Loop injection

Quantitative Calculations Quantitative analyses are often easier to conduct with HPLC than GC because injections are made with a fixed-volume injection loop instead of a syringe. As a result, variations in the amount of injected sample are minimized, and quantitative measurements can be made using external standards and a normal calibration curve. 

The amount of caffeine in an analgesic tablet was determined by HPLC using a normal calibration curve. Standard solutions of caffeine were prepared and analyzed using a lO-pL fixed-volume injection loop. Results for the standards are summarized in the following table. 

Preswelled Sephacryl S-1000 was prepared in a K26/100 column (88 X 2.6 cm). Equilibration with 0.005 M NaOH containing 0.002% NaN3 at a flow rate of 0.67 ml/min was achieved after 20 hr. Sample solutions were applied with a 5-ml injection loop. The mass and iodine-complexing potential of separated glucan components was determined off-line for each of the subsequently eluted 5-ml fractions. Based on the determined mass of carbohydrate for each of the fractions, elution profiles such as Fig. 16.1 were constructed. 

Figure 3. Fractionation of human serum proteins on Spherogel TSKSW 3000, The conditions were as in Figure 1. The analyses were made using (A) a 50-fiL injection loop with an analytical flow cell (B) a 100-L loop with a semipreparative flow cell or (C,D) a 500-L loop with a preparative flow cell.

The volume of the injection loops amounted to 20 pi the catalyst stream was set to 50 pi min In an electrothermal pre-heat zone the ethylene/comonomer mixture in toluene was brought close to reaction temperature before adding catalyst. The reaction was carried out at 175 °C and a pressure of 2.8 MPa. In several subsequent zones each of 16 cm length (volume 200 pi) along the reactor tubing, temperature was monitored by voltage pads. 

Automatic sampler equipped with a 50-pL injection loop... 

Inject a 5-mL aliquot (Vr,) of the sample extract via an injection loop. Collect the GPC fraction (llOmL) in an evaporation flask (150-mL round-bottom flask, longnecked). Rotary evaporate the sample carefully to 1 mL (but not to dryness) at 40 °C and 350-200 mbar (slow flask rotation, immerse flask slightly). 

In the loop interface the fluid from the extraction cell passes continuously through an injection loop and into a collection vessel. Injection of a predetermined fraction of the extract onto a packed column is made by switching the loop so that it is in-line with the flow of fluid to the analytical... 

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. 

The use of IR pulse technique was reported for the first time around the year 2000 in order to study a catalytic reaction by transient mode [126-131], A little amount of reactant can be quickly added on the continuous flow using an injection loop and then introduce a transient perturbation to the system. Figure 4.10 illustrates the experimental system used for transient pulse reaction. It generally consists in (1) the gas flow system with mass flow controllers, (2) the six-ports valve with the injection loop, (3) the in situ IR reactor cell with self-supporting catalyst wafer, (4) the analysis section with a FTIR spectrometer for recording spectra of adsorbed species and (5) a quadruple MS for the gas analysis of reactants and products. 

Loop A Load, Loop B Inject Loop A Inject, Loop B Load... 

This is the equivalent of the injection port for the GC technique. With GC you could inject through a rubber septum directly onto the column. With HPLC it s very difficult to inject against a liquid stream moving at possibly 1000 psig. That s why they invented injection port valves for HPLC you put your sample into an injection loop on the valve that is not in the liquid stream, then turn the valve, and voila., your sample is in the stream, headed for the column. 

A separate and independent injection loop dispenses the sample for non-purgeable organic carbon measurements. 

Fig. 2.3.3. Chromatogram of quaternary alkylammonium compounds. Columna, Shodex Asahipak GF-310 HQ (100 X 4.6 mm2) mobile-phase, 0.4 mM 4,4 bipyridyl, 0.8 mM HC1, 27% (m/v) acetonitrile flow rate 0.6 ml min-1 analyte concentration 1.0 p.M injection loop, 50 p.L. Reprinted with permission from Ref. [56] 1999 Elsevier.

The exchange-quenched solution is then injected onto the protein processing system which includes injection loops, protease column(s), a trap column, an analytical column, electronically controlled valves, and isocratic and gradient pumps. 

Loop 1 load, loop 2 inject Loop 1 inject, loop 2 load... 

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