Question: I am using LC-MS with positive ionization mode and the Diamond Hydride column. My mobile phase has 0.1% formic acid in A and B solvents. However, I see no peaks for succinic acid and alpha-ketoglutarate in the EICs. What is the problem?
Answer: These compounds are both acidic and will not be amenable to either an acidic mobile phase additive or detection by positive ion mode. Try using a 10mM ammonium acetate buffer in A and B solvents and negative ion mode. The ammonium acetate will keep the compounds in their ionic form and will furthermore be retained longer in ANP. Hence, there are two advantages to use of ammonium acetate with the Diamond Hydride column. As for detection, these compounds will be readily detected as [M-H]– ions in the EICs.