Ion‐sensitive field effect transistor‐based pH sensors have been shown to perform well in high frequency and long‐term ocean sampling regimes. The Honeywell Durafet is widely used due to its stability, fast response, and characterization over a large range of oceanic conditions. However, potentiometric pH monitoring is inherently complicated by the fact that the sensors require careful calibration. Offsets in calibration coefficients have been observed when comparing laboratory to field‐based calibrations and prior work has led to the recommendation that an in situ calibration be performed based on comparison to discrete samples. Here, we describe our work toward a self‐calibration apparatus integrated into a SeapHOx pH, dissolved oxygen, and CTD sensor package. This Self‐Calibrating SeapHOx is capable of autonomously recording calibration values from a high quality, traceable, primary reference standard: equimolar tris buffer. The Self‐Calibrating SeapHOx's functionality was demonstrated in a 6‐d test in a seawater tank at Scripps Institution of Oceanography (La Jolla, California, U.S.A.) and was successfully deployed for 2 weeks on a shallow, coral reef flat (Lizard Island, Australia). During the latter deployment, the tris‐based self‐calibration using 15 on‐board samples exhibited superior reproducibility to the standard spectrophotometric pH‐based calibration using > 100 discrete samples. Standard deviations of calibration pH using tris ranged from 0.002 to 0.005 whereas they ranged from 0.006 to 0.009 for the standard spectrophotometric pH‐based method; the two independent calibration methods resulted in a mean pH difference of 0.008. We anticipate that the Self‐Calibrating SeapHOx will be capable of autonomously providing climate quality pH data, directly linked to a primary seawater pH standard, and with improvements over standard calibration techniques.

中文翻译：

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离子敏感场效应晶体管pH传感器的自主原位校准

基于离子敏感场效应晶体管的pH传感器在高频和长期海洋采样方案中表现良好。霍尼韦尔·杜拉夫特（Honeywell Durafet）由于其稳定性，快速响应以及在大范围海洋条件下的特性而被广泛使用。但是，由于传感器需要仔细校准，因此电位pH值监测固有地很复杂。在将实验室校准与基于现场的校准进行比较时，已经观察到校准系数的偏移，并且先前的工作导致建议基于与离散样品的比较来执行原位校准。在这里，我们描述了将自校准设备集成到SeapHOx pH，溶解氧和CTD传感器套件中的工作。该自校准SeapHOx能够自动记录来自高质量，可追溯的主要参考标准：等摩尔tris缓冲液的校准值。自校准SeapHOx的功能在美国斯克里普斯海洋研究所（美国加利福尼亚拉霍亚）的海水缸中进行了6天测试，得到了证明，并成功地在浅层珊瑚礁平地（澳大利亚利萨德岛）上部署了2周）。在后者的部署中，使用15个机载样品进行的基于tris的自校准表现出优于使用100多个离散样品的基于标准分光光度法pH校准的重现性。使用tris校准pH的标准偏差范围为0.002至0.005，而对于基于标准分光光度法的pH方法，其标准偏差范围为0.006至0.009。两种独立的校准方法导致平均pH差为0.008。我们预计，自我校准的SeapHOx将能够自主提供气候质量的pH数据，该数据直接与主要海水pH标准相关联，并且将对标准校准技术进行改进。