What Is The Disadvantage To Smaller Particle Size Of The Stationary Phase
The Van Deemter equation is an empirical formula describing the relationship between plate height (H, the length needed for one theoretical plate) which is a measure out of column efficiency, and linear velocity (µ) (Figure one). Smaller plate elevation values corresponds to greater peak efficiencies, equally more plates, or analyte sectionalization, tin can occur over a fixed length of column.
The Van Deemter equation is governed past iii cumulative terms: (A) boil diffusion, (B) longitudinal diffusion, and (C) mass transfer. A loss in tiptop efficiency can be observed as a wider analyte band, and therefore, these three terms can also be viewed equally factors that contribute to ring broadening. Effigy 1illustrates the effect of these terms, both individually and cumulatively. Eddy diffusion, the A term, is caused by a turbulence in the solute menstruum path and is mainly unaffected past flow rate. Longitudinal diffusion, the B, or departure, term, is the movement of an analyte molecule outward from the eye to the edges of its ring. College column velocities will limit this outward distribution, keeping the ring tighter. Mass transfer, the C term, is the motility of analyte, or transfer of its mass, between the mobile and stationary phases. Through this blazon of diffusion, increased flows have been observed to widen analyte bands, or lower peak efficiencies.
Decreasing particle size has been observed to limit the consequence of flow rate on peak efficiency—smaller particles take shorter diffusion path lengths, assuasive a solute to travel in and out of the particle faster. Therefore the analyte spends less fourth dimension inside the particle where tiptop improvidence tin occur. Effigy two illustrates the Van Deemter plots for various particle sizes. We notice that as the particle size decreases, the curve becomes flatter, or less affected by higher column catamenia rates. Smaller particle sizes yield amend overall efficiencies, or less tiptop dispersion, across a much wider range of usable menstruation rates.
If nosotros look at an empirically adamant Van Deemter plot of efficiency versus menstruation rate, when using a 1.9µm particle size Pinnacle DB column (Figure iii), the benefit is apparent—column efficiency does non diminish when flow rate increases, equally denoted past the relatively flat gradient of the curve. Meridian efficiency was comparable even when the catamenia was increased to 1mL/min. This illustrates the most considerable affect that pocket-sized particles have on chromatographic separations—a much wider range of usable flow rates translates into significantly faster analysis times. This benefit, coupled with a shorter column length needed for like resolution, allows much higher sample throughput, without the compromising the chromatographic quality of the analytical method.
Effigy 1: The Van Deemter Equation describes the relationship between column menstruum rate and height efficiency, referred to as band broadening.
Figure 2: Smaller particle sizes yield higher overall peak efficiencies and a much wider range of usable flow rates.
Figure 3: An empirically determined Van Deemter plot shows that column efficiency does not diminish as flow charge per unit increases on a 1.ix µm particle size Pinnacle DB cavalcade—significantly reducing assay fourth dimension and increasing sample throughput.
| Column: | Pinnacle DB C18, ane.9 µm 50 mm X 2.one mm |
| Mobile Stage: | 55:45 water:acetonitrile |
| Flow charge per unit: | Varied |
| Wavelength: | 254 nm |
| Temperature: | Ambient |
| Injection: | two µL Reversed Phase Test Mix |
What Is The Disadvantage To Smaller Particle Size Of The Stationary Phase,
Source: https://www.restek.com/row/technical-literature-library/articles/how-do-small-particle-size-columns-increase-sample-throughput/
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