You should use sorption tubes with Tenax followed by thermal desorption. For static conditions you can also think about SPME. Remember to check during the method development if no artifacts are formed. Second thing- recovery, they like to adsorb on active sites on the system.

Regards

G

Hi Yaroslav,

take a look here:

https://www.sciencedirect.com/science/article/pii/S0021967301934685

https://www.sciencedirect.com/science/article/pii/S0045653502008214

Article Problems with the determination of environmental sulphur com...

Article Analysis of volatile sulphur compounds in breath by gas chro...

Article Determination of methanethiol at parts-per-million air conce...

https://www.sciencedirect.com/science/article/pii/S0039914011010204

Regards Markus

Thank you, Markus!

Thank you, Grzegorz Boczkaj !!

Could you recomend any recovery protocol. Could colunm oven 200C within 4 h be enough at He flow rate 1 -2 ml/min be enough? Please, give me oppinion if injections of a solvent (MeOH) or hydrogen gas can bring an additional pluses for the regeneration?

Hi Yaroslav,

First a few questions:

- What concentration do you expect?

- During what time do you want to sample, like 5-20 minutes or hours?

- How many liters do you think you have to sample to meet the requested detection limit?

- What kind of equipment do you have, can you analyse TD-tubes and canisters?

- Anything else we should know about the goals of your project?

On Tenax you can probably only sample a few hundred ml before methylthiol will break through, a bit more for dimethylsulfide. Ask your desorption tubes supplier for advice on what adsorbent is best for analysis of sulphur containing compounds. Test the breakthrough volume. Make sure your the metal part of the tube is silco treated, thiols will stick to untreated metal parts.

Be aware that adsorbent that have a high breakthrough volume for very volatile compounds will also retain water so it is best of the humidity of your sample is low. A high humidity could give problems when flash heating the coldtrap.

I would go for silco treated canister and use a specific sulphur detector and not a MS.

Regards,

Alex

Hi, Alex,

Thank you for the detailed questions (it always helps) and the description of some critical points

- I expect approx. 0.5-0.01 mg/m3 concentrations range for the analytes.

- I have no specific sampling time or volume limitations. I found 15 L special canisters and the volume for a point might be the limit if no a pre-concentration procedure possible on the sampling place. According time I hope 4 h max/a point will be enough.

- At the time I have no thermodesorber or special canisters-compatible line system with cryoconcentration function or smth like this.

And the goal of my project is to up-grade common GC-MS device to solve the tasks described.

E.g. in the work E. Borrás et al. / Talanta 148 (2016) 472–477 the authors described “in field” sampling stage like a SPE procedure using a charcoal-based cartridges 1m height (!?), low-volume pump working at 1 L min, 4 h collection time (~ 0.24 m3). The cartridges then were eluted with 2 ml (!?) eluent , 1 mkl was injected.

The scheme seems quite good for me, but I think about some optimizations like how to use larger amount of collected sample (because 1 from a 2 ml extract for a point was finally used) and, thus, reduce cartridges size at least to 40 cm and might be sampling volume, some automatization and modification of the first step, e.g. using some scaled cryoconcentration.

I will wait your further comments. Thanks again.

Yaroslav

After some literature exploration (e.g., Anal. Chem. 2005, 77, 6012-6018, Environ. Sci. Technol. 2015, 49, 6134−6140) I have found that for GS-MS analysis of MeSH it might be better to use N-ethylmaleimide (NEM) modification. One of two schemes might be proposed, likely.

a) like either solid sorbent trapping -elution (gas SPE) + elution + NEM + GC

b) NEM solution bubbling + SPE + GC [Environ. Sci. Technol. 2015, 49, 6134−6140]

The modification seems to improve MS sensetivity towards the modified analytes vs unmodified. Please, advise me also a good ready-to-use SPE cartrides with an appropriate sorbents for the schemes. Thank you all for commenting. It seems like I am close to decision with your help.

SPME may not be a good idea as it is hard to quantify the compounds in the air. I think it is much easier to use thermal desorption tubes than to use SPE cartridges, but you don't have a capability. I assume that the use of spe cartridges is your option at this moment.

For the SPE application, I assume that you need to pack each spe cartridge manually with the adsorbent(s). Otherwise, you need to contact suppliers, get some free ready-to-use spe cartridge samples, and evaluate them.

Methyl thiol and dimethyl sulfide are very volatile, and elute before most organic solvents (or coelute) on a gc column. The use of gc-scd is preferred than that of gc-ms for the analysis as the gc-scd is a sulfur-specific detector and solvents and contaminants derived from spe cartridges may not interfere with the sulfur compound detection. An alternative option is to use SIM rather than use TIC with your current gc-ms, which you need to determine.

I assume that you consider to derivertize the sulfur compounds, for example, with N-ethylmaleimide (NEM), making them heavier and eluting them later (better gc separation). But this adds another step, time and labor.

You need evaluate each option in your lab as an analytical method works in a lab, not in other in many cases. Good luck!

Thank you so much, Jae,

This is a good note that MeSH will likely escape from a sorbent before it will be eluted carefully, so the scheme b) seems to be better. I have to use MS, not SCD, and this is the question. And, thus, I am looking for an adequate technical decision. Due to the publications cited here and some other, I am going to be ensure it is possible to use smth like TD-GC-MS for DSM and NEM modification-SPE-GC-MS for MeSH for the purpose of their quantitative analysis at the level indicated above. Of course, SCD is better, but in the schemes MS seems to be quite comparable. Am I right or not?

Both methane thiol and methyl sulfide are detectable with GC/MS. The only concern that I have is that the extraction solvent for the SPE cartridge may interfere with the gc/ms analysis of the sulfur compounds. Hopefully, I am wrong. You need to do some preliminary experiments to determine this. Please consider just "a single" method for the analysis of both sulfur compounds at the same time. Please share your findings with us once you obtain some results.

Thank you, Jae, once more for the quick responce.

Of course, I will validate any scheem I will decide to try. And will wright here about success or failure. Hope, the first).

Hi Yaroslav,

Maybe I'm not very objective since my expertise lies with thermal desorption and canister analysis.

The problem with adsorption tubes en liquid extraction is that you only analyse a small fraction of your sample so you need to sample a large volume to get low detection limits. Since the compounds are very volatile they might breakthrough. Your extraction solvent can interfere with the compounds you want to analyse. The advantage is that you only need a common liquid injector.

With canister you only need to sample a small volume 1-6 liters, you can set your sample time between a few minutes to days. The compounds are quite stable in silco treated canisters, you can do multiple analyses from a canister. No solvent needed so no dilution of your sample. With the low range you mentioned of 10ng/l you only need a sub sample of a 100ml. Major disadvantage, you need to invest in canisters and a TD injector and both are expensive.

Regards, Alex

Thank you so much, Alex, you comments and RG profile indicate you are a good expert, I agree that canister+TD equipment is a good choice, I'll try. For thiols I would like to try also NEM derivatizarion to be able to detect lower concentration (according to cited papers). Also the approach is suitable for HPLC, which might be used in a parallel to control.

Thanks a lot