Correction of Nonlinear Derivative Diode Laser Data in Standard Addition Analyses

Modulation techniques are widely used for derivative presentation of spectral lines for lineshape studies and quantitative analyses. Modulation amplitudes generating the most acceptable signal-to-noise ratios produce distortion in the recorded spectrum and alter the apparent linewidth and absorptivity of the band. Methods of determining modulation-broadened linewidths and absorptivities relative to their molecular values are presented for 2nd-derivative spectra of Doppler limited (Gaussian lineshape) infrared transitions of water vapor. The results are discussed in terms of using the effective absorptivities for correcting derivative data that no longer scale linearly with absorber concentration.

Elimination of Baseline Variations from a Recorded Spectrum by Ultra-Low Frequency Filtering

A technique for the elimination of baseline variation is discussed and illustrated. The method involves ultra-low frequency filtering in the frequency domain (transform space) and is illustrated by applying it to several diode laser spectra of C2H6 (ethane). In the examples presented, the technique eliminates the effects of diode laser output energy variations as a particular mode is scanned. This technique may be especially valuable for diode laser spectroscopy where a multipass cell is used and where the cell cannot readily be removed from the beam to obtain a background scan. The technique should be applicable to baseline variation problems in general.

Quantitative Energy-Dispersive Analysis

INTRODUCTION. Quantitative analysis is possible with an E.D. system, provided its performance is adequate (stability especially). Such a system may be fitted to an electron probe, SEM, TEM, or STEM and used for the analysis of either thick or thin specimens, of which the former are considered primarily here, though in many respects the procedures discussed are equally applicable to thin specimens. Elements in the range Z = 11-30 are primarily of interest (i.e. those with K peaks in the energy range 1-10 keV), though heavy elements with L or M peaks in this energy range can be treated by the methods discussed as well.PEAK IDENTIFICATION. Often the analyst knows the elements present in the specimen. If not,a procedure for identifying peaks in the recorded spectrum is necessary. Various mathematical techniques are available for this purpose (e.g. cross-correlation with a gaussian).