Verification of the homogeneity of the matrix/analyte mixture on sample plate using MALDI-MS technique and new ionic liquid matrices

Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique for mass spectrometry and usually is used in combination with the time of flight analyzer. This technique so far was used to investigation of large biomolecules. Due to the solid state of acid matrices and resulting problems with homogeneity of sample spot and low repeatability of analysis, and high background in low m/z range the analysis of low molecular compound by MALDI-MS previously have been problematic. The breakthrough in this field occurred in 2001 after publishing a report by Armstrong at al. concerning ionic liquid matrices (ILMs) (Armstrong, Zhang, He, & Gross, 2001). ILMs are organic salts, belongs to the second generation of ionic liquids formed by the reaction of an equimolar amount of a crystalline standard MALDI matrix with an organic base. This combination allows the transfer of proton from the acid to the base giving the resulting product nature of protic ionic liquid (Greaves & Drummond, 2008). The aim of the research was verification of homogeneity of the matrix/analytical mixture on sample spot and the repeatability of the MALDI-TOF measurements. two selected standard (CHCA, HABA) and ionic liquid matrices (CHCA/TEA, HABA/a-MBA) were used. The experiment consisted of tested two methods of sample (matrix/analyte mixture) application on stain steel MALDI plate, namely dried droplet and thin layer. The examined group of low molecular weight compound were β-blockers (βB), β-agonist (βA) and tricyclic antidepressants (TCA).