Dear Sherif

you can measure Dissolved Oxygen (DO) by DO meter probe or by winkler method.

Dissolved CO2 Could be measured by Gas Sensing Electrode or Coulometric Titration method according ASTM D513.

dissolved H2S could be measured by Hach's hydrogen sulfide test kits.

Dear Mahdi

Many thanks for your cooperation and helps. I try Do meter for DO measurement but  It give me some error in analysis especially in batch treatment system, may be due to escape of dissolved oxygen during measurement time.   ASTMD513 has many interferences for CO2 measurements by both methods including H2S, Cl, Br, formic and acetic acids that already presents in high concentrations in the produced water.  I hope If there other selective methods for their determinations.

Thanks a lot

These gases might be measured by gas chromatography using proper column and detectors.

Thanks Prof. Cheng

If you can help by determine the GC column and detectors name and methods of analysis. (a research article will help)  

Years ago I have made some modelling work that comprises a discussion on the effect of temperature, atmospheric pressure, and of dissolved salts or organic solutes on the equilibrium dissolved oxygen concentration in aqueous solutions: C. M. G. A. Queirós, “Controlo do Oxigénio Dissolvido em Fermentadores para Minimização de Energia Consumida”, MSc Thesis, Instituto Superior Técnico, Universidade Técnica de Lisboa (Lisbon), 1997, pp. 13-16 (in Portuguese)

Thesis Controlo do Oxigénio Dissolvido em Fermentadores para Minimi...

Spectro photometer may solve your problem .