Peptide extracts were sandwiched between 2 layers of matrix.
A layer of matrix was dried on the plate (1 ml). Then the sample(1 ml of the above peptide digest) was placed on the matrix and dried. Finally 0.5 ml of matrix was added and dried. The matrix was
a-cyano-4-hydroxy-cinnamic acid (a-CHCA, 10 mg/ml in 70%
acetonitrile/30% 0.1% TFA) (Fluka). For external calibration in the
protein mass range, angiotensin I and angiotensin II standards were
used.