Now I am working on composting experiment based on ISO 14855-1 method to determine the biodegradability of plastics in a simulated composting condition. In the experiment, generated CO2 is absorbed in NaOH solution. According to the ISO methods, either DIC (dissolved inorganic carbon) or titrimetric method is suggested for the calculation of CO2 mass.
However, most previous researches employed the titrimetric method to measure generated CO2 mass instead of DIC measurement. In my impression, DIC measurement seems more precise than the titrimetric method.
Could you share your opinion or knowledge about this issue?
I appreciate your time in advance.
I will agree with your suggestion. Tritiation measures mainly HCO3 in the solution. However DIC will allow you to measure all carbon molecules including dissolved carbon dioxide. Then you can divide the quantities using the Arrhenius plot equation. Please look at this methodology developed by Stuttgart University.
Buchholz, J., M. Graf, B. Blombach, and R. Takors. 2014. Improving the carbon balance of fermentations by total carbon analyses. Biochem. Eng. J. 90:162-169.
Very interesting. I take this opportunity to ask if there is any information for the analysis of DIC and CO2 in liquid samples.
The methodology that I highlighted is an updated version of wet chemistry. It works in any kind of sample preparation where you would like to quantified DIC.
The problem is sample preparation. On ideal solutions, the main problem are CO2 losses during sampling or the quick equilibrium between atmospheric CO2 gas concentrations and the CO2 on the sample. On non-ideal solution, besides sampling losses, the problem is to breakdown the matrix to release CO2, as CO2 holdup might reduce the accuracy of your analysis.
There are direct methods to monitor dissolved CO2 which has been developed. There are indirect methods using ppCO2%, however they only work in ideal solutions (Henry's law). In non-ideal solutions, the methods based on ppCO2% are imprecise due to CO2 holdup and corrections factors based on Raoult's law should be applied.
I will recommend direct methods such as ATR-IR which are more precise if you would like to continuously monitoring dCO2.
The alkali trap with titration is an outrageous anachronism. In practice, any IR CO2 analyzer with multiplexing module (5-10 samples running in parallel) is the best solution to monitor the gaseous CO2 release. If microbial degradation will be accompanied by metabolic alkalization (pH>7), there is a need to use wet chemistry to measure HCO3-. Also, there could be insoluble carbonates in presence of Ca, Mg, Fe... With the solid-state incubation (soil-like texture), I would use the IR only. With the liquid system, especially without stirring - you need to add analyses of soluble and might be insoluble carbonates.
DIC (dissolved inorganic carbon) includes CO2. It is not a method, but a variable that can be measured by different methods.
The titrimetric method allows you to calculate both DIC and CO2.
However, the titrimetric method (which uses an acid) has been criticized recently due to an error that was not known until recently. When titrating the sample, the reaction does not just involve CO2 (or DIC). Part of the organic carbon ends up being degraded in the reaction and accounted as DIC/CO2.
This leads to an overestimation of the result. It does not know how to fix it yet - if it is possible.
Leon Rodrigues there are many negative sides of alkali trap: incomplete binding of CO2, zero levels of CO2 in the headspace inhibiting microbial activity, low precision of titrimetry, clumsy and bulky setup, low throughput, low temporal resolution, impossibly to record time series of CO2 production... I doubt that you can distinguish DIC and CO2 with titration: HCO3 will stay in the main part of the bioreactor rather than transfer to the alkali trap. Chemical decarboxylation of organic C at high pH is also very rare, perhaps only metoxyl groups of some polysaccharides but they are not volatile