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

Abstract

Several researchers have proposed spectrophotometric modifications of the Winkler titrimetric method for measuring dissolved oxygen (DO). These modifications, although simple, are not widely used because of concern about accuracy, calibration, and possible sources of interference. Here we show, using natural samples from lakes and rivers as well as samples manipulated in the laboratory, that the spectrophotometric method can provide accurate and very precise measurements of DO over a wide range of concentrations (4 to ∼13 mg O2 liter−1). Further, interference from dissolved organic carbon (color) and turbidity are minor. We propose corrections for both color and turbidity, where necessary, that can be easily incorporated into the measurement design. Because of the speed and simplicity of the spectrophotometric 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 easily distinguish changes in DO of 0.05 mg liter−1 with this method, which makes it useful for metabolic studies in many environments. To achieve a comparable CV by conventional titration would require about 100 min of effort.

High‐frequency measurements of productivity of planktonic algae using rugged nondispersive infrared carbon dioxide probes

“…Collos et al (1993) point out that in certain particular circumstances-e.g., when growth is vigorous-the upper time limit for the useful in situ incubation is only 3 h, which is short in comparison to the 24 h incubation of the monitoring program in Lake Valkea-Kotinen. The precision and accuracy of the oxygen method have been improved through developments in measuring techniques, but their widespread use is still limited (Roland et al 1999;del Giorgio and Bouvier 2002). Using radioisotopes, the sensitivity of primary productivity measurements can be greatly enhanced making the approach applicable also in lakes with low productivity but the problem of gross/net production still remains (c.f.…”

Regulation of bacterial growth efficiency in a large turbid estuary

“…The time-zero control samples were fixed immediately with Winkler reagents. Another set of 5 bottles was incubated in the dark at in situ temperature for 24 h. Dissolved oxygen was determined by a spec- (Reynolds 1972, Duval et al 1974, Ashton & Twinch 1985, Roland et al 1999. The dissolved oxygen consumption (mg DO 1-' h-') between the 2 measurements was converted to carbon respired (pg C l-' h-') assurning a respiratory quotient (RQ) of 1.…”

Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism

“…Changes in dissolved oxygen (DO) concentrations were measured and used to calculate the metabolism of the P. oceanica community along the imposed shading gradient. DO concentrations were determined spectrophotometrically using a modification of the Winkler titration method (Pai et al 1993, Roland et al 1999). Absorbance at 430 nm (Abs430) of the Winkler-fixed samples was measured with a Genesys 5 spectrophotometer and converted to DO concentration using a calibration linear regression: DO (mg l −1 ) = (6.7 × Abs430) + 0.0217; r 2 = 0.99).…”