Syringes, types

At the time of the solvent methanol experiments a metering pump was used. In some experiments the pulsating action of the pump can be disturbing, so a high-pressure syringe-type pump can be used. Since mass flow controllers are available now, the combination of a gas-pressurized feed tank on an electronic scale for liquid level indication and a mass flow controller seems to be a good choice. Both the feed tank and separator can be heated or cooled. In the case of the solvent methanol experiments. 

A central component of the LC instrument is the pump, for its characteristics can strongly influence an analysis (e.g., flow reproducibility). The three principal types of systems— pneumatic, syringe type and reciprocating piston—have been reviewed in the literature (18-20). 

The syringe type pump consists of mechanically driven piston emptying a large volume chamber 250 ml). In some... 

Type constant flow twin reciprocating constant flow syringe type constant pressure pneumatic amplifier... 

Compared to syringe type or reciprocating pumps, pneumatic amplifier pumps are very cheap. They tend to be rather difficult to dismantle for repairs, and some types are very noisy in operation. Because they do not provide a constant flow of mobile phase, they are not used much in analytical hplc. They can, however, operate at high pressures and flow rates and so are used mainly for packing columns, where high pressures are needed and variations in the flow rate through the column do not matter. 

Two types of constant flow pump have been used in hplc. Fig. 2.2c shows a syringe type pump. 

Pump characteristic Simple single- head Single- head smooth pulse Simple dual-head Dual-head, compressibility-corrected, smooth pulse Dual-head, closed loop flow control Triple head low-volume Syringe- type Hydraulic amplifier Simple Amplifier Amplifier with flow control... 

Computer-controlled motorized syringe-type precision burettes are generally employed nowadays for addition of titrant. The burettes are calibrated by weighing the amounts of distilled water they deliver over various time intervals. The delivery rate in units of volume per unit time is determined from the mass rate delivery using the density of water at the calibration temperature. 

In SPE, the extraction is carried out using a small column (syringe-type or cartridge) containing 0.1 to 1 g of sorbent. The sorbent is typically a modified silica gel or one of many copolymers. This chemical filter can only be used once. The low-cost SPE process, which can be readily automated, is generally more useful for hydrophobic or apolar compounds than it is for ionic substances. 

The stopped-flow method uses syringe-type pumps, (a), to feed the components, A and B, through a mixing cell, (c), into the reaction cell, (d), which can be an optical cell (Fig. 3.3-5). The pumps, mixing cell, and reactor are well thermostatted. The flow is stopped when the syringe, (e), is loaded and operates a switch, (f), to start the monitoring device. The change in concentration is detected either by spectroscopy or conductivity measurement. 

Figure 3.3-5. Stopped flow apparatus [19]. a, Syringe type pump b, thermostat c, mixing cell d, reaction cell e, stop syringe f, switch g, photo multiplier h, monochromatic filter i, lamp j, controller k, transducer 1, computer.

In the syringe-type pump the liquid is enclosed in a cylinder. A piston moves at a constant speed to push the liquid. Eluent compressibility induces time-consuming flow equilibrium. Nevertheless, the flow from a syringe pump is pulse free. For micro LC, flow rates of 50 yuL/min are utilized in spite of the drawback of column pressurization. With very low flow rates (in the nanoliter range) the use of pumps is tedious, and split-flow techniques are required. 

Be sure samples are consistent. For fixed volume sample loop, use 2-3 times loop volume to ensure loop is completely filled. Be sure automatic sampler vials contain sufficient sample. Check syringe-type injectors for air. In systems with wash or flushing step, be sure wash solution does not precipitate sample components. 

Each step was optimized first before transposing the sequence into a one-pot procedure where excess reagents were removed by filtration in a syringe-type filter before adding the next reactant. Starting from three different methylthioiminium salts 13, rhodanine derivatives 14 and methyliminium salts 17 (Fig. 5.6) a 3 X 3 X 3 parallel synthesis was conducted to furnish 27 different kinds of rhodacyanines 12 (Table 5.1). 

One strives to achieve a uniform distribution across the entire membrane surface. Again, like traditional chromatography, the dead volume must be minimized. The design of the standard dead-end filtration does not minimize the hold-up volumes in the inlet or outlet channels. The commonly available Luer-Lok connector for ease of use is one of the biggest contributors to housing related dispersion in the small syringe-type devices since the gap... 

The capillary tube-based system employs a set of tiny tubes of fixed length. When a tube is dipped into a source liquid, the tube is filled with liquid via capillary action, then compressed air blows the liquid in the tube into the destination well. Both types of tools can deliver nanoliter volumes with reasonable accuracy and precision. The limitation is that they can only deliver a fixed volume without changes of pin or tube settings. New syringe-type liquid handlers capable of delivering 100 nL or less are now on the market. 

The following contribution compU recently published cyclizations. Most of these examples have not been included in our former survey on the dilution principle [3 a] and are thought as a continuation and update of that former survey up to 1990. As shown there, some characteristic experimental standard methods are specified here as well. (For a standard apparatus and a modified motor-driven syringe-type version see [3d, e].)... 

The vast majority of pumps currently used in analytical HPLC are of the constant flow variety. With this type of pump, changes in the chromatographic system, for instance those leading to variations in the back pressure experienced by the pump, are compensated for, and the flow rate remains constant this is an important factor in most analytical applications. Two major types of constant flow pump exist the reciprocating piston design and the syringe type. 

Although several high-pressure pumps have been used in SFC, the syringe-type pump has been the preferred to deliver CO2 into the system. This choice is made due to the absence of pulses of syringe pumps and the possibility of flow rate and pressure control. 

Applied Separation s instrument, the Spe-ed Wiz, is an example of a semiautomated SPE system (Fig. 10.1), where some manual intervention is required. In this system, the analyst must manually pour the samples onto the SPE column, and add the elution receiver or test tube. The Spe-ed Wiz will condition the cartridge and prepare it for sample addition. The sample is manually added to the test tube and the Spe-ed Wiz will aspirate the sample, or (he lid can be closed to load the samples. After the sample is loaded on the columns (syringe type), the columns are rinsed, and elution tubes must be manually placed in the elution rack. The elution is automated. 

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