Enhancing carbohydrate ion yield by controlling crystalline structures in matrix-assisted laser desorption/ionization mass spectrometry

Highlights: • Carbohydrate sensitivity systematically increases as MALDI crystal size decrease. • Methanol recrystallization efficiently produces fine and amorphous sample crystal to provide enhanced sensitivity. • Accelerated Marangoni flow precisely controls sample crystal size for sensitivity optimization. • The improvement is effective for various carbohydrates and matrixes. • Methanol recrystallization and accelerated Marangoni flow do not change protein sensitivity. - Abstract: Carbohydrate analysis is challenging due to lack of sensitive detection and efficient separation methods. Although matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is a sensitive tool, the low ionization efficiency of carbohydrates makes mass analyses inefficient. This work systematically examines the correlation between MALDI-MS sensitivity and carbohydrate sample morphology. Depending on the properties of the matrix used, the morphology changes through sample recrystallization after drying or imposition of hydrodynamic flows during droplet drying. Observation shows that amorphous solids and finer crystals offer higher carbohydrate sensitivity and spatial homogeneity than larger crystals. Clear evidences of an inverse correlation between sensitivity and crystal size are obtained when various kinds of carbohydrates are mixed with different matrixes. Similar experiments on proteins and peptides showed a negative or negligible effect. The result serves as a general guideline for improving efficiency in routine carbohydrate analysis.