Acetonitrile adduct in esi positive mode.

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PatSD
PatSD
in Instrumentation and Mass Spectrometry
<p><span>We are seeing what we think is an acetonitrile adduct (+41 amu) in some of our samples. As new users of the UPLC system with a SQD mass spec we were wondering if anyone else has seen this and if there are any parameters we can change to get rid of it? If we inject the same sample on our older ZQ we don't see the adduct.</span></p><p><span>Any thoughts?</span></p>

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  • lizh
    lizh
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    Hi

    We polled some experts, they stated that without knowing all the details they speculated that it could be too low a desolvation temp and gas flow rates. Adding cone gas at 100 should help. This couloccur if you simply transferred ZQ conditions on an SQD without optimizing.

    Try and see what happens.

    Liz

  • gbyrd
    gbyrd
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    We occasionally see (M+H+CH3CN)+ adducts in our samples (alkaloid-type structures) when we use acetonitrile in the mobile phase. Increasing the sample cone voltage reduces the adduct intensity. Although I do not have any data, it seems that the adducts appear when more sample is loaded on the column.

    Gary

  • RD
    RD
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    The source temperature of the SQD will likely need to be set higher than that for the ZQ. The recommended source temperature for the SQD is 150 C, regardless of the application.

    Desolvation temperature and desolvation gas flow settings are adjusted according to mobile phase flow rate, At typical UPLC flow rates of > 0.5 ml/min, the desolvation temperature should be set to 450 C and the desolvation flow should be set to 900 L/hr.

    If solvent adduct formation is still an issue, Cone Gas flow can be adjusted to 50 - 100 L/hr.

    While increasing the Cone Voltage may decrease the intensity of the adduct, it is doing so by fragmenting the molecule. This would decrease the sensitivity of the analyte of interest and thus would generally be avoided as a means to minimize adduct formation.

    Rich

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