Mar 19, 2004 · The specific aim of the present study was three-fold: (i) obtain information on the theoretical plate heights and Knox parameters which can be achieved in 2D etched columns; (ii) gain insight in the selection of the appropriate characteristic dimensions bringing the flow resistance and band broadening of differently shaped chromatographic
Oct 1, 2019 · The loss in resolution by dispersion effects occurring outside the column is generally referred to as extra-column band broadening (ECBB), a topic always drawing large attention each time the quality of the columns exceeds that of the instruments, because each serious progress in column technology requires a concomitant reduction in system
Mar 29, 2021 · Sample introduction method was studied to reduce the extra-column effect in reversed-phase HPLC. Slow transport of a sample band (SToSB) in the pre-column space followed by the introduction of the band into the column at a near-optimum flow rate resulted in larger plate counts for a 1.0 mmID, 5 cm long column as much as 1.4-1.6 times for solutes with a retention factor (k) of 0.5-1.8 compared
Nov 29, 2018 · The goal is to eliminate or minimize the other sources of dispersion by design. This chapter provides an overview of the various mechanisms of band broadening and the mathematical results that make it possible to estimate their relative contributions. Key words. Electrophoresis; Electroosmosis; Taylor dispersion; Zeta potential; Debye layer
Dispersion in Optics The dependence of the refractive index on wavelength has two effects on a pulse, one in space and the other in time. Group delay dispersion (or Chirp) d2n/d 2 Angular dispersion dn/d Both of these effects play major roles in ultrafast optics. Dispersion also can disperse a pulse in time:
Sep 12, 2021 · Injecting the sample directly into the column minimizes band broadening because it mixes the sample with the smallest possible amount of carrier gas. The injector block is heated to a temperature at least 50 o C above the boiling point of the least volatile solute, which ensures a rapid vaporization of the sample’s components.
26.3: Band Broadening and Column Efficiency. 26.2: Migration Rates of Solutes. 26.4: Optimization of Column Performance. One of the most important occurrences in chromatographic systems is the broadening of peaks as compounds move through the chromatographic column.
The resulting band broadening is smaller the shorter are the pores, i.e. the smaller are the stationary phase particles. In addition, the diffusion rate of the sample molecules in a solvent is larger under lower viscosity conditions (i.e. they diffuse faster in and out of the pores) than it is in a more viscous medium.
Jun 1, 2016 · A chromatographic band broadens as analyte molecules sample these different velocity flow paths, and the extent of this broadening is characterized in the transcolumn eddy dispersion term. The second wall effect is manifested as a region of higher-than-average packing density occurring between 5 and 50 d p from the column wall.
This means, if the particle size of the packing material is decreased, separation efficiency increases. For example, if the particle size of the packing material is reduced from 5 µm to 1.7 µm [3´], theory predicts that efficiency should increase 3´, resulting in a 1.7´ increase in resolution [square root of 3]. Figure 17.
Jul 23, 2019 · dimensions, the XRD peaks broaden. The Scherrer equation, = κλ (D βθ) cos, quantitatively describes the broadening of a peak at a particular diffraction angle (θ), as it relates the crystalline domain size (D) to the width of the peak at half of its height (β).6 The Scherrer constant, κ, is typically considered
Mar 9, 2012 · This phenomenon is termed isocratic focusing and is shown to be most effective with analytes having retention factors in the range of 0.4-3. Additionally, it is shown that gradient compression plays a minor role in band compression when using this technique with analytes having retention factors of 1 or higher.
Jul 25, 2014 · Due to the instrument contribution to band broadening, the apparent efficiency of SEC columns packed with sub–2 μm particles can indeed be hampered when using inappropriate system. Considering the extra-column band broadening contribution of current UHPLC instruments, a further decrease of SEC column dimension is therefore not desired.
Dec 3, 2010 · Section snippets Peak variance and retention time in a chromatographic system. The different parts of the instrument that are involved in the dispersion of the sample band include the system drawing the sample from its vial into the injection loop, the one ejecting the sample into the needle seat, the needle seat capillary, the injection valve, the tube connecting the valve to the column, the
Aug 11, 2014 · Height = L / N. The term H is also known as the Height Equivalent to a Theoretical Plate, or HETP. This is also a measure of column efficiency, and since column length is fixed, a large value of N gives a small value of HETP. So to recap, Little band-broadening—narrow peaks—a more efficient column. More efficient column—large N—small HETP.