The Micro-estimation of Sodium, Potassium, Calcium, Magnesium, Chloride, and Sul- Phate in Sea Water and the Body Fluids of Marine Animals

INTRODUCTION MUCH progress has been made in the last ten or fifteen years, chiefly by medical biochemists working on problems of clinical interest, in improving the accuracy and sensitivity of the methods employed for the estimation of the principal inorganic constituents of blood and other mammalian body fluids. If, however, attempts are made to apply directly these methods to the micro-analysis of sea water, or of the blood and body fluids of marine invertebrates, they are often unsuccessful. This is only to be expected if one considers that the much higher concentration of salts in these fluids not only brings about a possibility of direct chemical interference, particularly in the form of co-precipitation, but also by decreasing the activity coefficients of their constituent ions may cause a significant increase in the solubility of " insoluble " salts. Furthermore, the higher concentration of all the ions in question means that methods are sometimes available for the analysis of the body fluids of marine animals which are not sufficiently sensitive to be used for mammalian material. Since in many physiological experiments on marine animals, especially those relating to excretion or permeability of the integument, it is necessary to be able to perform accurate analyses both of the body fluids and of the surrounding sea water, the former being often available only in small quantities, we have attempted to devise suitable methods. The aim we set ourselves was to find methods for the estimation of sodium, potassium, calcium, magnesium, chloride and sulphate, which could be performed on 1 ml. samples of sea water or of a body fluid of approximately similar composition, and whose maximum error did not exceed 2 %. In this aim we may claim to have largely succeeded; only in the methods for potassium and sulphate is the accuracy somewhat less than might be wished, but even for these two radicals the number of analyses in which the error exceeds 2 % is small, and may be practically eliminated by performing duplicate determinations