Chromatographic performance linear velocity

To allow the comparison of chromatographic performance with different phases, reduced (dimensionless) plate height, h, and reduced linear velocity, v, are typically... 

Gas Chromatographic Conditions. All analyses were performed on a Hewlett Packard 5890 GC equipped with a 5970 Mass Selective Detector or a Hewlett Packard 6890 GC equipped with a Nitrogen Phosphorous Detector (Hewlett Packard, Inc., Avondale, PA). A DB 35 (35% phenyldimethylpolysiloxane), 30 m x 0.25 mm ID X 0.25 [im column (J W Scientific, Inc., Folsom, CA) was used for all analyses. Carrier gas was helium at a linear velocity of 30 cm/sec. Samples were analyzed using split injections (split ratio = 30 1) with injector and detector (NPD) temperatures of 260°C and 250°C, respectively. Oven temperature programming was as follows initial temperature of 80°C for 1 min increase temperature at 3.5°C/min to 115°C increase at 15°C/min to 180°C increase at 60 C/min to 190°C hold at 190°C for 6 min. 

Fig 2. Rapid reversed-phase chromatography of standard proteins. Supports RP-300 (panels A B) Poros RII/H (panels C D). Chromatographic conditions linear 6-ml gradient of 0-100%B. Solvent A aqueous 0.1% TFA, Solvent B aqueous 0.1% TFA containing 60 % acetonitrile. Temperature 45°C. Chromatographic runs performed at superficial linear flow velocities of 173 cm/h (0.1 ml/min) (A, C) and 3465 cm/h (2.0 ml/min) (B, D). Proteins (5 pg) 1, ribonuclease-B 2, chick lysozyme 3, bovine serum albumin 4, myoglobin 5, carbonic anhydrase 6, ovalbumin. 

HPLC is a well-established analytical technique that has been used in laboratories globally over the past 35 years. One of the major drivers for the development of this method has been the evolution of packing materials used to effect the separation. The fundamental principles of this evolution are governed by the van Deemter equation, which is an empirical formula that defines the correlation between linear velocity (flow rate) and plate height (HETP or column efficiency). Since particle size is one of the variables, a van Deemter curve can be used to investigate chromatographic performance. 

Since particle size is one of the variables, a van Deanter curve can be used to investigate chromatographic performance. According to the van Deemter equation, when the particle size of the chromatographic sorbent is decreased, the efficiency of the separation process increases and the efficiency does not diminish at higher flow rates or linear velocities [43-45]. By using smaller particles, speed and peak capacity can be extended to new limits, termed UPLC. As shown in Figure 10.1, smaller... 

Therefore, it is possible to increase throughput, and thus the speed of analysis without affecting the chromatographic performance. The advent of UPLC has demanded the development of a new instrumental system for LC, which can take advantage of the separation performance (by reducing dead volumes) and consistent with the pressures (8000-15,000 psi, compared with 2500 to 5000 psi in HPLC). Efficiency is proportional to column length and inversely proportional to the particle size [41], Smaller particles provide increased efficiency as well as the ability to work at increased linear velocity without a loss of efficiency, providing both resolution and speed. Efficiency is the primary separation parameter behind UPLC since it relies on the same selectivity and retentivity as HPLC. In the fundamental resolution (Rs) equation [38], resolution is proportional to the square root of N. 

Chromatographic separation media based on core-shell silica particles are becoming popular for achiral analytical-scale HPLC separations [42], The major advantages of these materials include the shorter diffusion path length and consequently a higher column efficiency, as well as less dependence of column performance on the linear velocity of the mobile phase, primarily due to a smaller mass transfer term in the van Deemter equation (Figure 4.2) [43]. 

The peak dispersion in chromatography is generally characterized by the theoretical plate height (H) and the number of theoretical plates (N). The treatment of the mass transfer processes and the distribution equilibrium between the mobile and stationary phase in a column lead to equations that link the theoretical plate height as the crucial column performance parameter to the properties of the chromatographic systems, such as the linear velocity of the mobile phase, the viscosity, the diflusion coefficient of analyte, the retention coefficient of analyte, column porosity, etc. 

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