[javert]

Hi everyone.

I work in a analytical laboratory focused on water / wastewater and BOD (Biological Oxygen Demand) is one of our most ubiquitous requests. We always measure COD (Chemical Oxygen Demand) before BOD to perform more appropiate dilutions even if most of our clients are only interested in BOD for regulation purposes. Our COD measurement is the old dichromate / sulfuric acid method with added silver and mercury sulfate. I obviously dislike both the hazards of dealing with those sustances and the amount of hazardous wastes generated by the method, so I'm willing to replace it with something more modern.

I have heard about Total Organic carbon (TOC) before and it seems to be all the hype these days but as we know the technique bypasses the carbon oxidation states completely. I would expect Total Oxygen Demand (TOD) alternatives since it is the mirror of TOC in the sense it also employs combustion and measures the reactant consumed rather than the product formed and I can even imagine one product measuring both employing a single combustion chamber and two different detectors; however, I have drawn a blank while searching on the web or books. AWWA's Standard Methods barely mention TOD and doesn't have a method dedicated to it. ASTM does have one but I can't seem to find ASTM D6238 compliant analyzers. Most of the results are:

• A number of papers or articles claiming TOD is obsolete / disregarded / unreliable without citing any reason or claiming reasons that can be also be entirely argued against dichromate COD ("it also burns sulfur and nitrogen compounds")
• Online TOD analyzers, which seem to be oriented to the process of a single industrial process where the water is likely to have the same matrix all the time. Some of those appear as "Online COD" or "QuickCOD" but upon further inspections are actually TOD!

What I want is a laboratory TOD analyzer which is designed to handle multiple samples of water / wastewater coming from different processes (able to suppress memory effects) and which are either introduced manually to the system or via an autosampler. Both the lack of hazardous reagents and wastes and the shorter time of analysis are highly attractive.

Does any of you uses or have used a laboratory TOD analyzer? Can you give me the model and the brand? Which repeatability and bias can be expected of those apparatus?