HPLC

How HPLC Works

HPLC improves on standard liquid chromatography:

Component	Function	Typical Specs
Pump	Delivers mobile phase	1-400+ bar pressure
Autosampler	Injects samples	0.1-100 uL accuracy
Column	Contains stationary phase	2-5 um particles
Detector	Measures analytes	UV at 214/280 nm
Data system	Processes results	Integration, reporting

Separation Process

1. Sample dissolved and injected (typically 5-20 uL)
2. High-pressure pump pushes mobile phase through column
3. Gradient changes solvent composition over time
4. Peptides elute based on hydrophobicity
5. UV detector measures peptide concentration
6. Chromatogram shows peaks for each component

HPLC for Peptide Purity

Understanding Purity Percentages

Purity Level	Typical Use	Cost Factor
98%+	Pharmaceutical/clinical	Highest
95%+	Research (standard)	Medium
90%+	Screening/preliminary	Lower
85%+	Crude/unpurified	Lowest

How Purity is Calculated

Purity % = (Peak area of main peptide / Total peak area) x 100

Peak	Area	Percentage
Main peptide	950,000	95.0%
Impurity 1	25,000	2.5%
Impurity 2	15,000	1.5%
Impurity 3	10,000	1.0%
Total	1,000,000	100%

Common HPLC Methods for Peptides

Reverse-Phase HPLC (RP-HPLC)

Parameter	Typical Condition
Column	C18, 4.6 x 150 mm, 5 um
Mobile phase A	Water + 0.1% TFA
Mobile phase B	Acetonitrile + 0.1% TFA
Gradient	5-65% B over 30 min
Flow rate	1.0 mL/min
Detection	UV 214 nm
Temperature	25-40C

Method Variations

Peptide Type	Modification
Hydrophobic	Higher starting %B
Hydrophilic	Shallower gradient
Very large	C4 or C8 column
Charged	Ion-pairing agents

Interpreting HPLC Certificates

Typical certificate data:

Parameter	Value	Meaning
Purity (HPLC)	98.5%	Main peak percentage
Retention time	12.4 min	When peptide eluted
Method	RP-HPLC C18	Column and type
Detection	UV 214 nm	Peptide bond absorption
Gradient	10-60% ACN	Solvent program

Warning Signs

Red Flag	Concern
No method details	Can’t verify results
Very broad peak	Possible impurities coeluting
Multiple major peaks	Low purity batch
No retention time	Missing basic data

Analytical vs Preparative HPLC

Aspect	Analytical	Preparative
Purpose	Measure purity	Purify material
Column size	4.6 mm ID	20-50+ mm ID
Sample amount	ug to mg	mg to grams
Flow rate	1 mL/min	10-100 mL/min
Detection	UV or MS	UV
Cost	Lower	Higher

UPLC/UHPLC

Ultra-high performance variants:

Parameter	HPLC	UPLC/UHPLC
Pressure	Up to 400 bar	Up to 1500 bar
Particle size	3-5 um	1.7-2 um
Run time	20-60 min	5-15 min
Resolution	Good	Excellent
Sensitivity	Standard	Higher

Quality Control Applications

Application	Information Gained
Release testing	Batch meets purity spec
Stability testing	Degradation over time
Comparability	Batch-to-batch consistency
Impurity ID	What impurities are present
Potency	Amount of active peptide

Frequently Asked Questions

What does 98% purity actually mean?

A 98% HPLC purity means that when the peptide sample is analyzed, 98% of the detected material (by UV absorption at 214 nm) is the target peptide. The remaining 2% consists of related impurities such as deletion sequences, oxidized forms, or synthesis byproducts.

Why is 214 nm used for peptide detection?

The peptide bond absorbs UV light strongly at 214 nm. This wavelength detects all peptides regardless of amino acid composition. Detection at 280 nm only works for peptides containing tryptophan, tyrosine, or phenylalanine.

Is higher purity always better?

Higher purity reduces variables in research but increases cost significantly. For most research applications, 95% purity is adequate. Higher purity (98%+) matters for quantitative studies, in vivo work, or when impurities might interfere with results.