Recently, reversed-phase liquid chromatography (RPLC) has been commonly used to analyze nonvolatile components in biological samples. However, polar low-molecular-weight compounds such as hydrophilic amino acids (which profiles could be potentially considered also as the biomarkers), are often not sufficiently retained and represent a challenge for that mode of the chromatography. Therefore, hydrophilic interaction liquid chromatography in combination with electrospray mass spectrometry (HILIC-MS) is the alterative tool to be successfully employed to separate free amino acids in biological samples.

In the literature one can find that changes in amino acids measured in the cerebrospinal fluid can be noted in several disease states. Because there is a general problem with the fast, direct and efficient diagnosis of the metastasis of leukemia into central nervous system, the following questions arise: if there are changes at the level of various amino acids measured in cerebrospinal fluid of children with leukemia, can these changes be related to the presence of malignant cells in the central nervous system? Furthermore, is any relationship between the changed concentrations of amino acids in cerebrospinal fluid and plasma? And finally, are those changes diversified during the therapeutic intervention and may be treated as the possible biomarker at earlier diagnosis or as a response to therapy in children with leukemia? The results of the measurements of endogenous amino acid levels were thoroughly analyzed using statistical and chemometrics analysis. The found differences in the structure of the analyzed children with leukemia and control group were evaluated and discussed.