Eloi Camprubí-Casas

University of Texas Rio Grande Valley · Department of Biology

I have (at least) one organic compound in my aqueous samples which has a marked peak at ~0.1 ppm (see attached spectrum). I need to find out what it is. It is not TMS, since I use another internal standard at ~7.5 ppm. It's not a contamination from silicon grease (as some suggested in my previous question) since extensive negative controls performed on my experimental setup show absence of this peak. Other blanks show no other reagents I use have this peak.

CH4 is one of the potential products of my CO2-reduction (with H2) experiments. I did a spike test with this sample, and when I dissolve commercial methane into it the peak at 0.08 ppm does indeed become larger; supporting the idea that it's methane. I did GC-FID to see if I saw methane (see attached chromatogram). We don't have a suitable column for GC-MS unfortunately. The FID results show that whatever the peak at 1.35 min is, it isn't methane which has a peak at 1.52 min. The peak at 1.35 is absent in room air blanks, and I presume it's the same organic I see in the 1H-NMR results.

Another possible product of my experiments are (Ni or Fe) bound methyl groups: e.g. Fe-CH3, Fe-C3H9, etc. Which chemical shift should I expect from methyl protons attached to a metal atom? I suspect it would be similar to TMS, since that's exactly what TMS is, right? See the attached example of a Pt organometal chemical shift showing at 0.6 ppm.

I suspect I have some dissolved methane (and maybe propane) in my aqueous solutions. Please see attached spectrum (for both spectra: number of scans is 256; same receiver gain; same method; water suppression was poorer for my experimental sample). In green is my experimental sample and in red a control one with only pure water (red shows a few peaks which can only be some sort of contamination). If it was a liquid or solid species, I would buy a commercial standard and spike my NMR tube after acquiring the spectrum to see if a new peak(s) appears or the one I saw previously grows (confirming it's the same species).

Is this possible with gases? Should I simply add such gas in the headspace of the NMR tube, shake the contents for a while, and re-analyze?

On top of this, I'm of course performing all sorts of negative controls to make sure these putative gases don't come from a contamination and were indeed synthesised during my experiments (which is what I'm looking for).

Thank you,

Eloi

I'm trying to figure out the saturation concentration of H2 gas into water which has been presurised at 50 bar (and heated at 70 degrees C). I can't seem to find any relevant source of information on this regard.

I know that at 60 degrees C and 1 bar, saturation concentration of H2 is of about 1.2mg/L = 1.2 ppm = 0.6mM. Can't find any updated information regarding higher pressures.

There's a relevant but old paper (attached: Wiebe et al., 1932), but their units are given in 'absorption coeficients' (cc H2 at STP per gram of water). I know that increasing the pressure of the solution should increase the saturation concentration (or H2 solubility), but using the data from this paper I can't seem to get a higher theoretical value for dissolved H2.

I'd appreciate any help.

I am performing some experiments and I'd need to buy a dialysis membrane (not a filtration membrane) that is not made of organic molecules. Teflon (C-F) would work, but haven't been able to find any online. Anyone knows whether dialysis membranes made of silica (or other inorganic materials) exist?

In case it helps: I plan on precipitating FeS minerals on top of the membrane (to use them for catalysis).

I am developing a microfluidics chip most probably made of glass or polycarbonate polymers. My experimental plans will involve the precipitation of thin Fe(Ni)S minerals along some of the channels. Since I would like to use each chip more than once, I would like to remove the precipitates after each use. Unfortunately, not a lot of information on how to do so seems to be available.

I have read methods for the removal of iron oxides using aqua regia or concentrated acids, but they seem rather aggressive and would probably also damage the Pt electrodes which will also be present on the chip.

Would any organic solvent help me at getting rid of Fe(Ni)S precipitates? If not, are you aware of any solutions that could dissolve Fe(Ni)S minerals but that woudn't damage electrodes (probably made of Pt)?

Thank you!

I am planning experiments which should produce formaldehyde and I aim to quantify it. The amount generated will be small (upper nano to micromolar range). Ideally, I'd like to use tests that wouldn't involve long/complex sample manipulation, such as chemical derivatisation.

I am aware of many methods to quantify formaldehyde (e.g. PFBOA derivatisation), but is there any certified methods that don't involve derivatisation?

I am aware of some types of spectroscopy (e.g. Raman) being used for such intents, but as far as I am aware, their sensitivities are pretty poor.

Any ideas?

I'd need to buy some SPE cartridges for a purification step of my samples (which are going to be analysed using GC-MS after derivatisation with TMS).

Basically my samples contain sugars (non-ionic), plus lots of calcium ions (positive) and phosphates (negative). I’d like to essentially purify my uncharged sugars, which are my analyte, from all ions, both positive and negative. What type of SPE adsorbs both negative and positive ions but let non-charged species through?

Thanks a lot!

Eloi