What does the Lamp Anode Voltage trace (HPLC-DAD) actually show?

Hi, What does the Lamp Anode Voltage trace (HPLC-DAD) actually show? We have baseline noise that directly correlates with the fluctuations in the voltage trace. thanks

  • It probably shows the tension that lamp anode is getting. Have you tried replacing the lamp?

  • Thanks for your reply, that was my first thought...unfortunately our kits are separately maintained and there is pushback when it comes to replacing parts like lamps if they pass lamp intensity tests. Unfortunately this issue keeps happening and we need sufficient external evidence to present until a replacement can be actioned.  

  • Maybe run Noise and Drift Test on Lab Advisor? That will give you the evidence you need. Also, If it is not the lamp, it could be the mainboard

  • Once the lamp got ignited the light arc between anode and cathode has been sustained.

    The referring anode voltage typically stabilizes after a certain time and can be heavily influenced by environmental conditions.

    Fluctuations in the anode voltage always result in light output fluctuation and therefore are also corelating with the detector signal.

    With a UV-lamp it can be very usual that certain small fluctuations can be observed, especially directly after ignition while everything needs to warm up and stabilize.

    During the normal lifetime of the lamp the light arc regularly is moving to a different connection point at the cathode whenever there is a better emissivity.

    This movement is normal but the higher the emissivity difference between new and previous position the higher the difference in resulting voltage.

    Other factors for anode voltage fluctuations could also be:

    - changes in temperature

    - vibrations

    - electromagnetic interferences

    Fluctuations like the ones you are showing typically are a sign of a lamp reaching the end of its service lifetime.

    The cathode coating most likely is quite exhausted.

    Are you using lamps with RFID tag or can your detector even use these kinds of lamps?

    The lamps typically having a guaranteed lifetime of 2000h.

    Lamps with RFID tag quite reliably track the lamp's burn-time but without RFID tag it is always relying on the user to correctly track the time with the module's EMF counters in Lab Advisor Software for example. 

  • Instability in the anode voltage will cause baseline problems in your detector signal. For example, if the lamp doesn't light properly, the voltage will reset and you will see periodic changes in the baseline.  I have seen old lamps sometimes produce odd, irregular baseline spikes and changes.  All of these symptoms are indications of a lamp that is having problems and is likely to fail soon. If the instability continues, I think a lamp replacement is the obvious option.

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