The amount of Nuc-NH + in the solid sample should be high because the pKa of the matrix such as 3-HPA is about 1.14, and that of Nuc-NH + can be as high as 4.4 if the number for cytosine is used. Again, these numbers are for the cases with water as the medium and thus not accurate for solid MALDI samples. In addition, nucleic acid samples usually contain other materials such as residue solvents and co-matrices, which further make estimation difficult.