Hello everybody, there is a problem plagued me for a long time. My interest is to identify some polar amino acids and their derivates by UPLC-MS/MS. While, due to the high content of salt in soy sauce sample, the mass mass spectrometer would be likely demaged. Although I have tried to use organic solvent to extract or SPE column to elute my sample, the compounds I interest haven't appeared. I thought it might because of the similar polarity.
some detailed information: the column I use for UPLC is acquity HSS T3, the mobile phase are 0.1%HCOOH and ACN.
So sorry for my poor English and I hope I have expressed my situation correctly.
I think that there may be some confusion regarding your concern. As I understand it, most common Soy Sauces contain between 13 and 20% salt, by weight. Non-volatile compounds such as NaCl are certainly a concern, and not recommended for use with LC-MS systems (including TOF) in the mobile phase (the mobile phase must be volatile). Your issue is different. Your sample will first be diluted as the detector is highly sensitive. Injected as a sample (i.e. 5 uL) as part of a properly developed HPLC method (retained on the column with proper K primes etc. NOT flow injected or infused as the large amount of salts may interfere with ionization), the total concentration of salt should be extremely low and after being diluted in the flow path of the system should not result in excessive contamination. The use of RP chromatography to remove the salt is key, and will allow for better results w/o using other types of de-salting techniques. *Please contact someone at your school who has professional experience in operating and developing LC-MS methods for more information.
PS: Try developing the LC-MS (TOF) method to use high purity Formic Acid (0.1%), not acetic acid, which is less pure too. Again, ask the person at your school for recommendations.
PS2: Have you considered skipping the MS-TOF analysis and just use HPLC-MS (ESI) instead?
Using T3 (aqua c18) and reversed-phase is not suitable for polar amino acids. The best way is derivatization for both getting rid of salts and sensitive reverse phase identification. If you want to analyze the intact forms of polar amino acids you should choose the HILIC approach and zwitterionic, mix mode, or ion exchange resins. But in that case, salts are also major interferences since they are ionic and polar structures like amino acids. If you have to use this methodology, I recommend injecting very low amount of sample in high flow due to online dilution of the salts. If the pI of the selected amino acids is applicable for CEX or AEX it could also be an option to removal counter ions of the salts resulting.
William Letter Thanks for your meaningful answer. While I have an additional question for your PS2. if I just use HPLC-MS, the influence of salt will be less? I think it will also harm the mass system.
İsmail Emir Akyildiz thanks for your answer. I will spend some time studying about CEX and AEX.
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