Chemical Oxygen Demand

Skalar's robotic analyzers can be configured to automate COD according to the classical method ISO 6060 or to the small scale sealed tube method ISO 15705 and EPA 410.4.

1. COD according to ISO 6060

Steps of Automation
  • Sample preparation
  • Sample digestion
  • Flushing reflux condensers
  • Sample homogenization
  • Sample titration
  • Burette tip/stirrer between each measuremen
  • Calculation of COD value

COD analysis is commonly used to determine the amount of organic pollutants found in surface water and waste water. The COD value is a useful indicator for measuring the water quality.

All Skalar Robotic Analyzers can provide the automation for COD (according to ISO 6060/ EPA 410.1). This procedure includes a two-hour digestion with sulfuric acid, an oxidizing agent and a catalyst. After refluxing, the samples are cooled and are automatically titrated with iron-ammonium-sulfate to determine the excess of oxidizing agent.

SP5000 Automatic digestion system

altThe system is used for digestion during COD analysis (according to ISO 6060). It consists of a lift system, cooler rack, digestion block, tube rack and a controller with display. The controller sets the temperature and time for the heating and also takes care of all lift movements and the placing of the cooler rack. The samples are boiled for exactly 2 hours under reflux. The process runs completely automatically after the tube rack is loaded by the operator into the system. And after the digestion the tube rack is set ready to be rinsed.


Comparison Skalar COD
Analyzers (ISO 6060)
Sample capacity 40 tubes (2x20) 60 tubes(3x20) 40 tubes (2x20)
Extendable to 120
Probes Up to 2 Up to 5 Up to 5
Sample pipetting station Option Option Option
 Titrator Up to 2 Up to 5 Up to 5
Barcode reader Option Option Option

2. COD according to ISO 15705

Steps of Automation
  • Pipetting of the sample (option)
  • Sample pick up
  • Sample positioning in heating reactor
  • Sample heating for two hours at 150˚C
  • Sample transfer to cool down rack
  • Sample mixing
  • Measurement COD concentration

Typical analysis sequence for the small scale sealed tube method (st-COD), according to ISO 15705 and EPA 410.4, starts with pipetting either manually or automatically (option) the homogeneous sample into the reaction tubes. Tubes are placed in the sample racks and transferred to the analyzer. The analyzer picks-up the tubes, mixes them and automatically positioned them in the reactor where they are heated for two hours at 150 C. The analyzer keeps track of the reaction time. When the reaction is completed the analyzer places the tubes in a sample rack to cool down to 60 C, after which they are mixed whilst still being altwarm. When the samples are cooled down to ambient temperature they will be measured with a photometric detector at the required wavelength. The concentration is shown in the result screen of the software and the data can be transported to the LIMS system.

The analyzers can be used with commercial available or self-made COD reaction tubes and is compatible with several photometers. Skalar's SP10COD Robotic Analyzer (or for more capacity the SP50/SP1000) has been designed for the cost-effective automation of st-COD analysis


Comparison Skalar COD
Analyzers (ISO 15705)
Sample capacity 96 COD tubes 160 COD tubes 224 COD tubes
Barcode reader Yes Yes Yes



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