Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK.
Analyst. 2013 Nov 7;138(21):6372-9. doi: 10.1039/c3an01441j.
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.
腔增强技术可实现液相高灵敏度吸收测量，但与传统吸收方法相比，其通常更复杂且昂贵。到目前为止，这些方法在分析科学中的广泛应用受到了上述缺点的限制。在这项研究中，我们展示了一种新颖的 BBCEAS 仪器，它具有灵敏度高、设置和操作简单且经济的特点。我们使用带有低成本网络摄像头的棱镜光谱仪作为探测器，结合由两个 R = 0.99 介电镜和一个白光 LED 光源组成的光学腔，用于照明。在光学腔内，将放置在与光束成正常入射角度的 1 cm 石英比色皿中的样品用于进行高灵敏度的液相测量。通过相移腔衰荡光谱（PS-CRDS）直接确定以水为溶剂的腔增强因子（CEF），并通过用若丹明 6G 溶液进行校准来确定。这两种方法都得到了约 60 的非常匹配的 CEF 值。在 527nm 处，通过吸收（αmin）的最小可检测变化确定为 6.5×10(-5)cm(-1)，仅受所用特定网络摄像头探测器 8 位分辨率的限制，因此还有进一步改进的空间。该仪器用于对染料溶液进行代表性测量，并在广泛使用的 Griess 测定法的变体中测定亚硝酸盐浓度。Rhodamine 6G 的检测限（LOD）约为 850 pM，亚硝酸盐的检测限（LOD）约为 3.7 nM。该仪器的灵敏度与先前基于腔的液相研究相当，但成本仅为迄今为止报道的一小部分，从而为在该领域的广泛应用开辟了道路。文中讨论了进一步提高灵敏度的方法。
