Optical detection is an indispensable part of microfluidic systems for nutrient determination in seawater. Coupling total internal reflection capillaries with microfluidic chips is a practical alternative to increase the optical path length for high-sensitivity and a low detection limit in colorimetric assays, which has not been applied in microfluidic devices for seawater nutrients. Here, we present an online microfluidic system which integrated a total internal reflection capillary made of Teflon AF 2400 for the high-sensitivity detection of nitrite and nitrate in seawater. The off-chip capillary lengthens the optical path without changing the internal flow path of the microfluidic chip, enhancing the sensitivity, reducing the detection limit and widening the dynamic range of the system, which significantly improves the performance of the microfluidic system based on wet-chemistry. The detection limit for nitrite is 0.0150 μM using an external 20 cm capillary and 0.0936 μM using an internal 5 cm absorption cell, providing an over 6-fold improvement. Laboratory analysis of surface seawater samples collected from the South China Sea with this system and a one-month online deployment of an autonomous analyzer developed based on this system at a station revealed correlations between the nitrite and nitrate with tide, salinity and chlorophyll over slight variations and narrow ranges, demonstrating the high-sensitivity of this method.

中文翻译：

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基于液体波导毛细管池的高灵敏度片上实验室在线监测海水中亚硝酸盐和硝酸盐分析仪


光学检测是海水营养物测定微流体系统中不可或缺的一部分。将全内反射毛细管与微流控芯片耦合是一种实用的替代方案，可增加比色测定中高灵敏度和低检测限的光路长度，但尚未应用于海水营养物的微流控装置。在此，我们提出了一种在线微流体系统，该系统集成了由 Teflon AF 2400 制成的全内反射毛细管，用于高灵敏度检测海水中的亚硝酸盐和硝酸盐。片外毛细管在不改变微流控芯片内部流路的情况下延长了光路，增强了灵敏度，降低了检测限，拓宽了系统的动态范围，显着提高了基于湿法的微流控系统的性能。化学。使用外部 20 cm 毛细管时亚硝酸盐的检测限为 0.0150 μM，使用内部 5 cm 吸收池时亚硝酸盐的检测限为 0.0936 μM，提高了 6 倍以上。使用该系统对从南海采集的表层海水样本进行实验室分析，并在一个站点在线部署基于该系统开发的自主分析仪一个月，揭示了亚硝酸盐和硝酸盐与潮汐、盐度和叶绿素之间的相关性，且略有变化且范围窄，证明了该方法的高灵敏度。