Column voids

The retention time of the non-adsorbing methane (ti) is the measure of the column void volume or holdup. Ethylene is adsorbed by the catalyst, hence it does not reach the detector until the available surface is saturated, at which point ethylene breaks through and is detected by the sensor (t2). The adsorbed volume of ethylene is given simply by ... 

As noted before, the whole spectrum of particle sizes between 38 and 357 nm is encompassed with a AV of U.O ml or about 6% of the total column void volume. This low capacity of the HDC system is counterbalanced by its excellent resolution both of itself and in comparison to porous packing systems. The latter point is addressed in the next section. 

A large number of experimental methods have been proposed to estimate the column void volume without any single method emerging... 

Column Void Volume V. Retention volume corresponding to the column holdup time V. - V. 

Elution in the second dimension need not be executed until solute is present in the first sample loop. This predelay period allows the first-dimension column void solvent to be dumped to waste collection prior to the arrival of the first retained component. After some initial time, the regular sampling interval 7j = 7) = 7 3 is started. 

Figure 1 shows a typical chromatogram, which includes a time axis, an injection point, and an analyte peak. The time between the sample injection point and the analyte reaching a detector is called the retention time (t ). The retention time of an unretained component (often marked by the first baseline disturbance cansed by the elution of the sample solvent) is termed void time (tg)- Void time is related to the column void volume (Vq), which is an important parameter that will be elaborated later. 

The concept of column void volume (Vg) is important for several reasons. Void volume is the volume of the empty column minus the volume occupied by the solid packing materials. It is the liquid holdup volume of the column that each analyte must elute from. Note that the void volume is equal to the void time multiplied by the flow rate (T). 

Briefly, liposomes (10mM) were incubated for 30minutes at 37°C for egg phosphatidylcholine (EPC) and at 60°C for HSPC-based liposomes with 50 X 10 dpm of methylamine (1 x 10 dpm/mole). At the end of incubation an aliquot of this mixture was passed down a Sephadex G-50 minispin column equilibrated in 10 mM histidine-sucrose buffer 10%, pH 6.7 buffer. Liposomes were eluted at the column void volume and separated from the unencapsulated methylamine. The concentration of liposomes in the original liposomal dispersion and in the void volume fraction was determined from the organic phosphorus (phospholipid) concentration (see section Lipid Quantification and Chemical Stability above) (10,49,53). 

Vo = elution volume of the polymer Vo = column void volume Vt = total column volume... 

One unique challenge in using SCILs as stationary phases in HPLC is the determination of the column-void or mobile-phase volume. Accurate determination of retention factors, k, requires measurement of fg, the void volume. 

The values of IF/M calculated from equation (16.8) must be corrected for the weight of adsorbate contained in the column void volume, which can be obtained by subtracting the powder volume from the volume of the empty column. 

For studies on the relationship between log k and the percentage of strong solvent, olive oil was dissolved in the appropriate strong solvent at a concentration of 50 mg/ml. For time-normalization studies, olive oil was dissolved in the mobile-phase mixture at this same concentration level whenever possible. In cases where olive oil was not soluble in the mobile phase, it was dissolved in the strong solvent. The column void time was determined by measuring the av-... 

Improved separation of natural oil TGs using short columns packed with 3-//m alkyl bonded-phase particles was reported by Dong and DiCesare (88). The HPLC columns used were HS-3 high-speed columns packed with 3-/um C18 bonded-phase particle (100 X 4.6-mm ID) with a column void volume of ca. 0.8 ml and efficiencies in the range of 13,000-15,000 theoretical plates (measured under optimized conditions) and HS5 C,8 columns (125 X 4.6-mm ID packed with 5-yttm particles). Two detectors were used a modified refractive index detector having an 8-/rl flow cell and 0.007-in. ID inlet tubing and a variable-wavelength UV/visible detector. 

A sample data plot is shown in Figure 8. Feed gas is 40% N2 and 60% CH4. A mass balance is calculated for CH4 and N2 for each step in the process as well as for the complete adsorption cycle. The mass balance includes a Van der Waals calculation of the amount of gas stored in column voids and the volume of gas adsorbed on the zeolite. Typically, the independently calculated mass balances for CH4 and N2 were 100 3%. 

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