Reflection-Mode Data

The HPLC was interfaced to a Q-TOF Premier (Waters, Beverly, MA) mass spectrometer. The instrument was operated at 3.0 kV capillary voltage, 100°C source temperature, 150 °C desolvation temperature, desolvation gas 600 L/h, and scanning from 550 to 2000 Da in 1.0 s in single reflection mode. Data were collected using MassLynx software version 4.1 (Waters, Beverly, MA). 

Fig. 13.7 XRDI image around the region of a supporting pin for thermal treatment. 115 reflection in reflection mode. Data courtesy of Dr. Frans Voogt, Philips Semiconductor, Netherlands.

The interpretation of reflection mode data is a bit less straightforward than the transmission mode SPELs above, since one has to contend with slight differences... 

Unless the coverage of adsorbate is monitored simultaneously using spectroscopic methods with the electrochemical kinetics, the results will always be subject to uncertainties of interpretation. A second difficulty is that oxidation of methanol generates not just C02 but small quantities of other products. The measured current will show contributions from all these reactions but they are likely to go by different pathways and the primary interest is that pathway that leads only to C02. These difficulties were addressed in a recent paper by Christensen and co-workers (1993) who used in situ FT1R both to monitor CO coverage and simultaneously to measure the rate of C02 formation. Within the reflection mode of the IR technique used in this paper this is not a straightforward undertaking and the effects of diffusion had to be taken into account in order to help quantify the data obtained. 

FIGURE 7.1 NIR spectra from different fermentations of rye with yeast. The seven spectra have been measured in reflection mode in opaque mashes. Wavelength interval is 1100-2300 nm the number of data points is 241. The samples differ in the ethanol contents (62.2-84.1 g/L). 

Paddison et al. performed high frequency (4 dielectric relaxation studies, in the Gig ertz range, of hydrated Nafion 117 for the purpose of understanding fundamental mechanisms, for example, water molecule rotation and other possible processes that are involved in charge transport. Pure, bulk, liquid water is known to exhibit a distinct dielectric relaxation in the range 10—100 GHz in the form of an e" versus /peak and a sharp drop in the real part of the dielectric permittivity at high / A network analyzer was used for data acquisition, and measurements were taken in reflection mode. 

Despite resonant excitation conditions (Egmp(InN) 1.9 eV) the Raman spectrum of InN strongly resembles that of GaN although shifted to softer modes. Note, however, that the sequence of E2(LO) and Ai(LO) appears to be inverted compared to GaN. The Ei symmetry assignment of the reflection modes [1] was performed in [7] and by the present authors after a re-evaluation of the data. In addition, the large value of 694 cm 1 indicates an E1(LO)-plasmon coupled mode. It may be assumed that phonon frequencies in heteroepitaxial InN are subject to stress conditions in a similar way to that in heteroepitaxial GaN. 

The auto mode of analysis of the experimental J(t) versus t data provided magnitudes of model parameters that followed the experimental data better than those obtained in the manual mode of data analysis. The latter were very sensitive to estimates of instantaneous modulus and, in some instances, there were considerable differences between experimental data and model predictions (not shown here). Therefore, the results of auto mode data analysis are presented in Table 5-E the standard deviations of the parameters are also in Table 5-E in parentheses. The standard deviation of J was higher than those of the other parameters reflecting greater uncertainty in its estimation. 

While thin sections are often easier to prepare on IR-reflective substrates, the use of IR-reflective substrates does come at a cost to the IR data collection process, and even spectral quality. As noted above, the incident flux in reflection mode is reduced by almost 50% compared to transmission mode, as only half of the focusing objective is used to direct the beam onto the sample, while the second half is used for collecting the reflected beam. In addition, any inhomogeneities in the thin section can cause interference effects (e.g., oscillations) in the background of the IR spectra. These artifacts can alter peak shapes, intensities and frequencies. Thus, care must be taken with sample preparation, and only certain (generally homogeneous) samples can be investigated well in this mode. 

A series of foreign particulates was found in several bulk lots and final product lots (tablets) of a developmental drug. Black, red, and brown particles were isolated from the bulk drug material, whereas black particles were observed embedded into the tablets. Only the black particles will be focused upon in this discussion. Since the foreign materials were opaque, IR microspectroscopy data were obtained in the reflectance mode. Figure 7A displays the relatively simple IR spectrum of the isolated black particle. No absorption bands corresponding... 

---