I have been trying off and on for a few years to quantitate particulate organic carbon in coastal and urban stream surface water. We routinely measure TOC and DOC (defined in our case as OC < 1 um in size on a syringe filter). Of course one can simply subtract to arrive at the particulate organic carbon (POC), but we have found that oftentimes the result is small enough to be within the uncertainty that arises from the subtraction.
Lately, I have performed some of my own filtrations and then combusted the sample in a Shimadzu SSM5000A. Some issues I have had, however, are (1) I have oftentimes acidified the sample (for preservation) before I filtered it leading to (I believe) an alteration of particle sizes from the pH change and (2) it has been difficult to get glass fiber filters to have low amounts of organic carbon in them so they don't taint the result. I was curious if anyone had any experience in successfully arrived at consistent POC quantification according to what I have described here or perhaps by some other methods.
As you mentioned acidification will most likely alter particle size of POC in your sample. The standard protocols call for sample filtration before acidification if you want to perform other analyses in the same sample (nutrients?). I would recommend you to filtrate the sample as a first step. If you are working with seawater with very low particulate content I would also recommend to filtrate bigger volumes. I work in the Mediterranean and 1-2 liters seem to be enough.
This is the sample preparation I use in routine when analysing POC with an elemental analyser:
- collect POC on a glassfibre filter quickly after collection by filtration. Filter enough volume to have a well colored filter. If low concentrations in the samples, decontaminate glass filters prior to use: heat them at 450°C for 4h.
- Filters can then be dried immediately and kept dried idefinitely. Or they can be frozen, and dried before further analyses
- decarbonate filters in an acid fume chamber. You can use a glass dessicator, where you replace the usual bottom silicagel by fuming HCl 37% - you can then place your filters (in an appropriate device) on the grid on top of the acid, close the chamber and leave it for 8h.
- analyse
-Note: I also add blank decarbonated filters to my standards used for callibration
Why don't you define DOC as the result of an alkalinity titration? Then do your subtraction. That's the standard method, I thought. See if your values of POC=TOC-DOC are more precise this way. (Say hi to Jack for me.)
Of course, I have to identify the dissolved organic carbon in sample by adsorption system at 254 nm by specterophotometer
- Badges
- Science topic
- Similar topics
- Indexes