1.0 Scope
This method note describes a reversed-phase high-performance liquid chromatography (RP-HPLC) procedure for the purity determination of synthetic peptides by UV absorbance detection. The method is applicable to linear and cyclic peptides with molecular weights between 500 and 5000 g/mol that contain at least one aromatic residue or peptide bond absorbance at 220 nm.
Detection at 220 nm exploits the peptide bond n→π* transition, providing a universal signal response across most peptide sequences independent of aromatic residue content [1].
2.0 Equipment & Materials
| HPLC system | Any binary gradient HPLC with UV-Vis detector; degassed mobile phases required |
|---|---|
| Column | Reversed-phase C18, 4.6 × 250 mm, 5 µm particle size, 100 Å pore size (e.g., Waters Symmetry C18 or equivalent) |
| Guard column | C18 guard cartridge, 4.6 × 10 mm, 5 µm; replace after ≤200 injections |
| UV detector | Fixed or variable wavelength; set to 220 nm ± 1 nm |
| Mobile phase A | 0.1% (v/v) trifluoroacetic acid (TFA) in HPLC-grade water |
| Mobile phase B | 0.1% (v/v) trifluoroacetic acid (TFA) in HPLC-grade acetonitrile |
| Sample solvent | Mobile phase A; 1.0 mg/mL target concentration |
| Injection volume | 10 µL |
| Flow rate | 1.0 mL/min |
| Column temperature | 30°C ± 1°C; thermostatted column compartment required |
3.0 Mobile Phase Gradient
The linear gradient below applies to peptides of 10–20 amino acids. Shorter or more hydrophilic peptides may require a shallower initial gradient; longer or more hydrophobic peptides may require extending the %B plateau.
| Time (min) | Mobile Phase A (%) | Mobile Phase B (%) | Event |
|---|---|---|---|
| 0.0 | 95 | 5 | Initial hold |
| 2.0 | 95 | 5 | Equilibration complete |
| 22.0 | 35 | 65 | Linear gradient |
| 24.0 | 5 | 95 | Wash step |
| 26.0 | 5 | 95 | Wash hold |
| 28.0 | 95 | 5 | Re-equilibration |
| 35.0 | 95 | 5 | End; column equilibrated |
4.0 Sample Preparation
Weigh 1.0 ± 0.05 mg of lyophilized peptide into a 1.5 mL polypropylene microcentrifuge tube. Add 1.0 mL of mobile phase A (0.1% TFA in water). Vortex for 30 seconds; sonicate for 60 seconds in an ultrasonic bath if necessary to achieve complete dissolution. Visually confirm solution clarity. Filter through a 0.22 µm PVDF syringe filter into a 2 mL HPLC vial. Inject within 4 hours of preparation; store at 4°C if delayed.
| Target concentration | 1.0 mg/mL in 0.1% TFA / water |
|---|---|
| Filter | 0.22 µm PVDF; do not use cellulose acetate with TFA |
| Blanks | Inject mobile phase A as blank; run before sample and at method end |
| Replicate injections | Minimum 3 injections per sample for system suitability and RSD calculation |
5.0 System Suitability
System suitability must be established prior to sample analysis. Inject a reference standard of known purity (≥99.0% by certificate) at 1.0 mg/mL. Perform a minimum of five consecutive injections. All criteria below must be met before proceeding to sample analysis [2].
| Parameter | Symbol | Acceptance Criterion | Calculation |
|---|---|---|---|
| Theoretical plates | N | ≥2000 plates (main peak) | N = 5.545 × (tR / Wh)² |
| Tailing factor | T | 0.8 ≤ T ≤ 2.0 | T = W0.05 / (2 × f0.05) |
| Repeatability (RSD) | %RSD | ≤1.0% (n = 5, peak area) | USP <621> formula |
| Retention time RSD | %RSD (tR) | ≤0.5% (n = 5) | SD / mean × 100 |
| Signal-to-noise ratio | S/N | ≥10 at 0.1% impurity level | Per USP <1010> |
6.0 Acceptance Criteria
Purity is reported as area percent of the main peak relative to total integrated area (all peaks ≥0.05% area threshold). Solvent peaks and blank-origin peaks are excluded from integration.
| Parameter | Criterion | Notes |
|---|---|---|
| Main peak purity | ≥98.0% (area percent) | Lot release specification |
| Individual impurity | ≤1.0% (area percent) | Any single peak other than main |
| Total impurities | ≤2.0% (area percent) | Sum of all non-main peaks |
| Assay RSD | ≤1.0% (n = 3) | Triplicate injections of same solution |
7.0 References
- [1] Zhao S.S., Chen D.D.Y. (2014). Applications of capillary electrophoresis in characterizing recombinant protein therapeutics. Electrophoresis, 35(1):96–108. DOI:10.1002/elps.201300372
- [2] United States Pharmacopeia (2024). USP <621> Chromatography. In United States Pharmacopeia and National Formulary (USP–NF). United States Pharmacopeial Convention.
- [3] United States Pharmacopeia (2024). USP <1225> Validation of Compendial Procedures.
- [4] Snyder L.R., Kirkland J.J., Dolan J.W. (2010). Introduction to Modern Liquid Chromatography, 3rd ed. Wiley. ISBN:978-0470167540.
- [5] Dolan J.W. (2002). When does a chromatographic method need revalidation? LCGC North America, 20(6):524–530.