Calcium in sea water

It is now possible to indicate the role of coordination chemistry by means of a single example—the problem of determining calcium in sea water (4, 6). 

Fig. 13.13 Schematic diagram of titration system for high-precision determination of calcium in sea water. (Reproduced from [77] with permission of Taylor Francis Ltd).

One requirement of a messenger in processes such as muscle contraction that require quick response time is that it must be found in low concentrations in the absence of a signal. This requirement is satisfied for calcium. Although the concentration of calcium in sea water, human plasma, and the ER is about 10 mM, the concentration of calcium within the cytoplasm is 0.0001 mM. This difference provides very dramatic changes in the calcium concentration upon leakage of calcium into the cytoplasm from the ER. This gradient, however, requires very efficient ion channels for calcium (discussed in the next section). 

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