Irregular shaped silica particles of wide pore size distribution were the original support used to manufacture HPLC columns. At the time these supports were developed they were the best technology available. Due to inherent deficiencies and inconsistencies these columns limited chromatographers to the use of organic solvents and Normal Phase Chromatography and were not very reproducible.

To achieve reverse phase separations, silica had to be bonded with low polarity organo-silanes using siloxane bonding technology. These siloxane (Si-O-Si-C) bonds used in this process can be hydrolytically susceptible to attachment failure and during the lifetime of column can result in separation problems when working at extreme pH or with strong buffers or ion pair reagents.

The development of spherical shaped silica particles of 10µm and later 5µm particle size proved to be a great advancement in HPLC supports. The uniformity of shape and size allowed for better packed columns which resulted in an increase in precision and ruggedness. These tightly controlled particles did not create “fines” as irregular shaped particles do resulting in columns that lasted longer and were more stable. Even with this improvement, HPLC columns still suffered from frequent tailing problems when basic compounds were separated at desired pH. Today, Reverse Phase Separations are predominantly being performed on silica bonded with hydrocarbons mostly C8 and C18.

The next evolution in HPLC support development was the High Purity Silica which was specifically produced to minimize the amount of trace metals in the silica lattice. Spherical silica manufactured with low metal content (especially aluminum) minimizes the effect that the free, residual silanols would have on the chromatography when they are ionized (high pH). This step forward was termed Type-B silica to differentiate it from the lower purity, more acidic, higher metal content, spherical silica which preceded it. This major advancement in chromatography produced improved peak shape and increased pH tolerance and packed bed stability. Columns not only lasted longer, but produced better chromatography for many compounds of interest and were more stable.