Loop injection valves

Equipment. A LDC (Laboratory Data Control) Constametric III pump was used together with a Rheodyne 7120 20 yl loop injection valve and two LDC Spectromonitor III, variable wavelength UV-detectors. A Stanstead constant pressure pump was used for packing the columns. 

HPLC The sample was injected on to an ACS Model LC750 chromatograph with dual pumps (Applied Chromatography Systems Ltd, Luton, Beds, U.K.) by means of a loop injection valve,... 

At lower pressure (<7-10.5 MPa) syringe injection of the sample through a membrane is possible, but mostly loop injection valves are used for sample application. These valves may be operated at a pressure up to 42-49 MPa. 

Figure 6.16 External loop injection valves (a) load, and (b) inject.

The flow-injection manifold used for the analysis of iron (III) is given in figure 1. It consisted of three channels, the first two, mounted on a peristaltic pump, were used for propelling potassium iodide and hydrochloric acid streams. Both iodide and acid were mixed in a delay coil and downstream merged with the third channel used for the water carrier stream. The four-way loop injection valve was mounted on the water carrier stream. Another delay coil was used for the reaction to occur before detection at 360 nm. 

The SIPV replaces the Rheodyne 7125 loop injection valve in the chromatograph shown in Fig. 8-5 when it is desired to dissolve samples in carbon dioxide mobile phases. The SIPV overcomes most of the problems encountered when trying to chromatograph relatively large volumes of sample in supercritical carbon dioxide. This facility allows the chromatograph to be used in a very flexible manner at the preparative scale. 

The basic difference between this type of valve and the normal external loop sample valve is the incorporation of an extra port at the front of the valve. This port allows the injection of a sample by a syringe directly into the front of the sample loop. Position (A) shows the load position. Injection in the front port causes the sample to flow into the sample loop. The tip of the needle passes through the rotor seal and, on... 

Figure 14.2 Schematic diagram of the cliromatographic system used for the analysis of low concenti ations of sulfur compounds in ethene and propene VI, injection valve V2, column switcliing valve SL, sample loop R, restriction to replace the column SCD, sulfur chemiluminescence detector.

Figure4.62 Experimental set-up for liquid/liquid experiments (a) reservoir for the substrate in n-heptane (b) water reservoir (c, d) high-pressure liquid pumps (e) HPLC injection valve with sample loop for catalyst injection (f) micro mixer ...

Figure 5.28 Schematic of the experimental set-up. Water/ethylene glycol/SDS reservoir (a) high-pressure liquid pumps (b) catalyst/ substrate HPLC injection valve with 200 pi sample loop (c) hydrogen supply, equipped with mass flow controller (d) micro mixer (e) heating jacket (f) tubular glass or quartz reactor (g) back-pressure regulator (h) [64],...

Sample preparation, injection, calibration, and data collection, must be automated for process analysis. Methods used for flow injection analysis (FLA) are also useful for reliable sampling for process LC systems.1 Dynamic dilution is a technique that is used extensively in FIA.13 In this technique, sample from a loop or slot of a valve is diluted as it is transferred to a HPLC injection valve for analysis. As the diluted sample plug passes through the HPLC valve it is switched and the sample is injected onto the HPLC column for separation. The sample transfer time typically is determined with a refractive index detector and valve switching, which can be controlled by an integrator or computer. The transfer time is very reproducible. Calibration is typically done by external standardization using normalization by response factor. Internal standardization has also been used. To detect upsets or for process optimization, absolute numbers are not always needed. An alternative to... 

The equipment consisted of two Waters (Waters Corp. Milford, MA) M-45 pumps, a Waters 481 UV detector, a six-port Valeo sampling valve (A2L6P) with 0.08" holes in the valve body and rotor, a Rheodyne Model 7413 injection valve with a 1-pl loop, a valve interface box, and a Digital Equipment LSI-11/23-based microcomputer system. The microcomputer was used to control all valves, collect raw data from the UV detector, integrate the chromatogram, and store and plot results. 

The equipment used in this application included two Waters M-45 pumps, a Waters 481 UV detector with microbore cell, an air-actuated Rheodyne 7413 injection valve with a 1-pl injection loop, an air-actuated Valeo four-port sampling valve (A2CI4UW2) with no groove in the injection entry ports, an air-actuated Valeo three-port switching valve (AC3W), and a Digital Equipment LSI-11/23 microcomputer. The LC system was located in a purged cabinet suitable for use in Class I, division 2 areas. The cabinet was in a heated room about 40 feet from the reactor column. The two Valeo valves were mounted next to the reactor column, while the microcomputer was located in the control room. 

C. The Rheodyne Model 7010 injection valve, equipped with a 20-pl loop, was switched to injection at the apex of the sample band, as observed on the refractive index detector. The complex kinetics of the production of mono-, di-, and tri-brominated glycols is shown in Figure 14. Optimization of parameters such as the flow rate of acid resulted in a 15% reduction in batch cycle time and eliminated the need for manual analysis and intervention to obtain a desired endpoint composition. 

The loop for the 2nd-D was loaded with the effluent of the 1 st-D at 50 pL/min for 1 min 58 s, and then the injection valve was turned to inject the 100 pL fraction for 2 s onto the 2nd-D HPLC. The flow rate was 5 mL/min, and the valve was turned back for the next loading, resulting in fractionation of the lst-D every 2 min. In this case less than 2% of the effluent from the 1 st-D was wasted during sample injection. The 2nd-D effluent eluted at 5 mL/min from the 2nd-D column, passed through a UV detector, and then was split by using a T-joint at approximately a 1/140 split ratio, resulting in a flow rate of ca. 36 pL/min going into the spray capillary for ESI-TOF-MS detection. 

Figure 12 Schematic representation of 2D chromatography using an eight-port injection valve and two storage loops. (A) In the first position of the valve the storage loop 1 is loaded with the HPLC eluent, while the content of the storage loop 2 is analyzed by SEC. (B) In the second valve position storage loop 2 is loaded with HPLC eluent and the content of loop 1 is analyzed according the molecular size of the solute.

Figure 9 Schematic diagram of typical six-port rotary injection valve at (a) filling and (b) emptying position. (1) Sample-loop inlet, (2) carrier inlet, (3) outlet to the flow cell, (4) sample-loop outlet, (5) outlet to waste, and (6) sample inlet.

Online IS introduction allows loading of samples in the biological matrix without preparation. ISs were introduced online in the quantitation of propranolol and diclofenac in plasma (Alnouti et al. 2006). Plasma samples were loaded into the autosampler without pretreatment. Both the plasma sample (10 /iL) and IS (5 //I. from an IS microreservoir) were aspirated into an injection needle sequentially and injected into the sample loop. After the switching of an injection valve, the mixed solution in the sample loop was loaded into a cartridge containing washing solution for online SPE. The accuracy and precision of the online IS method were comparable (85 to 119% and 2 to 12%, respectively) to values obtained offline (86 to 106% and 2 to 16%, respectively). 

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