The operating principle of the autosampler is based on the split-loop injection principle. In this injection principle, the needle is part of the sample loop. Described here is the direct injection setup.

Sample draw, valves in bypass position

  • At the beginning of a sample injection process the needle moves from the needle seat to the pre-defined sample in the carousel. There the needle descends into the sample container.

  • The metering device draws the sample from the sample container through the needle into the sample loop. After that the needle withdraws from the sample container.

  • To remove residual sample from the needle between injections, the outside of the needle can be washed. In this case the needle moves to the wash port and descends into it. The needle wash pumps supply needle wash liquid to the wash port to rinse the outer surface of the needle to the wash waste.

  • The needle moves back to the needle seat, which seals the needle tip against the system pressure.

Injection of the sample, valves in inject position (see figure)

  • The injection valve switches to inject position to establish the required flow path so that the solvent from the pump flows through sample loop, needle seat and needle and flushes the sample through the injection valve onto the column.

Start of Gradient, valves in bypass position

  • When the sample has been pushed out of the autosampler completely, the injection valve switches back to bypass position. The gradient can start to provide the smallest gradient delay volume possible.
    NOTE: If applicable the autosampler can be configured to keep the inject valve in inject position to start the gradient immediately. Thus the complete sample loop is involved the gradient delay volume will be higher.

Washing process, valves in wash position

With the injection valve in bypass position, the solvent valve switches to wash position and the needle moves from the needle seat to the wash port and descends into it. In this position the outside and the inside of the needle will be washed with strong needle wash liquid from the wash port (7) and weak wash solvent supplied via the online degasser located in the pump (13).

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Figure: Operating Principle VN-Autosampler, Inject Position

No.

Description

1

Carousel

2

Sample loop

3

Needle

4

Needle seat

5

Wash port

6

Needle wash pump

7

Needle wash liquids (weak and strong)

8

Injection valve

9

Solvent valve

10

Wash waste

11

Pressure sensor

12

Metering device

13

Wash solvents (weak and strong) from degasser located in the pump

14

Selector Valve

15

Pump

16

Column