Conductivity detector baseline

Hi, we recently upgraded our old jasco/waters conductivity detector system to a H-Class plus quarternary fln uplc system with the 2432 detector. We run ammonia using isocratic elution using 3mM HNO3 in 70/30 (H2O/MeO). The same niosh method as before. Unexpectedly we get more baseline noise than before and way more than shown in waters manuals and app notes, we get about 0.05-0.1us/min in drift. This baseline oscilation has resulted in less accurate method as it has a frequency simmilar to peak width.

It is not the detector or the column that is the problem. Detector noise is very low and if we set flow to zero signal become stable. We do se noise even with column bypass. We run using 100% bottle A so not much mixing required. My take is mobile phase contaminants or pumps is problem. We do degass with helium and use good water from good MQ-system with UV and use lc-ms grade methanol. The pump on h-class with i2v active valve should be good for stable flow. A bit dissapointing to have lower sensativity than 20 year old jasco/waters system. Not sure what can be done to improve. Could use bottmed lc-ms grade water and get new HNO3, just to make sure we get clean mobile phase. Any other suggestions, flow dampener larger mixer? With uv everything works fine just the conductivity method that is not as good as I hoped for. We get power from UPS (uninterupted power supply).

Comments

  • Since the problem started after changing to the new system and was not seen before my tought is that it may be the related to new uplc. Is there a suggested cleaning procedure we should try on a newly installed H-Class system that will be used with conductivity detector? 
  • Is the new conductivity detector closer to your air ducts than the old one was?

    Have you tried turning on your flow cell temp. channel to see what kind of temp variations you're getting? We have a 2432 on a 2695 and see a range of 0.003°C at 1.5mL/min when column and flow cell are both set to35°C.

    Have you tried passivating the system?
  • Hi,
    The new system is in a more ventilated room with air conditioning, so should be more stable room temp. That said, temp readings seem very stable both on column manager and detector at 35C, hardly any measurable shifts. Cappilaries between modules  are short less than 20cm. Our old system did not even have column oven and was stable.

    We have not passivated the system, i have read some protocols and seems like a bit of work and is it needed on new h-class plus system? If so is there a protocol you would recommend?

    I think we have a conductivity of around 800 uS and baseline kan move 0.05uS in 1 min. Does this seem normal? 3mM HNO3 in methanol water mobilephase.
    Thanks
  • I'd remove teh column and try passivating with some 30% H3PO4 in water, then cycle through water, IPA, MeOH a couple of times. See if that helps.
  • Thanks for the advise and protocoll. Will discuss with my colleages if we need more sensativity and then we will try passivating the system.
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