Pump, sampling control

Fig. 2.9 Schematic diagram of experimental set-up 1 inlet tank, 2 pump, 3 control valve, 4 temperature and pressure measurement ports, 5 sample of porous medium, 6 top of test section, 7 housing, 8 copper rod, 9 heater, 10 insulation, 11 exit tank, 12 electronic scales. Reprinted from Hetsroni et al. (2006a) with permission...

A stainless steel column (4.6 mm internal diameter by 250 mm length) packed with 7 micron Zorbax ODS (Dupont) was equilibrated with 82 % Acetonitrile in water at a flow rate of 2.0 ml/min. provided by a Spectra Physics Model 87(X) pump and controller. The effluent was monitored at 230 nm using either a Tracor UV-Visible detector Model 970A or a Jasco Uvidec UV detector Model 1(X)-V. Peaks were recorded and calculated on a SpectraPhysics recording integrator. Model 4200 or Model 4270. Samples of 0.5 mg/ml in toluene were applied to the column automatically with a Micromeritics Autosampler Model 725 equipped with a 10 pi loop. 

Kinetic Studies. Peracetic Ac id Decomposition. Studies with manganese catalyst were conducted by the capacity-flow method described by Caldin (9). The reactor consisted of a glass tube (5 inches long X 2 inches o.d.), a small centrifugal pump (for stirring by circulation), and a coil for temperature control (usually 1°C.) total liquid volume was 550 ml. Standardized peracetic acid solutions in acetic acid (0.1-0.4M) and catalyst solutions also in acetic acid were metered into the reactor with separate positive displacement pumps. Samples were quenched with aqueous potassium iodide. The liberated iodine was titrated with thiosulfate. Peracetic acid decomposition rates were calculated from the feed rate and the difference between peracetic acid concentration in the feed and exit streams. 

Application of a potential between reservoirs 1 (sample) and 4 (injection waste) electrokinetically pumps sample solution as indicated in Fig. 3. In this way, a geometrically defined 150 pm (90 pi) section of the separation channel can be filled [19]. If the injection potential is applied long enough to ensure that even the slowest sample component has completely filled the injection volume, a representative aliquot of sample can be analyzed (so-called volume defined injection). This is in contrast to electrokinetic sample injection in conventional capillaries, which is known to bias the sample according to the respective ionic mobilities [61]. These characteristic differences are shown schematically in Fig. 4. It should be noted that this picoliter sample injector is exclusively controlled by the application of electric fields and does not require any active elements with moving parts such as valves and external pumps. The reproducibility of the peak height of the injected sample plugs has been reported to be within 2 % RSD (relative standard deviation) and less [19,23]. 

A more expensive alternative is to use standard AutoAnalyser type systems, based on multichannel peristaltic pumps, to pump samples and reagents and/or diluents at the desired rates to give automatic mixing at the desired ratio. Flame photometric detectors have been used for many years with AutoAnalysers, especially in clinical laboratories. Curiously, in the past, this approach has less often been routinely used in environmental analytical laboratories employing flame spectrometry, perhaps because an attractive feature of flame spectrometry is the speed of response when used conventionally. Over the past few years, however, there has been an increasing tendency towards fully automated, unattended operation of flame spectrometers. This undoubtedly reflects, at least in part, the improvements in safety features in modern instruments, which often incorporate a comprehensive selection of fail-safe devices. It also reflects the impact of microprocessor control systems, which have greatly facilitated automation of periodic recalibration. 

FIGURE 5 Basic configuration of expanded-bed column operation. Pump 2 pushes down the flow adaptor, pump I controls the upward flow of the sample and the various buffers. Valve VI is a four-way valve directing the flow to and from the column. 

The general arrangement of an hplc system is fairly simple, as shown in Fig. 9.17. Solvent is pumped from a reservoir through a piston pump which controls the flow rate. From the pump the solvent passes through a pulse damper which removes some of the pulsing effect generated in the pump and also acts as a pressure regulator. In between the pulse damper and the column there is an injection valve which allows the sample to be introduced into the solvent stream. 

After ejecting the CO molecule to the substrate at a constant isotropic pressure of O2 (5 X 10 mbar), the resulting product molecules (CO2) were detected by an absolutely calibrated quadrupole mass spectrometer. The differentially pumped, computer-controlled mass spectrometer (Balzers QMG 421) is mounted in line-of-sight with the sample. At the entrance, near the ionizer of the quadrupole mass spectrometer, a skimmer with an opening of 3 mm is mounted. The skimmer is biased to —150 V in order to prevent electron-stimulated desorption induced by emitting electrons from the ionizer of the mass spectrometer. After amplifying... 

Feed introduction Feed injection via pump Sample loop Feed container Check the volume behind the injection point Adjust the size, do not use too large loops Control temperature, stir, over-pressurize with nitrogen... 

A less expensive method that can be used at low pressures is to use just one pump, a control valve, and a mixing chamber. Figures 19-22 to 24, p. 198, show the effect of gradient elution on a sample. The explanations are by Waters Corporation applications analysts. 

Figure 5.12. (a) Manifold for hydrodynamic injection. The sample volume is aspirated by pump 1, operating at a pumping rate of y mL/min, and a fixed volume of sample from reservoir 5 passes into conduit L. Subsequently pump 2 is activated, pumping at rates x = z mL/ min, and the sample is flushed through reactor C to the detector D. The operations of the two pumps is controlled by the timer T, the time sequence of events being as depicted in ib). 

Figure Z2- Modular FIA system (Eppendorf)- The system consists of a sampler, selector, four-channel pump, sample injector, reaction system manifold), master module (detector, controller for data processing, and master system control) (by permission of Eppendorf, Hamburg, Cer-many).

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