Assessment and Correction of Turbidity Effects on Raman Observations of Chemicals in Aqueous Solutions

Abstract

Improvements in diode laser, fiber optic, and data acquisition technologies are enabling increased use of Raman spectroscopic techniques for both in lab and in situ water analysis. Aqueous media encountered in the natural environment often contain suspended solids that can interfere with spectroscopic measurements, yet removal of these solids, for example, via filtration, can have even greater adverse effects on the extent to which subsequent measurements are representative of actual field conditions. In this context, this study focuses on evaluation of turbidity effects on Raman spectroscopic measurements of two common environmental pollutants in aqueous solution: ammonium nitrate and trichloroethylene. The former is typically encountered in the runoff from agricultural operations and is a strong scatterer that has no significant influence on the Raman spectrum of water. The latter is a commonly encountered pollutant at contaminated sites associated with degreasing and cleaning operations and is a weak scatterer that has a significant influence on the Raman spectrum of water. Raman observations of each compound in aqueous solutions of varying turbidity created by doping samples with silica flour with grain sizes ranging from 1.6 to 5.0 μm were employed to develop relationships between observed Raman signal strength and turbidity level. Shared characteristics of these relationships were then employed to define generalized correction methods for the effect of turbidity on Raman observations of compounds in aqueous solution.

In-line Monitoring of Monomer and Polymer Content During Microgel Synthesis Using Precipitation Polymerization via Raman Spectroscopy and Indirect Hard Modeling

“…According to Sinfield et al. 29 the turbidity can be found in the Raman signal since the reciprocal of the Raman water signal measured at the OH stretching band varies directly with the beam attenuation by turbidity. In this study, the turbidity was computed from Raman measurements by integrating the peak area in the range of 3100–3300 cm –1 .…”

“…To observe the formation of microgel particles during precipitation polymerization, the change in turbidity during reaction was measured using the integrated turbidity sensor in the Mettler-Toledo RC1su Reaction Calorimeter as well as by integration of the Raman water signal. According to Sinfield et al 29 the turbidity can be found in the Raman signal since the reciprocal of the Raman water signal measured at the OH stretching band varies directly with the beam attenuation by turbidity. In this study, the turbidity was computed from Raman measurements by integrating the peak area in the range of 3100-3300 cm -1 .…”

Coupled Turbidity and Spectroscopy Problems: A Simple Algorithm for Volumetric Analysis of Optically Thin or Dilute, In Vitro Bacterial Cultures in Various Media

“…For use with MM cultures and other situations, such an association would be required to implement a BSN training set based on using Raman features as the IE. Relevant results are available in the Supplemental Material for this paper, but we will discuss the effects of turbidity induced spectral distortion [49][50][51] in constructing Raman based BSN training sets in detail in a separate publication. We used 101-7 baselinecorrected raw data for 900-1902 cm À1 to minimize the fluorescence contribution.…”

Characterization of Raman Spectroscopy System Transfer Functions in Intensity, Wavelength, and Time

“…The choice of substrate is significant in that one must be sure the substrate itself does not provide a Raman return intensity on par with that of the desired sample. While analysis of simple solutions is straightforward, analysis of turbid liquids (e.g., biologic fluids and natural water samples) may require use of specialized corrections to enable quantitative evaluation [13]. Raman can also be performed on gases, but detection is often more challenging due to the reduced molecular density of this form of matter.…”