Rapid and precise determination of dissolved oxygen by spectrophotometry: Evaluation of interference from color and turbidity

Several researchers have proposed spectrophotometric modifications of the W inkler titrimetric method for measuring dissolved oxygen (DO). These modifi cations, although simple, are not widely used because of concern about accu racy, calibration, and possible sources of interference. Here we show, usin g natural samples from lakes and rivers as well as samples manipulated in t he laboratory, that the spectrophotometric method can provide accurate and very precise measurements of DO over a wide range of concentrations (4 to s imilar to 13 mg O-2 liter(-1)). Further, interference from dissolved organi c carbon (color) and turbidity are minor. We propose corrections for both c olor and turbidity, where necessary, that can be easily incorporated into t he measurement design. Because of the speed and simplicity of the spectroph otometric method, it is easy to replicate measurements and thereby increase precision without greatly increasing analytical time. In 10 min of effort, we were able to achieve a coefficient of variation (CV) within one bottle of 0.09%, or 0.8% among different bottles. With n = 7 bottles, one can easi ly distinguish changes in DO of 0.05 mg liter(-1) with this method, which m akes it useful for metabolic studies in many environments. To achieve a com parable CV by conventional titration would require about 100 min of effort.