Preparative, solvent-delivery system

A modern solvent delivery system consists of one or more pumps, solvent reservoirs, and a degassing system. HPLC pumps can be categorized in several ways by flow range, driving mechanism, or blending method. A typical analytical pump has a flow range of 0.001-10 mL/min, which handles comfortably the flow rates required for most analytical work (e.g., 0.5-3 mL/min). Preparative pumps can have a flow range from 30 mL/min up to L/m. 

In the basic system the mobile phase is contained in a reservoir. This reservoir may or may not be pressurized (to approximately 3-6 psi). The mobile phase should be prefiltered before being placed into this reservoir, yet a filter is usually placed in the reservoir to be a sinker to hold the inlet at the bottom of the reservoir and to remove any accidental contamination of coarse particulate matter (20-30 /um) before it reaches the solvent delivery system (the pump). Since this is a low-pressure line, Teflon tubing (1 in. OD or larger) is usually used to ensure that sufficient volume of mobile phase reaches the solvent delivery system. Addition considerations for mobile phase preparation are given in Chapter 6. 

Figure 11-9. Four-channel LC/MS system to support higher throughput analysis and purification. A Waters 2525 solvent delivery system is used to deliver flow to an array of CIS analytical or preparative columns.

High-performance liquid chromatography is performed using a Hewlett-Packard 1090 chromatograph equipped with a ternary-solvent delivery system, an autoinjector with a 0 -20- u.L injection loop, an oven compartment, and a diode-array UV detector. An ELS detector (Alltech Associates, Deerfield, IL) is connected in series to the UV detector. Hexane, 2-propanol, and water were used for the analysis of nonionic surfactants. Water and tetrahydrofuran (THF) are used for the analysis of anionic surfactants. No preliminary sample preparation is used other than dilution. The nonionic surfactants are diluted 1 40 (v/v) with hexane. The anionic surfactants (alkyl ether sulfates and synthetic and petroleum sulfonates) are diluted 1 20 (v/v) with water-THF (50 50). The calcium sulfonate surfactants were diluted 1 20 (v/v) with a THF-38% hydrochloric acid solution of pH 1. Hydrochloric add is required to prevent salt precipitation by converting any excess water-insoluble caldum carbonate into water-soluble calcium chloride. All diluted samples are... 

In this case, the mobile phase can be prepared manually (premixed) or it can be mixed automatically using the HPLC solvent delivery system. 

Figure 13 Schematic diagram of preparative M-RPC. (1, upper part of the stationary chamber 2, lower part of the stationary chamber 3, collector 4, tubes in the collector 5, motor shaft with tube 6, glass rotor 7, stationary phase 8, screw 9, quartz glass cover plate 10, solvent delivery system 11, safety glass 12. mobile phase inlet 13, eluent outlet.) (Reproduced from Ref. 9 with permission.)...

The pumping of supercritical fluids at high flow rates and high pressures requires the use of specialised solvent delivery systems, whereas for the analytical and preparative scales a modified HPLC solvent delivery system will prove adequate. 

In the above trial [70] rifaximin was dissolved in chloroform and applied by repeated painting. After the solvent had dried a red sludge persisted over the dental structures allowing a continuous antimicrobial effect. Better delivery systems, such as subgingival controlled release preparations [12], are, however, needed to fully exploit the rifaximin potential in periodontal disease. In this connection, a gum-like device [71] has been developed that allows a controlled and continuous release of the antibiotic within the oral cavity. Large double-blind controlled trials using this and other formulations are now needed to establish the best therapeutic regimen for this indication. 

The use of small columns such as microbore liquid chromatographic columns, requiring smaller sample size, and computer-controlled solvent delivery and collection systems should lead to the development of fully integrated and automated cleanup systems. Small sample sizes facilitate miniaturization of sample preparation procedures, which in turn brings several benefits including reduced solvent and reagent consumption, reduced processing time, less demand for bench space, and ease of automation. 

The basic components of a preparative HPLC system shown in Figure 4.5 simplifies the overall process. In a more realistic form the colour coded schematic diagram of Figure 4.6 shows a typical plant layout for a facility housing a 30 cm diameter column. The section outlined in green covers solvent delivery, red is used for the post column solvent flow, sample feed is shown in blue and the stationary phase preparation area is in turquoise. 

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