ISO 17289-2014 pdf free.Water quality一Determination of dissolved oxygen一Optical sensor method.
ISO 17289 specifies an optical method for the determination of dissolved oxygen in water using a sensor working on the basis of fluorescence quenching.
Measurement can be made either as a concentration of oxygen in milligrams per litre, percentage saturation (% dissolved oxygen), or both. Depending on the instrument used, detection limits of 0,1 mg/I or 0,2 mg/I can be reached according to the manufacturer’s manual. Most instruments permit measurement of values higher than 100 %, i.e. supersaturation.
NOTE Supersaturation is possible when the partial pressure of oxygen is higher than in air. Especially in case of strong algae growth, supersaturation up to 200 % and more is possible.
If waters with a saturation higher than 100 % are measured, it is essential to make arrangements to prevent the outgassing of oxygen during the handling and measurement of the sample. Similarly, it is important that the transport of oxygen into the sample is prevented if the saturation is below 100%.
The method is suitable for measurements made in the field and for continuous monitoring of dissolved oxygen as well as measurements made in the laboratory. It is one of the preferred methods for highly coloured and turbid waters, and also for analysis of waters not suitable for the Winkler titration method because of iron- and iodine-fixing substances, which can interfere in the iodometric method specified in ISO 5813.
The method is suitable for drinking waters, natural waters, waste waters, and saline waters. If used for saline waters such as sea or estuarine waters, a correction for salinity is essential for concentration measurement of oxygen.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
3 Principle
Optical sensors that measure luminescence/fluorescence lifetime or luminescence/fluorescence phase shift are normally composed of a luminophore or fluorescent dye situated in a sensor cap, a light source [e.g. a light emitting diode (LED)J, and a photodetector. The pulsed or modulated light from the source causes excitation of the luminophore, which is quenched in the presence of oxygen. The photodetector converts the resulting light emission into an electrical signal that can be sampled and processed to compute the phase shift or fluorescence or luminescence lifetime. This phase shift or excitation lifetime is used to quantify dissolved oxygen concentrations.
Temperature has two different influences. The first influence relates to the variation of the quenching process of the membrane with the temperature. So the primary signal of the probe has to be compensated with a built-in temperature sensor. State-of-the-art meters are able to do this automatically. The second influence is given by the sample and the temperature dependence of the solubility of oxygen in it. Also salinity can have a significant effect.
For calculating the percentage of saturation of samples being in contact with an atmosphere, it is necessary to take the atmospheric pressure into account. This can be performed manually or by implementing a pressure sensor for automatic compensation.
Most sensors have a second LED to be used as internal reference for compensation purposes.
4 Interferences
No interferences in waters as described in Clause I.ISO 17289 pdf free download.