Mobile loop

Biol. Chem. 269, 15957-15960, 1994 Lawrence, D.A., The role of reactive-center loop mobility in the serpin inhibitory mechanism, Adv. Exp. Med. Biol. 425, 99-108,1997 Whisstock, J., Skinner, R., and Lesk, A.M., An atlas of serpin conformations. Trends Biochem. Sci. 23, 63-67, 1998 Gettins, P.G., Serpin stractnre, mechanism, and fnnction, Chem. Rev. 102, 4751 804, 2002 Hnntington, J.A., Shape-shifting serpins — advantages of a mobile mechanism. Trends Biochem. Sci. 31, 427 35, 2006. 

A means for injecting samples in which the sample is loaded into a short section of tubing and injected onto the column by redirecting the mobile phase through the loop. 

In the load position the sampling loop is isolated from the mobile phase and is open to the atmosphere. A syringe with a capacity several times that of the sampling loop is used to place the sample in the loop. Any extra sample beyond that needed to fill the sample loop exits through the waste line. After loading the sample, the injector is turned to the inject position. In this position the mobile phase is directed through the sampling loop, and the sample is swept onto the column. 

Kovat s retention index (p. 575) liquid-solid adsorption chromatography (p. 590) longitudinal diffusion (p. 560) loop injector (p. 584) mass spectrum (p. 571) mass transfer (p. 561) micellar electrokinetic capillary chromatography (p. 606) micelle (p. 606) mobile phase (p. 546) normal-phase chromatography (p. 580) on-column injection (p. 568) open tubular column (p. 564) packed column (p. 564) peak capacity (p. 554)... 

Two modifications of the duidized-bed reactor technology have been developed. In the first, two gas-phase duidized-bed reactors coimected to one another have been used by Mobil Chemical Co. and Union Carbide to manufacture HDPE resins with broad MWD (74,75). In the second development, a combination of two different reactor types, a small slurry loop reactor followed by one or two gas-phase duidized-bed reactors (Sphetilene process), was used by Montedision to accommodate a Ziegler catalyst with a special particle morphology (76,77). This catalyst is able to produce PE resins in the form of dense spheres with a diameter of up to 4—5 mm such resins are ready for shipping without pelletization. 

One of the first examples of the application of reverse-phase liquid chromatography-gas chromatography for this type of analysis was applied to atrazine (98). This method used a loop-type interface. The mobile phase was the most important parameter because retention in the LC column must be sufficient (there must be a high percentage of water), although a low percentage of water is only possible when the loop-type interface is used to transfer the LC fraction. The authors solved this problem by using methanol/water (60 40) with 5% 1-propanol and a precolumn. The experimental conditions employed are shown in Table 13.2. 

For the LC separation, 10 ml of sample was injeeted through a loop. The LC flow-rate was 1000 p.1 min and at the end of the enriehment proeess this was redueed to 100 p.1 min . The mobile phase eomposition was optimized to eliminate matrix polar eompounds and elute the phthalates in a small fraetion. 

Although the problems associated with septum injectors can be eliminated by using stop-flow septumless injection, currently the most widely used devices in commercial chromatographs are the microvolume sampling valves (Fig. 8.3) which enable samples to be introduced reproducibly into pressurised columns without significant interruption of the mobile phase flow. The sample is loaded at atmospheric pressure into an external loop in the valve and introduced into the mobile phase by an appropriate rotation of the valve. The volume of sample introduced, ranging from 2 piL to over 100 /iL, may be varied by changing... 

It should be stressed that only those surfaces that actually come in contact with the sample need to be bio-compatible and the major parts of the valve can still be manufactured from stainless steel. The actual structure of the valve varies a little from one manufacturer to another but all are modifications of the basic sample valve shown in figure 13. The valve usually consists of five parts. Firstly there is the control knob or handle that allows the valve selector to be rotated and thus determines the load and sample positions. Secondly, a connecting device that communicates the rotary movement to the rotor. Thirdly the valve body that contains the different ports necessary to provide connections to the mobile phase supply, the column, the sample loop if one is available, the sample injection port and finally a port to waste. Then there is the rotor that actually selects the mode of operation of the valve and contains slots that can connect the alternate ports in the valve body to provide loading and sampling functions. Finally there is a pre-load assembly that furnishes an adequate pressure between the faces of the rotor and the valve body to ensure a leak tight seal. 

Where peak dispersion has not been constrained to very small volumes the external sample loop injector can be used and the external loop sample system, which employs six ports, is depicted in figure 15. In the external loop sample valve, three slots are cut in the rotor so that any adjacent pair of ports can be connected. In the loading position shown on the left, the mobile phase supply is connected by a rotor slot to port (4) and the column to port (5) thus allowing mobile phase to flow directly through the column. In this position the sample loop is connected to ports (3) and (6). Sample flows from a syringe into port (1) through the rotor slot to the sample loop at port (6). At the same... 

In November 1997, Ferrari (France) invited Solvay to help them to solve a problem of recycling PVC coated textile for light mobile structures, especially ones used for shortterm applications (advertising). The Vinyloop is aphysical recycling process making use of an organic solvent to separate the PVC compound from the other materials in a PVC composite. It is a closed loop process the solvent is completely recycled. Aspects outlined include history and a description of the process, precipitated PVC compound evaluation and financial data... 

The apparatus employed for this study was a Waters Associates Model ALC/GPC 300 with a differential refractometer as mass detector operated at room temperature. A 2 ml sample loop with polymer concentrations of 0.01-0.1 wt.% cUid a 5 ml siphon were employed with mobile phase flowrates in the reuige 1-8 ml/min. 

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