Quantitation fluorescence spectrometry

Chemical analysis of the metal can serve various purposes. For the determination of the metal-alloy composition, a variety of techniques has been used. In the past, wet-chemical analysis was often employed, but the significant size of the sample needed was a primary drawback. Nondestmctive, energy-dispersive x-ray fluorescence spectrometry is often used when no high precision is needed. However, this technique only allows a surface analysis, and significant surface phenomena such as preferential enrichments and depletions, which often occur in objects having a burial history, can cause serious errors. For more precise quantitative analyses samples have to be removed from below the surface to be analyzed by means of atomic absorption (82), spectrographic techniques (78,83), etc. 

For example, X-ray fluorescence spectrometry may provide rapid but rather imprecise quantitative results in a trace element problem. Atomic absorption spectrophotometry, on the other hand, will supply more precise data, but at the expense of more time-consuming chemical manipulations. 

Theory Instruments In energy dispersive x-ray fluorescence spectrometry, a sample is bombarded by x-rays that cause the atoms within the sample to fluoresce (i.e., give off their own characteristic x-rays) and this fluorescence is then measured, identified and quantified. The energy of the x-rays identify the elements present in the sample and, in general, the intensities of the x-ray lines are proportional to the concentration of the elements in the sample, allowing quantitative chemical... 

Atomic Fluorescence Spectrometry. Principles of Quantitative Analysis... 

M. Bos and H. T. Weber, Comparison of the training of neural networks for quantitative X-ray fluorescence spectrometry by a genetic algorithm and backward error propagation. Anal. Chim. Acta, 247(1), 1991, 97-105. 

The Fluorescence Properties of Paper. Luminescence properties provide highly distinctive forensic characteristics, as shown by Jones (8). In a current study in this Institute, the fluorescence properties of several types of paper were determined under excitation with Hg radiation, and this work will be reported in greater detail elsewhere (33). We note here that quantitative fluorescent emission spectrometry is not, per se, sufficient for forensic paper identification almost all papers that show any significant fluorescence emit a similar spectrum due to a... 

Molecular fluorescence spectrometry has long been regarded as a useful technique for the determination of polycyclic aromatic hydrocarbons (PAHs) and related materials, due to the very high sensitivities which can be achieved. However, molecular fluorescence spectra measured in liquid solution usually are broad and relatively featureless hence, spectral interferences are common in the liquid-solution fluorometric analysis of multicomponent samples. Moreover, the fluorescence of a particular component of a complex sample may be partially quenched by other sample constituents if quenching occurs to a significant extent, the fluorescence signal observed for a particular compound present at a particular concentration will also depend upon the identities and concentrations of other substances present in the sample. Under these conditions, it is virtually impossible to obtain accurate quantitative results. Therefore, it is generally observed that molecular fluorescence spectrometry in liquid solution media is useful for quantitative determination of individual components in complex samples only if the fluorescence measurement is preceded by extensive separation steps (ideally to produce individual pure compounds or, at worst, simple two- or three-component mixtures). 

The selection of the method of analysis is a vital step in the solution of an analytical problem. A choice cannot be made until the overall problem is defined, and where possible a decision should be taken by the client and the analyst in consultation. Inevitably, in the method selected, a compromise has to be reached between the sensitivity, precision and accuracy desired of the results and the costs involved. For example. X-ray fluorescence spectrometry may provide rapid but rather imprecise quantitative results in a trace element problem. Atomic absorption spectrophotometry, on the other hand, will supply more precise data, but at the expense of more time consuming chemical manipulations. 

There are many possible permutations for coupling one of the chromatographic or immunoaffinity separations with one or another of the spectrometric detection technologies. HPLC with UV or fluorescence spectrometry/ and HPLC with MS/ are among the most widely used quantitative analytical methods in the pharmaceutical development of new chemical entities because of their general applicability and... 

While luminescence in vapor-deposited matrices accordingly should be a powerful technique for detection and quantitation of subnanogram quantities of PAH in complex samples, it suffers from two major limitations. First, it is obviously limited to the detection of molecules which fluoresce or phosphoresce, and a number of important constituents of liquid fuels (especially nitrogen heterocyclics) luminesce weakly, if at all. Second, the identification of a specific sample constituent by fluorescence (or phosphorescence) spectrometry is strictly an exercise in empirical peak matching of the unknown spectrum against standard fluorescence spectra of pure compounds in a hbrary. It is virtually impossible to assign a structure to an unknown species a priori from its fluorescence spectrum qualitative analysis by fluorometry depends upon the availabihty of a standard spectrum of every possible sample constituent of interest. Inasmuch as this latter condition cannot be satisfied (particularly in view of the paucity of standard samples of many important PAH), it is apparent that fluorescence spectrometry can seldom, if ever, provide a complete characterization of the polycyclic aromatic content of a complex sample. 

The results of quantitative analyses for pyrene and chrysene in the Synthoil and shale oil samples are compared with those obtained for the same samples by MI fluorescence spectrometry in Table I. Several relevant conclusions emerge. First, both oils contain signiflcant concentrations of the highly carcinogenic compound benzo [a] pyrene the shale oil sample contains nearly 2 ppm of this hazardous substance. Second,... 

Fluorescence spectrometry is a powerful analytical tool by virtue of its high sensitivity however, the usual presence of emission and excitation spectral interferences calls for additional sample pretreatments. This technique has been used in combination with SFE mainly in the determination of PAHs, which possess well-known luminescence properties. Screening these compounds from soil entailed the use of a high-pressure flow-cell such as that of Fig. 7.17B and allowed the extraction and determination of five individual PAHs in soil with relative standard deviations less than 5% also, it provided qualitative and semi-quantitative information from the screening of natural soil samples [113]. 

Luster, J., Lloyd, G., Sposito, G., and Fry, 1. V. (1996). Multi-wavelength molecular fluorescence spectrometry for quantitative characterization of copper(n) and aluminum(III) complexation by dissolved organic matter. Environ. Sci. Technol. 30, 1565-1574. 

X-ray spectroscopy, just like many other spectroscopy methods, belongs to the class of relative analysis methods. This means that quantitative evaluation is possible only by comparison of the analysis results with calibration results. The following methods are used for the evaluation of x-ray fluorescence spectrometry ... 

With proper correction for matrix effects. X-ray fluorescence spectrometry is one of the most powerful tools available for the rapid quantitative determination of all but the lightest elements in complex samples. For example. Rose, Bornhorst. and Sivonon have demonstrated that twenty-two elements can bo determined in powdered rock samples with a commercial EDXRF spectrometer in about 2 hours (1 hour instrument time), including grinding and pellet preparation. Relative standard deviations for the method are better than 1% for major elements and better than y/o for trace elements. Accuracy and detection limits as determined by comparison to results from international standard rock samples were comparable or better than other published procedures. For an e.xcellent overview of XRF analysis of geological materials, see the paper by Anzelmo and Lindsay. ... 

Currie, L. A. Detection and Quantitation in X-ray Fluorescence Spectrometry, Chapter 25, X-ray Fluorescence Analysis of Environmental Samples, T. Dzubay, Ed., Ann Arbor Science Publishers, Inc., p. 289-305 (1977). 

Tolin M, Cotiero E, Calliah I. 1991. Quantitative determination of copper and zinc in biological samples (human hair) Comparison between atomic- absorption spectrometry and X-ray fluorescence spectrometry. Ann Chim (Rome) 81 (1-2) 39-49. 

The problems encountered in x-ray fluorescence spectrometry are well suited to the use of digital computers. Many of the quantitative models used to convert measured intensities to concentrations are mathematically complicated and difficult to solve by hand. In energy-dispersive spectrometers peak overlaps often require mathematical fitting techniques to separate the elemental intensities. Digital computers provide the computational power to make these tasks manageable. In many applications the fluorescence spectrometer is required to measure the composition of a large number of specimens of the same type on a repetitive basis. For such applications computer automation provides efficient control of calibration procedures, specimen presentation, and selection of excitation and measurement conditions. 

R. Tertian, Quantitative chemical analysis with x-ray fluorescence spectrometry— an accurate and general mathematical correction method for the interelement effect, Spectrochem. Acta, 24B AA1 (1969). 

One of the very first quantitative applications of x-ray fluorescence spectrometry involved the analysis of copper-based alloys for trace metals. IWenty years later the rapid development in the use of speciality alloys for, among others, the aircraft industry, required the availability of fast, accurate multielement instrumental methods. In the early 1950s two methods seemed to hold promise— x-ray fluorescence and ultraviolet emission (UVE). At that time, x-ray fluorescence was a technique limited to a wavelength range of about 0.5 to 8.0 A, in other words, all elements down to atomic number 14(Si). Even though it was unable to measure the lower atomic numbers, especially the important element carbon, it was able to provide data for S and R This, along with (at that time) a perceived minimum problem of interelement interferences, made x-ray fluorescence an ideal choice for the nonferrous industry. However, the UVE technique was the method of choice for most ferrous industry-based problems. This situation was to persist into the 1960s until the classic work of Shiraiwa and Fujino [14] provided the means for accurate... 

The measurement of low concentrations of compounds by fluorimetry is normally the main purpose of fluorescence labelling of compounds which have no native properties that allow sensitive detection. Where there is fluorescence quenching by known or unknown components of the sample solutions or a lack of specificity of the fluorescence measurements, the application of alternative methods for the determination of fluorescent derivatives may be necessary. In such cases fluorescence may be used to monitor the chromatographic separation even though alternative quantitation methods are applied. Radioactivity measurement and mass spectrometry are frequently used. If a reagent is selected for a certain analytical purpose, besides its reactivity and the fluorescence and chromatographic characteristics of its derivatives, its accessibility to radioactive labelling and its suitability for qualitative and quantitative mass spectrometry should therefore also be considered. 

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