User manual

Agilent 1260 Infinity High Performance Autosampler User Manual 77

Optimizing Performance

How to Achieve Lowest Carry Over

Carryover is measured when residual peaks from a previous

active- containing injection appear in a subsequent blank solvent injection.

There will be carry over between active injections which may lead to

erroneous results. The level of carryover is reported as the area of the

peak in the blank solution expressed as a percentage of the area in the

previous active injection. The Agilent 1260 Infinity Autosampler is

optimized for lowest carryover by careful design of the flow path and use

of materials in which sample adsorption is minimized. A carryover figure

of 0.002 % should be achievable even when a triple quadrupole mass

spectrometer is the detector. Operating settings of the autosampler allow

the user to set appropriate parameters to minimize carryover in any

application involving compounds liable to stick in the system.

The following functions of the autosampler can be used to minimize

carryover:

• Internal needle wash

• External needle wash

• Needle seat backflush

• Injection valve cleaning

The flow path, including the inside of the needle, is continuously flushed

in normal operation, providing good elimination of carryover for most

situations. Automated delay volume reduction (ADVR) will reduce the

delay volume but will also reduce the flushing of the autosampler and

should not be used with analytes where carryover might be a problem.

The outside of the needle can be washed using a wash vial in a specific

location or the needle can be washed using the flush port. If a wash vial

in a tray location specified by the user is chosen then this vial should

have no septum and should contain a solvent suitable for washing the

sample from the needle. The septum is not used to avoid wiping

contamination off the needle on the downstream only to re- apply it on the

upstroke. The needle can be dipped into the vial multiple times. This will

be effective in removing a small degree of carryover but for more effective

washing of the outside of the needle use the flushport.