Several parts of an injection system can contribute to carryover:
needle outside
needle inside
needle seat
sample loop
seat capillary
injection valve
The autosampler continuous flow-through design ensures that sample loop, needle inside, seat capillary, and the mainpass (main path) of the injection valve is always in the flowline. These parts are continuously flushed during an isocratic and also during a gradient analysis. The residual amount of sample remaining on the outside of the needle after injection may contribute to carryover in some instances. When using small injection volumes or when injecting samples of low concentration immediately after samples of high concentration, carryover may become noticeable. Using the automated needle wash enables the carryover to be minimized and also prevents contamination of the needle seat.
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