Injector valve manual

An injector valve operates in two modes— the fixed-loop mode or the partial-loop mode. In the fixed-loop mode, a sample is overfilled into the loop at 2-4 times the loop volume and the entire loop content is injected. In the partial-loop fill mode, a variable sample aliquot, measured precisely by a syringe at <50% of the loop volume, is injected. Note that the sample slug is introduced into the end of the sample loop and is back flushed onto the column to minimize band dispersion by the sample loop (Figure 9). Due to the emphasis on productivity, manual injectors are seldom used in the pharmaceutical laboratory except for preparative applications. 

Figure 4.6. (a) A diagram of a manual injector valve. A schematic of a Rheodyne 7125 injector valve during the LOAD (b) and INJECT (c) cycle during a partial-loop injection operation. 

The HPLC analysis was performed on an Agilent 1100 series LC (Santa Clara, CA), equipped with a quaternary pump (G1311A) and a UV multiwave length detector (G1365B), set at 220 and 280nm. The injector was a Rheodyne manual injector valve, model 77251 (Santa Clara, CA), equipped with a 20-1 sample loop. The column temperature was controlled using a ThermaSphere TS-130 oven from Phenomenex set at 40 °C. 

If reconnecting the column fails to correct the leak, then other common areas to search for leaks are the detector flow cell, the pump (around the pistons), and the injector valve. The same process should be followed until the source of the leak is identified and corrected. New parts maybe required for example, the pump piston seals may have worn out. Always consult the manufacturer s user manual when attempting to replace any part. If in doubt, contact the manufacturer and ask for installation of the new part. It will be necessary to undertake system performance qualification on the replacement of any worn out or damaged part (see Chapter 8). 

Figure 2.4 (a) Diagram of a six-port loop injector being filled by injection of the analyte solution from a syringe. In this mode the loop is bypassed and the mobile phase flows directly from pump to column through the injector valve via ports 2 and 3. In order to inject the sample in the loop onto the column the valve is rotated so that internal connections are now made between ports 1 and 2, and between ports 3 and 4. Reproduced from literature of Rheodyne Corporation, Technical Note 5 (2001), Achieving Accuracy and Precision with Rheodyne Manual Sample Injectors, with permission (www.rheodyne.com). 

Perkin- F.lmer 8410 Yes Yes Single detector instrument (detector chosen on purchase) FID BCD FTD FPD TCD 1. Plash vaporisation 2. Split-splitless injector 3. Manual or automatic as sampling valves 4. Manual or automatic liquid sampling valves No No No No No Yes/Yes Yes, down to -80 C... 

Ga.s Eeeders. Chlorine gas is usually fed from a chlorine cylinder equipped with a pressure gauge, reducing valve, regulating valve, feed-rate indicator, and aspirator-type injector for dissolving the chlorine gas in water. The feeder can be manually, or more desirably automatically, controlled utili2ing continuous amperometric or potentiometric measurement of the free chlorine residual. The chlorine solution is normally introduced into the return line to the filter. 

The maximum injection volume depends on the volume of the sample loop in the injection valve. The reproducibility of manual injection depends on the skill of the operator. The use of a small sample loop and an overflow injection of the sample solution so that the loop is fully flushed with sample are basic requirements for quantitative analysis. The highest injection reproducibility can be obtained by an auto-injector with a fixed sample loop. The smallest reasonable injection volume is 1 (A. A nl-scale injection valve can be constructed however, the memory effect at the surface of contact parts affects quantitative analysis compared with the use of a /d-scale injection valve. For a semi-micro system, a low hold-up volume injection valve is desired. The minimum injection volume is 80 nl. For a preparative-scale injection, the sample loop can be easily replaced with a larger-volume loop, such as a 200 jA, instead of the standard 20 /A loop. 

An HPTC injector allows the introduction of a precise sample volume onto the column. A typical manual injector consists of a 6-port valve with a rotor, a sample loop and a needle port (Eigure 9). A sample solution is introduced into the sample loop using a 22-gauge blunt tip syringe in the TOAD position. The sample is then injected into the column by switching the valve to INJECT. The typical external sample loop size ranges from 6 pT to 2 mT. For many years, the Rheodyne 7125 injector was the industry-standard. In the early 1990s, it was replaced by the Rheodyne 7725 injector, which injects samples without momentary flow disruptions. ... 

Figure 3.5—The two positions of a loop injector, a) Load sample b) Inject sample. Schematic of the model 7125 valve from Rheodyne Inc. Injection valves can be manual, pneumatic or electrical (reproduced with...

Sample introduction is a major hardware problem for SFC. The sample solvent composition and the injection pressure and temperature can all affect sample introduction. The high solute diffusion and lower viscosity which favor supercritical fluids over liquid mobile phases can cause problems in injection. Back-diffusion can occur, causing broad solvent peaks and poor solute peak shape. There can also be a complex phase behavior as well as a solubility phenomenon taking place due to the fact that one may have combinations of supercritical fluid (neat or mixed with sample solvent), a subcritical liquified gas, sample solvents, and solute present simultaneously in the injector and column head [2]. All of these can contribute individually to reproducibility problems in SFC. Both dynamic and timed split modes are used for sample introduction in capillary SFC. Dynamic split injectors have a microvalve and splitter assembly. The amount of injection is based on the size of a fused silica restrictor. In the timed split mode, the SFC column is directly connected to the injection valve. Highspeed pneumatics and electronics are used along with a standard injection valve and actuator. Rapid actuation of the valve from the load to the inject position and back occurs in milliseconds. In this mode, one can program the time of injection on a computer and thus control the amount of injection. In packed-column SFC, an injector similar to HPLC is used and whole loop is injected on the column. The valve is switched either manually or automatically through a remote injector port. The injection is done under pressure. 

The sample is introduced into the chromatograph via a sample injector. To minimize dispersion and the broadening of peaks, the sample must be injected as a sharp plug. Valve injectors are usually used in commercial instrumentation, because the sample is introduced with minimal interruption of flow. The injection devices are the basis for both manual and automatic injection because of their ease of use, reliability, and ease of automation.6 A typical injection valve, the six-port valve, is illustrated in Figure 3.14. 

Sample injector The sample injector is located between the solvent pump and the HPLC column, and serves to deliver or inject the sample dissolved in solvent onto the column. The most common form of sample injector is the so-called loop-and-valve injector. Sample is injected from a specialized syringe (manually) or delivered by means of an autosampler (automatically) into a small diameter loop. The loop-and-valve injector allows switching by means of a valve between initial delivery of solvent alone to the column (so-called column equilibration), to subsequent delivery of the sample onto the column. 

Fig. 2 Schematic diagram of a cross section of a cold on-S column injector with a duck-hill valve. 1 Cool tower needle guide, 2A disk septum for automated injections, 2B isolatioi valve for manual injections, 3 frit, 4 carrier gas, 5 oven waU, j 6 ferrule, 7 capillary colunrn, 8 column nut. (Modified froir ...

Loop-based injection is used for sample insertion and a similar procedure is used for displacing the tubular detector D between monitoring sites a and b (Figs 7.9 and 7.10, lower). Consequently, this strategy has usually been accomplished using two loop-based injectors or a double injection valve/commutator [81], where a flow cell with two small transmission lines replaces one of the sampling loops. Although the flow system can be manually operated, computer-controlled valves or commutators have been preferred. 

Samples can be introduced manually into the valve with a syringe to fill the sample loop. Automated sampling valves are routinely used today in which samples are taken from an autosampler for unattended operation. The major limitation of valve injectors is that the sample size is fixed, and the loop must be changed in order to vary the injected sample size. There are automated motor-driven adjustable syringes that provide enough pressure to inject the sample past a check valve that prevents backflow. 

Both the rotary valve and the proportional injector supply highly reproducible, variable injected volumes (held in loops) and are fast and convenient to operate manually. In addition, they allow for easy automation of the injection operation. 

K. Uchida, M. Tomoda, and S. Saito, The Development of a Manually Operated Sample Injector Employing a Pair of Six-Valve Systems [in Japanese]. J. Flow Injection Anal., 3(1) (1986) 18. 

The sample introduction system must be capable of introducing a known and variable volume of sample solution reproducibly into the pressurized mobile phase as a sharp plug without adversely affecting the efficiency of the column. The superiority of valve injection has been adequately demonstrated for this purpose and is now universally used in virtually all modern instruments for both manual and automated sample introduction systems [1,2,7,31,32]. Earlier approaches using septum-equipped injectors have passed into disuse for a several reasons, such as limited pressure capability, poor resealability, contamination of the mobile phase, disruption of the column packing, etc., but mainly because they were awkward and inconvenient to use compared with valves. For dilute sample solutions volume overload restricts the maximum sample volume that can be introduced onto the column without a dramatic loss of performance. On-column or precolumn sample focusing mechanisms can be exploited as a trace enrichment technique to enhance sample detectability. Solid-phase extraction and in-column solid-phase microextraction provide a convenient mechanism for isolation, concentration and matrix simplification that are easily interfaced to a liquid chromatograph for fully or semi-automated analysis of complex samples (section 5.3.2). 

Sample introduction is done either with a hand injector or a manual valve (in many cases supplied by Valeo or Rheodyne) or with an autosampler. 

The sample injector The sample injector can be a simple septum injector and a hypodermic syringe that can place the sample directly on to the column or a high-pressure sample valve (that can be manually or mechanically operated) fitted with an appropriate sample loop. 

Fig. 1 VersaFlash high throughput flash purification (HTTP) system shown with two stacked prepacked 40 x 75 mm (51 g) cartridges inserted in the support stand and 110 x 300 mm (1.35 kg), 80 X 150 mm (410 g), and 23 X 110 mm (23 g) cartridges on the right side of the eluent pump. The 3-way valve injector at the upper right allows direct application of sample onto cartridges using a syringe. The outlet tubing can be used for manual sample collection or connection to an automated fraction collector or UV detector.

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