Ocean and Earth Sciences, National Oceanography Centre Southampton, University of Southampton, Southampton, SO14 3ZH, UK.
Ocean and Earth Sciences, National Oceanography Centre Southampton, University of Southampton, Southampton, SO14 3ZH, UK; GEOMAR Helmholtz Centre for Ocean Research, 24148 Kiel, Germany.
Anal Chim Acta. 2015 Oct 15;897:69-80. doi: 10.1016/j.aca.2015.09.026. Epub 2015 Sep 25.
The oceans are a major sink for anthropogenic atmospheric carbon dioxide, and the uptake causes changes to the marine carbonate system and has wide ranging effects on flora and fauna. It is crucial to develop analytical systems that allow us to follow the increase in oceanic pCO2 and corresponding reduction in pH. Miniaturised sensor systems using immobilised fluorescence indicator spots are attractive for this purpose because of their simple design and low power requirements. The technology is increasingly used for oceanic dissolved oxygen measurements. We present a detailed method on the use of immobilised fluorescence indicator spots to determine pH in ocean waters across the pH range 7.6-8.2. We characterised temperature (-0.046 pH/°C from 5 to 25 °C) and salinity dependences (-0.01 pH/psu over 5-35), and performed a preliminary investigation into the influence of chlorophyll on the pH measurement. The apparent pKa of the sensor spots was 6.93 at 20 °C. A drift of 0.00014 R (ca. 0.0004 pH, at 25 °C, salinity 35) was observed over a 3 day period in a laboratory based drift experiment. We achieved a precision of 0.0074 pH units, and observed a drift of 0.06 pH units during a test deployment of 5 week duration in the Southern Ocean as an underway surface ocean sensor, which was corrected for using certified reference materials. The temperature and salinity dependences were accounted for with the algorithm, R=0.00034-0.17·pH+0.15·S(2)+0.0067·T-0.0084·S·1.075. This study provides a first step towards a pH optode system suitable for autonomous deployment. The use of a short duration low power illumination (LED current 0.2 mA, 5 μs illumination time) improved the lifetime and precision of the spot. Further improvements to the pH indicator spot operations include regular application of certified reference materials for drift correction and cross-calibration against a spectrophotometric pH system. Desirable future developments should involve novel fluorescence spots with improved response time and apparent pKa values closer to the pH of surface ocean waters.
海洋是人为大气二氧化碳的主要汇，这种吸收会导致海洋碳酸盐系统发生变化，并对动植物产生广泛影响。开发能够跟踪海洋中不断增加的二氧化碳分压和相应降低的 pH 值的分析系统至关重要。使用固定化荧光指示剂点的微型传感器系统因其设计简单、功耗低而具有吸引力。该技术越来越多地用于海洋溶解氧测量。我们介绍了一种详细的方法，用于使用固定化荧光指示剂点来确定 pH 值在 7.6-8.2 范围内的海洋水的 pH 值。我们描述了温度（5-25°C 时为-0.046 pH/°C）和盐度依赖性（5-35 时为-0.01 pH/psu），并初步研究了叶绿素对 pH 值测量的影响。传感器点的表观 pKa 值在 20°C 时为 6.93。在实验室漂移实验中，在 3 天的时间内观察到 0.00014 R（约 0.0004 pH，在 25°C 时，盐度为 35）的漂移。我们达到了 0.0074 pH 单位的精度，并在南大洋进行了为期 5 周的测试部署期间观察到了 0.06 pH 单位的漂移，该漂移通过使用经过认证的参考材料进行了校正。该算法考虑了温度和盐度依赖性，R=0.00034-0.17·pH+0.15·S(2)+0.0067·T-0.0084·S·1.075。本研究为适合自主部署的 pH 光电极系统迈出了第一步。使用短持续时间低功耗照明（LED 电流 0.2 mA，照明时间 5 μs）提高了点的寿命和精度。进一步改进 pH 指示剂点的操作包括定期使用经过认证的参考材料进行漂移校正，并与分光光度 pH 系统进行交叉校准。未来的理想发展应包括具有改进的响应时间和更接近表面海洋水 pH 值的表观 pKa 值的新型荧光点。
