Low Li-7 tune higher on In-115 and U-238 on Agilent 7700

Question

We have an agilent 7700. When we tune our Li-7 is coming in very low (2,300). Our In-115 and our U-238 are higher than before. What levels should we be getting for a 1ppb tune solution? What is the best method to tune for improving our Li-7 signal? Can we tune just the extraction cell in manual tune?

cschulz · Answer

Hi, 
 without any comparison it is hard to say what is going on. Have you changed anything and then this behavior occurred? 
 If you want to focus the intrument performance for lower masses, you can set this by right clicking in the tune window and select "Tune - Set Acq Parameters for Sensitivity" 
 There you have the option to set the mass balance: 
 
 Do you only measure light elemtens? And why do you tune with In and U? 
 
 Best Regards 
 Chris

cschulz · Answer

Hi 
 [Mass Balance] 
 The mass balance is a parameter for weighting the sensitivity variation for the lens voltage with the mass in the lens autotune. As the value is smaller, the tuning shows better sensitivity for lower masses. As it is larger, the tuning shows better sensitivity for higher masses. Note however that when the sensitivity is high for lower masses, the off-mass background may increase. Usually, configure the setting so that Tl is two to four times more sensitive than Li. 
 0%: Runs autotune with the focus on low and medium masses. 50%: Runs autotune with equal focus on all masses. 100%: Runs autotune with the focus on medium and high masses 
 
 Hope this clarifies.