Elimination of Mode Hopping and Frequency Hysteresis in Diode Laser Raman Spectroscopy: The Advantages of a Distributed Bragg Reflector Diode Laser for Raman Excitation

The use of normal Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS) of cationic-coated, silver substrates to detect nitrate and sulfate ions in aqueous environments is examined. For normal Raman spectroscopy using near-infrared excitation, a linear concentration response was observed with detection limits of 260 and 440 ppm for nitrate and sulfate, respectively. Detection limits in the low parts-per-million concentration range for these anions are achieved by using cationic-coated, silver SERS substrates. Adsorption of the anions on the cationic-coated SERS substrates is described by a Frumkin isotherm.

Section: Introductionmentioning

confidence: 99%

Detection of Nitrate and Sulfate Anions by Normal Raman Spectroscopy and SERS of Cationic-Coated, Silver Substrates

Mosier‐Boss

Lieberman

2000

“…While diode lasers can be designed to reliably lase in a single mode, the frequency of the mode is dependent on several factors such as the temperature of the device, the power level, and the amount of back-reflection into the laser. 37 The laser used in this study does not exactly reproduce the same laser wavelength in day-to-day operation. Therefore, Raman spectra measured on different days will have an apparent relative shift in the line positions.…”

Section: Methods Developmentmentioning

confidence: 96%

Red-Excitation Dispersive Raman Spectroscopy is a Suitable Technique for Solid-State Analysis of Respirable Pharmaceutical Powders

Vehring

2005

Dispersive Raman spectroscopy with excitation by a red diode laser is suitable for quantitative crystallinity measurements in powders for pulmonary drug delivery. In spray-dried mixtures of salmon calcitonin and mannitol, all three crystalline polymorphs of mannitol and amorphous mannitol were unambiguously identified and their mass fractions were measured with a limit of quantification of about 5%. The instrument design offered high sensitivity and adequate background suppression, resulting in a low limit of detection in the range of 0.01% to 1%. This spectroscopy method has significant advantages over established techniques regarding specificity, sensitivity, and sample requirements.

“…Raman spectra were acquired using an 852 nm DBR GaAs diode laser (Photodigm) run in constant current mode. 12,15 The Raman spectrometer has been described in detail previously. 13,16 The spectrometer has a spectral resolution of 13 cm −1 at full width half maximum.…”

Section: Methodsmentioning

confidence: 99%

Quantitative Raman Spectroscopy when the Signal-to-Noise is Below the Limit of Quantitation due to Fluorescence Interference: Advantages of a Moving Window Sequentially Shifted Excitation Approach

Marshall

Cooper

2016

Self Cite

Raman spectroscopy is a useful analytical tool. However, its application is often limited because shot noise from fluorescence obscures the Raman signal. In such cases, quantitative analysis is not possible when the signal-to-noise ratio (SNR) drops below two. A method is described for performing quantitative Raman spectroscopy that not only removes fluorescence backgrounds, but also results in a significant improvement in the SNR. The Raman data is extracted using a moving window sequentially shifted excitation algorithm. To demonstrate the capabilities of the method, a binary mixture of two analytes at varying concentrations is quantified in the presence of a highly fluorescent dye. Linear calibration plots were constructed and validated for the binary model using individual Raman peaks with SNR ranging from 0.073-12.6; r(2) values are greater than 0.96 in all cases, with all but the weakest peaks yielding values greater than 0.997. The presented method demonstrates a universal and autonomous approach for the quantitative analysis of highly fluorescent samples via Raman spectroscopy. The lower limit on the SNR ratio for quantitative Raman analysis with the described method is 0.1. In order to assess the effectiveness of the presented method, the entire set of experiments was also processed using the more common shifted excitation Raman difference spectroscopy (SERDS) approach. The advantages of the proposed method over SERDS are demonstrated for both the detection limit and the SNR of the processed spectra.