In coastal waters, temporal and spatial variations of pH are much larger than those in the open ocean. For example, the average range of diel pH variation in Tampa Bay, Florida, can be as great as 0.22 (Yates et al., 2007). In the controlled environments of marine aquaria and especially aquaculture, pH measurement requirements are likewise less stringent than those in open ocean settings. For a saltwater aquarium,

a pH range of 8.1–8.3 is acceptable (Blasiola, 2000). A typical aquaculture pond should have a pH range of 7–8 (Egna and Boyd, 1997). In many operational settings, the use of pH test strips or consumer-level potentiometric probes is common. These methods offer the benefits of low cost and portability but have precisions on the order of 0.1–0.5 pH units. Few options have been available in the intermediate ranges of simplicity, accuracy, and precision.

Recently, TGF-beta inhibitor technological innovations have paved the way for the development of new sensors to fill this intermediate niche at low cost. Light-emitting-diodes (LEDs), widely used in many spectrophotometric devices (Dasgupta et al., 1993, Gaião et al., 2008, Li et al., 2003, Ma et al., 2011, Veras et al., 2009 and Vreman et al., 1998), are inexpensive, power-saving, compact, and sufficiently robust for field use. The combination of LED light sources, integrated optical detection circuits, and simple microcontrollers enables the development of sturdy, easy-to-use photometers that can provide pH field measurements of much higher accuracy and precision than pH electrodes but at roughly the same cost. This paper describes ABT-737 clinical trial the development of a portable microcontrolled LED photometer for spectrophotometric seawater pH measurements using meta-cresol purple (mCP). The instrument components are commercially available and the design is sufficiently simple that

“do-it-yourself” (DIY) construction is possible. A one-time calibration method was also developed to improve the accuracy of the pH measurements. The performance of the photometer was evaluated by comparisons against the performance of a high-accuracy benchtop spectrophotometer in laboratory, shipboard, and aquarium settings. much The indicator mCP was purified from sodium salt (Alfa Aesar, Batch H11N06) according to the procedure of Patsavas et al. (2013). A 10 mmol·L− 1 mCP stock solution in 0.7 mol·kg− 1 NaCl was used for all measurements. The R-ratio of the stock solution was adjusted to 1.6 by an addition of 1 N HCl or 1 N NaOH (Sigma-Aldrich). Tris acidimetric SRM 723e (tris(hydroxymethyl)aminomethane) was obtained from the National Institute of Standards and Technology (NIST) for preparing the tris-buffered synthetic seawater ( Dickson et al., 2007). High-purity salts (NaCl, KCl, and Na2SO4) were obtained from Sigma-Aldrich. The terms on the right side of Eq.