Hello,
I have some issues with organic acid analysis using GC/MS and would like to discuss them with you. Here are the analysis conditions:

Column: HP-5MS UI
Oven temp.: 40℃ / hold 5min
10℃/min rate -> 310℃ / hold 4min(Total 36 min)
Inlet temp.: 240℃
Split mode - 10:1
Mass mode: Positive
Mass full scan mode (70ev)

The organic acids to be analyzed are: acetic acid, lactic acid, propionic acid, and butyric acid. We used N-tert-Butyldimethylsilyl-N-methyltrifluoroacetamide with 1% tert-Butyldimethylchlorosilane (MTBSTFA + 1% TBDMSCl, Sigma, 00942) as the derivatization reagent. Diethyl ether (DE) was used as the solvent for dissolving the organic acids. For the pretreatment process, the organic acid standard substance was dissolved in DE at an appropriate concentration, and 100 uL (microliters) of the solution was placed into an insert vial. Then, 5 uL (microliters) of MTBSTFA derivatization reagent was added, and the vial was capped, vortexed, and reacted at 70℃ for 30 minutes before injection into the GC/MS system.

Here are the issues that occurred:

For lactic acid, only one peak was observed in the standard substance, but when measured using the same method after DE extraction and derivatization, several peaks appeared. When we performed library searching using mass spectrum, we got the results shown in reference (1) and couldn't interpret them. We would like to know the cause of this issue.

Image
I attached the image in URL format since I cannot directly upload it. To view the image, right-click and select "Open image in new tab."

The shape of the peak. Peaks, which are presumed to be derived from the derivatization reagent (RT 3.8 min~, 6.3 min~), appeared, but the shape of the peak is not symmetrical and has a very high area. These peaks did not appear in the standard substance or blank (DE+MTBSTFA). Peaks that are not symmetrical at RT 3.4 min~ and 11.1 min~ were observed in the standard substance and blank (DE+MTBSTFA). We are curious if there is a problem with the analysis method.

Image
I attached the image in URL format since I cannot directly upload it. To view the image, right-click and select "Open image in new tab."
Thank you for reading this long message. Have a happy day.