Natural Organic Matter (NOM) is measured in drinking water as a predictor of the formation of potentially carcinogenic disinfection by-products (DBPs).
The PeCOD COD analyzer has been shown to be a useful tool in this measurement, but the method has now been refined even further for optimized results in drinking water samples, increased sensitivity and a calculated MDL of just 0.5 mg/L.
This low level of measurement is known as “Blue Range” COD analysis in the PeCOD terminology. Further refinement of the method has increased the sensitivity to offer an Advanced Blue PeCOD method, described below.
Blue Range COD analysis using the PeCOD needs the blank solution, calibration solution and sample to be mixed in a 4:3 ratio (4 parts DI water / Calibrant / Sample to 3 parts Blue Electrolyte solution).
The Advanced Blue method uses a 3:1 ratio to increase the amount of sample present in the sensor, while still maintaining enough electrolyte to sucessfully analyze the sample.
The 3 mixes required are;
- Blank solution; 3 parts DI water, 1 part Blue Electrolyte
- Calibration solution; 3 parts calibrant stock solution, 1 part Blue Electrolyte
- Sample; 3 parts sample, 1 part Blue Electrolyte
Analyser and Software Preparation
To set the PeCOD analyser up for Advanced Blue anyalysis, set the COD range to Blue on the touch screen menu, by going to Setup > Analysis Method > COD Range, selecting Blue and pressing enter to save.
Next, open the Labterm software and refresh the parameter table to make sure that parameter 72 is set to BLUE. You must then change parameter 63 from 1.75 to 1.33 – this setting is the dilution factor which the system applies to results automatically to reflect the electrolyte ratio.
Calibration results for the Advanced Blue method have similar passing criteria to previous methods.
The C value for calibration should be between 50 and 150 µC.
The Iterm should be at least 80% of the baseline (20µA) i.e. 16µA, however for very low COD detection this may need to be above 90% of the baseline, i.e. 18µA.
M Value = 0.02 – 006
C Value = 50 – 150
Iterm > 80% of Baseline
Full explanation of the calibration values is given on technical bulletin 2015-006 – please contact Camlab using the form below to request a copy if required.
Before running the calibration you should ensure that the blank and calibration solutions are mixed in the appropriate ratio. If working with an automated L100 PeCOD analyser, ensure the activate pump steps for Advanced Blue sample analysis are adding 15ml of sample and 5ml of Blue Electrolyte.
Analysis by this method allows chloride of up to 266 mg/L before dilution with Blue Electrolyte. A chloride concentration above this may cause negative bias of the results.
For further information on the PeCOD analyser for faster, safer COD testing of drinking water and other samples, follow the links above or contact us;