What does the Automatic setting of Loop Offline mean? - WKB221963

ENVIRONMENT

• ACQUITY APC Sample Manager - FTN
• ACQUITY Arc Sample Manager FTN-R
• ACQUITY UPLC Sample Manager - Flow Through Needle PLUS (SM-FTN PLUS)

ANSWER

Automatic setting calculates the amount of time for 5 times the needle and loop volume to pass through the needle before taking it offline. 

Time needed = [ (Needle + Loop volume) x 5 ] / (Flow rate) 

This will calculate the time needed for mobile phase to pass through before taking the loop offline and setting the needle to load position. 

In a system configuration and method that consist of the following:
Needle: 15 µL
Loop: 100 µL
Total volume: 115 µL or 0.115 mL 
Flow rate at 0.5 mL/min

It would take (0.115 x 5) / 0.5 = 1.15 min 

If the run time is shorter than the time needed to loop offline (e.g.,1 min), the loop will not be taken offline.

ADDITIONAL INFORMATION

We do not usually recommend the loop offline, because it removes the needle and loop from being flushed (flow through needle and loop). This option could cause carryover and baseline disturbances.