Vapor phase measurement fluorescence

Several formal and informal intercomparisons of nitric acid measurement techniques have been carried out (43-46) these intercomparisons involve a multitude of techniques. The in situ measurement of this species has proven difficult because it very rapidly absorbs on any inlet surfaces and because it is involved in reversible solid-vapor equilibria with aerosol nitrate species. These equilibria can be disturbed by the sampling process these disturbances lead to negative or positive errors in the determination of the ambient vapor-phase concentration. The intercomparisons found differences of the order of a factor of 2 generally, and up to at least a factor of 5 at levels below 0.2 ppbv. These studies clearly indicate that the intercompared techniques do not allow the unequivocal determination of nitric acid in the atmosphere. A laser-photolysis, fragment-fluorescence method (47) and an active chemical ionization, mass spectrometric technique (48) were recently reported for this species. These approaches may provide more definite specificity for HN03. Challenges clearly remain in the measurement of this species. 

Chemical Characteristics of the Oxidative Fluorescence-Producing Reaction and Presumptive Implication of Malonaldehyde The reaction producing measurable fluorescence on polyamide powder can be carried out in the gas phase by exposure to the volatiles from oxidizing polyunsaturated lipids, whether acids, esters, triglycerides, or phosphatides. It can be also carried out within either the oil phase or a water emulsion, and, as noted above, it can be followed in the vapor above an emulsion, providing the pH is 5.5 or below. 

Figure 15-27. Normalized fluorescence excitation spectra of ABN, DMABN, and DIABN in a free jet. The excess energies are with respect to their origin bands. Inset plots represent the fluorescence lifetimes (in ns), measured as a function of the S excess vibrational energy. Vapor-phase absorption spectra of ABN and DIABN are also shown (dashed curves). (Reprinted with permission from Ref. [60].)...

The chelates can be purified, and mixtures of the complexes can be separated by fractional sublimation and distillation. In the gas phase, in solution, and in the solid state, Tb(thd)3 emits a brilliant green fluorescence when irradiated at 3660 A. with an ultraviolet lamp. Fluorescence is also exhibited by Eu(thd)3, Dy(thd)3, and Sm(thd)3. The praseodymium complex is thermally stable in the gas phase when heated for prolonged periods of time. Vapor pressure measurements on this complex showed no increase in pressure when the sample was heated at 250° for 6 hours. Thermogravimetric analyses and discussions of trends in volatility of the rare-earth-thd chelates have been published. 

Emission lifetimes for benzene with vapor phase are subject to similar variations with pressure and excitation wavelength as are fluorescence yields. Data are collected in Table 6 and can be seen to show considerable variation with source and experimental technique. Recent measurements, using a single-proton counting technique (114) have shown the emission lifetimes of high pressure CgHg and CgDg to be 77 and 92 ns, respectively, at 25°C. The temperature dependence of the fluorescence lifetime is also shown in Fig. 7. 

Figure 8. Excitation energy dependence of the S, decay rate (reciprocal of the measured fluorescence lifetime) in vapor-phase naphthalenes. Excitation source was a deuterium flash lamp. (From ref. [4] with permission.)...

Frost, M.R., Harrington, W.L., Downey, D.F., Walther, S.R. (1996) Surface metal contamination during ion implantation comparison of measurements by secondary ion mass spectroscopy, total reflection x-ray fluorescence spectrometry, and vapor phase decomposition used in conjunction with graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry. Journal of Vacuum Science Technology B Microelectronics and Nanometer Structures, 14, 329— 335. 

Planar laser-based imaging measurements of fluorescence and particle scattering have been obtained during flame synthesis of the iron-oxide/silica superparamagnetic nanocomposites. The results indicate that the vapor phase FeO concentration is very sensitive to the amount of precursor added, indicating a nucleation controlled growth. The FeO vapor concentration in the main nucleation zone was insensitive to the amount of silicon precursor injected, implying that nucleation of each component occurred independently from the other. 

Visual observation using a microscope is valuable both for monitoring a sample and as an analytical tool. Phases such as liquid, vapor, and solid are clearly identifiable. Even different solid phases usually have distinctive appearances that allow them to be distinguished from each other. In many cases, visual observation is all that is required for determining phase relationships of a chosen system over a range of P and T. Not only can relative sizes of the phases be used to measure their relative abundances, but optical properties such as refractive index can be used as an indication of changes in crystal structure (e.g., quartz) and composition (e.g., albite melt). Visual observation in conjunction with other analytical techniques is important as well. For instance, when fluorescent diamonds are selected for use in studies using an intense X-ray beam, visual observation can provide information about the location of the X-ray beam with respect to the sample. 

The samarium and gadolinium metals were reported to include no more than 0.1 wt% total impurities in either metal, but a detailed chemical analysis was not reported. Alloys were prepared by standard arc-melting techniques, and since samarium has a high vapor pressure, the alloys were analyzed by X-ray fluorescence to assess loss of samarium. Loss of gadolinium was not a problem in the alloy preparation since the vapor pressure of gadoUnium is at least four orders of magnitude less than that of samarium. The phase relations in this system were established by metallography. X-ray diffraction, thermal analysis, density and microhardness measurements and effusion experiments. 

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