Laser-induced atomic fluorescence spectrometry

International Organization for Standardization laser-excited atomic fluorescence spectrometry laser-induced atomic fluorescence spectrometry... 

Principles and Characteristics The analytical capabilities of the conventional fluorescence (CF) technique (c/r. Chp. 1.4.2) are enhanced by the use of lasers as excitation sources. These allow precise activation of fluorophores with finely tuned laser-induced emission. The laser provides a very selective means of populating excited states and the study of the spectra of radiation emitted as these states decay is generally known as laser-induced fluorescence (LIF, either atomic or molecular fluorescence) [105] or laser-excited atomic fluorescence spectrometry (LEAFS). In LIF an absorption spectrum is obtained by measuring the excitation spectrum for creating fluorescing excited state... 

Baiocchi, C., Giacosa, D., Saini, G., and Cavalli, P. (1994). Determination of thallium in Antarctica snow by means of laser induced atomic fluorescence and high resolution inductively coupled plasma mass spectrometry. Int.J. Environ. Anal. Chem. 55(1 //4), 211. 

Laser-induced Atomic and Molecular Fluorescence Spectrometry.343... 

For detection of carbohydrates in principle, ultraviolet (UV), laser-induced fluorescence, refractive index, electrochemical, amperometric, and mass spec-trometric detection can be used. Mass spectrometry, with its various ionization methods, has traditionally been one of the key techniques for the structural determination of proteins and carbohydrates. Fast-atom bombardment (FAB) and electrospray ionization (ESI) are the two on-line ionization methods used for carbohydrate analysis. The ESI principle has truly revolutionized the modern mass spectrometry of biological molecules, due to its high sensitivity and ability to record large-molecule entities within a relatively smaU-mass scale. 

XRD, X-ray diffraction XRF, X-ray fluorescence AAS, atomic absorption spectrometry ICP-AES, inductively coupled plasma-atomic emission spectrometry ICP-MS, Inductively coupled plasma/mass spectroscopy IC, ion chromatography EPMA, electron probe microanalysis SEM, scanning electron microscope ESEM, environmental scanning electron microscope HRTEM, high-resolution transmission electron microscopy LAMMA, laser microprobe mass analysis XPS, X-ray photo-electron spectroscopy RLMP, Raman laser microprobe analysis SHRIMP, sensitive high resolution ion microprobe. PIXE, proton-induced X-ray emission FTIR, Fourier transform infrared. 

In the case of atomic absorption and atomic fluorescence the selectivity is thus already partly realized by the radiation source delivering the primary radiation, which in most cases is a line source (hollow cathode lamp, laser, etc.). Therefore, the spectral bandpass of the monochromator is not as critical as it is in atomic emission work. This is especially true for laser based methods, where in some cases of atomic fluorescence a filter is sufficient, or for laser induced ionization spectrometry where no spectral isolation is required at all. 

A few examples are given in the table below of reactions of PH3 with other atoms or radicals and of ion-molecule reactions, where PHg was not detected but was assumed to have been formed (abbreviations k = rate constant, f = vibrational excitation, MW = microwave, UHF = ul-trahlgh frequency, FP=flash photolysis, LIF=laser-induced fluorescence, MS=mass spectrometry, ICR = ion cyclotron resonance, FA = flowing afterglow). 

In atomic laser spectroscopy, the laser radiation, which is tuned to a strong dipole transition of the atoms under investigation, penetrates the volume of species evaporated from the sample. The presence of analyte atoms can be measmed by means of the specific interaction between atoms and laser photons, such as by absorption techniques (laser atomic absorption spectrometry, LAAS), by fluorescence detection (laser-induced fluorescence spectroscopy, LIFS), or by means of ionization products (electrons or ions) of the selectively excited analyte atoms after an appropriate ionization process (Figures lA and IB). Ionization can be achieved in different ways (1) by interaction with an additional photon of the exciting laser or of a second laser (resonance ionization spectroscopy, RIS, or resonance ionization mass spectrometry, RIMS, respectively, if combined with a mass detection system) (2) by an electric field applied to the atomization volume (field-ionization laser spectroscopy, FILS) or (3) by collisional ionization by surrounding atoms (laser-enhanced ionization spectroscopy, LEIS). 

Atomic emission detector (AED), electrochemical detection (ELCD), electron capture detection (ECD), evaporative light scattering detector (ELSD, including condensation nuclea-tion-CN), fluorescence detector (FLD, including laser-induced fluorescence), inductively coupled plasma-mass spectormetry (ICP-MS), mass spectrometry (MSD), MS/MS, MS(n), thermoionic detector (NPD), spectrometric detection (UV, Vis, DAD) ... 

Wcssman reviewed a number of instruments used for uranium analyses and ranked their relative measurement sensitivities [32]. The methods include atomic absorption spectrophotometry, colorimetry, neutron bombardment, fission etched track detectors, fluorimetry, laser-induced fluorescence spectrometry, a-spectrometry, isotope dilution mass spectrometry, and spark source mass spectrometry. The majority of urinary bioassay measurements have been performed by fluorimetry, while environmental survey and baseline measurements have been performed by fluorimetry, a-spectrometry, and induced coupled plasma source mass spectrometry. 

Every effort is made here to achieve the highest possible absolute power of detection. Microdistribution analysis represents the primary field of application for microprobe techniques based on beams of laser photons, electrons, or ions, including electron microprobe analysis (EPMA), electron energy-loss spectrometry (EELS), particle-induced X-ray spectrometry (PIXE), secondary ion mass spectrometry (SIMS), and laser vaporization (laser ablation). These are exploited in conjunction with optical atomic emission spectrometry and mass spectrometry, as well as various forms of laser spectrometry that are still under development, such as laser atomic ab.sorption spectrometry (LAAS), resonance ionization spectrometry (RIS). resonance ionization mass spectrometry (RIMS), laser-enhanced ionization (LEI) spectrometry, and laser-induced fluorescence (LIF) spectrometry [36]-[44],... 

Preferred methods in trace determination of the elements include atomic absorption spectrometry (AAS), optical emission spectrometry (OES) with any of a wide variety of excitation sources [e.g., sparks, arcs, high-frequency or microwave plasmas (inductively coupled plasma, ICP microwave induced plasma, MIP capacitively coupled micro-wave plasma, CMP), glow discharges (GD). hollow cathodes, or laser vaporization (laser ablation)], as well as mass spectrometry (again in combination with the various excitation sources listed), together with several types of X-ray fluorescence (XRF) analysis [51]. 

AES, atomic emission spectrometry AP(C)I, atmospheric pressure (chemical) ionization CGC, capillary gas chromatography DAD, diode array detection ESI, electrospray ionization FI, fluorescence detection ICP, indcutively coupled plasma LIE, laser-induced fluorescence Nl, negative ion NMR, nuclear magnetic resonance PFPD, pulsed flame photometric detector SRM, selected reaction monitoring. 

In laser vaporisation experiments, generating a plume , the laser s frequency may be synchronised with the resonance line of the element (analyte) to be analysed. The basic principles are (i) absorption of the radiation by the analyte (LAAS laser atomic absorption spectrometry) (ii) fluorescence (LIE, laser-induced fluorescence LEAFS) or (Hi) production of ionisation products (ions and electrons). LIF is an analytical method of high precision that is suitable for the measurement of diatomic species in the plume. Excitation spectroscopy or laser-excited fluorescence is not concerned with the spectral composition of the fluorescence but with how the overall intensity of emission varies with the wavelength of excitation. 

Figure 2 (A) Schematic diagram of longitudinal laser-induced fluorescence with electrothermal atomization. (B) Transverse laser-induced fluorescence. From Ebdon L (1998) Introduction to Analytical Atomic Spectrometry. Reproduced by permission of John Wiley Sons Limited.

The study of bimolecular gas reaction rate coefficients has been one of the primary subjects of kinetics investigations over the last 20 years. Largely as a result of improved reaction systems (static flash photolysis systems, flow reactors, and shock tubes) and sensitive detection methods for atoms and free radicals (atomic and molecular resonance spectrometry, electron paramagnetic resonance and mass spectrometry, laser-induced fluorescence, and laser magnetic resonance), improvements in both the quality and the quantity of kinetic data have been made. Summarizing accounts of our present knowledge of the rate coefficients for reactions important in combustion chemistry are given in Chapters 5 and 6. 

Since the mid-1960s, a variety of analytical chemistry techniques have been used to characterize obsidian sources and artifacts for provenance research (4, 32-36). The most common of these methods include optical emission spectroscopy (OES), atomic absorption spectroscopy (AAS), particle-induced X-ray emission spectroscopy (PIXE), inductively coupled plasma-mass spectrometry (ICP-MS), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray fluorescence spectroscopy (XRF), and neutron activation analysis (NAA). When selecting a method of analysis for obsidian, one must consider accuracy, precision, cost, promptness of results, existence of comparative data, and availability. Most of the above-mentioned techniques are capable of determining a number of elements, but some of the methods are more labor-intensive, more destructive, and less precise than others. The two methods with the longest and most successful histoty of success for obsidian provenance research are XRF and NAA. 

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