1 / 12

Comprehensive Review: Rate Theory Approach in Chromatography Analysis

Learn about the Van Deemter Equation, peak broadening mechanisms, and key chromatographic quantities based on the summation of variances theory. This alternative approach combines individual peak width contributions for chromatography analysis.

thuong
Download Presentation

Comprehensive Review: Rate Theory Approach in Chromatography Analysis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Alternative Approach: Rate Theory Based on the principal of the summation of variances. σT2 = σ12 + σ22 + σ32 + … So all contributions to the broadening of a peak can be combined in this way

  2. σT2 = σ12 + σ22 + σ32 + … σ1, σ2, etc. are individual contributions to peak width σT

  3. Rate Theory Considers 3 main sources of peak broadening: 1. Eddy Diffusion (A) 2. Longitudinal Diffusion (B) 3. Resistance to Mass Transfer (C)

  4. 1. Eddy Diffusion (A): Particular pathways may differ in length. This mechanism is independent of flow rate (A)

  5. 2. Longitudinal Diffusion (B): A plug of solute in a liquid will tend to spread out into neighboring solvent. This mechanism is proportional to the inverse of the flow rate (B/u)

  6. 3. Resistance to Mass Transfer (C): Different analyte molecules may encounter more random interactions with the stationary phase. This mechanism is directly proportional to the flow rate (Cu)

  7. Rate Theory All 3 will contribute to the height (H) of a theoretical plate depending on the rate of flow (u) H = A + B/u + Cu “Van Deemter Equation”

  8. Historical “Van Deemter Equation” H = A + B/u + Cu uopt uopt

  9. Modern “Van Deemter Equation”: H = B/u + Csu + Cmu

  10. u (cm/s) upractical uopt Rule of Thumb: Save time by using u ≈ 2 uopt

  11. Review of Chromatographic Quantities K = Partition Coefficient, Distribution Coefficient N = Total number of theoretical plates in a column H = Height Equivalent to one Theoretical Plate (mm) L = Length of a chromatographic column (mm) tr = Retention Time for a chromatographic peak (min) W = Base width of a chromatographic peak (min) σ = standard dev. in a chromatographic peak (min) F = Mobile phase flow rate (mL/min) u = linear velocity of mobile phase (mm/min)

  12. Some Useful Derived Quantities H ≡ σ2/L = L/N = A +B/u + Cu = B/u + Csu + Cmu N = (tr/σ)2 = 16(tr/W)2 = 5.54(tr/W1/2)2 k′ = K(Vs/Vm) = (tr – t0)/t0 α = KB/KA = k′B/ k′A = (tB – t0)/(tA – t0) where: tB>tA Rs = (tB – tA) / (WB+WA)/2 = 2(tB – tA)/W where: WB ≈ WA u = L/t0 Vm = t0F W = 4σ W1/2 = 2.35σ

More Related