We have used dicyandiamide (a well known nitrification inhibitor) in soil and I want to determine the degradation of dicyandiamide with time. An HPLC method is available for its determination, however at present don't have the facility to use HPLC. Could someone please give any other suitable method using equipments like atomic absorption spectrophotometer or UV-visible spectrophotometer.
Looks like a methanol extraction for your soil sample would work. The problem is the spectrophotometer. You will be measuring everything in the sample extract at a specific wavelength (I think 215/220). So the spectrophotometer will pick up anything that absorbs at that wavelength... that's why HPLC is used, to separate interferences away from your target compound. So anything that is extracted out of the soil with methanol and absorbs at 210 will be part of your signal. If you could combine the extraction with anther separation technique like solid phase extraction, (SPE) you will have a much better chance at coming up with a solution. I've attached a link to an article that uses SPE for analysis of DCD.
https://www.sciencedirect.com/science/article/pii/S1001074215002107
You need a separation technique before the assay. Unfortunately all other techniques besides HPLC introduce big variability. Therefore you should assess the percision if it suits your scope.
The method to determine DCD in soil samples using a UV-VIS spectrophotometer has been adopted by many researchers. Some examples are as follows.
Jacinthe, P.A. and Pichtel, 1991. Interaction of nitrapyrin and dicyaniamide with soil humic compounds. Soil Science Society of America Journal, 56(2): 465-470.
Rajbanshi, S.S., Benckiser, G., Ottow, J.C.G., 1992. Effects of concentration, incubation temperature and repeated applications on degradation kinetics of dicyandiamide (DCD) in soils. Biology and Fertility of Soils, 13: 61-64.
Vilsmeier, K., 1979. Kolorimetrische Bestimmung von Dicyandiamid in Boden. Z Pflanenernaehr Bodenkd, 142: 792-798.
Weiske, A., Benckiser, G., Herbert, T., Ottow, J.C.G., 2001. Influence of nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) in comparison to dicyandiamide (DCD) on nitrous oxide emissions, carbon dioxide fluxes and methane oxidation during 3 years of repeated application in field experiments. Biology and Fertility Soils, 34: 109-117.
I recommend you check out the sensitivity and correlation between the adsorption (A) and DCD concentration in your samples at 540 nm first. However, sometimes pretreatment (e.g., pH adjustment) is required for the soil extracts depending on the specific samples. Let me know if you need any references and would like to expand the discussion.
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