Push-loop autosampler

FIGURE 10 A schematic of a push-loop autosampler which mimics the operation of a manual injection. 

Figure 4.6 Filling the loop by three different autosampler designs a, pull-loop b, push-loop c, integral-loop injection. 1 = sample vial, 2 = syringe with stepper motor, 3 —loop, 4 —from pump, 5 —to column, 6 = to waste, 7 = low-pressure seal, 8 = high-pressure seal, 9 = position of the movable loop when the valve is switched and the sample transferred to the column.

Most of the autosamplers have a piston metering S3rrmge t)rpe pump to suck the preestablished sample volume into a line and then transfer it to the relatively large loop ( 100 ml) in a standard six-port valve. The simplest autosamplers utilize the special vials with pressuarization caps. A special plunger with a needle, push the cap down to the vial and displace the sample through the needle into the valve loop. Most of the autosamplers are microprocessor controlled and can serve as a master controller for the whole instrument... 

Some autosampler models use air pressure or a piston to push sample out of the vial into the injection loop others pull the sample into the loop with vacuum or a syringe barrel. Various techniques are employed to wipe or wash the outside of the injection needle before the next injection to prevent sample-to-sample contamination. Other systems just wash the inside of the needle by pulling in some of the next sample and spitting it out to a waste vial or back into the last vial used. 

Autosampler—A multiple sample injector, usually with a rack or carousel to hold sample vials or a sample well plate, designed for unattended programmed operation in which a sample is loaded by either pushing or pulling sample into the loop injection loop with air or hydraulic pressure. 

The injection system may be manual or automated, but both rely on the injection valve. An injection valve is designed to introduce precise amounts of sample into the sample stream with variation usually less than 0.5% volume difference from injection to injection. Figure 2.7 schematically represents a 6-port and 2-position device valve. In one position the sample is loaded and the other it is injected. In the load position, the sample from the syringe or autosampler vial is pushed into the injection loop. The loop may be partially filled (partial loop injection) or completely filled (fuU loop injection). Partial loop injection depends on the precision filling of the loop with small known amounts of material. If partial loop injection is used, the loop must not be filled to more than 50% of the total... 

Fig. 6. BEST NMR (Bruker Efficient Sample Transfer) (36,37). The sample is sucked from a well plate 1 by the autosampler needle 2 and transferred into a sample loop 3. The sample can be surrounded by gas and liquid buffer regions or gaps to separate it from the transport liquid. A dilutor syringe 4 is then filled with the appropriate volume of transfer liquid, which is used to push the contents of the sample loop 3 after appropriate valve switching 5 into the probehead 6.

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