Mobile phase recycler

Mobile phase recycled but detector not adjusted. 10. Detector (UV) not set at absorbance maximum but at slope of curve. 9. Reset baseline. Use new materials when dynamic range of detector is exceeded. 10. Change wavelength to UV absorbance maximum. 

Figure 13. 2,4-0 analyzer with mobile phase recycling... 

In Zone III the compounds which have higher affinity to the sorbent are adsorbed and transported with the stationary phase to Zone I. There they are desorbed by a mixture of fresh eluent introduced between Zones I and IV and the recycled eluent from Zone IV. The less adsorbed compounds in Zone III are moved with the mobile phase to Zone IV. There they adsorb and are transported in that form together with the stationary phase (column) to Zone II, where they finally become desorbed. 

There are different ways to connect the columns to build a SMB system. An important aspect is always the position of the recycling pump. The recycling pump ensures the internal flow of the mobile phase. Most often the recycling pump is placed between the last and the first column, i. e. columns 12 and 1 in Fig. 2. Once the recycling pump is fixed with respect to the columns, it moves with respect to the zones and is alternatively located in zones IV, III, II, and I. The flow rates required in the different zones are different and so the pump flow rates vary from... 

When the constraint on m4 is not fulfilled, some of the weakly adsorbed component B is carried over by the recycled mobile phase and starts to pollute the extract. 

The general flow scheme of a production liquid chromatograph is similar to that of the corresponding GC unit, shown in Figure 19.5, with four main differences. First, thermostatting requirements for the column are less strict, and may sometimes even be dispensed with. Secondly, the feed is injected as a liquid, and not vaporised. Thirdly, if the product is to be separated from the mobile-phase solvent, distillation or evaporation and solvent recycle are incorporated in the loop(28,41,42). Finally, the liquid streams are filtered to ensure column longevity, and de-aerated to prevent air bubbles forming. 

In general, chromatography is a powerful but relatively expensive separation technique whose advantages and disadvantages need to be evaluated carefully in selecting a separation system. The expense arises chiefly from the packings and the need in many cases to recycle the mobile phase. GLC and some LC and SFC packings need occasional replacement. Published cost data are as yet limited. 

The instruments for polymer HPLC except for the columns (Section 16.8.1) and for some detectors are in principle the same as for the HPLC of small molecules. Due to sensitivity of particular detectors to the pressure variations (Section 16.9.1) the pumping systems should be equipped with the efficient dampeners to suppress the rest pulsation of pressure and flow rate of mobile phase. In most methods of polymer HPLC, and especially in SEC, the retention volume of sample (fraction) is the parameter of the same importance as the sample concentration. The conventional volumeters— siphons, drop counters, heat pulse counters—do not exhibit necessary robustness and precision [270]. Therefore the timescale is utilized and the eluent flow rate has to be very constant even when rather viscous samples are introduced into column. The problems with the constant eluent flow rate may be caused by the poor resettability of some pumping systems. Therefore, it is advisable to carefully check the actual flow rate after each restarting of instrument and in the course of the long-time experiments. A continuous operation— 24h a day and 7 days a week—is advisable for the high-precision SEC measurements. THE or other eluent is continuously distilled and recycled. 

The final approach to the reduction of eluent consumption is the optimal recycling of solvents. Indeed, preparative and industrial chromatography can be designed as a unit operation that includes solvent recycling dry feed mixture is injected while dry separated compounds are recovered. Many techniques can be applied depending on the situation in isocratic (that is with a constant mobile phase composition) or gradient conditions, and with organic and/or supercritical eluents. 

Figure 1. Chromatograms showing the optical resolution on micro- crystalline triacetylcellulose of (a) Troger s base, (II), and (b) pavine (I), with a mobile phase of ethanol-water (9 1). The chromatograms record the absorbance (A), the differential absorbance of LCP and RCP radiation, (AA), and the g-ratio (AA/A), as a function of the elution volume, (V). In (b) the fractions of pavine eluted in the volume between the vertical dashed lines are incompletely resolved, the volume being recycled to achieve a further separation. (Ref. 19).

For step 1, the mobile phase is ethyl acetate and the solid phase normal silica. The feed concentration is fixed to 5.8 g per liter, the feed flow rate is 5.3 mL/min, and the recycling flow to 151 mL/min. 

FIGURE 6-11. Demonstration of resolution improvement using recycle, (a) Separation of 26-hydroxycholesterol 3, 26-diacetate from human aorta. After seven recycles, resolution of the 25S-epimer (first peak) is achieved from the 25R-epimer (second peak). Column pPorasil (silica, 10 pm), 3.9 mm ID x 60 cm (2 columns). Mobile phase 2.5% (v/v) ethyl acetate in hexane. Flow rate 1 mL/min. Detector refractometer. (Reproduced from J. Redel, J. Chromatogr. 168, 273 (1979) with permission.)... 

Baseline drift is an obvious objection which can be envisioned to occur when using recirculation. However, it has been reported (17) that the use of batch recirculation did not result in baseline drift when analyzing organic acids using UV detection. In this report 3.5 L of mobile phase was prepared and after about 3 L of column effluent was collected the mobile phase was recycled. It was possible to reuse the mobile phase about five times before fresh mobile phase was prepared. Samples included waste digester and artificial gut liquids , foods (including soy sauce), and wines. 

FIGURE 10-2. Recycle of two peaks on a totally porous packing. Mobile phase 10% CH2CI2 in isooctane (50% water saturated). Flow rate 2.0 mL/min. Detector UV, 254 nm, 1.0 AUFS. Sample naphthalene and biphenyl. Column Porasil A, 2 mm ID x 122 cm. (Note Actual separation will depend upon quality of mobile phase and column packing.)... 

Fig. 13. Elution profile of the preparative purification of 1 g of L-Leu-Gly-Gly-Gly. Chromatographic conditions column, PrepPak-SOfl/Cu cartridge mobile phase, 95% water-5% methanol-0.05% trifluoroacetic acid, pH 2.3 flow rate, 100 ml/min. The arrows indicate where fractions were pooled fraction 5 was recycled once and the desired fraction 5a was collected. Reprinted with permission from Bishop ct al. (103). Copyright by Elsevier Scientific Publishing Co.. Amsterdam.

The goal of this study is to obtain Acanthoside-D at a high purity and to establish an optimal separation and purification condition of preparative recycle HPLC by changing the mobile phase compositions of water, acetonitrile and methanol. 

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