Correction of Nonlinear Derivative Diode Laser Data in Standard Addition Analyses

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Abstract
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.