Analysis of Mixtures of Low Molecular weight Drugs

Importance of the topic

Simultaneous separation and analysis of low molecular weight drugs by reversed-phase liquid chromatography (RP-LC) is essential for pharmaceutical quality control, formulation development, stability testing and forensic or clinical screening. Efficient multi-analyte methods reduce analysis time, consumable use and enable consistent monitoring of active pharmaceutical ingredients (APIs) across different chemical classes (for example nonsteroidal anti-inflammatory drugs, loop diuretics and corticosteroids). The presented method demonstrates a practical RP-LC workflow for baseline-resolving a mixture of six small-molecule drugs within a single gradient run, illustrating suitability for routine laboratories seeking robust, high-throughput assays.

Objectives and study overview

The application example aims to demonstrate chromatographic separation of a six-component mixture of low molecular weight drugs using a modern sub-2 µm C18 stationary phase. Specific goals were to achieve complete resolution of structurally diverse analytes (steroid, loop diuretic, NSAIDs, and an organic acid) using a single gradient program and UV detection at 254 nm on a UHPLC platform. The study provides a straightforward gradient, operational parameters and expected elution order for analytical implementation.

Methodology and instrumentation

Method type: Reversed-phase UHPLC using a gradient of aqueous formic acid and acetonitrile.

Analytes separated (identifiers shown in example chromatogram):

• Hydrocortisone (steroid)
• Furosemide (loop diuretic)
• Ketoprofen (NSAID)
• Probenecid (uricosuric agent)
• Diclofenac (NSAID)
• Indomethacin (NSAID)

Chromatographic conditions (summary):

• Stationary phase: Shim-pack Velox C18, 100 mm × 3.0 mm I.D., 1.8 µm
• Mobile phase A: 0.1% formic acid in water; Mobile phase B: acetonitrile
• Gradient program (B%): 27% (0–1.00 min) → linear to 50% (approx. 9.33 min) → 80% (9.34–13.37 min) → 95% (13.38–19.44 min)
• Flow rate: 0.7 mL/min
• Column temperature: 40 °C
• Injection volume: 5 µL
• Detection: UV at 254 nm
• Analysis time: full gradient extended to ~19.5 min

Used instrumentation

• UHPLC system: Nexera X3 (Shimadzu)
• Column: Shim-pack Velox C18, 100 × 3.0 mm, 1.8 µm (P/N 227-32008-02)
• Detector: UV at 254 nm

Main results and discussion

The method achieves chromatographic separation of six chemically diverse small-molecule drugs in a single gradient run on a sub-2 µm C18 phase. The reported elution order (earliest to latest) is hydrocortisone, furosemide, ketoprofen, probenecid, diclofenac and indomethacin. Key practical outcomes include:

• Efficient peak capacity across the gradient window to resolve acidic NSAIDs and neutral/polar compounds.
• Reasonable total run time (~20 min) for complete elution and column re-equilibration using a stepped gradient to high organic content.
• Use of 0.1% formic acid enhances reproducible retention and peak shape for ionizable analytes under UV detection.

Discussion points and limitations:

• UV detection at 254 nm provides broad applicability for aromatic compounds (NSAIDs) but may be less sensitive or selective for non-chromophoric substances; alternative detectors (MS) would improve selectivity and sensitivity for complex matrices.
• The method uses acetonitrile and an acidic aqueous modifier; matrix effects and sample preparation (not specified) will influence performance for biological samples and should be validated.
• Sub-2 µm packing yields high efficiency but requires UHPLC-capable hardware and appropriate system backpressure handling.

Benefits and practical applications

This RP-UHPLC method is readily adaptable for routine pharmaceutical analysis and laboratory screening tasks. Practical advantages include:

• Simultaneous assay of multiple APIs from different therapeutic classes, reducing per-sample analysis time.
• Good chromatographic efficiency enabling shorter columns and faster gradients without major loss of resolution.
• Compatibility with common sample preparation workflows used in QC labs (dilution, protein precipitation, simple SPE) when validated.

Potential use cases: quality control of multi-component formulations, stability and forced-degradation studies, impurity profiling where UV-detectable impurities are expected, and preliminary screening in regulatory or forensic laboratories.

Future trends and potential applications

Opportunities to extend and modernize the approach include:

• Coupling to mass spectrometric detection for enhanced selectivity, structural confirmation and lower detection limits—especially useful for complex matrices or trace-level impurities.
• Further method acceleration using shorter columns with equivalent particle technology or core-shell phases, combined with optimized gradient slopes to preserve resolution while reducing run time.
• Exploration of greener mobile phases (reduced organic consumption, alternative solvents) and miniaturization to lower environmental and cost footprints.
• Implementation of automated sample prep and data-processing workflows to support higher throughput and regulatory-compliant quantitation.

Conclusion

The documented gradient UHPLC method on a Shim-pack Velox C18 column provides robust, baseline separation of six low molecular weight drugs spanning steroidal, diuretic and NSAID classes using a straightforward acidic aqueous/acetonitrile gradient and UV detection at 254 nm. The approach is practical for routine QC and screening applications; however, laboratories should consider detector choice, sample preparation and validation parameters when transferring the method to regulated workflows.

References

1. Application News 01-00778 (JP, ENG), Shimadzu Corporation, First Edition: Feb. 2026.
2. Shim-pack, Shim-pack Velox, Nexera and CoreFocus are trademarks of Shimadzu Corporation.