Liquid-phase broadband cavity enhanced absorption spectroscopy (BBCEAS) studies in a 20 cm cell

Abstract

Sensitive liquid-phase measurements have been made in a 20 cm cell using broadband cavity enhanced absorption spectroscopy (BBCEAS). The cavity was formed by two high reflectivity mirrors which were in direct contact with the liquid-phase analytes. Careful choice of solvent was required to minimise the effect of background solvent absorptions. Measurements were made on the broad absorber Sudan black, dissolved in acetonitrile, using a white LED light source and R $ 0.99 cavity mirrors, leading to a cavity enhancement factor (CEF) of 82 at 584 nm. The sensitivity as measured by the minimum detectable change in the absorption coefficient (a min ) was 3.4 Â 10 À7 cm À1 . Further measurements were made on the strong absorber methylene blue dissolved in acetonitrile at 655 nm. A white LED was used with the R $ 0.99 cavity mirrors, leading to a CEF of 78 and a min ¼ 4.4 Â 10 À7 cm À1 . The use of a more intense red LED also allowed measurements with higher reflectivity R $ 0.999 cavity mirrors, leading to a CEF of 429 and a min ¼ 2.8 Â 10 À7 cm À1 . The sensitivity was limited by dark noise from the detector but nevertheless appears to represent the most sensitive liquid-phase absorption measurement to date.

Trace species detection in the near infrared using Fourier transform broadband cavity enhanced absorption spectroscopy: initial studies on potential breath analytes

“…There are clear advantages in having this capability: to measure several compounds simultaneously and to increase the amount of information in a particular measurement, thereby statistically enhancing the output (for example, in measuring several spectral lines to record an isotopic ratio); and to improve specificity, where target species exhibit relatively broad spectral signatures. Several schemes have been reported for BB-CEAS involving different sources and detection apparatus, and including application to the measurement of liquid and/or surface borne species [10,13,14,15,18,19]. On the whole, these studies have been at visible wavelengths, and as broad band optical sources both light emitting diodes and discharge lamps have featured predominantly and have been used with either imaging spectrometers or Fourier transform interferometers as detection systems.…”

Near-infrared broad-band cavity enhanced absorption spectroscopy using a superluminescent light emitting diode

“…Several studies have been reported that combine different broad-band sources such as arc-lamps [1][2][3][4][5][6] and light emitting diodes (LEDs) [7][8][9][10][11][12] with dispersive and interferometric detection schemes to detect gas phase species such as iodine oxides, 5 NO x compounds, 7,8,10,11 and solutions containing dyes (e.g. coumarin 334, brilliant blue-R, and rhodamine B and 6G) 9,12,13 which absorb at visible wavelengths. High power supercontinuum sources have also been demonstrated in cavity enhanced spectroscopy, 14,15 but these are devices that represent a major financial investment, generate a wide spectral output, usually much larger than the stop band of the high reflectivity cavity mirrors, and generally have optimised performance in the visible and near-IR (<1 mm).…”

Cavity-Enhanced Spectroscopy in Condensed Phases: Recent Literature and Remaining Challenges

“…This nonlinear behavior is most obvious under experimental conditions in which the optical absorption loss dominates the total per-pass losses. The nonlinear behavior is shown in Figure 4 from Seetohul et al [21]. This adds additional difficulty to quantitative analysis using CES.…”

“…This results in distortion of absorption spectra compared to the case of a uniform path length. Figure 3 shown below from Seetohul et al [21] illustrates cavity enhancement factor can vary 2 Journal of Spectroscopy 3-fold as a function of wavelength. The absorption spectrum collected by the CES spectrometer is consequently distorted as illustrated in Figure 3(b).…”

“…0.01 per pass. In later work, the authors removed the cuvette windows and increased the path length of the cell to 20 cm, which lowered the detection limit of the system to 3 × 10 −7 cm −1 [21]. One of the unique features of broadband CES is the ability to rapidly collect absorbance spectra across several hundred nanometers.…”