Analytical Methods Overview — Quality Control and Characterization¶

Official QC Methods Reference

This document provides a comprehensive overview of analytical methods used for peptide quality control and characterization at SENO Biotechnology. For commercial inquiries, visit the SENO Biotechnology Official Website.

1. HPLC Purity Analysis (Reversed-Phase)¶

Standard Method Parameters¶

Parameter	Setting
Stationary Phase	C18, 150 × 4.6 mm ID, 3 – 5 µm particle size, 100 Å pore
Mobile Phase A	0.1% (v/v) TFA in H₂O
Mobile Phase B	0.1% (v/v) TFA in acetonitrile
Gradient	5% B → 65% B over 25 min
Flow Rate	1.0 mL/min
Detection	UV absorbance at 220 nm (peptide bond), 280 nm (aromatic residues)
Injection Volume	5 – 20 µg peptide (10 – 20 µL of 0.5 – 1.0 mg/mL solution)
Column Temperature	25 °C (controlled)
Run Time	30 min (including re-equilibration)
Data Acquisition	0 – 25 min gradient + 5 min re-equilibration

Purity Calculation¶

$$\text{Purity (\%)} = \frac{\text{Peak area of target peptide}}{\sum{\text{All integrated peak areas}}} \times 100$$

Reporting Thresholds¶

Peak Area (% of total)	Reporting Requirement
≥0.05%	Report and identify if possible
0.05 – 0.5%	Report as minor impurity
<0.05%	Report as trace (below reporting threshold)

2. Mass Spectrometry (ESI-MS)¶

Parameter	Setting
Ionization Mode	Electrospray positive (ESI+)
Scan Range	200 – 2000 m/z
Scan Time	1 s
Sample Concentration	1 – 10 µg/mL in 50% ACN/H₂O + 0.1% formic acid
Infusion Rate	10 – 20 µL/min (direct infusion)
Capillary Voltage	3.5 – 4.5 kV
Desolvation Temperature	250 – 350 °C
Cone Voltage	20 – 60 V (optimized per peptide)

Mass Interpretation¶

Observed Species	m/z Value	Neutral Mass Calculation
[M+H]⁺	m/z₁	M = (m/z₁ − 1) × 1
[M+2H]²⁺	m/z₂	M = (m/z₂ × 2) − 2
[M+3H]³⁺	m/z₃	M = (m/z₃ × 3) − 3
[M+Na]⁺	m/z₍M+Na₎	Confirm by +22.0 Da shift

3. Water Content (Karl Fischer Coulometric Titration)¶

Parameter	Setting
Method	Coulometric (generation of I₂)
Sample Size	5 – 50 mg peptide (weighed accurately)
Anode Solution	Hydranal Coulomat AG
Cathode Solution	Hydranal Coulomat CG
Extraction Time	2 – 5 min with stirring
Acceptance (Bulk)	≤1.0% (w/w)
Acceptance (Formulated)	≤0.5% (w/w)

4. Residual Solvents (GC-FID Headspace)¶

Parameter	Setting
Column	DB-624 or equivalent (30 m × 0.32 mm × 1.8 µm)
Detector	Flame ionization (FID)
Injection	Headspace, 80 °C for 30 min equilibration
Carrier Gas	Helium, 2.0 mL/min
Oven Program	40 °C (5 min) → 10 °C/min → 200 °C (5 min)
Target Analytes	Acetonitrile, TFA, methanol, ethanol, DMF, DCM, diethyl ether, 2-methyl-2-butene

ICH Q3C Limits¶

Solvent	Class	Limit (ppm)
Acetonitrile	Class 2	410
Methanol	Class 2	3000
DCM	Class 2	600
DMF	Class 2	880
Ethanol	Class 3	5000
TFA	Not classified	Report

5. Endotoxin Testing (LAL)¶

Parameter	Setting
Method	Limulus Amebocyte Lysate (gel-clot or chromogenic)
Sample Preparation	Dissolve in LAL reagent water (LRW)
pH Range	6.0 – 8.0 (adjust if necessary)
Inhibition/Enhancement	Spike recovery 50 – 200%
Acceptance (Research Grade)	<0.05 EU/mg
Acceptance (High-Purity)	<0.01 EU/mg

6. Peptide Content Determination¶

UV Spectrophotometric Method¶

$$\text{Content (\%)} = \frac{A_{280} \times \text{Dilution factor}}{\varepsilon \times \text{Sample weight (mg)}} \times 100$$

Where ε (molar extinction coefficient at 280 nm) is calculated from: - Tryptophan: ε = 5690 M⁻¹cm⁻¹ - Tyrosine: ε = 1280 M⁻¹cm⁻¹ - Cystine: ε = 120 M⁻¹cm⁻¹

Alternative: Amino Acid Analysis¶

Hydrolysis: 6 N HCl, 110 °C, 24 h
Derivatization: AccQ-Tag, OPA/FMOC, or ninhydrin
Quantification: HPLC or UPLC with UV or fluorescence detection
Correction factors applied for acid-labile residues (Ser, Thr, Met)

7. Optional Characterization Methods¶

Method	Purpose	When Used
SEC-HPLC	Aggregation/dimer detection	Long peptides, stored solutions
Ion-exchange chromatography	Charge variant analysis	Peptide salts, counterion determination
HILIC	Hydrophilic impurity detection	Very polar peptides
CD spectroscopy	Secondary structure assessment	Conformational studies
DSC	Thermal stability	Formulation development
NMR (1D, 2D)	Structural confirmation	Advanced characterization (>95% purity)