Spectral detection of light transmission through capillaries filled with a fluid sample is a powerful solution for evaluating its composition. In this work, we present an optical method to distinguish water and alcohol samples in a rectangular glass micro-capillary, coupled to an external fluidic path and laid flat onto an aluminum bulk mirror, from the spectral transmittance in the near-infra-red (NIR) wavelength range 1.15-1.65 μm, which becomes sample-specific thanks to the contribution given by the spectral absorption properties of the fluid. The readout beam of broadband radiation is shone on the upper flat side of the micro-capillary with an incidence angle of 14°, crosses the glass walls and the channel depth twice, since it is reflected by the mirror, and it is then coupled to the monochromator input of an optical spectrum analyzer. The theoretical transmission spectra of the capillary filled just with air as well as with distilled water, isopropanol, ethylene glycol, and 95% ethanol (with 5% water content) are derived using analytical equations including the wavelength-dependent attenuation due to fluid absorption. Experimental results relative to the wavelength dependence of the ratio between the spectral transmittance in the presence of the fluid sample and of just air are found to be in agreement with the calculated theoretical behavior. Grapical abstract.

中文翻译：

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基于近红外区吸收特性的用于识别溶剂的微光流体平台。

通过充满流体样品的毛细管的光透射光谱检测是评估其组成的强大解决方案。在这项工作中，我们提出了一种光学方法，用于从矩形的微毛细管中将水和酒精样品与近红外光谱的透射率区分开来，该矩形微毛细管耦合到外部流体路径并平放在铝质体镜上NIR）波长范围1.15-1.65μm，这归因于样品的光谱特性，这归因于流体的光谱吸收特性。宽带辐射的读出光束以14°的入射角照射在微毛细管的上平坦侧，由于它被反射镜反射，两次穿过玻璃壁和通道深度两次，然后耦合到光谱分析仪的单色仪输入。仅使用空气以及蒸馏水，异丙醇，乙二醇和95％的乙醇（含水量5％）填充的毛细管的理论透射光谱是使用分析方程式得出的，其中包括由于流体吸收而引起的波长相关衰减。发现在流体样品存在下和空气中存在的光谱透射率之间的比率与波长相关的实验结果与计算的理论行为一致。语法摘要。发现在流体样品存在下和空气中存在的光谱透射率之间的比率与波长相关的实验结果与计算的理论行为一致。语法摘要。发现在流体样品存在下和空气中存在的光谱透射率之间的比率与波长相关的实验结果与计算的理论行为一致。语法摘要。