Reservoirs mobile phase

FIGURE 6.4 Horizontal ES chamber 1 — mobile phase reservoir, 2 — capillary siphon, 3 — small cover plate with distributor plate, 4 — base plate, 5 — adsorbent layer, 6 — carrier plate, 7 — main cover plate, 8 — additional cover plate used to close the chamber. (From Soczewinski, E., Planar Chromatography, Vol. 1, Kaiser, R.E., Ed., Huethig, Heidelberg, 1986, pp. 79-117. With permission.)... 

FIGURE 6.8 Horizontal DS-II chamber (a) before development, (b) during development 1 — cover plate of the mobile phase reservoir, 2 — mobile phase reservoir, 3 — chromatographic plate facedown, 4 — body of the chamber, 5 — main cover plate, 6 — cover plates (removable) of the troughs for vapor saturation, 7 — troughs for saturation solvent, 8 — mobile phase, 9 — mobile phase distributor. 

Figure 5.2 A, valve, column and flow cell asseidily of a ainiaturized liquid chromatograph for use with small bore columns (Reproduced with permission from ref. 14) and B, mobile phase reservoir designed for solvent degassing by heat and helium sparging (Reproduced with permission from ref. 34. Copyright Elsevier Scientific Publishing Co.)...

Air from a cylinder at pressures up to about 10 bar (150 psi) is applied to a gas piston that has a relatively large surface area. The gas piston is attached to a hydraulic piston that has a smaller surface area. The pressure applied to the liquid = gas pressure x area of gas piston/area of hydraulic piston. With 10 bar inlet pressure and a 50 1 area ratio, the hydraulic pressure obtained is 500 bar (7500 psi). On the drive stroke, the outlet valve on the pump head is open to the column and the inlet valve closed to the mobile phase reservoir. At the end of the drive stroke, the air in the chamber is vented and air enters on the other side of the gas piston to start the return stroke. On the return stroke the outlet valve closes, the inlet valve opens and the pump head refills with mobile phase. The pump can be started and stopped by operation of a valve fitted between the cylinder regulator and the pump. 

The mobile phase reservoir is made of an inert material, usually glass. There is usually a cap on the reservoir that is vented to allow air to enter as the fluid level drops. The purpose of the cap is to prevent particulate matter from falling into the reservoir. It is very important to prevent particulates from entering the flow stream. The tip of the tube immersed in the reservoir is fitted with a coarse metal filter. It functions as a filter in the event that particulates do find their way into the reservoir. It also serves as a sinker to keep the tip well under the surface of the liquid. In addition, in specially designed mobile phase reservoirs, this sinker/filter is placed into a well on the bottom of the reservoir so that it is completely immersed in solvent, even when the reservoir is running low. This avoids drawing air into the line under those conditions. These details are shown in Figure 13.3. 

FIGURE 13.3 Mobile phase reservoir, shown on the right, with vented cap and a coarse filter on the tip of the flow tube shown inside a well on the bottom of the reservoir. 

A common cause of unusually high pressure is a plugged in-line filter. In-line filters are found at the very beginning of the flow line in the mobile phase reservoir, immediately before and/or after the injector, and just ahead of the column. With time, they can become plugged due to particles that are filtered out (particles can appear in the mobile phase and sample even if they were filtered ahead of time), and thus the pressure required to sustain a given flow rate can become quite high. The solution to this problem is to backflush the filters with solvent or clean them with a nitric acid solution in an ultrasonic bath. 

Mobile phase compositions for this experiment are polar methanol-water mixtures in the ratios 90/10, 80/20, and 70/30 by volume. The stationary phase is C18. Prepare 200 mL of each mobile phase and then filter and degas each through 0.45-/./m filters with the aid of a vacuum (instructor will demonstrate). Slowly pour each (so as to avoid reaeration by splashing) into individual mobile phase reservoirs that are labeled appropriately. 

Why do air bubbles form in the flow stream between the mobile phase reservoir and the pump when the mobile is not degassed ... 

Why is a metal in-line filter placed just ahead of the column when there already is a filter in the fine dipped into the mobile phase reservoir Why do we worry about filtering the mobile phase and sample in the first place ... 

A reciprocating piston pump is a pump that utilizes a piston in a cylinder to pull and push the liquid mobile phase from the mobile phase reservoir through the HPLC system. Two check valves (backflow preventers) are in-line to help force the liquid in only one direction. See Figure 13.4. 

The gradient elution method for HPLC is the method in which the mobile phase composition is changed in some preprogrammed way in the middle of the run. The device that accomplishes this is called the gradient programmer and is placed between the mobile phase reservoir and the pump. It is useful in experiments in which altering the mobile phase composition assists with the resolution of the mixture. 

Electrochemical detection places a number of restrictions on the mobile phase used in the chromatographic separation but is well suited to reversed-phase separations. Even so, the mobile phase must be oxygen-free, which requires bubbling an inert gas such as helium through the mobile phase reservoir as well as the sample. Additionally, both the mobile phase and the sample must be free of metals to ensure baseline stability during the readings. Despite these constraints, electrochemical... 

Place the solution of methanol from Activity A-3 (100% methanol) in the mobile phase reservoir. 

Figure 1.4 Modular HPLC system, (a) Labelled mobile phase reservoir mobile phase is degassed and filtered, (b) Pump capable of delivering pulse-free flow at pressures up to 6000psi. (c) Injection valve in industrial applications an autosampler would normally be used, (d) Column often with dimensions 250 x 4.6 mm i.d. (e) Detector most popular means of detection is by UV absorbance. (0 Labelled waste mobile phase reservoir, (g) Int ator or PC-based data handling of signal from detector.

HPLC apparatus consists of a mobile-phase reservoir, a sample injection system, a column, a detector, and a recorder. The operation of most of these components is self-evident, and a schematic diagram of an HPLC apparatus is shown in Fig. 3. 

Contamination of mobile phase reservoirs can often become a possible source of problems such as blocked... 

A-1 Mobile-Phase Reservoirs and Solvent Treatment Systems... 

The more volatile component evaporates from the mobile phase reservoir ... 

Figure 5.2. (a) All-glass solvent filtration flask using 0.45-pm membrane filters. (Legends 1. funnel, 2. clamp, 3. filter holder, 4. vacuum flask), (b) Kontes microfiltration system, which can also be used as a mobile phase reservoir. Mobile phase can be pulled into the flask from the Teflon tube without having to pour in from the top in traditional vacuum filtration flask. 

ATequ represents the selectivity between the two anions with respect to the cation of the stationary phase. As different anions have different they are therefore retained on the column during different times. The time at which a given ion elutes from the column can be controlled by adjusting the pH. Most of instruments use two mobile phase reservoirs containing buffers of different pH, and... 

Figure 8. Schematic of typical apparatus for SEC 1, mobile-phase reservoir 2, solvent metering pump 3, pressure gauge 4 and 5, pulse damper 6, thermostat 7, sample injection valve 8, SEC chromatographic columns 9, detector 10, recorder and 11, computer.

Fill the mobile phase reservoir bottle by the pump and insert the filter end inlet line into it. 

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