We are using an AVS 7 on our 5110. Recently, we have been having bad replicates (~6-10 % RSD), when they should be much less. It is always the 1st replicate running low. (For example, we run 1ppm checks and my first rep is 0.8 and by the 3rd/4th rep its reading 1.05 or so).  I am leaning towards the rotor seal needing replaced, but I cannot get anyone to help troubleshoot it yet. Customer service didn't have much experience with the valve. 

Anyone had this issue? Was it the rotor, or something else?

  • Hi,

    Can i get a few more details from you as to what you are running?

    Pump tubing - Carrier and internal standard?

    Loop volume

    AVS pump speed and timing settings

    How many reps and what is the read time?

    What is stabilisation time?

    Are the second two replicates generally within the variation you expect?

    Does the internal standard show the same poor RSD?

    Do you see any liquid dripping from the bottom of the valve?

    I have seen the first replicate run low before and the issue was the timing. If the loop has only just filled when the valve switches, you can get a dilution effect in the start of the measurement. I set the valve uptake delay so that the sample in the loop fills to half way between the valve and the FMI pump.



  • Thanks, it sounds to me like there is a bit of dilution happening between the sample and the rinse at the start of the loop. If the internal standard RSD is still good, it means that the delivery to the spraychamber is fine but there is an issue with only the sample path. The issue deson't sound like air bubbles though, as air bubbles would cause poor RSD on the internal standard too. The change in flow could be caused by wear and tear on the rotor and stator assembly.


    Some things to check:

    1. To test the flow rate issues, you could increase your valve uptake delay by 0.5 to 1.0 seconds and see if that helps your RSD. Set the uptake delay to allow the sample to reach the pump before it switches. If this improves RSDs, check the sample tubing that leads to the valve for any kinks, damage, and changes in length. Also, check the loop for damage as well. Replace any damaged sample lines, and try again with your current settings.
    2. There can be buildup on the rotor from sample that is partially blocking the sample path that could slow down the sample flow. Removing the valve and cleaning the rotor and stator could help this. I recommend cleaning this once a month for optimal performance. Sonicator is good for clean these parts.
    3. If the probe has been changed/replaced and the length of the probe is different it could cause this issue. If the probe is a different internal diameter, this will also affect the flow rate. The recommended probe for the AVS is 1.0 mm inside diameter, and has blue markers on the probe line. Also any kinks in the probe can cause issues with flow rate.
    4. Replacing the rotor and stator could also help. Over time the rotor wears from the switching back and forth, and begins to swarf. Small particles begin to wear off the rotor surface and can affect flow rates. (Part: Stator and Rotor for 7 port valve, P/N: G8495-60003). I would suggest replacing both at the same time as the surfaces mate to each other over time.


    Let me know how you go.



  • Sure!

    We run solid and water samples (up to 15-20% acid matrix) sometimes with percent level elements. 

    We do use carrier and internal standard (AVS 7)

    We use a 1,mL loop size (We have always used this size and not had replicate issues)

    I do not have the software up at the moment, but we use the recommended AVS pump speed and timing based on the loop size 

    4 reps at 10sec each (likewise this has always been sufficent in the past. Pushing the limits of the 1.0ml loop)

    Yes, the final 2 replicates are generally what the recovery is for known samples. 

    Internal standard does NOT have poor RSD. 

    No liquid dripping from valve


    I appreciate the time trying to help me work through this. What is the most perplexing is that we have been using the same set conditions for over a year and just now seeing issues. That is what is making me think it is more than just a setting thing, and possibly something needs replaced. 

  • Glad to hear it is performing better. PVC or tygon is pretty good for that part of the pump, even with high acid. 



  • Update! I had already previously done your suggestions for 1 and 2 (although I had not sonicated the parts, that I will keep in mind for the next cleaning). Our probe has not been replaced in a while, so no issue coming from that end. 


    Customer service had suggested yesterday to replace the tubing coming from the stator to the vacuum and from the vacuum to the waste. It had become hardened due tot he high acid matrix we use, and the type supplied (silicon I do believe) isn't made for that. After replacing with 1/8" ID PVC tubing I had on hand, my % RSD have dropped to be consistently less than 2%. This is a huge improvement, and is what I am used to seeing with the samples we run. 


    The rotor/stator combination and the rotor are out of stock online; not due to be in until Dec 4. So I will be ordering those to be delivered once in stock, but I am pleased that it seems the tubing might have greatly helped the issue. My 1st replicate is still a bit lower than the others, but the variability in the run is much more consistent. I am hoping with a new rotor, % RSD will drop to less than 1% consistently. 


    Thanks for all the suggestions and helping me work through this issue! If it doesn't seem to be a long-term fix, I will update again. 

  • This question has been marked as assumed answered.

Was this helpful?