Typical Separations

Particular attention has been paid to separation of common anions (see Table 6.1) because they are present in so many types of samples. Complete resolution of common anions may take approximately 20 min (Dionex AS9HC, 9.0 mM sodium carbonate), but the use of a column of lower exchange capacity or the use of a 2.0 mm i.d. column can reduce the separation time to approximately 10 min or less. For high throughput of simple, well-characterized samples, use of a column with unusually low exchange capacity will give a good separation of seven common anions in a approximately 2 min (Fig. 6.5). 

A large sample volume may be used to achieve very low limits of detection. The chromatogram in Fig. 6.8 was obtained with a column and gradient similar to that in Fig. 6.8, but a 1000 pL sample injection was used to detect sample anions in the very low ppb range. 

The mobile phase used for anion chromatography with suppressed conductivity detection must (i) have adequate strength for elution of sample anions and (ii) produce products with very low conductivity after passing through the suppressor unit. 

A mixture of sodium bicarbonate and sodium carbonate has been widely used as an eluent for many years. Carbonate with a 2- charge is a stronger eluent than bicarbonate. By using a mixture of the two, the eluent strength can be adjusted as 

The ultimate eluent in terms of suppressed conductivity is the hydroxide ion, which gives water as the suppressor product With the advent of anion-exchangers with an increased afflnity for hydroxide and suppressors that tolerate a higher eluent concentration, the use of sodium or jxttassium hydroxide has become more popular. However, it is difficult to remove all of the carbonate from chemical solutions of sodium hydroxide. Electrolytic generation is now the preferred way to produce hydroxide eluents for IC. The product is almost entirely free of carbonate and the electrolytic generation provides excellent control of the concentration. Electrolytic generators are described in Chapter 1. 

Peaks (1) fluoride, (2) chlorite, (3) bromate, (4) chloride, (5) nitrite, (5) orthophosphate, (7) sulfate, (8) bromide, (9) chlorate, 

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Figure 5.23 shows the phase envelopes for the different types of hydrocarbons discussed, using the same scale on the axes. The higher the fraction of the heavy components in the mixture, the further to the right the two-phase envelope. Typical separator conditions would be around 50 bara and 15°C. 

AH three processes give perfluoropolyethers with a broad distribution of molecular weights. They are typically separated into fractions by vacuum distillation. 

Blood can be collected ia the form of whole blood donations. In the United States, one unit, ie, 450 mL, of blood is collected from a healthy volunteer blood donor who is allowed to donate blood once every 10 weeks. A unit of blood is typically separated iato a red cell fraction, ie, red cell concentrate a platelet fraction, ie, random donor platelets (RDP) and plasma. 

Fig. 4. Typical separation sizes of the basic screen types (6).

FIG. 14-109 Typical separators using impingement in addition to centrifugal force, a) Hi-eF purifier. (V D, Anderson Co.) (h) Flick separator. (Wutster line separator. (Centrifix Co7j>., Bull. 220.)... 

Typical separation efficiency curves of an air classifier versus particle size are given in Fig. 20-14. The amount of top size in the fines may be very low, but there is typically 10 to 30 percent fines in the coarse product that is, the low end of the cui ve tends to flatten out at 10 to 30 percent. In addition, the separation at the cut size is typically a gradu cui ve. Data of this sort, which are needed to evaluate closed-circuit mill performance, are seldom available. See subsection on characteristics of size classifiers for a testing method. 

Recycle/reuse involves the use of pollutant-laden streams within the process. Typically, separation technologies are key elements in a recycle/reuse system to recover valuable materials such as solvents, metals, inorganic species, and water. 

If spiral growth occurs due to the existence of screw dislocations, the results depend upon whether the diffusion length ijy is smaller or larger than the typical separation of the spiral arms i. In the first case the situation hardly changes from the purely kinetic situation without diffusion, but in the second case interaction between steps comes into effect [90] and phenomena such as step bunching [91] take place. We can estimate qualitatively the... 

Strigle presents typical separation efficiency ranges for Intalox metal tower packing, for systems with relative volatility not greater than 2.0. 

Molecules are much closer to one another in liquids and solids. In the gas state, particles are typically separated by ten molecular diameters or more in liquids or solids, they touch one another. This explains why liquids and solids have densities so much larger than those of gases. At 100°C and 1 atm, H20(/) has a density of 0.95 g/mL that of H20(g) under the same conditions is only 0.00059 g/mL For the same reason, liquids and solids are much less compressible than gases. When the pressure on liquid water is increased from 1 to 2 atm, the volume decreases by 0.0045% the same change in pressure reduces the volume of an ideal gas by 50%. 

Frequently, however, there are substances present that prevent direct measurement of the amount of a given ion these are referred to as interferences, and the selection of methods for separating the interferences from the substance to be determined are as important as the choice of the method of determination. Typical separation procedures include the following ... 

Cold crank performance, battery life expectancy, and freedom from maintenance are generally co-affected by the separators, whereas ampere-hour capacity remains largely unaffected at a given separator thickness. The properties of the different leaf and pocket separators are compared in Table 10. These typical separator properties (lines 1-4) are reflected in the electrical results of battery tests (lines 5-8). The data presented here are based on the 12 V starter battery standard DIN 43 539-02 tests based on other standards lead to similar results. 

Thermal-mechanical analysis (TMA) has proven a more reproducible measure of melt integrity [20]. The TMA test involves measuring the shape change of a separator under load while the temperature is linearly increased. Typically, separators show some shrinkage, then start to elongate, and finally break (see Fig. 5). 

Separation processes are based on some difference in the properties of the substances to be separated and may operate kinetically, as in settling and centrifugation, or by establishing an equilibrium, as in absorption and extraction. Typical separation processes are shown in Table 6.1. Better separations follow from higher selectivity or higher rates of transport or transformation. The economics of separation hinges on the required purity of the separated substance or on the extent to which an unwanted impurity must be removed (Figure 6.13). 

Figure 2.4 Comparison of a typical separation on a packed and a open tubular column. The seunple (solvent extract of river water) is the same in both cases. (Reproduced with permission from ref. 135. Copyright Ann Arbor Science Publishers).

Braman and Tompkins [98] found that stannane (SnH4) and methylstan-nanes (CH3SnH3, (CH3)2SnH2 and(CH3)3SnH) could be separated very well on a column comprising silicone oil OV-3 (20% w/w) supported on Chromosorb W. A typical separation achieved on a water sample is shown in Fig. 10.2. 

Figure 4.59 illustrates some typical separations employing different modes of HPCE. 

Possible combinations and typical separation methods using them in a not-all-inclusive list... 

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