Gradient setup

Figure 8.74 Solvent compensation without a second delay column in an inverse gradient setup for charged aerosol detection.

FIG. 18 Setup of the cylindrical simulation cell with periodic boundary condition in the axial (z) direction. In the NEMD simulation, a constant gradient in the potential 4>(z) is applied, and concentration c(z) is maintained constant by recycling ions. 

The stirred batch reactors are easy to operate and their configurations avoid temperature and concentration gradient (Table 5). These reactors are useful for hydrolysis reactions proceeding very slowly. After the end of the batch reaction, separation of the powdered enzyme support and the product from the reaction mixture can be accomplished by a simple centrifugation and/or filtration. Roffler et al. [114] investigated two-phase biocatalysis and described stirred-tank reactor coupled to a settler for extraction of product with direct solvent addition. This basic experimental setup can lead to a rather stable emulsion that needs a long settling time. 

FIGURE 16.5 Schematic of instrumental setup for 2D micro-RPLC-CZE. A split injection/ flow system is used to deliver a nanoliter per second flow rate to the micro-RP-HPLC column from the gradient LC pump. The HPLC microcolumn has 50 pm i.d. and 76 cm length, and the electrophoresis capillary has 17 pm i.d., L — 25 cm, and/= 15 cm. The valve is air-actuated and controls the flow of flush buffer (reprinted with permission from Analytical Chemistry). 

The trade-off might be that the selectivity of the gradient HPLC method for the individual cyclic oligomers is better. One way to increase resolution of the LCCC procedure is to couple this type of separation with a SEC separation in a 2D experimental setup. The higher selectivity of the 2DLC separation could help to resolve individual oligomers of different functionalities. 

Collect fractions starting from the bottom of the gradient, while recording an absorbance profile at 254 nm (which is dominated by the very abundant ribosomal RNA). We use a setup consisting of a peristaltic pump, ultraviolet (UV) detector, and fraction collector commonly used for chromatography experiments (GE Healthcare Life Sciences). 

In addition to Ti and T2, which reflect the rotational motion of water, NMR can also be used to measure the translational motion of water. If an additional, relatively small (compared to B0), steady magnetic field gradient is incorporated into a pulsed NMR experimental setup, a translational diffusion coefficient (D, m2/s) can be measured (called pulsed field gradient NMR). 

Up to this point, water mobility values obtained are average values for an entire sample. However, if magnetic field gradients in the x, y, and z directions are incorporated into a pulsed NMR experimental setup, the spatial distribution aspects of water mobility (7), T2, and D) can also be measured via the use of magnetic resonance imaging (MRI) techniques. 

There are many variations on setting up the inlets to the MUX interface, depending on the needs of the laboratory. In one setup, one pump is used to deliver the flow through a flow splitter and multiple probe injector to four LC columns.The flow from each column is then fed into the MUX interface. In another variation, on-line SPE is coupled with LC. One pump, followed by a flow splitter, and one four-injector autosampler are used to feed samples into four extraction columns. A second pump is used (again with a flow splitter) to run gradients on the four LC columns into the MUX interface. In yet another system, an eight-channel UV MUX system is utilized. ... 

Fig. 1.44 2D-LC setup. The first ion exchange dimension is performed with a column with an i.d. of 1 mm, at a flow rate of 50 pL min while the second dimension uses a nanocolumn with an i.d. of 0.75 mm and a flow rate of 300 nL min. First dimension ion exchange has ten salt steps 0, 5, 10, 15, 20, 25, 50, 75, 100, 200 mM KCI. Second dimension is typically an organic gradient 5% to 80% acetonitrile with 0.1% formic acid in 30 min.

Two-dimensional lECxRP setups by using an ion exchange column by means of salt gradient in the first dimension and an RP column in the second dimension have been extensively employed for... 

Salt (ionic strength) gradients in lEC discussed in Section 5.4.3.3 are frequently used in the separation of complex peptides, proteins, and other biopolymer samples as a complementary technique to RP solvent gradient separations, often in a 2D setup [99,100]. The gradients usually start at a low salt (chloride, sulfate, etc.) concentration and typically run from 0.005 to 0.5 M. A buffer is used to control the pH acetonitrile and methanol may be added to improve the resolution and urea to improve the solubility of proteins that are difficult to dissolve. Ion exchangers with not strongly hydrophobic matrices usually prevent protein denaturation in aqueous mobile phases. 

The effect of the dwell volume on the retention times of analytes increases with decreasing retention factor at the start of gradient elution and with increasing ratio VpIV, and becomes very significant in the instrumental setup with the dwell volume comparable to or larger than the column hold-up volume, which is more likely to occur in micro- or in capillary LC than in conventional analytical LC (see Figure 5.4) [12]. 

Fig. 2.1. Correlation between tunneling conductance and force. The tunneling conductance and the force gradient are measured simultaneously. The origin of the abscissa is the equilibrium point, where the net force is zero. It corresponds to a tunneling conductivity of 10 O. The experimental setup is schematically shown in the inset. (Reproduced from Diirig et al., 1988, with permission.)...

The setup for a Faraday experiment is represented schematically in Fig. 11.54. If a sample of mass in and specific susceptibility y is placed in a nonuniform field H that has a gradient in the x direction (SHISx) the sample will experience a force (/) along jc due to the gradient ... 

Merzhanov et al (Ref 3) also made an investigation of the thermal explosion of Dinitrohy-droxydiethylnitramine (mp 52.5°) and of Tetryl (mp 130°) in the liq phase under conditions where the reaction zone was free of temp distribution and the entire thermal gradient was at the walls of the container. The method exptl setup were the same as previously used by the authors (Ref 1). The activation energy, thermal effect critical temp were reported for both expls (Ref 6)... 

Run Module The run module is used to set up the LC conditions, including the pump (e.g., gradient method), UV methods (e.g., wavelength), and autosampler (e.g., sequence setup). Apart from the LC, the method for radiochemical detection and the volume of liquid scintillant for radioactivity counting is also programmed in this module. The autosampler (as set up by the mn module) is used to trigger the Start Run for all other instruments through external contact closures. 

At a reactor temperature of 300 °C the temperature gradient between reactor centre and edge was about 40 °C and thus not acceptable. Different heat sources had been studied. The best solution proved to be a commercial heating plate used in Ceran top stoves. For libraries of 10 cm diameter a heating plate of 1,2 kW and outer diameter of 17 cm has been used. This heat source heats an air pad, which in turn heats the reactor bottom mounted above the heater (see Fig. 7.9 below). With this setup the temperature gradient has been reduced to <4°C at 300 °C (Fig. 7.3), which was found acceptable for a primary screening technique. 

Fig. 2 (a-i) Series of SFM phase images (z-range 0°-10°) of a 39-nm thick S47H10M4382 film after annealing for 6.5 h in saturated toluene vapor in the gradient electrode setup. The arrow in (a) indicate the direction of the electric field vector. Scale bar. 500 nm. Reprinted with permission from Macromolecules [20], Copyright 2008 American Chemical Society... 

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