By Anonymous on Wednesday, March 17, 2004 - 06:14 pm:
Hi folks, has anyone of you ever met the following problem? I cannot set my UV detector to zero. The value only decreases a little bit, say, from 0.250 to 0.248,when i push the "SET ZERO" button. This UV detector is for CE but i think it doesn't make any difference in this case for CE and HPLC so i put this message over here. Thank you!
By DR on Thursday, March 18, 2004 - 06:02 am:
There is probably an offset at work, by design. There is frequently another adjustment for a % or number of mV of offset applied. The reason for this is that baselines sometimes dip after an injection, or there may be a negative peak that needs to be quantified.
By Anonymous on Thursday, March 18, 2004 - 11:14 am:
Thank you DR! I ran the water for test but still couldn't get problem fixed. The value was still around 0.250.
By DR on Monday, March 22, 2004 - 06:29 am:
As it should be, provided you have a 250mv or µV offset. Hitting "Zero" (balance on Agilents) does not cause a potential of 0 across the terminals of the detector. It causes a potential of 0+offset voltage to be applied. This allows for integration in the event of a negative dip in the baseline. Most detectors allow for the user to set the offset voltage within a range (0-0.1v) while some (Shimadzu SPD-10a for example) do not. Default offsets vary a lot. If your detector has an adjustable offset voltage, it is probably buried in the service menus with polarity, lamp monitor reset commands etc.