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📶 UV Peak / Purity Helper

Check for possible co-elution by comparing UV absorbance ratios at two wavelengths across a chromatographic peak — a simplified educational approximation of full PDA peak purity analysis.

Absorbance at two wavelengths, measured at three points across the peak:

Up-slope — A(λ₁)

Up-slope — A(λ₂)

Apex — A(λ₁)

Apex — A(λ₂)

Down-slope — A(λ₁)

Down-slope — A(λ₂)

Deviation Threshold % — flag if exceeded

Absorbance Ratios (A(λ₁)/A(λ₂))

💡 Note: This is a simplified educational indicator, not a substitute for full PDA spectral contrast/purity angle algorithms built into chromatography software (e.g. Empower, Chromeleon), which compare entire UV spectra point-by-point rather than just two wavelengths. Use this to build intuition for how peak purity checks work, not as a final purity determination.

📖 Example: λ₁/λ₂ ratios: up-slope 0.412/0.201≈2.05, apex 0.850/0.415≈2.05, down-slope 0.380/0.186≈2.04 — all within 2% of each other, consistent with a pure, single-component peak.

Frequently asked questions

How does this compare to real PDA peak purity software?

Dedicated chromatography software (e.g. Empower, Chromeleon) calculates a purity angle and purity threshold by comparing full UV spectra (all wavelengths, not just two) at many points across the peak using vector/matrix mathematics. This tool simplifies that concept to just two wavelengths as an educational approximation — real spectral contrast analysis is considerably more sensitive and rigorous.

Why check the ratio at up-slope, apex, and down-slope specifically?

If a second, co-eluting compound has a different UV spectrum than the main peak, its relative contribution to the total absorbance will differ across the peak (since the two compounds' concentration profiles overlap only partially). Comparing the wavelength ratio at multiple points is a simple way to detect this changing composition, which a pure single-component peak would not show.

What if I only have single-wavelength UV data, not a full spectrum?

This simplified two-wavelength approach still requires absorbance at two different wavelengths at each point — if your detector only records a single wavelength, this consistency check cannot be performed at all, and you would need a full PDA/diode-array detector capable of multi-wavelength or full-spectrum acquisition.

Accuracy & how this is derived

Derivation: Simplified two-wavelength ratio consistency check: absorbance ratio A(lambda1)/A(lambda2) is compared at three points across a peak, and percent deviation from the apex ratio is calculated at the up-slope and down-slope points.

Validated against: Conceptually consistent with PDA spectral contrast / purity angle principles used in chromatography software, simplified to two wavelengths for educational use — not equivalent to full spectral purity algorithms.

⚠️ 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

A simplified approach to UV peak purity checking

Peak purity assessment in HPLC-UV analysis checks whether a chromatographic peak consists of a single compound or hides a co-eluting impurity with a different UV absorption spectrum, typically by comparing the full UV spectrum recorded at multiple points across the peak using a photodiode array detector. This tool illustrates the underlying concept with a simplified two-wavelength ratio comparison: if a peak is spectroscopically homogeneous, the ratio of absorbance at two chosen wavelengths should remain essentially constant from the peak's up-slope through its apex to its down-slope, while a meaningfully shifting ratio suggests the peak's composition is changing across its width, a sign of possible co-elution.