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Spectrophotometric measurements of pH in-situ: Laboratory and field evaluations of instrumental performance

机译：分光光度法原位测量pH：仪器性能的实验室和现场评估

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Automated in-situ instrumentation has been developed for precise and accurate measurements of a variety of analytes in natural waters. In this work we describe the use of 'SEAS' (spectrophotometric elemental analysis system) instrumentation for measurements of solution pH. SEAS-pH incorporates a CCD-based spectrophotometer, an incandescent light source, and dual pumps for mixing natural water samples with a sulfonephthalein indicator. The SEAS-pH optical cell consists of either a liquid core waveguide (LCW, Teflon AF-2400) or a custom-made PEEK cell. Long optical path lengths allow use of indicators at low concentrations, thereby precluding large indicator-induced pH perturbations. Laboratory experiments show that pH measurements obtained using LCW and PEEK optical cells are indistinguishable from measurements obtained using conventional spectrophotometric cells and high-performance spectrophotometers. Deployments in the Equatorial Pacific and the Gulf of Mexico demonstrate that SEAS-pH instruments are capable of obtaining vertical pH profiles with high spatial resolution. SEAS-pH deployments at a fixed river-site (Hillsborough River, FL) demonstrate the capability of SEAS for observations of diel pH cycles with high temporal resolution. The in-situ precision of SEAS-pH is assessed as 0.0014 pH units, and the system's measurement frequency is approximately 0.5 Hz. This work indicates that in-situ instrumentation can be used to provide accurate, precise, and highly resolved observations of carbon-system transformations in the natural environment.
机译：已经开发了自动原位仪器，用于精确和准确地测量天然水中的各种分析物。在这项工作中，我们描述了使用“ SEAS”（分光光度元素分析系统）仪器来测量溶液的pH值。 SEAS-pH装有基于CCD的分光光度计，白炽灯光源和双泵，用于将天然水样品与磺酞指示剂混合。 SEAS-pH光学电池由液芯波导（LCW，Teflon AF-2400）或定制的PEEK电池组成。较长的光程允许使用低浓度的指示剂，从而排除了指示剂引起的较大pH扰动。实验室实验表明，使用LCW和PEEK光学池获得的pH测量值与使用常规分光光度计池和高性能分光光度计获得的测量值没有区别。在赤道太平洋和墨西哥湾的部署表明，SEAS-pH仪器能够获得具有高空间分辨率的垂直pH分布图。 SEAS-pH在固定河流站点（希尔斯伯勒河，佛罗里达州）的部署证明了SEAS能够以高时间分辨率观察diel pH循环。 SEAS-pH的原位精度评估为0.0014 pH单位，系统的测量频率约为0.5 Hz。这项工作表明，就地仪器可以用来对自然环境中的碳系统转化提供准确，精确和高度解析的观测结果。

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