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📊 HPLC Calculations

Calculate all five key HPLC system suitability parameters — retention factor, resolution, theoretical plates, tailing factor and assay.

Retention Factor (k')

k' = (tR − t₀) ÷ t₀

tR — Retention Time (min)

t₀ — Dead Time (min)

Retention Factor (k')

Resolution (Rs)

Rs = 2 × (tR2 − tR1) ÷ (W1 + W2)

tR1 (min)

tR2 (min)

W1 — Peak Width 1 (min)

W2 — Peak Width 2 (min)

Resolution (Rs)

Theoretical Plates (N)

N = 16 × (tR ÷ W)²

tR — Retention Time (min)

W — Peak Width at base (min)

Theoretical Plates (N)

Tailing Factor (T)

T = W₀.₀₅ ÷ (2 × f)

W₀.₀₅ — Width at 5% height

f — Front half-width at 5%

Tailing Factor

Assay Calculation (%)

Assay% = (AT × WS × PS) ÷ (AS × WT) × 100

AT — Sample Peak Area

AS — Standard Peak Area

WS — Standard Weight (mg)

WT — Sample Weight (mg)

PS — Standard Purity (%)

Assumes the standard and sample solutions are prepared using an equivalent dilution scheme. If they're diluted to different final volumes, factor that in separately before comparing peak areas.

Assay Result

💡 About the pass/fail badges: These reflect commonly cited general guidance (e.g., USP-style conventions), not a universal specification. Always check the acceptance criteria in your specific validated method or monograph.

⚠️ Verify before use: This calculator is a convenience aid. Cross-check critical system suitability results independently before relying on them.

📖 Example (Tailing Factor): Peak width at 5% height = 0.38 min, leading half-width from peak apex = 0.18 min → T = 0.38 / (2 × 0.18) = 1.06 (acceptable ≤ 2.0 per USP). Copy this for your system suitability report.

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System suitability

All 5 parameters required for ICH and USP system suitability testing.

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Pass/Fail guidance

Each result shows whether it meets standard acceptance criteria.

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✔ Formulas last verified against primary references: March 2025 · Report an error

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Frequently asked questions

What is retention factor (k') and why does it matter?

Retention factor measures how much longer a compound is retained on the column compared to an unretained species, calculated as (tR - t0)/t0. It's a column-independent way to describe retention that can be compared across different columns and flow rates, unlike raw retention time alone.

What's an acceptable k' range for a well-designed method?

A commonly cited guideline is k' between 2 and 10 for good separation and reasonable run time — too low (below ~1-2) risks interference from the solvent front, while too high (above ~10-20) means unnecessarily long run times without proportional gains in resolution.

How is assay percentage calculated against a reference standard?

Assay % compares the sample's response (typically peak area) to that of a reference standard of known purity and concentration, run under identical conditions, then scaled by any dilution or weight differences between the two to express the sample's content as a percentage of label claim or expected value.

Accuracy & how this is derived

Derivation: Retention factor uses the standard k' = (tR - t0)/t0 formula. Assay calculation compares sample and standard responses proportionally, correcting for known differences in concentration, dilution, or weight between the two.

Validated against: Standard chromatographic calculations described in USP General Chapter <621> Chromatography.

⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.

✔ Last updated: July 2026 · Report an error

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HPLC system suitability parameters: interpretation guide

USP General Chapter <621> defines the system suitability parameters required before and during validated HPLC runs. Theoretical plates N ≥ 2000 for most analytical applications. Tailing factor T ≤ 2.0 (USP). Resolution Rs ≥ 1.5 for baseline separation of adjacent peaks. These values must be measured from the same injection used for the sample, not from a separate calibration run. Report all SST parameters in your analytical method validation report alongside the acceptance criteria from your method SOP.