The automated needle wash feature can be enabled in the method parameter tab (enable needle wash) or as part of an injector program. When started, the needle moves into the wash port, and a stream of fresh wash solvent rinses its outer surface. The washing always takes place immediately after the sample draw procedure. This measure ensures that all sample traces are rinsed off from the surface of the needle before it moves into the seat. Contaminations can cause carryover problems later. To ensure that the needle seat does not get contaminated, use the automated needle wash.
The wash port is in the needle station and has a flapping mechanism. During the needle wash procedure, the gripper arm moves the wash port into a position that allows the needle to move into the well for washing. Fresh solvent from the peristaltic pump of the hydraulic box constantly replaces the waste solvent in the wash well during the entire wash procedure. The exhausted solvent overflows the upper edge of the wash well and gets routed into the waste handling system. This operation of the automated wash feature allows the needle to be rinsed with a constant stream of fresh wash solvent, which is necessary for minimizing carryover.
Choose the wash solvent with great care. It should be strong enough to completely solubilize the analyte and sample matrix while being gentle enough not to damage components of the wash system. For more information on solvent compatibility, see Solvent Information.
The peristaltic pump delivers with a flow rate of 5 mL/min. Since the wash port has a volume of ca. 0.5 mL, replacing the entire volume with fresh solvent takes about 6 seconds. When selecting the duration of the washing, one must consider what level of carryover is acceptable and how long the overall injection cycle can be. For routine situations where carryover is less of a problem, the needle wash procedure can be as short as two to three seconds. When the analyte tends to adsorb to the surface of the needle or low levels of carryover are necessary, the wash cycle might need to be elongated to 10 to 20 seconds.
For very critical applications where the outside of the needle cannot be cleaned sufficiently with one wash port solvent you can use an injector program and an additional wash vial with an appropriate and stronger solvent for cleaning. The wash vial should contain solvent in which the sample components are soluble, and the vial should not be capped. If the wash vial is capped, small amounts of sample remain on the surface of the septum, which may be carried on the needle to the next sample.
The injector program includes the command WASH. When this command is included in the injector program, the needle is lowered once into the specified wash vial or flushport before injection.
For example:
WASH > Location P2-A1 or flushport
Draw 5 µL from Sample Location P1-A1
INJECT
Line 1 moves the needle to vial P2-A1 or the flushport. Line 2 draws 5 µL from the current sample vial P1-A1. Line 3 injects the sample (valve switches to main pass).
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