(A) Paper spray MS analysis of cholesterol in human serum with (B) blank paper and (C) paper preloaded with betaine aldehyde chloride (5 μl, 100 μg/ml). A total of 2 μl of human serum spotted onto the paper and 10 μl of ACN/CHCl3 (1:1, v:v) utilized as solvent for paper spray.
BA: Betaine aldehyde; HV: High voltage; M: Molecular.
Adapted with permission from [43].