HILIC separation of peptides using cysteine functionalized 10 nm GNP monolayer monolith (a), and PEI-cysteine functionalized 10 nm GNP dual-layer monolith (b). Conditions: Columns: 159 mm 100 μm i.d. (a), 165 mm × 100 μm i.d. (b). mobile phase: A - 10 mmol/L triethylammonium phosphate buffer (pH 2.8), B - 5 vol.% of 10 mmol/L triethylammonium phosphate buffer (pH 2.8) in acetonitrile, gradient from 100 to 60% B in A in 10 min, flow rate 1.0 μL/min, UV detection 210 nm, temperature 25°C. Peaks: Impurity (1), Phe-Gly-Phe-Gly (2), Val-Try-Val (3), Gly-Phe (4), Gly-Leu (5), Gly-Try (6), Lys-Val (7), Gly-Gly-Gly (8).