Silica-based reversed-phase columns have been commonly used since the 1970s due to their mechanical strength and pressure resistance, but traditional silica C18 columns are unstable in alkaline conditions (above pH 8). In the 2000s, hybrid silica materials with ethylene chains bonded to the silica were developed, improving chemical stability. This study evaluated the durability of these hybrid silica materials and hybrid C18 columns (with end-capping) under highly alkaline conditions (pH 11.5). Results showed that durability varied greatly depending on how the ethylene chains were bonded, with up to a 1000-fold difference in silica dissolution. The hybrid C18 columns showed smaller differences, indicating that end-capping contributes more to durability in alkaline conditions than the hybrid silica itself.