Effect of salts on UV-MALDI MS analysis of carbohydrates

SILVANA L. GIUDICESSI ; ROSA ERRA-BALSELLS; YASUTO SATO; HIROSHI NONAMI

Fucchu, Tokio

Congreso; Joint Conference on Environmental Engineering in Agriculture; 2007

Environmental Control in Biology

Herein we report the efficiency of several UV-MALDI MS matrices: commercial HCl.nor-Harmane, mixtures of nor-Harmane with HCl and with NH4Cl and two chloroderivatives of nor-Harmane specially prepared. We used the following matrices in MeCN:H2O (1:1, v/v): commercial nor-Ho.hydrochloride (HCl.nor-Ho, SIGMA), nor-Ho+ 0.1% HCl (nor-Ho.HCl), nor-Ho+ NH4Cl in 1:1 molar ratio (nor-Ho.NH4Cl) and two freshly prepared compounds, 6-Cl-nor-Ho and nor-Ho.hydrochloride (HCl.nor-Ho*). β-Cyclodextrin (Bcd) and maltoheptaose (Ma) were used as analytes. Samples were prepared by sandwich method. UV-MALDI-TOF MS experiments were conducted in linear, positive (+) and negative(-) modes. HCl.nor-Ho matrix showed less clusters than nor-Ho but lower analyte signals in (+) mode. New peaks were present in (-) mode: [Cl]- at m/z 35, [nor-Ho+ Cl]- at m/z 203, [Ma+ Cl]- at m/z 1187 and [Bcd+ Cl]- at m/z 1169. These results indicate that HCl.nor-Ho yields a higher population of ions as [X+ Cl]-. All the other nor-Ho mixtures showed spectra with the same signals as nor-Ho in (+) mode and also the same signals as HCl.nor-Ho in (-) mode. These matrices, specially 6-Cl-nor-Ho and HCl.nor-Ho*, have less efficiency than nor-Ho, showing spectra with lower S/N ratio and poor peaks. It seems that nor-Ho.HCl and nor-Ho.NH4Cl have the same behavior as matrix than HCl.nor-Ho. They release significant amounts of [Cl]- ions in the desorption/ionization process. These matrices are able to create a medium with high cloride anion concentration. These ions join to analyte and matrix molecules, leading to [Analyte+ Cl]- and [Matrix+ Cl]- signals. This property gives the opportunity for those neutral analytes hardly detectable in (-) mode to ionize efficiently.