No idea why you have the problem you report. But for P measurements the Dr Lange kits are popular and acceptably accurate.

Hi Sooi,

I agree with Jeremy. Additional here is a second alternative to the Dr. Lange kits:

https://www.hach.com/phosphate-test-kit-total-ortho-meta-model-po-24/product?id=7640214961

Regards

Markus

Dear Vinck

You follow APHA method for analysis for Ortho and Total phosphate& you may find out attached method

Regards

Rameswar Gouda

If you have access to it ICP-OES is a very easy way to analyze for total P. For your Ion Chromatography issues, the pH of your sample may be to blame. Samples with very low or very high pH can have an effect on your retention times.

There may be no problem with your method at all. Sample handling is probably the biggest source of error in this type of work. You mentioned that the results change the most when you let time elapse. First chemical addition effects are often hard to fully measure because rates slow as concentrations slow. So that , even though an effluent is discharged it does not mean that reactions have stopped. By taking a sample and letting it set you are in comparison to the industrial process adding more retention time, but the effluent going out of the plant is not getting the benefit of this retention. Secondly, even though solids are small and not apparent settling occurs over time so that what you think is a representative sample (through put to the analytical equipmnet) is not. This is an especially important factor as solids content increases and is the source of very large errors throughout the waste treatment field when measuring influent as opposed to effluent. As an example my research shows that for normal municipal influents for many pollutants an error of as much as 20% occurs after only 2 or 3 seconds of not shaking a sample when splitting samples. My recommendation is to try to mimic the time as close to the actual conditions of the treatment system to capture what is going out in the discharge then follow this religously. Second examine your method to make sure after taking the sample at every step to make sure what enters your equipment is representative of the entire sample.

if you need a quick data, you can use sensor (HACH in-site measurement). But its accuracy was with the high photphat concentration (P > 5mg/L). For a low concentration, lab analysis was better. You can use standard menthod for waster and waterwater to know how analysis method was.

The method is clearly specified in APHA's (American Public Health Association) 'Standard Methods for Water and Wastewater'. In general it is a Molybdenum Blue spectrophotometric method. The regulatory authorities set the permissible limit.