For research use only. Not for use in diagnostic procedures.
Several peaks had a shift in retention time than what was expected but not all.
It is better to purchase small volumes of formic acid in individual ampules, use it immediately in new solvents and then throw the ampules away. Even when you make your mobile phase every week and use fresh standards, pipetting formic acid from the same container repeatedly runs the risk of contaminating the formic acid stock.
Impurities can accrue when taking aliquots of formic acid multiple times from the same bottle, and these impurities can impact positive ion analysis especially.