Dear Sir. Concerning your issue about the detection of hydrogen sulfide and methane in wastewater by gas chromatography with flame ionization detector (GC-FID) . Sulfur and nitrogen containing malodorous compounds were identified and quantified in the samples taken from each step of sewage treatment employing aerated biofilters for advanced treatment. The sulfur compounds hydrogen sulfide, carbon disulfide, methyl mercaptan, dimethyl sulfide and dimethyl disulfide were detected by using GC-FPD with a headspace method and a modified purge and cold trap method. With a purge and cold trap method and a FPD system, the minimum detectable concentration of dissolved sulfur containing volatiles reached the ng l−1 level. As nitrogen containing compounds, indole, 3-methylindole, trimethylamine, dimethylamine and n-propylamine were present in the same wastewater samples. To determine indole and 3-methylindole, n-hexane extraction method was used, and for identifying and quantifying primary and secondary phase aliphatic amines, derivatization with o-phtalaldehyde (OPA) and N-succinimdyl-p-nitrophenylacetate (SNPA) was applied with HPLC. Trimethylamine was identified by directly injecting the filtered samples into GC-FTD. Detectable concentration of dissolved low aliphatic amines and indoles was about 10 μg l−1. Large amounts of nitrogen containing compounds remained after secondary treatment compared with sulfur containing compounds. I think the following below links may help you in your analysis:

https://www.sciencedirect.com/science/article/pii/004313549400145W

http://www.aga.is/internet.lg.lg.isl/is/images/AGA%20HIQ%20Flame%20Ionization%20Detector%20Datasheet%20UK648_102263.pdf?v=1.0

http://www.aga.is/internet.lg.lg.isl/is/images/AGA%20HIQ%20Flame%20Ionization%20Detector%20Datasheet%20UK648_102263.pdf?v=1.0

Thanks

Dr pal,

i think Dr. Isam Eldin explain everything about your question, I want to modify small things

Gas chromatography or gas liquid chromatography (GLC) can be used to analyse qualitative and quantitative organic compounds after

1. extraction such as liquid liquid extraction or Solid extraction .

2. concentration using rotary evaporator

3. purification such as silika and alumina

4. injection using split split injector, programmed temperature injector, purged pack , Headspace injector for gas samples

5. selecting column (polar, nonpolar and soon)

6. selecting detector

each of these item can be modified or cancelled according to your application.

Flame Ionized detector can burn every thing and analyse it into calculated signals you can create stander curve using height or area ( linear, quadratic, point to point and so on) after selecting the best extraction method and purification method and selecting suitable column.

thanks

Dear Sanjay Pal,

It will be hard to detect H2S using FID. The best detectors are FPD, PFPD or SCD or even AED. You can try to use also ECD - it is possible at ppm level to detect H2S.

You can use FID for methane.

For analysis of wastewater for this compounds a headspace technique will be the best choice. Remember that you need acidify your wastewater sample before thermostating the sample for headspace. THis will increase the concentration in the gas phase, i.e. it will increase the sensitivity of your method.

You can check my publications to understand this protocols:

Article New Procedures for Control of Industrial Effluents Treatment Processes

Article Process Control and Investigation of Oxidation Kinetics of P...

Article Investigation of volatile low molecular weight compounds for...

regards,

G

It's not hard to detect H2S by FID. It's impossible. The FID works by creating positive ions formed when you combust organic compounds (CH+). You do not form positive ions when you combust H2S. You will see the methane with no problem, but certainly not the H2S (except for the quenching effect it has on a flame).

H2S is quite a difficult GC procedure; it sticks to everything and decomposes in your injector port. It takes specially conditioned systems and columns to be able to successfully analyze H2S by GC. Since your question indicates that you have limited experience with this I would highly recommend that you use an alternate method.

It is not that difficult to analyse H2S by GC using standard columns like PLOT column with porapak Q stationary phase. One thing - you need sulfur selective detector as I mentioned before. One of "old" good solution for presence of active places in your system that will affect the H2S i.e. it will adsorb on them is to inject several times H2S high concentration sample. This excess will deactivate all adsorption sites. Do it until you will obtain constant responce for same injection volume for your control sample.

best regards,

G

FID is not the detector for H2S. You can use Flame Photometric Detector (FPD) for H2S. Methane can be detected by FID since it is a hydrocarbon. For the analysis of these compounds in wastewater, you can employ GC with Head Space. You can use a low incubation temperature so that water vapour generation will be low. If the concentrations of these two compounds are extremely low, then a Dynamic mode of Head Space analysis will be very useful.

You need to put 20ml of the wastewater in a 40ml septum vial ( VOA vial ).

Acidify the water to release the H2S ( it's hydrosulfonic acid when dissolved in water ) into the headspace of the vial. Then use a gas tight syringe to inject 1ml into a GC equipped with a FPD detector. Alternatively inject 1-2ul of the water itself into the GC, acidified or not. You can NOT detect H2S at all with an FID detector because the FID only responds to molecules with a C-H bond. There is no carbon in H2S.

I hope this message finds you well. Your inquiry regarding the detection of hydrogen sulfide (H2S) and methane (CH4) in wastewater using gas chromatography with a flame ionization detector (GC-FID) is an important aspect of environmental monitoring and safety management. Below, I outline a comprehensive approach to accurately measure these compounds, ensuring clarity and precision in your analytical procedures.

Introduction

Gas chromatography with a flame ionization detector (GC-FID) is a widely utilized analytical technique for the quantification of volatile and semi-volatile organic compounds. While FID is highly sensitive to hydrocarbons, making it suitable for methane analysis, detecting hydrogen sulfide directly with FID can be challenging due to its non-hydrocarbon nature. However, with proper sample preparation and methodological adjustments, both compounds can be effectively quantified.

Sample Collection and Preparation

GC-FID Analysis

Considerations

• Method Validation: Validate the method by assessing parameters such as linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy, and precision.
• Quality Control: Include quality control samples with each batch of analyses to ensure the ongoing reliability of the data.
• Safety: Handle all chemicals, especially alkylating agents, with appropriate safety precautions to prevent exposure and chemical hazards.

Conclusion

Detecting hydrogen sulfide and methane in wastewater using GC-FID involves careful sample preparation, including the derivatization of H2S, and meticulous optimization of the GC method. By following the outlined approach and adhering to rigorous analytical standards, you can achieve accurate and reliable quantification of these critical environmental pollutants.

Should you require further assistance or clarification on any step of this protocol, please do not hesitate to contact me.

Best regards,

This protocol list might provide further insights to address this issue.