Net Peptide Content Calculator

Calculate the true active peptide content in a vial by accounting for purity, counterion/salt form, water content, and residual solvent from Certificate of Analysis (COA) values.

COA Values

Gross vial weight

The total weight of peptide powder in the vial (label amount)

Peptide content / purity (HPLC)

From the Certificate of Analysis (HPLC purity percentage)

Counterion / salt form

Typical acetate salt correction (~13% counter-ion)

Water content

From Karl Fischer titration on the COA (typically 2-8%)

Residual solvent (optional)

Residual solvent percentage from COA, if available (e.g. ACN, TFA, DMF)

Net Peptide Content

8.23 mg

from 10.00 mg gross vial weight

Overall correction factor

0.823

Difference from label

-1.77 mg (17.7% less)

Step-by-Step Breakdown

Gross vial weight

10.00 mg

After purity correction (×0.98)

9.80 mg

10.00 × 0.98 = 9.80

After salt form correction (×0.87)

8.53 mg

9.80 × 0.87 = 8.53

After water content correction (×0.97)

8.27 mg

8.53 × 0.97 = 8.27

After residual solvent (×0.995)

8.23 mg

8.27 × 0.995 = 8.23

Net peptide content

8.23 mg

Overall correction factor: 0.823 | Difference from label: -1.77 mg (17.7% less than label)

Content Reduction Waterfall

Visual breakdown of how each correction factor reduces the peptide amount from gross weight to net active content.

Remaining amount

Loss from correction

Net peptide content

Formula

Net = Gross × (Purity / 100) × Salt Factor × (1 - Water / 100) × (1 - Solvent / 100)

= 10 × 0.98 × 0.87 × 0.97 × 0.995 = 8.23 mg

Counterion / Salt Form Reference

Salt Form	Correction Factor	Counter-Ion Weight	Notes
Free base	1.00	0%	No counter-ion present
HCl	0.92	~8%	Common for small peptides; range 0.90-0.95
Acetate	0.87	~13%	Very common; range 0.85-0.90
Citrate	0.85	~15%	Less common; range 0.82-0.88
TFA	0.75	~25%	Largest correction; range 0.70-0.80; common from HPLC purification

Actual correction factors vary by peptide size and number of basic residues. These are typical average values. For precise work, calculate from the molecular weight of the free-base peptide and its salt form.

Why This Matters

A vial labeled "10 mg" rarely contains 10 mg of active peptide. The label weight reflects the total gross powder weight, which includes not just the peptide itself, but also counter-ions from the salt form, residual moisture, and trace solvents from manufacturing.

In practice, a "10 mg" vial typically contains only 7-9 mg of actual active peptide. This discrepancy matters for accurate dosing -- if you calculate doses based on the label weight alone, you may be under-dosing by 10-30%.

Key factors that reduce actual content:

Purity (HPLC): Even high-purity peptides (98%) contain 2% non-peptide impurities (truncated sequences, deletion sequences, oxidation products).
Salt form / counter-ions: Most peptides are supplied as salts (acetate, TFA). The counter-ion adds mass but no biological activity. TFA salts can have up to 25% of their weight as counter-ion.
Water content: Lyophilized peptides absorb moisture. Karl Fischer titration on COAs typically shows 2-8% water content -- this is dead weight.
Residual solvents: Trace amounts of manufacturing solvents (acetonitrile, TFA, DMF) may remain. Usually small (0.1-1%) but still reduce active content.

High-quality COAs report all of these values, allowing you to calculate the true peptide content. Vendors who only report purity without salt form or water content leave significant uncertainty in the actual amount of active peptide you receive.

Educational purposes only

This calculator is provided for educational and informational purposes only. It does not constitute medical advice. Salt form correction factors are approximate averages and vary by peptide. Always consult a qualified professional and verify calculations independently.

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COA Values

Gross vial weight

The total weight of peptide powder in the vial (label amount)

Peptide content / purity (HPLC)

From the Certificate of Analysis (HPLC purity percentage)

Counterion / salt form

Typical acetate salt correction (~13% counter-ion)

Water content

From Karl Fischer titration on the COA (typically 2-8%)

Residual solvent (optional)

Residual solvent percentage from COA, if available (e.g. ACN, TFA, DMF)

Step-by-Step Breakdown

Gross vial weight

10.00 mg

After purity correction (×0.98)

9.80 mg

10.00 × 0.98 = 9.80

After salt form correction (×0.87)

8.53 mg

9.80 × 0.87 = 8.53

After water content correction (×0.97)

8.27 mg

8.53 × 0.97 = 8.27

After residual solvent (×0.995)

8.23 mg

8.27 × 0.995 = 8.23

Net peptide content

8.23 mg

Overall correction factor: 0.823 | Difference from label: -1.77 mg (17.7% less than label)

Counterion / Salt Form Reference

Salt Form	Correction Factor	Counter-Ion Weight	Notes
Free base	1.00	0%	No counter-ion present
HCl	0.92	~8%	Common for small peptides; range 0.90-0.95
Acetate	0.87	~13%	Very common; range 0.85-0.90
Citrate	0.85	~15%	Less common; range 0.82-0.88
TFA	0.75	~25%	Largest correction; range 0.70-0.80; common from HPLC purification

Net Peptide Content Calculator

COA Values

Net Peptide Content

Step-by-Step Breakdown

Content Reduction Waterfall

Formula

Counterion / Salt Form Reference

Why This Matters

Key factors that reduce actual content:

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How to Read a Certificate of Analysis (COA) for Peptides

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Net Peptide Content Calculator

COA Values

Net Peptide Content

Step-by-Step Breakdown

Content Reduction Waterfall

Formula

Counterion / Salt Form Reference

Why This Matters

Key factors that reduce actual content: