Pneumatic injection

In paper or gel electrophoresis, the sample may be applied with a syringe or a micropipette similar to the application of samples to thin-layer plates. In some cases, there may be wells in the gel that accept the solution containing the species to be separated. In CE, samples may be applied using electromigration, hydrostatic, or pneumatic injection. In all cases, the ions to be separated must be soluble in and compatible with the stationary phases and buffers used. 

Automatic headspace samplers are available from manufacturers of gas chromatographs. These devices are based on the technique of sampling an amount of vapor above the sample itself. Samples are sealed, neat or in a suitable solvent, in containers, and hold at a preset temperature in a thermostatted liquid bath. The headspace vapor results as a partition equilibrium is established between the liquid or solid and the gaseous phase of the volatiles. As each sample is presented to the analyzer, the vessel is punctured and a portion of the headspace gas is withdrawn by a pneumatic injection technique and forced into the column. The main application for those samplers is in the routine analysis of low-boiling fractions in samples containing nonvolatile solids or high-boiling components. Some of the more popular applications today are ... 

Where pneumatic injection systems are used, finer grades (e.g., 2 to 6 mm) are specified to suit the characteristics of the system [27.5]. 

Figure 27 Electropherogram of a mixture of nicotinic acid and related compounds. Conditions applied voltage, 25 kV sample injection, 7 s pneumatic injection capillary, unmodified fused-silica (57 cm X 50 xm i.d.) buffer, acetonitrile-buffer [10 mM KH2PO4 (pH 2.50), titrated with phosphoric acid] detection wavelength, 254 nm. iV -MNA, iV -methylnicotinamide (see Fig. 1). (From Ref. 70.)... 

Radial density gradients in FCC and other large-diameter pneumatic transfer risers reflect gas—soHd maldistributions and reduce product yields. Cold-flow units are used to measure the transverse catalyst profiles as functions of gas velocity, catalyst flux, and inlet design. Impacts of measured flow distributions have been evaluated using a simple four lump kinetic model and assuming dispersed catalyst clusters where all the reactions are assumed to occur coupled with a continuous gas phase. A 3 wt % conversion advantage is determined for injection feed around the riser circumference as compared with an axial injection design (28). 

As indicated, pig iron production requires input of a reducing agent. Stahlwerke Bremen uses plastic waste as a substitute for fuel oil. Plastics are injected into the blast furnace in a similar way to coal powder or fuel oil. In order to remove fibres and metal particles a separation takes place. Large particles are separated via a screen of > 18 mm. The smaller plastic waste particles (< 18 mm) go to the injection vessel. There, an injection pressure of about 0.5 MPa is built up. Via a pneumatic process the plastics can be dosed and discharged into the blast furnace. The bulk density of the plastics has to be 0.3 tonnes/m. ... 

Wagner, H. P., Pepich, B. V., Hautman, D. P., and Munch, D. J., Analysis of 500 ng/1 levels of bromate in drinking water by direct-injection suppressed ion chromatography coupled with a single, pneumatically delivered postcolumn reagent, /. Chromatogr. A, 850, 119, 1999. 

As the vast majority of LC separations are carried out by means of gradient-elution RPLC, solvent-elimination RPLC-FUR interfaces suitable for the elimination of aqueous eluent contents are of considerable use. RPLC-FTTR systems based on TSP, PB and ultrasonic nebulisa-tion can handle relatively high flows of aqueous eluents (0.3-1 ml.min 1) and allow the use of conventional-size LC. However, due to diffuse spray characteristics and poor efficiency of analyte transfer to the substrate, their applicability is limited, with moderate (100 ng) to unfavourable (l-10pg) identification limits (mass injected). Better results (0.5-5 ng injected) are obtained with pneumatic and electrospray nebulisers, especially in combination with ZnSe substrates. Pneumatic LC-FI1R interfaces combine rapid solvent elimination with a relatively narrow spray. This allows deposition of analytes in narrow spots, so that FUR transmission microscopy achieves mass sensitivities in the low- or even sub-ng range. The flow-rates that can be handled directly by these systems are 2-50 pLmin-1, which means that micro- or narrow-bore LC (i.d. 0.2-1 mm) has to be applied. 

In ICP-AES and ICP-MS, sample mineralisation is the Achilles heel. Sample introduction systems for ICP-AES are numerous gas-phase introduction, pneumatic nebulisation (PN), direct-injection nebulisation (DIN), thermal spray, ultrasonic nebulisation (USN), electrothermal vaporisation (ETV) (furnace, cup, filament), hydride generation, electroerosion, laser ablation and direct sample insertion. Atomisation is an essential process in many fields where a dispersion of liquid particles in a gas is required. Pneumatic nebulisation is most commonly used in conjunction with a spray chamber that serves as a droplet separator, allowing droplets with average diameters of typically <10 xm to pass and enter the ICP. Spray chambers, which reduce solvent load and deal with coarse aerosols, should be as small as possible (micro-nebulisation [177]). Direct injection in the plasma torch is feasible [178]. Ultrasonic atomisers are designed to specifically operate from a vibrational energy source [179]. 

Typically it took about 160 to 200 seconds to inject a pulse of about 455 kg coarse tracer particles into the bed pneumatically from the coaxial solid feed tube. It can be clearly seen from Figs. 38 to 42 that the tracer particle concentration increases from essentially zero to a final equilibrium value, depending on the location of the sampling port. The steady state was usually reached within about 5 minutes. There is considerable scatter in the data in some cases. This is to be expected because the tracer concentration to be detected is small, on the order of 4%, and absolute uniformity of mixing inside a heterogeneous fluidized bed is difficult to obtain. 

Kennedy, O. C., Wypych, P. W., and Arnold, P. C., The Effect of Blow Tank Air Injection on Pneumatic Conveying Performance, Pneumatech 3, Int. Conf. on Pneumatic Conveying Technol., Jersey, Channel Islands, UK (1987)... 

Selves, T. P., Barnes, R. N., and Reed, A. R., The Use of Flow Diverting Air Injection to Actively Control the Split Ratio of Pneumatically Conveyed Particulate Materials, 5th Int. Conf. on Bulk Materials Storage, Handling and Transportation, IEAust. Proc, 1 263-271, Newcastle (1995)... 

To enhance automation capacity, a direct transfer of the acceptor phase to a HPLC system can be arranged by setting up a pre-column that allows the injection of as much volume of analyte as possible (Figure 1.33). Pneumatically or electrically actuated valves controlled by a computer provide... 

Today s gas chromatograph is a modern, computer-controlled instrument, consisting of an integrated inlet, column oven and detector, with electronically controlled pneumatics and temperature zones. It has an inlet capable of both the split and splitless-injection techniques and it has a highly sensitive (detection limit in the pictogram range) detector... 

A modern gas chromatograph, whether configured for packed or capillary column use, consists of several basic components. All of them must be properly chosen and operated for successful analysis. These are pneumatics and gas-handling systems, an injection device, an inlet, a column oven and column, a detector and a data system. Since the inception of GC in the 1950s, instrumentation has evolved significantly as new techniques and technologies were developed. This section provides an overview of the major components of a modern gas chromatograph, with details about how to choose components based on analytical needs, and applications. 

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