We have a old waters 2487 UV detector in our lab and we were trying to hook it up with a normal phase HPLC, but the channel with 190 nm wavelength is always jumping round creating hung background noise and the other channel with 254 nm does not move at all. The same thing happens with even no solvents going through. I am just wondering if the Hexane/EtOAc have anything to do with the noise at 190nm. We zeroed the detector and have done everything properly.
You are probably at or above the UV cut-off of your mobile phase solvents. Also, the detection limits for detecting analytes is severely compromised if this is the case.
Ethyl acetate does absorb well at 200 nm, and it probably also absorbs light at 190 nm. For ethyl acetate, pack a wavelength longer than 254 nm.
Dissolved oxygen and other gases cause problems at 190 nm, but not 254. My above comments refer to absorbance at 190. 210 or 214 nm would be a better choice for dual channel detection
Indeed, EtOAc absorbs strongly in the far UV (shorter than 240 nm) so there is no point in trying to record absorbance at 190 nm while using this solvent as the mobile phase. Actually, even zeroing will not help here.
It would be best if you found a solvent with a similar polarity to ethyl acetate that has a lower uv cutoff. EtOAc has a double bond which absorbs around 260 nm.
What is the sample you are analyzing? Depending on the analytes you may be able to use solvents that are compatible with the wavelengths required for quantification.
I am agreed with all comments of Edward Unsworth. dissolved gases' noise can be eliminated by effective degassing of the solvent. but your comment that "with no solvent the noise is appearing" shows that it can be from some electronic or electrical noise. ground and insulate the system properly. specially wire connections should be rust free and in good contact. you may also flush the detector cell with some strong solvent like Chloroform-methanol (1:1) at very slow flow rate (0.2 ml/min) for 2-3 hours but before this read the detector manual. whether its cell can tolerate the chloroform or not. to work below 210 nm is typical of such noises.
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