If you know temperature, pressure and pH you can use standard tables for comparison.

These pages will help you:

http://en.wikipedia.org/wiki/Carbon_dioxide_data#Spectral_data

http://en.wikipedia.org/wiki/Carbonic_acid

You need to know ionic strength in addition to pH, P, and T.

thanks for the info, but in my experiment the CO2 in liquid solution is consume to form other chemicals such as methanol and methane.  Initially he solution will be saturated with CO2 by bubbling CO2 for a period of time. from there i can find my initial concentration base on T and pH, so i need to know the rate at which CO2 is converted/consumed.

At constant T, P, and ionic strength, if you know pH you know Pco2. So track the pH change and that will relate to the CO2 consumption. Sometimes it is better to use a pump to add acid, keeping the pH the same and calculate your reaction rate from the amount of acid you add.

The relation of pH and CO2 amount was published. Use the attached figure from my paper: 

26. Al-Rawajfeh, A. E.; Al-Amaireh, M. N.; Influence of CO2 Injection on the Feed Water Chemistry and Scaling in Multiple-Effect Distillers. Desalination & Water Treatment, 7 (2009) 191-197.

An excellent way is to use a sensor. I attach you the link to a report that I did based on acidification of alkaline water using CO2 gas. There you may find more information about the prototype that I built and the measurement of the CO2. There I worked with partial pressure, but the sensor can be programmed to provide directly concentration of CO2 gas in mg/L. Hope it helps!

https://www.google.no/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CB0QFjAA&url=http%3A%2F%2Fwww.vegvesen.no%2FFag%2FPublikasjoner%2FPublikasjoner%2FStatens%2Bvegvesens%2Brapporter%2F_attachment%2F622363%3F_ts%3D145d09f1610%26download%3Dtrue%26fast_title%3DUsing%2BCO2-gas%2Bto%2Blower%2Bthe%2BpH%2Bof%2Btunnelling%2Bwaste%2Bwater%2B%253A%2Blaboratory%2Btest%2Band%2Bassessment%2Bof%2Btoxic%2Bpotential&ei=MZMjVcrqCcKSsAHh1oPgBg&usg=AFQjCNH0WfY99tpSINyGUyqQt3Es9B8gtQ

I guess it depends a lot on your system.

In the absence of paramagnetic compounds 13C-NMR might work (add a standard, increase relaxation time).

Never read about it, but quantitative IR analysis could work as well for CO2 determination.

To calculate the concentration of CO2 in solution would suffice holder with a strong base such as NaOH using an indicator turn in pH above 7, quickly you will know the concentration.

Dear Khozema Ahmed Ali,

Your problem can be solved only by Orsat Apparatus method, that is frequently used in QC labs of chemical industries for the determination of CO2 concentration in the gas stream by absorption method.

the link about the information of Orsat apparatus is given below;

http://en.wikipedia.org/wiki/Orsat_gas_analyser

You must try it.

Best of luck.

Muhammad Imran, Pakistan

You an also check this link for more details

http://www.babcock.com/library/documents/br-1823.pdf

Regards.

Another  simple way  is to use UV-visible spectrometer. You will have absorbance around 300-350nm. very wide peak.

thank you all for all the great inputs

Neutralization titration with standardized sodium carbonate with phenolphathein as indicator will solve your problem.

All the best.

Sorry to be late

Most of all above mentioned methods will not help you except spectroscopy. Because  pH can be changed to acidic by carbonic acid or formic acid that you will have during your experiment.  In this case you will not know which one is dominant. Making pH and other methods useless.

Use FTIR, UV-vis, NMR, HPLC. 

Besides other methods I  suggest using method called "BaCl2"

http://pubs.acs.org/doi/abs/10.1021/ac60281a024

This method is based on the reaction CO2 with solution of BaCl2. The amount of precipitated BaCO3 is determined by back titration with standard solution of HCl and KOH. It's time-consuming method but accurately. I use it for determination of CO2 in amine solutions.

You might take a known excess of sodium hydroxide before and then determine the amount of sodium hydroxide remaining after CO2 absorption titrimetrically.

Recommend Amir Abidov answer

The concentration of CO2 in the liquid phase can be determined by direct titration method using Chittick apparatus. .

Titulação com hidróxido de sódio dá uma boa precisão para a concentração

According to the method proposed by Shailesh Kumar, there is a good description of that method: Article Chemical absorption of CO2 into aqueous piperazine (PZ) solu...

@Amir Abidov Could you explain how C-13 NMR can be used for such quantifications? Can it be used effectively with short relaxation delays?

Thanks in advance.

Khozema Ahmed Ali check our papers on research gate and my thesis on research gate. we usually use Bacl2 method

You can titrate the CO2 trap in a container (20 ml NaOH) retrieved from the field , add 2ml BaCl, 2drops of phenolphthalein indicator, then titrate with 0.1N HCl till the solution changes to colourless. (Adapted from Yetunde Oyeyiola, Ladoke Akintola University of Technology, Ogbomoso, Nigeria)

Calculating the concentration of carbon dioxide (CO2) in solution, particularly in aqueous solutions, involves several steps and considerations. The method chosen depends on the required accuracy, available equipment, and specific context of the experiment or application. Here are some common methods: 1. **Titration Method**: - **Principle**: This method is based on titrating the solution with a known concentration of a strong acid or base and using a pH indicator or pH meter to find the endpoint. - **Procedure**: Typically, the solution is titrated with a standard acid (like HCl) if CO2 is in the form of bicarbonate (HCO3-) or carbonate (CO32-) in solution. The amount of acid needed to reach a specific pH endpoint is used to calculate the CO2 concentration. - **Advantages**: This method is accurate and doesn't require sophisticated equipment. 2. **Gas Sensors or Probes**: - **Principle**: Direct measurement using CO2 gas sensors or probes that can detect CO2 concentration in an aqueous solution. - **Procedure**: Insert the sensor into the solution, and it will provide a reading based on the partial pressure of CO2 in the solution. - **Advantages**: Quick and suitable for continuous monitoring. 3. **Infrared Gas Analyzers**: - **Principle**: These analyzers measure CO2 concentration based on the absorption of infrared light, which correlates with the CO2 concentration in the solution. - **Procedure**: A sample of the gas phase in equilibrium with the solution is analyzed. - **Advantages**: High accuracy and suitable for a wide range of concentrations. 4. **Henry’s Law**: - **Principle**: Henry’s Law states that the concentration of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid. This method is ideal for theoretical calculations or when the system is at equilibrium. - **Procedure**: The CO2 concentration in solution can be calculated if the partial pressure of CO2 above the solution is known, using the formula: \([CO2] = k_H \times P_{CO2}\), where \(k_H\) is Henry’s constant for CO2 at the given temperature, and \(P_{CO2}\) is the partial pressure of CO2. - **Advantages**: Useful for theoretical calculations and understanding the dynamics of CO2 dissolution in solutions. 5. **Considerations**: - **Temperature and Pressure Sensitivity**: CO2 solubility is sensitive to temperature and pressure, so these parameters must be controlled or accounted for in calculations. - **Chemical Equilibrium**: In aqueous solutions, CO2 can exist in different forms (dissolved CO2, bicarbonate, carbonate), and the equilibrium between these forms depends on the pH and temperature of the solution. 6. **Calibration and Validation**: - Ensure that any sensors or analytical methods are properly calibrated and validated against known standards. The choice of method depends on the specifics of the experimental setup, the required precision, and available resources. For laboratory experiments, titration is often preferred for its simplicity and accuracy, whereas sensors and probes are more suited for field measurements and continuous monitoring.

l This list of protocols might help us better address the issue.