Concern about residue solvents and impurities in amino acids

Wow, interesting timing! I actually just bought a new Thermo GC-FID a few weeks ago to bring residual solvent testing in-house! We have traditionally sent off to other labs for residual solvent testing if there is an issue with a specific batch. Sometimes we catch signals we can't identify on FTIR or NMR, and sending off for a GC analysis is the best way to ID and quantify them if they are solvent residues. Most of the harmful solvent residues are from organic based solvents, which have carbon atoms in them. So we see them clearly on the IR. They usually have hydrogens, too. So NMR sees them as well. Solvents are actually put into three classes: class 1, 2, and 3. Class 1 are the most toxic, with 3 being the least. So for example, benzene and 1,2-dichloroethane are class 1 solvents. We can actually see benzene on HPLC/UPLC as well, since benzene rings are optically active chromophores. So it can be seen on FTIR, NMR, and things with a UV detector, like HPLC/UPLC. Most don't show up on HPLC/UPLC, though. This is where gas chromatography comes in. That uses a gas mobile phase with a flame ionization detector to ID and quantify things by how they combust. Since we know exactly how all the solvents combust, and we know their response factors, we can use that technique to know exactly what volatile compound it was and quantify it. It's a really cool methodology that is super accurate without having to really do method development. The volatile solvents in a sample will combust the same no matter what the sample is. So now instead of sending out to another lab on a case-by-case basis, we are going to be testing every batch in-house with our new GC-FID! I also just bought another UPLC with a mass spec detector as well. So we will have an in-house mass spec and a second UPLC for method development and validation. Our lab is getting pretty insane!

As for amino acids being more prone to solvent residues, that's not really the case. Solvents are used in the production of almost every single product out there, from synthetic to natural extracts. Extracts generally use water, ethanol, or a combination of both. However, some shitty extracts try to get their numbers up by using methanol, ethyl acetate, acetone, etc. That's not allowed, per FDA guidelines. However, some Chinese and Indian companies cut corners. For synths, it just depends on the synthesis pathway. You can't really make an overarching statement like amino acids are more prone to harsh solvents. In fact, I would say they are less likely to use them. Amino acid synths are much better documented and perfected than ones for novel synthetic compounds. Many amino acid synthesis pathways use biosynthesis or enzymatic routes instead of the more traditional organic chemistry, too. In fact, the class of compounds we saw residual solvents most in were SARMs.