Bonded phaseCustom Development
Widening the options for PharmX
the next generation of drugs

Spherical particles pack densely with an even void distribution, giving low column pressure and uniform flow. Compared with irregular silica, a spherical substrate keeps the bed stable under repeated packing and recompression in dynamic axial compression (DAC), which is a prerequisite for transferring a laboratory method to an industrial preparative column.

Almost all the surface area of fully porous silica lies inside the pores, so pore size and surface area are strongly coupled: widen the pore size by one step and surface area falls with it, changing both the total bondable functionality and the loading capacity. Pore size is therefore not an independent parameter but the master variable governing both molecular accessibility and the loading ceiling.

Aluminium, iron and other metals in the substrate activate neighbouring silanols and raise their acidity appreciably, causing basic drugs and chelating compounds to tail and introducing uncontrolled selectivity drift between batches. Total metal impurities in the SilicaOne substrate are held below 10 ppm, removing this variable from the process risk list.

Preparative columns run at high linear velocity with frequent packing and unpacking and in-line acid and alkali cleaning; particle fracture immediately raises column pressure, blocks frits and shortens column life. Custom projects fix the skeletal strength target at the substrate selection stage against the intended column pressure and cycle count, rather than looking only at chromatographic parameters.

Chain length builds a ladder of hydrophobic strength: C18 for routine reversed phase and high-load preparative work; C8 gives a narrower elution window and better recovery for hydrophobic peptide systems where retention is excessive; C4 for proteins and strongly hydrophobic macromolecules; short C1–C2 chains for rapid elution of very hydrophobic samples; C30 for shape selectivity towards carotenoids, fat-soluble vitamins and the like.

Phenyl phases recognize aromatic ring density and substitution pattern through π–π interaction, giving selectivity orthogonal to what C18 can offer — the key to separating positional isomers, polycyclic systems and analogues with conjugated structures. Spacer length is adjustable, to shift the balance between π–π and hydrophobic interaction.

An amide or similar polar group is embedded between the alkyl chain and the silica surface, forming a polar layer that shields residual silanols: peak shape for basic compounds improves markedly, phase collapse does not occur in 100% aqueous conditions — suiting high-aqueous gradients and LC-MS compatible methods — and the selectivity differs from conventional C18.

For strongly hydrophilic compounds that are barely retained under reversed-phase conditions. Diol phases are neutral with mild hydrogen bonding, suiting carbohydrates and hydrophilic peptides; amide phases are more polar and retain more strongly, suiting nucleotides, amino acids and polar metabolites. The high acetonitrile content of the mobile phase naturally favours electrospray ionization, making these highly LC-MS compatible.

Cyano phases are of intermediate polarity and can be used in both normal and reversed phase, suiting fast methods for moderately polar compounds. Non-endcapped phases retain a controlled number of residual silanols, turning hydrogen bonding into an extra dimension of recognition for structural analogues that conventional endcapped phases cannot resolve. Aminopropyl phases provide Lewis base sites, for normal-phase carbohydrate separation and weak anion exchange.

Hydrophobic and charged sites are built onto the same particle surface, with retention controlled by two independent variables — ionic strength and pH — giving orthogonal separation on a single column. This suits charged peptides, amphoteric compounds and systems that must be desalted and separated at once; both the type of ion-exchange group and the charge density can be tailored to the target's titration curve.

The long fatty acid side chain brings strong hydrophobicity and a tendency to aggregate, so the main peak is over-retained on a conventional high carbon load C18 and the elution window is compressed. The entry point is to lower effective hydrophobicity and raise process tolerance: 100–200 Å pores with a medium-to-low carbon load C8 or C4, high bonding density and full endcapping to support dilute-alkali regeneration, with the aim of pulling deletion peptides, epimers and deamidation impurities away from the main peak without sacrificing loading.

With over fifty amino acids and existing as a hexamer, the molecular size calls for wider pores to avoid restricted diffusion. The 200 Å platform with C8 is the classic window; the critical separations are the A21 deamidation product, disulfide-scrambled isomers and residual precursor. The focus of customization is maintaining resolution and recovery at high loading, which usually requires a careful balance between bonding density and pore accessibility.

Positional isomers with extensive conjugation and similar hydrophobicity often co-elute entirely under a purely hydrophobic mechanism. The customization approach introduces π–π interaction as a second dimension of recognition: a phenyl or phenylalkyl phase with adjusted spacer length changes the elution order while leaving retention strength largely unchanged. Polycyclic aromatic systems, fullerene derivatives and preparation of aromatic impurities are typical beneficiaries.

Oligosaccharides, nucleosides and nucleotides, amino acids, polar metabolites and strongly hydrophilic peptides have k′ too small under reversed-phase conditions and elute with the dead volume. There are two customization routes: where retention must be raised substantially, go to HILIC (diol or amide); where retention is merely weak, use a polar-embedded or 100% aqueous compatible C18. Both routes can be screened in parallel at bench scale before the phase is fixed.

Large molecular size and high charge density make pore size and non-specific adsorption the primary problems. A 300 Å to ultra-wide-pore platform ensures pore accessibility, while short C4 chains or hydrophilic terminal modification reduce irreversible adsorption; charged systems can go further to ion-pair reversed phase or RP-IEX mixed mode, using ionic strength and pH as a second dimension of control.

Bonding is not only for chromatographic separation. Functionalized silica modified with thiol, ethylenediamine, thiourea and other coordinating groups can remove residual palladium, platinum, copper and iron catalysts selectively by complexation and chelation, complementing chromatographic purification on the same process chain. Both capacity and the type of coordinating group can be tailored to the residual metal profile.

The bonding density, endcapping strategy and surface chemistry of a dedicated phase are designed for your impurity profile. Even reproducing the gradient and mobile phase, a competitor will not obtain the same impurity resolution or purity curve on a general-purpose medium — the critical link in the process is not traded on the open market.

Raising the load per batch, shortening the gradient, reducing the number of cycles and cutting solvent consumption — any one of these feeds straight into the cost per unit of capacity. The larger the preparative scale, the greater the cost leverage a custom phase provides, often covering the development investment within a few batches.

Once the phase and batch consistency are written into a regulatory filing, an interruption in media supply becomes a process risk. An in-house bonding line, per-batch COAs, a retention sample scheme and long-term supply arrangements turn that risk from an uncontrollable external variable into a manageable contractual term.

An NDA can be signed from the requirements discussion stage, setting out ownership and permitted use of the formulation, process parameters and chromatographic data. A customer-specific grade is managed internally under its own item number, does not enter the public catalogue, and is not used in proposals for other customers.