Column length reducing

Recovery factor Reduced column length Reduced plate height Reduced velocity Relative retention ratio Retardation factor d Retention time Retention volume Selectivity coefficient Separation factor... 

Pressure, column outlet Po Reduced column length A... 

A Vigieux-type column 60 cm. in length and 2 cm. in outside diameter was used for the fractionation. The submitters state that they have also used a column of similar dimensions, packed with glass helices, for a fractionation at atmospheric pressure. They recommended the Vigreux column under reduced pressure, as used by the checkers. 

The efficiency obtained from an open tubular column can be increased by reducing the column radius, which, in turn will allow the column length to be decreased and, thus, a shorter analysis time can be realized. However, the smaller diameter column will require more pressure to achieve the optimum velocity and thus the reduction of column diameter can only be continued until the maximum available inlet pressure is needed to achieve the optimum mobile phase velocity. 

The minimum column length increases as the value of (a) is reduced and, at the... 

Conventionally, analytical SEC columns have been produced with an internal diameter of 7.5 mm and column lengths of 300 and 600 mm. In recent years environmental and safety issues have led to concerns over the reduction of organic solvent consumption, which has resulted in the development of columns for organic SEC that are more solvent efficient (13). By reducing the internal diameter of the column, the volumetric flow rate must be reduced in order to maintain the same linear velocity through the column. This reduction is carried out in the ratio of the cross sectional areas (or internal diameters) of the two columns. Eor example, if a 7.5-mm i.d. column operates at 1.0 ml/min, then in order to maintain the same linear velocity through a 4.6-mm i.d. column the flow rate would be... 

The initial configuration proposed by Valko et al. for log P gradient determination was based on a gradient cycle time of about 15 min with a 150-mm column [40]. This procedure was modified by Mutton, who stated that resolution could be maintained when the gradient time and/or column length were reduced or the flow rate increased [59, 60]. 

In 2001, Valko et al. reduced the column length to only 50 mm and increased the flow rate to 2mLmin [42]. The gradient time was diminished to 2.5 min with a gradient cycle time of 5 min. Measurement of CHI and evaluation of log P were excellent with a 3-fold improved productivity. In these conditions, the system dwell volume (Vd) becomes essential and only dedicated chromatographic devices with Vjy lower than 0.8 mL can be used [42]. Special attention should be paid to the injected volume, which must remain lower than 3 pL to avoid any overloading or extra-column volume contributions. 

Injected quantity. When column length or internal diameter is reduced, the injected volume should be decreased proportionally to avoid any overloading of the column and variability of retention times. 

We can reduce column length to maintain constant efficiency and save analysis time because compounds will elute earlier. For example, if we consider a 4.6 x 50 mm column with 5 fim particles and change to modem sub-2-micron (e.g., 1.8 fim) particles, we should achieve the same efficiency with a column only 18 mm long because N - L/dp. With the same flow rate, the compounds should elute 2.8 times earlier (5 /.un/1.8 /an). 

Several of these points are met by applying the optimization steps discussed above, e.g., using smaller particles, shortening column lengths, and reducing solvent viscosity to reduce backpressure. When we consider a virtual column—a packed bed in a purely theoretical sense— we commonly accept that reducing particle size proportional to column length results in columns with at least the same theoretical efficiency. This is true, but only in the theoretical world. 

The relationship between column length and particle size is L = NH = Nhdp = 10,000 x 2 x 1.5 x lO cm = 3 cm. Assuming the column has a reduced plate number of 2 at its optimum flow velocity, v = vopt= 1, then a 3 cm column could produce 10,000 plates when packed with 1.5 /.mi particles. 

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