Detector cell volume

The peaks shown were obtained using a low dispersion UV detector (cell volume, 1.4 pi) in conjunction with a sample valve with a 1 pi internal loop. All tubes were of... 

Small particle size resins provide higher resolution, as demonstrated in Fig. 4.41. Low molecular weight polystyrene standards are better separated on a GIOOOHxl column packed with 5 /u,m resin than a GlOOOHg column packed with 10 /Ltm resin when compared in the same analysis time. Therefore, smaller particle size resins generally attain a better required resolution in a shorter time. In this context, SuperH columns are best, and Hhr and Hxl columns are second best. Most analyses have been carried out on these three series of H type columns. However, the performance of columns packed with smaller particle size resins is susceptible to some experimental conditions such as the sample concentration of solution, injection volume, and detector cell volume. They must be kept as low as possible to obtain the maximum resolution. Chain scissions of polymer molecules are also easier to occur in columns packed with smaller particle size resins. The flow rate should be kept low in order to prevent this problem, particularly in the analyses of high molecular weight polymers. 

If the correctly sized flow cell and connecting tubing are not used, the high efficiency of a column or high theoretical plate number columns cannot be effectively used. The detector cell volume contributes hold-up volume. The larger is the cell volume, the greater the peak broadening. The cell volume... 

Equation (67) clearly shows that when d is decreased either the detector cell volume has to be decreased proportionally or the column diameter should be increased in order to avoid significant peak distortion. With typical values such as 6 = 0.1 [Pg.26]

Column internal diameter Volumetric flow rate Injection volume UV-detector cell volume Sensitivity improvement0... 

It is important, first, to realize that efficiency is not a function solely of the column. Bad extracolumn parameters, such as detector cell volume or tubing diameters, can make the best column in the world look terrible. Second, efficiency measurements are very poor ways of comparing or purchasing columns unless all other parameters are constant. Many columns are bought and sold because they have a higher plate count than someone else s column. The efficiency calculations could have been made with different equations, on different compounds, on different machines, at different flow rates, all of which will have a profound effect on efficiency. The only valid use of plate counts that I have found is in column comparisons where all other variables are equal, or in following column aging over a period of days or months. 

Figure 8.4 Effect of detector cell volume on separation efficiency (A) l-/xl cell (B) 8-ptl cell. Conditions column 250 mm X 1.5 mm I.D. Qg (5 fixn) mobile phase acetonitrile (90%)/ water (10%) flow rate, 100 /d/min injection volume, 1 /it detection, UV absorbance at 250 nm. Peaks 1, benzene 2, naphthalene 3, biphenyl 4, fluorene 5, anthracene. (Reprinted from Ref. 1 with permission.)...

System Detector Cell Volume, Path Length Fec [rL] (Extra-column Volume) Wec [pL] (Extra-column Band Spreading)... 

The different forms of dispersion profiles that are obtained from various types of connecting tubes used in LC are shown in figure 9. These dispersion curves were obtained using a low dispersion UV detector (cell volume, 1.4 pi) in conjunction with a sample valve with a 1 pi internal loop. All tubes were of the same length and a flow rate of 2 ml/min was employed. The peaks were recorded on a high speed... 

In order to maintain the resolution achieved in the column, external peak broadening must be reduced and hmited as much as possible. In general, a 5%-loss in resolution due to external peak broadening is acceptable. In practice, this means that with a 3. 6-imn-lD colunm, a 20-pl injection volume and a 6-12 pi detector cell volume can be used in combination with short, small internal-diameter coimecting tubes. Avoiding external peak broadening is especially important when the colunm internal diameter is reduced [6]. 

A difficulty with multidetection SEC is that downstream chromatograms are shifted (and eventually distorted) with respect to the first-emerging chromatogram. This is a consequence of the interdetector capillaries and the (downstream) detector cell volumes. Such corrections are outside the scope of the present article. 

The detector time constant and detector cell volume are both involved. The slit width along the length of S the capillary is proportional to the latter. A value of ... 

Almost all detectors currently used in HPLC have been evaluated to be used in CLC. The major modification required, in most cases, is a decrease in the detector cell volume in order to accommodate the small sample volume without considerable peak broadening. Ultraviolet-visible (UV-vis), fluorescence, electrochemical, mass spectrometric, and several other detectors have been successfully used with CLC. 

Because of the small elution peak volume obtained from narrow-bore packed columns, conventional concentration dependent detectors such as UV-vlslble absorbance, fluorometrlc, and electrochemical detectors must be purged with makeup solvent or miniaturized to allow minimum extra-column contribution to peak spreading. A cell volume 0.1 i Is desirable for narrow-bore packed columns of I.D. Ishll et. al. reported the reduction of an UV detector cell volume to OAiiZ by using a quartz tube of... 

The conductivity of the eluent (often water-methanol or water-acetonitrile mixtures) is usually increased by adding quaternary ammonium or other inorganic lipophilic salts. Constructions are frequently based on the wall-jet principle where the eluent is sprayed on the surface of the electrode, resulting in very low detector cell volumes [18, 25). 

Increasing counting time by increasing detector cell volume 155... 

PLOT column and the need for small detector cell volumes to avoid extra-column band broadening. 

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