To assess compost CO2, I sealed compost with NAOH solution. So how can I titrate incubated NAOH solution to predict CO2 content? (Titrant, Indicator & Endpoint)
Titrant - 1M hydrochloric acid (HCl)
Indicator - Phenolphthalein indicator solution, c(C20H14O4). Dissolve 1g of phenolphthalein in 100 ml of ethyl or isopropyl alcohol. Add 100 ml water.
End Point - Pink colour just changes to white (colourless in the case of blanks) with one drop of the acid. (it should be stirred vigorously)
http://www.wrap.org.uk/sites/files/wrap/DevLabTestCompostStability.pdf
Sheikh Mohammad Famim Ahmed recommendation is perfect! But adding Barium Chloride to the sample before titration also helps.
All above answers are perfect.The strength of HCl may be selected on the basis of known strength of NaOH solution. At first, standardization of NaOH solution could be done by the above method and a known amount of NaOH should be taken for absorption of CO2. Volume of HCl consumed for that amount of NaOH should be noted as blank in the first titration and after absorption of CO2 , the remaining alkali solution should be measured by second titration with standard acid . In these titrations, phenolpthalien indicator should be used. If acid is taken in burette, phenolpthalien color change will be pink in alkali and colorless at end point.. The difference between the blank value and the final value will be the amount of alkali required for absorption of CO2. Calculate the equivalent amount of CO2 absorbed.
Don't forget that when you enclose the compost to determine CO2 emitted by the compost by titration, that you also enclose air with about 340 ppm CO2, the amount of atmospheric CO2 depending on the volume of your enclosing recipient! Did you correct for the amount of atmospheric CO2 you enclosed with the compost?
Secondly, open flow systems with CO2 scrubbed out from the input (with ,... yes NaOH) and a physically based CO2 sensor like shown in the URL here below continuously monitor the CO2 emission of your compost. Your measurements are hence not limited to one sample! Quite important to get representative samples of your compost CO2 emission.
https://nl.co2meter.com/blogs/nieuws/6010192-how-doet-een-NDIR-co2-sensor-werk
CHeers,
Frank