CONSUMPTION OF STRONG NEEDLE WASH

I am Using a method for Bio analytical work. In that MY Weak and strong needle washes were defined 500 uL, When we submit a batch of 200 to 250 samples and observe in on next day there is a vatiation in the consumption of Weak and strong needle wash. Weak needle wash consumes around 600MmL and Strong needle wash consumes 200mL,Why there is a diffrence.Will this effect the sensitivity.My sensitivity on LCMS got down to 3 times.( This I confirmed after in jecting the same samples after flushing the Needle again and injecting same samples).what can be the problem.I think some thing like this trouble shootings can be given as a Presentation or CD so that instrument down time can be reduced.thanks.

Answers

  • Hello:

    First of all the weak and strong wash are used to clean the sample manager flow paths to prevent carryover. They can help the chromatography too if chosen judicially. If you choose inappropriate solvents though peak area and peak height %RSD's can vary, but this should not affect the MS performance directly.

    The actual usage of the weak and strong varies slightly with method. I cannot give exact amounts for wash usage, I can look up, but the Sample Manager uses weak wash when it uses strong wash though the path does differ. Do not assume that the weak wash is diverted to waste when the strong wash is being used. The method tells you how much approximately is drawn, but it is not the empirical amount used. Therefore, you should expect to use as least as much again of weak wash as strong. I will attach a detailed document on washes. However, I do not think there is anything wrong with the sample manager and the usage difference you are seeing is real. We do usually recommend a ratio of 3x weak wash to strong wash. The strong washes only purpose is to solubilize any sample and and remove it and any sample diluent from the Sample Manager loop and fluidics before being replaced with more weak, prior to the next sample being run. You are better off to have a less amount of a strong SW and save time than more of a less strong (wrt the sample) wash solvent.

    The issue that you have lost MS sensitivity is unlikely to be directly related to the Sample Manager, but rather to some interference with the signal. This is most likely to do with some kind of contamination or other application inefficiency. The samples could be a source. I do not have enough information about the method to be able to comment much more than this. If you send your method and information on the samples and sample preparation I hope to assist further. A chomatogram or two would be helpful as well.

    There are trouble shooting tools available on the Waters web site, and I would look at the topics around loss of MS sensitivity. However, send us some more data and we can assist further.

    Liz

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