanced capabilities of fs-LA-ICP-MS for direct solid sampling are highlighted, and it is discussed about current methods used for quantitative analysis and depth profiling, the ablation process of UV-ns and UV-fs, the influence of the laser beam profile, aerosol structure and transport efficiency, as well as the influence of the ICP-MS (e.g., vaporization and ionization efficiency in the plasma, and type of mass analyzer).
Article
A novel method for obtaining elemental, fragmental, and molecular information of organometallic compounds has been developed using high irradiance laser induced time-of-flight mass spectrometry (LI-TOFMS) with a buffer-gas-assisted ion source. This technique permits direct and matrix-free analysis of solid analyte with minimal sample preparation. In addition, it shows special advantages in integrated acquisition of elemental, fragmental, and molecular information from a single target, on the basis of which identification of organometallic complexes is simplified and expedited.
Article
This article reviews the development of and applications for high irradiance laser ionization orthogonal time-of-flight mass spectrometry (LI-O-TOFMS). LI-O-TOFMS has solved the bottleneck problems in traditional high irradiance laser ionization mass spectrometry, which allows the instrument to acquire explicit spectra with high resolution. A buffer-gas-assisted ion source effectively reduces the kinetic energy of the ions and suppresses the multiply charged ion interference. The pulse train data acquisition technique was applied to reduce the spectrum interference from multiply charged ions and polyatomic ions according to the temporal profiles of different ion packets in the repelling region. Relatively high laser irradiance (≥10(10) W/cm(2)) is preferable for achieving uniform relative sensitivities for different elements in the samples of different matrices. LI-O-TOFMS has been used in the standardless, semiquantitative analysis of solids, which is proved to be a fast and convenient technique for solid sample analysis. By increasing the laser irradiance and reducing the buffer gas pressure, the determination of nonmetallic elements in solids can also be achieved without losing spectral explicity. Recent applications, such as elemental analysis of a single egg cell and acquiring elemental, fragmental, and molecular information of chemicals, were given to demonstrate the potential of the new technique. All of these results reveal that LI-O-TOFMS is an advanced tool in the elemental analysis of solids in terms of modern mass spectrometry.