Ibuprofen lysine is ibuprofen based medication which is uses lysine as counter-ion of the ibuprofen. The use of lysine makes the drug more soluble in water. Lysine is very hydrophilic compound with low UV activity, while ibuprofen is hydrophobic compound with good UV activity. These properties are making straight analysis of Ibuprofen Lysine (ibuprofen lysinate) a challenging task. Ion-pairing reagent required for retention of lysine in reversed-phase chromatography. Both compounds can be quantitated in one run without use of IP reagent. Because of the huge difference in UV activity of ibuprofen and lysine, a separate method for quantitation of lysine in ibuprofen lysinate might be required. Separation involving switching valve and guard column allows to trap ibuprofen on the guard and wash it away during analysis of lysine. This HPLC method allows to quantitate lysine separately from ibuprofen. Detailed set up of switching valve/guard system is described in our newsletter. Method can be adapted to quantitation of single compound in complex mixtures.