Solid sample fluorescence

Dry Oil Oxidation Fluorescence may be measured within or over an oil or within or over an emulsion of lipid in water providing the pH is below 5.5. When plate fluorescence is to be measured, solid sample fluorescence spectrophotometry is necessary (23). A Hitachi Solid Sample Holder Attachment for Model MPF-2A Hitachi-Perkin Elmer Fluorescence Spectrophotometer (Figure 4) was... 

LIF is also used witii liquid and solid samples. For example, LIF is used to detect lJO ions in minerals the uranyl ion is responsible for the bright green fluorescence given off by minerals such as autunite and opal upon exposure to UV light [23],... 

The example of a X emission X-ray fluorescence spectrum of a solid sample of tin, shown in Figure 8.30, shows four prominent transitions. The method of labelling the transitions is, unfortunately, non-systematic but those in the lower-energy group are labelled a and the... 

Thus, the contribution of coherent and non-coherent (Compton) scattering in attenuation of primary radiation and fluorescence increase in comparison with the solid samples. 

Glow discharge is essentially a simple and efficient way to generate atoms. Long known for its ability to convert solid samples into gas-phase atoms, GD techniques provide ground-state atoms for atomic absorption or atomic fluorescence, excited-state atoms for atomic emission, and ionised atoms for MS [158], Commercial instrumentation has been developed for all these methods, except for GD-AFS and pulsed mode GD. 

In a competitive process, the excess energy can be dissipated by emission of a second or Auger electron from an outer shell of the atom, leaving it in a doubly ionised excited state. The relative importance of AES and XRF depends upon the atomic number (Z) of the element involved. High Z values favour fluorescence, whereas low Z favours AES. This fact, taken together with X-ray absorbance in air, makes XRF into a method which is not very sensitive for elements with atomic numbers below Z 10. Measurements of solid samples are normally made under vacuum, as the absorption of air renders analysis of elements lighter than Ti impossible. 

Three analytical techniques which differ in how the primary vacancies are created share the use of such X-rays to identify the elements present. In X-ray fluorescence, the solid sample is irradiated by an X-ray beam (called the primary beam), which interacts with the atoms in the solid to create inner shell vacancies, which then de-excite via the emission of secondary or fluorescent X-rays - hence the name of the technique. The second uses a beam of electrons to create the initial vacancies, giving rise to the family of techniques known collectively as electron microscopy. The third and most recently developed instrumentation uses (usually) a proton beam to cause the initial vacancies, and is known as particle- (or proton-) induced X-ray emission (PIXE). 

X-ray fluorescence spectrometry was the first non-destructive technique for analysing surfaces and produced some remarkable results. The Water Research Association, UK, has been investigating the application of X-ray fluorescence spectroscopy to solid samples. Some advantages of nondestructive methods are no risk of loss of elements during sample handling operations, the absence of contamination from reagents, etc. and the avoidance of capital outlay on expensive instruments and highly trained staff. 

Figure 14 (a) Excitation distribution along the channel axis of a zeolite L crystal consisting of 90 slabs (occupation probability p = 0.3) under the condition of equal excitation probability at f = 0 calculated for front-back trapping. Fluorescence of the donors is taken into account. (1) t = 5 psec, (2) f = 10 psec, (3) t = 50 psec, and (4) t = 100 psec after irradiation, (b) Predicted fluorescence decay of the donors in absence of acceptors (dotted curve), in the presence of acceptors at both ends (solid curve), and fluorescence decay of the acceptors (dashed curve), (c) Measured fluorescence decay of Py -loaded zeolite L (ppy = 0.08) (dotted curve), Py -loaded zeolite L (p y = 0.08) with, on average, one Ox acceptor at both ends of each channel (solid curveX and fluorescence decay of the Ox acceptors (dashed curve), scaled to 1 at the maximum intensity. The experiments were conducted on solid samples of a monolayer of zeolite L crystals with a length of 750 nm on a quartz plate. 

Niobium content in its ores, alloys or compounds may be measured quantitatively by dissolving the solid samples into aqueous phase followed by x-ray fluorescence, colorimetry, or gravimetry measurement. Samples may be dis-... 

Routine inorganic elemental analysis is carried out nowadays mainly by atomic spectrometric techniques based on the measurement of the energy of photons. The most frequently used photons for analytical atomic spectrometry extend from the ultraviolet (UV 190-390 nm) to the visible (Vis 390-750 nm) regions. Here the analyte must be in the form of atoms in the gas phase so that the photons interact easily with valence electrons. It is worth noting that techniques based on the measurement of X-rays emitted after excitation of the sample with X-rays i.e. X-ray fluorescence, XRF) or with energetic electrons (electron-probe X-ray micro-analysis, EPXMA) yield elemental information directly from solid samples, but they will not be explained here instead, they will be briefly treated in Section 1.5. 

In X-ray fluorescence, self-absorption due to optical quenching of the sample is always observed. For solid samples, radiation can be observed only at a depth of a few micrometres. The intensity P of radiation, after travelling a distance dx in a material which a lineic absorption coefficient p (cm ), will decrease by dP for a penetration angle of 90°. The integrated form of the expression dP = —pP dx is comparable to that described in colorimetry ... 

X-ray fluorescence is a rapid and low-cost method that can be performed on solid samples. However, the depth of penetration of X-rays in most solid samples is relatively shallow. High-precision XRF on geological samples such as obsidian requires preparation of homogeneous, powdered samples pressed into pellet form. If some loss of precision and accuracy due to irregular size, shape, and thickness of samples is acceptable, obsidian specimens can be analyzed non-destructively. Samples smaller than 1 cm in diameter or with element concentrations less than 5 ppm are generally not suitable for XRF. XRF can determine about 10-15 elements in obsidian (K, Ti, Mn, Fe, Zn, Ga, Rb, Sr, Y, Zr, Nb, Pb, and Th). Fortunately, many of the measurable elements are the incompatible elements which provide discrimination between sources. 

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