An interlaboratory study as useful tool for proficiency testing of chemical oxygen demand measurements using solid...

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Water Quality Analysis

Background:

• Proficiency testing (PT) is crucial for assessing laboratory performance in environmental analysis.
• The first Chemical Oxygen Demand (COD) Proficiency Testing (ADG) scheme was initiated in 2008.
• Anaerobic digestion research groups often face challenges with accurate COD determination due to diverse methodologies.

Purpose of the Study:

• To evaluate the performance of laboratories involved in anaerobic digestion research through a COD proficiency testing scheme.
• To identify variations in analytical methods and assess the reliability of COD results.
• To emphasize the importance of continuous participation in PT schemes for method validation and result comparison.

Main Methods:

• Four samples (raw materials and high concentration suspended solids) were distributed to participating laboratories.
• Twenty-six laboratories from sixteen countries participated, reporting results via a central coordinator.
• Participants' analytical procedures were classified into open and closed reflux methods, with potassium dichromate as the oxidant.
• Theoretical Oxygen Demand (ThOD) values were used as assigned values due to the unreliability of consensus values.

Main Results:

• A high spread in participants' results indicated significant variability in COD determination.
• Sixty-four percent of the reported z-scores were outside the accepted limits (z-score < or = +/-2).
• Diverse experimental procedures were observed among participants, despite the use of potassium dichromate.

Conclusions:

• Continuous participation in PT schemes is essential for ensuring the comparability and reliability of COD results.
• The lack of standardized methods and certified reference materials hinders the traceability of COD determination.
• The study underscores the need for method harmonization and improved quality control in COD analysis within the anaerobic digestion research community.