Transmission spectrometry conventional

Carburization of rhenium filaments has been used to optimize Th and Pa ionization efficiency for TIMS analysis on single filaments (Esat 1995). ReC has a greater work function than Re metal, and elemental oxidation state is maintained in the reduced or metal state by the presence of carbon in the filament. Using this method and a mass spectrometer with improved ion optics, Esat (1995) was able to improve Th transmission and ionization efficiency by about a factor of 30 over conventional methods. Using more conventional mass spectrometry, Murrell et al. (personal communication) were able to improve ionization efficiency for Pa and Th by a factor of 5-10 over conventional graphite sandwich loads on Re filaments (Goldstein et al. 1989 Pickett et al. 1994). For Pa analysis, one drawback is that Pa and U ionization commonly overlap using this... 

Liquids are one of the easiest classes of materials to study quantitatively via single- or multi-reflection ATR because a well-defined contact surface is obtained. The particular advantage of ATR over conventional transmission for the study of liquids is that the requirements on the liquid cell can be relaxed, especially where small thicknesses are required for transmission measurements. Simpson [97] used HATR-FTIR for the multicomponent analysis of formulated oils. Internal reflection spectrometry can also be used to identify solutes in volatile solvents since the solvent can be readily evaporated, leaving the solute as a thin layer on the surface of the IRE. Repetitive analysis of liquid samples is made easy by the wipe on/wipe off sampling afforded by the horizontal ATR accessory. Table 1.14 lists the preferred accessories for various solid sample types. When both single-bounce and multi-bounce are indicated, single-bounce is more suitable for examining the main component multi-bounce qualifies for lower concentration components or weaker spectral features. 

Two types of FT-Raman spectrometer are commercially available. The first is an instrument that can be operated as a conventional FT-NIR spectrometer and modified to measure FT-Raman spectra the second is a dedicated FT-Raman spectrometer. Examples of the two types of instruments are shown in Figures 18.8 and 18.9. Provided that all the considerations discussed above are accounted for properly, acceptable Raman spectra can be measured on both types of instruments. However, since the dedicated instrument has been designed explicitly for Raman spectrometry, the optical efficiency is usually superior. If an instrument is going to be used primarily for Raman spectrometry, we recommend that a dedicated instrument be purchased. If only a few Raman measurements are expected to be needed each week and NIR transmission and refiection measurements are also needed, it may well be financially advisable to purchase the more versatile instrument. 

The use of IR and MR spectrometry for qualitative measurements is extensive and wide ranging, and for this purpose transmission spectra are conventionally recorded as a function of wavenumber. In order to make quantitative measurements, it is necessary to convert the transmittance readings to absorbance. A, the relation between the two being ... 

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