Chromatography Calculator

Chromatography separates mixtures by passing them through a column, and the Chromatography Calculator computes the key performance metrics that tell you how well your column and method are working. Enter your retention time, void time, peak widths, column length, column diameter, and flow rate to get the primary output — Retention Factor (k'). Secondary outputs include Theoretical Plates (N), Plate Height (HETP), Linear Velocity, and optionally Resolution (Rs) and Selectivity (α) when you provide a second peak's retention time and peak width.

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For resolution calculation between two peaks

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Results

Retention Factor (k')

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Theoretical Plates (N)

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Plate Height (HETP)

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Resolution (Rs)

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Selectivity (α)

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Linear Velocity

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Frequently Asked Questions

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

Retention factor (k') is a measure of how long a compound is retained on the column relative to the void time. It's calculated as (tR - t0) / t0, where tR is retention time and t0 is void time. A k' value between 2-10 is generally optimal for good separation.

How do I calculate theoretical plates (N) for my column?

Theoretical plates (N) can be calculated using N = 16(tR/Wb)², where tR is retention time and Wb is peak width at base. Higher N values indicate better column efficiency and narrower peaks.

What is considered good resolution between two peaks?

Resolution (Rs) values greater than 1.5 indicate baseline separation between peaks. Rs = 1.0 gives about 98% separation, while Rs = 1.5 provides complete baseline separation. Resolution is calculated as Rs = 2(tR2 - tR1)/(W1 + W2).

How does column length affect plate height?

Plate height (HETP) is calculated as column length divided by theoretical plates (L/N). Longer columns typically provide more plates but also higher plate heights. The goal is to minimize HETP for maximum efficiency.

What is selectivity and how does it differ from resolution?

Selectivity (α) measures the relative retention of two compounds, calculated as k'2/k'1. It indicates how well the stationary phase can distinguish between compounds. Resolution depends on selectivity, efficiency, and retention.

How do I optimize my HPLC method using these parameters?

Focus on achieving k' values of 2-10, maximizing theoretical plates, and ensuring Rs > 1.5 for critical separations. Adjust mobile phase composition for selectivity, flow rate for efficiency, and column dimensions for resolution.

What factors affect column efficiency in HPLC?

Column efficiency is affected by particle size, column packing quality, flow rate, temperature, and mobile phase viscosity. Smaller particles, optimal flow rates, and proper temperature control improve efficiency and reduce plate height.

How do I interpret linear velocity results?

Linear velocity shows how fast the mobile phase moves through the column. It's calculated from flow rate and column dimensions. Optimal linear velocity balances analysis time with separation quality, typically 1-3 mm/s for most applications.