Two methods for the assessment of the oxygen content of small volumes of seawater

Modified micro-Winkler and couloximetric methods are described for the measurement of oxygen in small volumes of water. The former uses a sample size of 1 cm3, while the latter is routinely run with 25-μl samples. Both are accurate, producing results <2% above and 4% below expected values calculated from two previously published sets of tables for the oxygen content of air-saturated seawater. They are also precise assessments, with the se of the micro-Winkler results being 0.23% of the mean of five repeated measurements, while the same figure for the couloximeter is 0.21%. They overcome many of the problems associated with standard methods of measuring oxygen content, such as temperature, salinity and pressure-related effects as well as obviating the need for relatively large quantities of water. Being an essentially inert system the couloximeter may be used for measuring the oxygen content of fluids which pose problems for other methods, such as blood and haemolymph. It is also an absolute method, requiring no calibration. These techniques have been used in the past for measuring oxygen consumption in polar marine invertebrates at temperatures below 0°C and temperate crustacean species