High sensitivity liquid phase measurements using broadband cavity enhanced absorption spectroscopy (BBCEAS) featuring a low cost webcam based prism spectrometer

Abstract

Cavity enhanced techniques enable high sensitivity absorption measurements in the liquid phase but are typically more complex, and much more expensive, to perform than conventional absorption methods. The latter attributes have so far prevented a wide spread use of these methods in the analytical sciences. In this study we demonstrate a novel BBCEAS instrument that is sensitive, yet simple and economical to set up and operate. We use a prism spectrometer with a low cost webcam as the detector in conjunction with an optical cavity consisting of two R = 0.99 dielectric mirrors and a white light LED source for illumination. High sensitivity liquid phase measurements were made on samples contained in 1 cm quartz cuvettes placed at normal incidence to the light beam in the optical cavity. The cavity enhancement factor (CEF) with water as the solvent was determined directly by phase shift cavity ring down spectroscopy (PS-CRDS) and also by calibration with Rhodamine 6G solutions. Both methods yielded closely matching CEF values of ~60. The minimum detectable change in absorption (αmin) was determined to be 6.5 × 10(-5) cm(-1) at 527 nm and was limited only by the 8 bit resolution of the particular webcam detector used, thus offering scope for further improvement. The instrument was used to make representative measurements on dye solutions and in the determination of nitrite concentrations in a variation of the widely used Griess Assay. Limits of detection (LOD) were ~850 pM for Rhodamine 6G and 3.7 nM for nitrite, respectively. The sensitivity of the instrument compares favourably with previous cavity based liquid phase studies whilst being achieved at a small fraction of the cost hitherto reported, thus opening the door to widespread use in the community. Further means of improving sensitivity are discussed in the paper.

Cavity-Enhanced Immunoassay Measurements in Microtiter Plates Using BBCEAS

“…Fielder et al [21] made the first demonstration of liquid-phase BBCEAS whilst Seetohul et al [17] reported the first HPLC-BBCEAS measurements. Qu et al [20] made BBCEAS measurements using a simple low cost webcam based spectrometer. The sensitivity of the measurements in the present study compares favorably with all the previous studies showing that similar levels of sensitivity can be achieved in microtiter plates as in cuvettes.…”

Portable, low cost and sensitive cavity enhanced absorption (CEA) detection

“…Qu et al 19 LED Cuvette 527 6.5 × 10 −5 8.5 × 10 −10 9.1 × 10 5 Seetohul et al 13 LED HPLC cell 556 1.9 × 10 −5 2.1 × 10 −9 1.1 × 10 5 Fiedler et al 20 LAMP Cuvette 607 2.0 × 10 −5 --This study LED Cuvette 554 5.1 × 10 −6 7.1 × 10 −11 9.4 × 10 4 studies and will have significantly higher sensitivity than conventional single pass absorbance instruments. We can also envisage further increases in the sensitivity of the CEA spectrometer by improving the approach for mirror alignment e.g.…”

Espectroscopia óptica de baixo custo: uma estratégia para a introdução de conceitos de física quântica no ensino médio

“…[19]. Também é reportada a utilização dos softwares Labview [20], RSpec [3], e MATLAB [21]. Para aquisição de espectros ópticos instantâneos, excelentes para demonstrações rápidas, existe a opção de instalar o software livre Theremino Spectrometer [22].…”