--- title: "Resolution, Efficiency and the van Deemter Curve" description: "Two peaks are separated only if the distance between them beats their width. Width comes from three broadening processes with different dependences on flow rate, which is why every column has a best s" canonical: https://lightmysky.com/learn/science/resolution-efficiency-and-the-van-deemter-curve-mt_RUjdSb5Rgw source: https://lightmysky.com/learn/science/resolution-efficiency-and-the-van-deemter-curve-mt_RUjdSb5Rgw.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Resolution, Efficiency and the van Deemter Curve Two peaks are separated only if the distance between them beats their width. Width comes from three broadening processes with different dependences on flow rate, which is why every column has a best speed rather than a fastest one. Subject: Science · Area: Chemistry · Ages 19 to 20 Page: https://lightmysky.com/learn/science/resolution-efficiency-and-the-van-deemter-curve-mt_RUjdSb5Rgw ## Ready when they can - Calculates resolution from retention times and peak widths and states the value needed for a clean separation - Names the three broadening contributions and says how each varies with flow rate - Reads a van Deemter curve to find the optimum flow and explains the shape at each end - Chooses between a longer column and a more selective phase to fix a stated separation, with a reason ## Lesson: Splitting peaks at the best speed Two peaks split only when their gap beats their width. Resolution is two times the gap divided by the sum of the two widths. At 1.5 the peaks just touch baseline, so aim for 1.5 or more for a clean split. Width grows from three sources. Eddy paths spread molecules whatever the speed. Diffusion rules at slow flows and fades as you push faster. Resistance to hopping between phases rules at fast flows and grows with speed. **Example.** Peaks at 100 and 106 seconds with widths 4 and 4 give resolution two times 6 over 8, which is 1.5. The plate height curve dips at one best flow: high on the slow end from diffusion, high on the fast end from hopping lag, lowest between. **Tip.** Pick the fix by the cause. A near-zero gap is a selectivity problem, so change the phase. A fair gap with wide peaks is an efficiency problem, so run longer at the best flow. **Recap.** Beat width with gap, run at the curve dip, and fix gap problems with phase. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [How a Chromatographic Separation Works](https://lightmysky.com/learn/science/how-a-chromatographic-separation-works-mt_uKOPELqWzG) ## Opens up - [Gas Chromatography: Columns, Temperature Programming and Detectors](https://lightmysky.com/learn/science/gas-chromatography-columns-temperature-programming-and-detectors-mt_C70HPdO2Dk)