The analytical challenge is more subtle than it might first appear. Most existing methods for baricitinib were developed for bulk powder, tablets, or blood plasma. Each of those matrices is comparatively forgiving. A transdermal nano-formulation, by contrast, is a chemical jungle: polymers, adhesives, permeation enhancers, and nano-carrier excipients all crowd the chromatogram, and any of them can co-elute with the drug and corrupt the result. Diffusion experiments add another layer of difficulty, because receptor fluid samples collected over many hours contain low drug concentrations that demand sensitivity, and repeated sampling demands stability. Spectrophotometric approaches lack the sensitivity for these dilute samples, while LC-MS/MS methods, though exquisitely sensitive, require expensive instrumentation and complex sample preparation that few quality control laboratories can justify for routine release testing. The Hyderabad team set out to fill that gap with a method that is simple, cheap, and robust enough for everyday use.

The heart of the method is an unusual choice of stationary phase. Baricitinib is a moderately polar molecule studded with hydrogen bond donors and acceptors, and on conventional C18 columns those features tend to interact with residual silanol groups on the silica surface, producing peak tailing and erratic retention. During preliminary experiments, the researchers found exactly that behavior. Their solution was the Phenomenex Synergi Polar-RP column, which embeds a polar group within the alkyl chain of the stationary phase. This polar-embedded design shields the analyte from unwanted silanol interactions and improves selectivity for moderately polar compounds, yielding sharper, more symmetrical peaks and better retention control, particularly under the aqueous-rich mobile phase conditions the method requires. The 80 angstrom pore size and 150 millimeter column length struck an optimal balance between efficiency and analysis time.

The mobile phase was tuned with equal care. The final system pairs 10 millimolar potassium dihydrogen phosphate buffer at pH 3.0 with acetonitrile in a 70:30 ratio, run isocratically at 1.0 milliliter per minute on an Agilent 1260 Infinity II system with diode array detection at 254 nanometers. The acidic pH is not arbitrary: it holds baricitinib in a consistent ionization state and suppresses the ionization of residual silanol groups, both of which sharpen the peak and improve reproducibility. Acetonitrile won out over methanol after direct comparison, offering stronger elution strength, lower viscosity, reduced backpressure, and crucially lower UV absorbance at the detection wavelength, which produced a stable baseline and better sensitivity. Under these conditions baricitinib elutes at almost exactly 5 minutes, with theoretical plate counts of 5402 for assay samples and 9657 for diffusion samples and tailing factors near 1.05, indicating excellent column efficiency and near-ideal peak symmetry in both matrices.

Validation followed the International Council for Harmonisation Q2(R2) guidelines, the global benchmark for analytical method performance. For the assay of the finished nano-formulation, the method proved linear from 12 to 100 micrograms per milliliter with a correlation coefficient of 0.999. Recovery studies, in which known quantities of drug were spiked into pre-analyzed formulation matrix at three levels, returned mean recoveries between 98.14 and 100.56 percent, confirming that the methanol-based extraction, which involves an hour of sonication with intermittent agitation, pulls the drug out of the nano-carrier matrix completely and without degradation. Intra-day and inter-day precision both produced relative standard deviations below 2 percent, and peak purity analysis confirmed that no excipient interfered at the analyte’s retention time. The assay of the actual transdermal nano-formulation came in at 99.8 plus or minus 0.15 percent drug content, a result that speaks to both the uniformity of the formulation and the accuracy of the measurement.

For the Franz diffusion application, the team revalidated the method in the diffusion matrix, where samples are drawn from receptor fluid rather than extracted from the formulation. Calibration was linear from 5 to 75 micrograms per milliliter, again with a correlation coefficient of 0.999, and recoveries ranged from 99.36 to 100.83 percent. The diluent for this variant is simply the dissolution medium itself, pH 7.4 phosphate buffer containing 0.5 percent Tween 80, which eliminates an extra sample preparation step and reduces the chance of error. Robustness testing, which deliberately perturbs flow rate, organic phase composition, and detection wavelength, showed no meaningful impact on retention time, plate count, or tailing factor. Solution stability studies demonstrated that both standards and samples remain stable for 24 hours at bench-top conditions and up to 48 hours refrigerated at 2 to 8 degrees Celsius, a practical boon for laboratories that batch-process diffusion samples collected across a full day of experiments.

With the analytical platform secured, the researchers turned it loose on the question that matters most for a transdermal product: how does the drug actually move? Using a Franz diffusion cell with a 10 milliliter receptor compartment, a 1 square centimeter effective diffusion area, and a pretreated Strat-M membrane held at 37 degrees Celsius, they sampled at 0.5, 1, 2, 4, 6, 12, and 24 hours, replacing each withdrawn aliquot with fresh medium to maintain sink conditions. The cumulative permeation data showed a controlled and sustained release profile stretching across the full 24-hour window, with drug crossing the membrane at a steady, predictable rate rather than dumping in an initial burst. For a once-daily anti-inflammatory that currently relies on oral dosing, a formulation capable of steady transdermal delivery could smooth plasma concentration peaks and troughs and potentially reduce systemic exposure.

The release kinetics told a coherent mechanistic story. When the diffusion data were fitted to four classical models, the Higuchi equation emerged as the clear best fit, with a correlation coefficient of 0.9951. The Higuchi model describes drug release governed by Fickian diffusion through a matrix, and its dominance here indicates that diffusion, not matrix erosion or swelling, is the primary engine of release. The zero-order model also performed reasonably well at 0.9539, suggesting a nearly constant release rate over time, while the first-order model at 0.9291 and the Korsmeyer-Peppas model at 0.6398 lagged behind, the latter indicating that anomalous transport does not describe the system. Together, the kinetic analysis paints a picture of a nano-formulation that releases baricitinib through a diffusion-controlled mechanism, exactly the behavior a formulator would want in a patch-like delivery system intended for steady, around-the-clock drug supply.

What distinguishes this work from the crowded field of baricitinib analytical papers is its deliberate bridging of two worlds that rarely meet. Stability-indicating HPLC methods and quality-by-design approaches have thoroughly covered bulk drug and tablets, and LC-MS/MS methods have conquered plasma pharmacokinetics, but none of the prior literature was designed to handle polymer-laden transdermal matrices or the repeated-sampling demands of permeation studies. By validating a single, inexpensive RP-HPLC platform for both the assay of the finished nano-formulation and the quantification of release samples, Tabassum and Makula have effectively handed formulation scientists a complete analytical toolkit: one method that certifies content uniformity on day one and then tracks every microgram that crosses the membrane over the next 24 hours. As JAK inhibitors continue to migrate toward dermatological applications such as atopic dermatitis and alopecia areata, where topical and transdermal delivery could localize therapy and limit systemic side effects, methods like this one will become the quiet infrastructure that makes such products testable, regulatable, and ultimately manufacturable. The study, funded by ANRF and conducted at JNTU Hyderabad, is open access, allowing laboratories worldwide to adopt the chromatographic conditions and validation framework directly.

Subject of Research: Validated RP-HPLC quantification of baricitinib in transdermal nano-formulations and its application to in vitro Franz diffusion release studies

Article Title: Quantification of Baricitinib and Franz diffusion study in transdermal nano-formulation by optimized and validated liquid chromatographic method

Article References: Tabassum, S., & Makula, A. (2026). Quantification of Baricitinib and Franz diffusion study in transdermal nano-formulation by optimized and validated liquid chromatographic method. Discover Chemistry, 3(1), Article 512. https://doi.org/10.1007/s44371-026-00897-x

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00897-x

Keywords: baricitinib, RP-HPLC, transdermal drug delivery, nano-formulation, Franz diffusion, method validation, ICH Q2(R2), drug release kinetics, Higuchi model, JAK inhibitor, pharmaceutical analysis, quality control