(a) To detect the drug ibuprofen by liquid chromatography– mass spectrometry, would you choose the positive or negative ion mode for the spectrometer? Would you choose acidic or neutral chromatography solvent? State your reasons.

(b)If the unfragmented ion has an intensity of 100, what should be the intensity of M+1?

Ibuprofen is a medication in the nonsteroidal anti-inflammatory drug class that is used for treating pain, fever, and inflammation. This includes painful menstrual periods, migraines, and rheumatoid arthritis. It may also be used to close a patent ductus arteriosus in a premature baby.

For the analysis of ibuprofen, it is best to use the negative ion mode of the spectrometer

Give its structure , the hydrogen in the carboxylic acid side chain is the most likely to dissociate , creating a CO2 anlon . A neutral is also best to be used , as to not protonate CO2-

TO solve for the M =1 peak intensity of an unfragmented ion having an intensity of 100 , we first deduce ibuprofen ‘s molecular formula by creating a condensed structural formula based on the structure given:

Given the condensed structural formula in the figure above , the molecular formula of ibuprofen is deduced to be C₁₃H₁₇O_2-. Using the values from table 21-2 , we calculate the intensity of the M+1 peak.