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Quantitative Raman spectroscopy of highly fluorescent samples using pseudosecond derivatives and multivariate
A O'Grady1, A C Dennis, D Denvir
1Andor Technology Ltd., Belfast, Northern Ireland.
Analytical Chemistry
|May 17, 2001
Summary
A new pseudo-second-derivative (PSD) spectroscopy method effectively suppresses luminescence backgrounds in Raman analysis. This technique offers improved signal-to-noise ratios and robust quantitative results, even with high background interference.
Area of Science:
- Analytical Chemistry
- Spectroscopy
- Chemometrics
Background:
- Intense luminescence backgrounds pose challenges for quantitative Raman spectroscopy and multivariate analysis.
- Standard background suppression methods like second derivatives amplify noise from CCD detectors.
- Existing methods struggle with significant variations in background intensity.
Purpose of the Study:
- To introduce and validate a novel pseudo-second-derivative (PSD) spectral analysis method.
- To demonstrate the superior performance of PSD spectra in quantitative Raman analysis compared to traditional methods.
- To show the applicability of PSD for robust multivariate calibration under high luminescence conditions.
Main Methods:
- Development of a shifted, subtracted Raman (SSR) spectrum by subtracting shifted spectrometer positions.
- Differentiation of SSR data to generate pseudo-second-derivative (PSD) spectra.
- Application of partial least-squares (PLS) calibration to PSD and second-derivative spectra for quantitative analysis of binary mixtures.
Main Results:
- PSD spectra exhibit suppressed backgrounds and significantly higher signal-to-noise (S/N) ratios than standard second derivatives.
- PLS calibration using PSD data achieved a standard error of prediction (SEP) of 3.2% for samples with moderate backgrounds (10x Raman intensity).
- PSD analysis provided a satisfactory SEP of 3.3% even for samples with extreme luminescence backgrounds (100x Raman intensity), outperforming standard second derivatives which failed calibration.
Conclusions:
- The pseudo-second-derivative (PSD) method offers a robust and effective approach for quantitative Raman spectroscopy in the presence of luminescence.
- PSD analysis provides stable and reliable calibrations with improved S/N ratios, suitable for general analytical applications.
- This technique is computationally undemanding, does not require specialized equipment, and handles fluctuating background levels effectively.