BOC Sciences provides integrated pH adjustment and co-solvent formulation services that help pharmaceutical and biotechnology teams overcome poor aqueous solubility—one of the most persistent challenges in drug development. Our approach combines pH solubility profiling, buffer system design, co-solvent screening, and synergistic pH–co-solvent optimization to convert poorly soluble active pharmaceutical ingredients (APIs) into stable, application-ready solution formulations. Each project is supported by analytical characterization, compatibility assessment, and formulation stability evaluation, giving clients a clear, data-driven path from compound profiling to a practical formulation recommendation.
pH adjustment and co-solvent formulation are two complementary solubility enhancement strategies widely used in formulation development. pH adjustment modifies the ionization state of an API by shifting the solution pH away from the drug's pKa. For weakly acidic drugs (pKa ≤ 7), raising the pH promotes deprotonation and increases aqueous solubility; for weakly basic drugs (pKa ≥ 5), lowering the pH achieves the same effect through protonation. Co-solvent addition, by contrast, reduces the polarity of the aqueous solvent system using water-miscible organic solvents such as PEG 300/400, propylene glycol, glycerin, or ethanol, thereby improving the solvation of non-polar drug molecules.
For weakly basic APIs, BOC Sciences systematically evaluates acidifying agents to shift solution pH below the drug's pKa, maximizing the fraction of ionized, soluble species.
For weakly acidic APIs, we screen alkalizing agents to elevate pH above the drug's pKa, converting the neutral form into a more soluble ionized species.
Beyond simple pH adjustment, BOC Sciences designs buffer systems that maintain a stable pH microenvironment during storage, dilution, and administration.
When a single pH modifier is insufficient, we design and test combined pH modifier systems that achieve the target solubility while maintaining compatibility with co-solvents, surfactants, and other excipients.
Co-solvent selection must account for the intended route of administration, as each route imposes distinct constraints on solvent type, concentration, and tolerability. BOC Sciences screens and optimizes co-solvent systems tailored to each administration route, drawing on an extensive portfolio of pharmaceutically accepted water-miscible solvents.
Oral solutions and suspensions require co-solvents that enhance solubility while maintaining palatability and gastrointestinal tolerability.
Injectable formulations demand the most stringent co-solvent selection, balancing solubilization power against injection site tolerability and hemocompatibility.
Ophthalmic formulations require co-solvent systems that are non-irritating to ocular tissues, compatible with preservative systems, and stable at near-physiological pH and osmolality.
Topical and transdermal formulations use co-solvents to dissolve the API while modulating skin penetration, evaporation rate, and sensory properties.
Nasal and pulmonary delivery routes impose unique requirements on co-solvent selection, including mucosal tolerability, aerosolization compatibility, and rapid dissolution at the absorption site.
Rectal and vaginal formulations benefit from co-solvent systems that ensure complete API dissolution in small-volume vehicles while maintaining mucosal compatibility at the slightly acidic to neutral pH of the target site.
BOC Sciences helps formulation teams move from compound profiling and pKa measurement to pH modifier selection, co-solvent screening, combined optimization, and a data-supported formulation recommendation ready for downstream development.
pH adjustment and co-solvent addition are often presented as separate techniques, but in practice, formulation scientists frequently combine them to address the solubility limitations that neither strategy alone can fully resolve. A weakly basic API, for example, may achieve adequate solubility at pH 3–4 via protonation, yet the remaining non-ionized fraction—still significant if the drug has substantial hydrophobic character—can precipitate upon dilution or storage. Adding a low percentage of a suitable co-solvent (e.g., 10–20% PEG 400 or propylene glycol) to the pH-adjusted solution can solubilize this residual neutral fraction, creating a formulation that is more robust against pH shifts, temperature changes, and dilution stress.
Conversely, a neutral, highly lipophilic compound that responds well to co-solvent solubilization may still benefit from pH adjustment if the API contains weakly ionizable functional groups that influence its aggregation behavior or chemical stability. BOC Sciences evaluates pH and co-solvent effects in a single, integrated screening matrix—varying pH, buffer species, co-solvent identity, and co-solvent volume fraction simultaneously—to identify the combination that delivers the target solubility, acceptable viscosity, physiological compatibility, and storage stability. This integrated approach avoids the common pitfall of optimizing pH and co-solvent independently, only to find that the combined system underperforms due to solvent-induced pKa shifts, buffer precipitation, or unexpected excipient incompatibility.
BOC Sciences applies pH adjustment and co-solvent strategies across a broad range of liquid formulation types. For each formulation type, we provide targeted screening, optimization, and characterization support tailored to the specific solubility and stability demands of that dosage form.
| Formulation Type | How BOC Sciences Supports Your Project |
| Aqueous Solutions | Screen acidifying and alkalizing agents to maximize API ionization; design buffer systems for pH stability; add low-level co-solvent when residual neutral species require solubilization. Deliver pH-solubility profile, optimized buffer composition, and short-term physical stability confirmation. |
| Co-Solvent Solutions | Evaluate individual and blended water-miscible co-solvents (PEG 300/400, propylene glycol, glycerin, ethanol, DMA); optimize co-solvent ratio to reach target solubility at minimal organic load. Deliver co-solvent–solubility response curves and a lead formulation with dilution stability data. |
| Buffered Parenteral Solutions | Combine pH adjustment with co-solvent optimization for injectable formulations; design buffer capacity to resist pH drift upon plasma dilution; adjust osmolality and confirm sterilization compatibility. Deliver an injection-ready formulation with supporting stability studies data. |
| Oral Solutions and Syrups | Adjust pH for solubility and chemical stability; incorporate co-solvents (glycerin, PEG 400, propylene glycol) for taste masking and viscosity control; screen preservative compatibility. Deliver a palatable, physically stable oral liquid with confirmed dosing accuracy. |
| Emulsions and Microemulsions | Optimize aqueous phase pH to stabilize ionizable APIs at the oil–water interface; incorporate co-solvents to improve API loading in the appropriate phase; map phase behavior across pH and co-solvent variables. Deliver a stable emulsion with droplet size and zeta potential characterization. |
| Suspensions | Adjust pH to suppress API solubility in the continuous phase, reducing Ostwald ripening; use co-solvents to enhance wetting and dispersibility; assess sedimentation volume and redispersibility. Deliver a physically stable suspension with confirmed content uniformity. |
| Ophthalmic Solutions | Adjust pH to near-physiological range (5.5–7.4) using low-capacity buffer systems to minimize ocular irritation; add low-level co-solvent (≤10% w/v) to enhance solubility while preserving tonicity. Deliver a clear, isotonic ophthalmic formulation with confirmed pH and preservative compatibility. |
| Topical and Transdermal Vehicles | Optimize pH for ionization states that favor skin permeation; design co-solvent blends (ethanol, propylene glycol, glycerin) balancing solubility, evaporation rate, and penetration; assess viscosity and spreadability. Deliver a topical vehicle with confirmed API solubility and application-relevant rheology. |
Share your compound's structure, pKa (if known), target concentration, intended route of administration, current solubility challenges, and any formulation constraints. Our team will design a project-specific screening plan covering pH modifier selection, co-solvent evaluation, combined matrix optimization, and analytical confirmation—all tailored to your development timeline and application requirements.
BOC Sciences reviews the compound's structure, pKa (measured or calculated), log P/D, intrinsic solubility, solid-state form, target product profile, intended administration route, and any known formulation constraints. We then define the screening space—pH range, co-solvent candidates, and target API concentration—and confirm the experimental design with the client before work begins.
Our team executes the screening plan, measuring equilibrium solubility across the defined pH range with selected acidifying or alkalizing agents, and across a matrix of co-solvent identities and volume fractions. Analytical readouts include HPLC or UV-Vis solubility, pH measurement, visual clarity assessment, and osmolality where relevant.
Lead pH–co-solvent combinations are subjected to a stress testing cascade: dilution-induced precipitation assessment (simulated administration), thermal cycling, freeze–thaw stability, and short-term accelerated storage. Analytical data—HPLC purity, pH drift, osmolality, and visual appearance—are used to rank formulation candidates.
Clients receive a comprehensive report including the pH-solubility profile, co-solvent–solubility response curves, combined matrix data, lead formulation composition, compounding procedure, and analytical results from stress testing. The report is designed to support formulation decisions and downstream development activities.
Many promising drug candidates stall in early development because their aqueous solubility falls below the threshold needed for a practical liquid formulation. Weakly acidic APIs (e.g., carboxylic acid-containing compounds with pKa 3–6) and weakly basic APIs (e.g., amine-containing compounds with pKa 6–10) are particularly amenable to pH adjustment, yet determining the optimal pH—one that balances solubility against chemical stability and physiological compatibility—requires systematic experimental profiling, not rule-of-thumb estimation. BOC Sciences generates a full pH-solubility curve using equilibrium solubility measurement at multiple pH points, then cross-references the data with chemical stability trends to recommend a pH window that delivers the target concentration without compromising API integrity.
A formulation that is clear and stable at its formulated pH can precipitate rapidly when diluted into physiological fluids, injected into a bloodstream at pH 7.4, or mixed with gastric contents at pH 1–3. This pH-dependent precipitation risk is one of the most common causes of formulation failure. BOC Sciences evaluates dilution behavior in vitro by adding the pH-adjusted formulation to biorelevant media (simulated gastric fluid, simulated intestinal fluid, or isotonic buffer at pH 7.4) and monitoring precipitation kinetics, particle size of any precipitate, and residual soluble API. Formulations that show precipitation are refined by adjusting buffer capacity, adding a co-solvent to protect the neutral fraction, or introducing a surfactant to inhibit nucleation.
Co-solvents are powerful solubilizers, but each has a practical upper limit dictated by the intended route of administration. Exceeding these limits risks local irritation, hemolysis, or systemic toxicity, while co-solvent–excipient incompatibility can lead to buffer salt precipitation, antioxidant degradation, or preservative inactivation. BOC Sciences addresses this by screening co-solvents at graded concentrations against route-relevant compatibility endpoints, evaluating co-solvent–buffer–API ternary compatibility by HPLC and visual inspection, and designing multi-co-solvent blends that achieve the required solubility at a lower total organic solvent load than any single co-solvent alone.
Formulation conditions that work well at the milligram scale in a 2-mL vial do not always translate directly to gram-scale batches. Mixing order, local pH gradients during pH adjustment, co-solvent evaporation during extended processing, and incomplete dissolution kinetics can all introduce variability at larger scales. BOC Sciences identifies critical process parameters during the optimization phase, confirms the compounding procedure at intermediate scale, and provides a detailed batch record that specifies addition order, mixing times, temperature control points, and hold-time limits—reducing the risk of batch failure during scale-up.
Collaborate with BOC Sciences to access systematic pH solubility profiling, co-solvent screening across administration routes, combined pH–co-solvent optimization, and data-rich formulation recommendations for your poorly soluble compounds.
We test pH modifiers and co-solvents together in one screening run—not separately. This lets us catch hidden interactions, like co-solvent-driven pKa shifts, before they cause problems later. Our analytical platform gives you real-time solubility and stability data at every step.
We choose co-solvents based on your specific route of administration. The solvents safe for an oral syrup are not the same as those suitable for an injectable. We match the excipient to the application from day one.
Every decision is backed by HPLC, UV-Vis, and pH measurements—never by visual estimates. You receive numerical solubility enhancement factors and clear evidence for each recommendation. HPLC testing and UV-Vis testing underpin our entire workflow.
The formulation we develop at screening scale is designed to scale. We map out mixing order, pH adjustment rate, and solvent addition sequence during optimization so you avoid surprises during scale-up. Our process R&D team handles the transition seamlessly.
Client Needs: A medicinal chemistry team had identified a lead compound—a weakly basic small molecule with a calculated pKa of 7.2 and very low intrinsic aqueous solubility (<5 μg/mL at neutral pH)—for preclinical oral PK studies. They needed a solution formulation at 5 mg/mL that would remain physically stable through dosing procedures and not precipitate upon dilution in simulated gastric fluid.
Challenges: The compound's pKa was close to the physiological pH range, meaning a substantial pH shift was required to achieve meaningful ionization. Early attempts by the client using a fixed pH 3.0 citrate buffer produced a clear solution initially, but the API crystallized within hours at room temperature. The narrow gap between the solubility-achieving pH and the pH where chemical degradation accelerated complicated buffer selection.
Solution: We first constructed a full pH-solubility profile from pH 2.0 to 8.0 using HCl and citric acid as acidifying agents, measuring equilibrium solubility by HPLC at 12 pH points. Three acidifying agents and four buffer systems were then screened at the optimal pH range, with solubility, pH drift, and HPLC purity monitored over 72 hours. Dilution behavior was tested in simulated gastric fluid, and a final citrate buffer system with a low percentage of a compatible co-solvent was selected to suppress the residual neutral fraction.
Outcome: The client received a pH-adjusted oral solution formulation achieving the target 5 mg/mL concentration with confirmed 72-hour room-temperature stability and no visible precipitation upon 10-fold dilution in simulated gastric fluid, supported by a full analytical data package.
Client Needs: A discovery team required a co-solvent-based solution vehicle for a non-ionizable, highly lipophilic compound (calculated log P > 5) intended for intravenous administration in a rodent PK study. The target concentration was 2 mg/mL, and the formulation needed to be clear, physically stable for at least 24 hours at room temperature, and free of visible particles after dilution with isotonic saline.
Challenges: The compound had no ionizable functional groups, eliminating pH adjustment as a viable strategy. Its extreme hydrophobicity required high co-solvent levels that risked exceeding parenteral tolerability limits. Binary co-solvent–water systems at 40–60% organic solvent achieved the target solubility but showed rapid precipitation upon saline dilution, while lower co-solvent levels failed to reach the 2 mg/mL target.
Solution: We screened six individual co-solvents (PEG 300, PEG 400, propylene glycol, glycerin, DMA, and ethanol) and 14 binary and ternary co-solvent combinations at graded volume fractions, measuring equilibrium solubility by HPLC at each condition. Ternary systems were evaluated for dilution-induced precipitation by adding the formulation dropwise to isotonic saline and monitoring turbidity and residual soluble API over 6 hours. A ternary PEG 400–propylene glycol–water system at a moderate total organic load was identified as the lead candidate, followed by compounding procedure optimization and a 48-hour physical stability confirmation.
Outcome: The client received a parenteral-compatible co-solvent formulation at 2 mg/mL with confirmed 48-hour physical stability, acceptable dilution behavior in saline, and a detailed compounding batch record for reproducible preparation at the animal facility.
pH adjustment changes the ionization state of a compound and is generally most effective for weakly acidic, weakly basic, or amphoteric molecules with ionizable functional groups. A co-solvent changes the polarity and solvent capacity of the liquid phase, which may improve the solubility of hydrophobic, neutral, or weakly ionizable compounds. Although the mechanisms differ, both strategies require evaluation of chemical stability, excipient compatibility, viscosity, dilution behavior, and precipitation during preparation or storage. The appropriate approach depends on the compound profile, target concentration, formulation type, and intended administration route.
Combined optimization may be appropriate when pH adjustment alone cannot achieve the required concentration or when the pH needed for solubilization falls outside the compound’s preferred stability range. For some ionizable compounds, moderate pH adjustment increases the soluble ionized fraction, while a co-solvent improves solvation of the remaining unionized material. Development studies can examine pH, buffer composition, co-solvent type and concentration, component addition order, dilution conditions, and storage behavior together. This integrated approach helps identify a practical balance among solubility, chemical stability, physical stability, and formulation handling properties.
pH adjustment is particularly relevant to compounds containing acidic, basic, or amphoteric functional groups whose ionization changes within a practical formulation pH range. Assessment may include pKa, intrinsic solubility, target concentration, pH–solubility behavior, solid-state properties, and pH-dependent degradation. Neutral or highly hydrophobic compounds usually show a limited response to pH modification alone and may require co-solvents or other solubilization approaches. The selected conditions should also minimize exposure to extreme pH, salt formation problems, solid-form conversion, buffer-related precipitation, and loss of solubility during storage or dilution.
Co-solvent selection is guided by the intended administration route, API solubility profile, target concentration, formulation composition, and expected dilution conditions. Oral, parenteral, ophthalmic, topical, transdermal, nasal, pulmonary, rectal, and vaginal formulations can have different requirements for solvent type, concentration, viscosity, volatility, and compatibility with other components. Screening may compare single, binary, and multicomponent systems for solubilization performance, physical stability, chemical stability, dilution-induced precipitation, and preparation reproducibility. The resulting data support the selection of candidate solvent systems for further formulation development and route-specific compatibility assessment.
Useful starting information includes the compound structure, molecular weight, pKa or logP/logD data, available solubility and stability results, target concentration, intended administration route, acceptable formulation components, and any previously observed precipitation or degradation. When these data are incomplete, a project may begin with foundational solubility and stability screening. Deliverables can include pH–solubility profiles, acidifying and alkalizing agent comparisons, buffer system recommendations, co-solvent screening data, candidate formulation compositions, dilution and stress-evaluation results, and a scientific summary outlining the experimental findings and recommended directions for subsequent formulation development.
BOC Sciences screened multiple acidifying agents and buffer systems for our weakly basic lead compound and delivered a clear pH-solubility profile within a short turnaround. Their buffer capacity testing and dilution stability data gave us confidence in the formulation before advancing to PK studies.
— Senior Formulation Scientist, Mid-Size Pharma
Our compound was non-ionizable and extremely hydrophobic, so pH adjustment was not an option. BOC Sciences designed a logical co-solvent screening cascade—single solvents first, then binary and ternary blends—and identified a ternary system that balanced solubility against parenteral tolerability. The dilution precipitation data were especially valuable.
— Principal Investigator, Biotech Startup
We had struggled for weeks with a formulation that looked clear after preparation but precipitated within hours. BOC Sciences identified that our buffer capacity was too low and our co-solvent fraction was insufficient to hold the neutral species. Their combined pH–co-solvent approach solved the problem in a single round of screening.
— Director of CMC, Specialty Pharmaceutical Company
The final report was well-organized and easy to interpret—pH-solubility curves, co-solvent response data, dilution stability results, and a clear formulation recommendation with compounding instructions. It was exactly what our team needed to proceed with confidence.
— Lead Development Chemist, University Drug Discovery Unit
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