Diameter, column, resolution

Resolution in GC is dependent on the stationary phase, the stationary phase thickness, column length, column diameter, column temperature, and the linear velocity of the carrier gas.1,2... 

We use the second-dimension separation from Fig. 6.6 with a 25 pL injection volume and 2.5 min sampling time the separation is an RPLC method that uses a monolithic column. Thus, 10 pL/min is the maximum flow rate in the first-dimension. Fig. 6.7 shows the development of the first-dimension column that utilizes a hydrophilic interaction (or HILIC) column for the separation of proteins at decreasing flow rates. The same proteins were separated in Fig. 6.6 (RPLC) and 6.7 (HILIC) and have a reversed elution order, which is known from the basics of HILIC (Alpert, 1990). It is believed that HILIC and RPLC separations are a good pair for 2DLC analysis of proteins as they appear to have dissimilar retention mechanisms, much like those of NPLC and RPLC it has been suggested that HILIC is similar in retention to NPLC (Alpert, 1990). Because the HILIC column used in Fig. 6.7 gave good resolution at 0.1 mL/min and no smaller diameter column was available, the flow was split 10-fold to match the second-dimension requirement... 

The oil is taken up in diethyl ether and absorbed onto approximately 15 g of flash silica (Merck silica gel 60 mesh 0.040-0.063 mm), then applied to a 10-cm diameter column packed with 500 g of flash silica eluting the product with pentane/diethyl ether 85 15. (The checkers used 10 1 hexanes/ether for improved resolution.)... 

Larger diameter columns were also available for preparative chromatography. In later years, GPC analysis times were reduced and resolution was Improved by using shorter columns that were packed with smaller particle size material. A typical family of GPC columns that is available today contains 7pm particles... 

The simplest way of scaling-up of chromatography is to simply increase the column diameter. In this case, good care must be taken of the distribution of the mobile phase liquid over the cross section of the column. When particles of the same dimension and characteristics are packed in a larger-diameter column with the same height, the linear velocity and the sample volume per unit cross-sectional area should be kept unchanged to obtain the same resolution. 

Figure 24-4 Effect of open tubular column inner diameter on resolution. Narrower columns provide higher resolution. Notice the increased resolution of peaks 1 and 2 in the narrow column. Conditions DB-1 stationary phase (0.25 xm thick) in 15-m wall-coated column operated at 95°C with He linear velocity of 34 cm/s. [Courtesy JSW Scientific. Folsom. CA.]...

A newly developed 7-ray computed tomography scanner was implemented to study liquid flow distribution in a 30.48-cm-diameter column packed with corrugated structure using countercurrent air-water flow. Validation experiments confirm that spatial resolution of 2.5 mm can be achieved by the new CT unit. 

Nanoflow HPLC—HPLC system with accurately controlled reciprocating and syringe pumps designed to use capillary and small diameter, high-resolution columns as front ends for electrospray and nanospray mass spectrometer interfaces. 

The equivalent load of 8 g on a 10 cm diameter column was actually shown to give even better resolution (Figure 5.8). However, for this particular project this loading was still too low to give the required productivity so the effect of increased loading was investigated further. 

The column used for this separation was adapted in size to the small quantities of peptides extracted from each slice. It was found that micro-chromatography with 0.3 mm diameter columns yield the best compromise for chromatographic resolution... 

Selecting an appropriate column for capillary GC is a difficult task and one which is usually left to the technician. However, it is important to be aware of some general issues and what influence they can have on the separation. The column internal diameter can affect both resolution and speed of analysis. Smaller internal diameters columns (0.25 mm i.d.) can provide good resolution of early eluting peaks (Fig. 32.5a). However, the problem is that the analysis times of the eluting components may be longer and that the linear dynamic range (see p. 210) may be restricted. In contrast. 

Resolution vs. column dlometer Fig. 4-4. Effect of column diameter on resolution. (Beckman Instruments Co.)... 

While extremely large numbers of theoretical plates are possible with larger diameter columns (22, 23), calculations from chromatographic theory of the Internal diameters and column lengths necessary to achieve relatively high efficiencies in reasonable analysis times Indicate that column diameters of 50 to 100 ym l.d. are necessary for high-resolution SFC (23). For example, more than 10 effective theoretical plates are possible In less than two hours on 30-m long columns of 50 ym l.d. 

If we make columns narrower, lower detection results from narrower and taller peaks. If a 4-jxL sample is injected into a 2.1-mm-diameter column, it will be diluted about fivefold less, and the peak will be five times higher than when injected into a 4.6-mm column of the same length. The flow rate is proportional to the square of the column diameter, and the optimum flow rate for the same resolution is about five times less for the smaller column, resulting in less volumetric dilution of the sample. Of course, the same sensitivity can be achieved with conventional columns by injecting a fivefold larger sample, 20 /xL. So only if we are sample... 

The second mode is referred to as the sample overload technique and sacrifices column efficiency and resolution in favour of sample throughput. The use of wide diameter columns (>10mm) packed with large microporous particles (>50pm) allows isolation of gram quantities of material in relatively short elution times as the column can be operated at high flow rates without seriously degrading resolution. By its nature this technique... 

While an examination of the chromatogram, shows that the 10-mm diameter column was overloaded at the 50-mg sample the data in Table 10.1 indicate excellent recovery independent of sample or column size. In the preparative chromatography nonlinear effects caused by column overload are often observed, " and this affects the separation resolution as sample... 

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