Efficient procedure for the measurement of preresonant excitation profiles in UV Raman spectroscopy

Abstract

Resonance Raman spectroscopy (RRS) is a promising technique for investigating samples with low concentrations of single constituents or many different constituents. The wavelength dependent resonance enhancement (resonance profile) of the respective molecule yields information about the targeted species and reveals the optimal wavelength for high resolution RRS. A significant increase of the Raman scattered intensity can already be achieved in the vicinity of the molecules' absorption band (preresonance). Measuring such preresonance and resonance profiles requires precise control of excitation conditions and careful assessment of the spectral accuracy of the setup. We present a comprehensive procedure for the acquisition of preresonance profiles in Raman spectroscopy. An experimental setup for recording the single spectra is combined with an efficient algorithm for data postprocessing. The procedure is demonstrated on amino acids measured in the UV and can be applied to any molecule and wavelength range.

Raman Spectroscopy for Quantitative Analysis in the Pharmaceutical Industry

“…In such cases, the samples must have electronic transitions close to the laser line´s frequency. Thus, the incident radiation frequency coincides with an electronic transition of the molecule, and as a result of this combination, a more intense Raman spectrum is obtained (18,19).…”

“…The diversity of the types of device configurations allows amplifying the sensitivity of the technique and allows a variety of applications, ranging from the quantification of drug substances in tablets and mixtures of powders to multiplex samples (3,(10)(11)(12)(13)(14)(15)(16)(17), samples in low concentrations (18,19), molecular traces (20)(21)(22), samples inside packs (23) and materials in nanometric scale (Table 1) (24,25). Conventional Raman spectroscopy requires high sample concentration and it is affected by fluorescence.…”

Raman Sensing and Its Multimodal Combination with Optoacoustics and OCT for Applications in the Life Sciences

“…We followed this standard approach making use of the atomic emission lines of a neon lamp in [36]. Alternatively, the tunable excitation source can be used for spectral calibration when excitation is provided by the optical parametric oscillator in our experiments [35]. Here, the accuracy of the wavelength selection of the laser system limits the accuracy of the spectral calibration of the spectrograph.…”

“…We developed a procedure to acquire this spectral device response function measuring the intensity, i.e., the peak height, of a single laser pulse of the excitation laser as recorded by the spectrometer and relating it to its pulse energy measured via a power meter. A full spectrum of this relation yields a device response function which can be applied to correct the spectral Raman intensity as measured by the spectrograph [35].…”

“…Raman peaks appear as perpendicular lines. Dark blue regions in the map mark spectral ranges where no Raman signal could be measured due to lack of appropriate filters (reproduced with permission from [35]).…”