Manual injectors

A simple system is comprised of an isocratic pump, a manual injector, a UV detector, and a strip-chart recorder. A schematic diagram of an HPLC instrument is shown in Fig. 15.4. This simple configuration is rarely used in most modern laboratories. A typical HPLC system is likely to consist of a multi-solvent pump, an autosampler, an on-line degasser, a column oven, and a UV/Vis or photodiode array detector all connected to and controlled by a data-handling workstation. Examples of modular and integrated systems are shown in Fig. 15.5. Some of the important instrumental requirements are summarized in Table 15.2. 

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. ... 

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. 

Qu an 11 a 11o n me t ho d System number Manual injector Total injections Sample rate Sample amount Scale factor Response factors Channel to calibrate... 

When the injectable has migrated to the tip, introduce the needle into the needle holder on the micromanipulator or into the manual injector. 

Inject a 1- to 5-pl aliquot of the chlorophyll solution onto the HPLC system using a microsyringe with a manual injector or using an autoinjector under computer control. 

The most common job for these systems is the fast-running isocratic separation. They could be built up from the QC isocratic, but dial-a-mix isocratic is faster and more convenient since they switch easily from job to job. These systems come in the same two flavors as the research gradient, low- and high-pressure mixing, but replace the manual injector with an autosampler, allowing 24-hr operation. For thermally labile samples that need to be held for a period of time before being injected, there are autosampler chillers available. 

The need for unattended and precise sample injection for HPLC has lead to development of a wide variety of automated sample injection devices. Autosamplers function in essentially the same way as manual injectors, except that the sample is introduced automatically from a sample vial held in a carousel or an X-Y grid (Fig. 3.15). The carousel format provides a reliable and rapid means of moving samples past an injection station, whereas the XY grid format allows a convenient random access configuration. 

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. 

LC Analyses, LC analyses were performed by using a Waters 600 pump equipped with a Rheodyne Model 7725i manual injector (50 pL loop) and a Waters Model 991 photodiode array detection system. Chromatographic separation was achieved on a YMC Pack PolymerCtS (YMC Inc. Wilmington, NC) column with a OPTI-SOLV mini filter (Optimise Technologies Inc., Portland, OR). The linear gradient was 60% H2O (solvent A)/40% acetonitrile (solvent B) which was held for 10 min, then increased by 8% acetonitrile/min to 20% H2O/80% acetonitrile, and held for 15 min. The flow rate was 0.8 mL/min. 

With manual injector, make sure there is a container under the overflow, keep injection needles clean to avoid contamination, flush with isopropanol if necessary. 

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. 

Manual injectors are operationally qualified for repeatability and carryover. Autosamplers are additionally checked for accuracy. Injection systems are qualified after the solvent dehvery system and the detector. To eliminate subjective effects, the chromatographic column is excluded from the setup for qualifying injectors. The column is replaced by a low internal diameter, significant length stainless steel tubing, generating a pressure drop similar to that in a packed column (about 100 bar). 

In the standard laboratory-based form of the instrumentation, a Model 6000A solvent delivery pump was employed in conjunction with a Model U6K universal injector both obtained from Waters Associates. In the first version of an automated system, the solvent delivery pump remained, but the manual injector was replaced by its automatic counterpart, the Model 7126 Automatic Sample Injector from Rheodyne. 

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