Reduced parameters separation time

The flow rate of the mobile phase is an important parameter which determines the elution time. In the dipeptide separation, the optimum flow rate producing the best peak resolution is present in all spiral disks. In the four-spiral disk systems (columns III and IV), which retain a large volume of the stationary phase, the application of a high flow rate of up to 10 mL/min is possible to reduce the separation time, without substantial loss of peak resolution. In the separation of proteins with PEG-phosphate, the low flow rate produced the best peak resolution with higher retention of the stationary phase. 

Upon substitution of the reduced parameters given above the separation time for a packed column and an open tubular column would be Identical if d 1.73 dp given the current limitations of open tubular column technology the column diameter cannot be reduced to the point %diere these columns can compete with packed columns for fast separations. This is illustrated by the practical txanple in Figure 6.3 (57). Ihe separation speed cannot be Increased for an open tubular column by increasing the reduced velocity since the reduced plate height is increased... 

Recently, a substantial effort has been made to optimize column internals for reactive separations and to reduce the number of expensive hydrodynamics experiments via the CFD simulations (67,119,122). Such simulations can be regarded as virtual experiments carried out in order to predict the performance of the internals by varying geometrical and structural parameters, thus reducing the optimization time. 

To illustrate more clearly the effect of these variables on analysis time, reduced parameters can be used for the plate height and velocity. Reduced parameters effectively normalize the plate height and velocity for the particle diameter and the diffusion coefficient to produce dimensionless parameters that allow comparison of different columns and separation conditions. The reduced plate height and reduced velocity are expressed, respectively, as... 

Liquid chromatographic separations will never be as fast as gas chromatographic separations because mass transfer properties in liquids are inferior to those in gases [138,154,235,236,251]. Most fast separations in liquid chromatography are accomplished at the maximum available inlet pressure. Adopting reduced parameters (section 1.5.3) the separation time is given by... 

However, it is important to mention that simultaneous analysis of multiclass compounds with quite different ph)isicochemical characteristics often imposes compromises between the performance parameters and extraction, separation, and detection conditions acceptable for the majority of compounds but not optimal for all of them. Another potential pitfall of multiresidue determination methods is an enhanced matrix effect, particularly when studying complex samples, such as wastewater. In multiresidue methods, usually simple sample pretreatment is used to reduce the analysis time. This simplification of the sample cleanup step can result in dirty extracts with high coextractive substance content, which may lead to significant ion suppression (or enhancement) when using LC-MS/MS. 

Triglycerides in seed oils are readily soluble in SC-CO2 at 40 C and at pressures higher than 280 bars. The main parameters important for efficient oil extraction in this method are particle size, pressure and residence time. Small particles of about 1mm mean diameter or less and high pressures (300-500 bar) can strongly reduce the extraction time. After extraction, the SC-CO2 tryglicerides solution is sent to a separator working at subcritical conditions. This operation reduces the solvent power of CO2 and allows the recovery of oil. The complete elimination of gaseous CO2 from oil is also accomplished in this step. The SC-CO2 extraction of seed oils has been tested up to pilot seale for several seed oils. 

How can one pass from traditional to fast GC The question involves more than reducing the length of the capillary column by half in order to halve the elution time. By operating in such a way, one indeed decreases the elution time but also the separation power of the column. This example shows that one must try to adjust different parameters to reduce the analysis time while conserving thin and well-separated chromatographic peaks. 

Increasing the speed of analysis has always been an important goal for GC separations. All other parameters being equal, the time of GC separations can be decreased in a number of ways (1) shorten the column (2) increase the carrier gas flow rate (3) reduce the column film thickness (4) reduce the carrier gas viscosity (5) increase the column diameter and/or (6) heat the column more quickly. The trade-off for increased speed, however, is reduced sample capacity, higher detection limits, and/or worse separation efficiency. 

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