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lconnor1
lconnor1
in Instrumentation and Mass Spectrometry
<p>I am currently making a 0.2 uL injection using a 2 uL injection loop in PLNO injection mode. Load ahead is enabled. Loop offline disabled. Refer to screen dump in attached doc.</p><p>Mobile phase A1 is 9%v/v MeOH in Ammonium formate pH 9.6</p><p>Mobile phase B2 is 9%v/v Ammonium formate in MeOH pH 9.6</p><p></p><p>When I inject a standard containing morphine, codeine, oripavine and thebaine in 1% v/v acetic acid in MilliQ Water, the normalised area for each compound is lower than the normalised peak areas for the same compounds dissolved in a diluent composed of 30:10:70 - Ethanol:Acetic Acid:MilliQ Water.</p><p></p><p>Are there any advanced settings I can alter in my instrument method to reduce the differences?</p><p>Is a change to Full Loop overfill factor applicable?</p><p>Are air gaps set ok?</p><p>Should I increase needle overfill flush and how would this help?</p><p></p><p>Are the differences likely due to changes in sample viscosity or adsorption within the needle/sample loop?</p>

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  • WesleyCrozier
    WesleyCrozier
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    Is it possible that the compounds are not fully dissolved in 1% acetic acid?  It looks like these compounds are far more soluble in alcohols.

  • lconnor1
    lconnor1
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    We recently changed from using Empower software to Empower 2 software. When using Empower software, there was not an issue - the area for the compounds of interest in both diluents was the same. Since changing to Empower 2 there is a significant difference in peak areas for thebaine ~7 - 20%. At this stage we have tried adjusting many of the injector settings and needlewash solution without success. There seems to be a software related effect deeper in Empower 2 that has change. Any ideas?

  • RD
    RD
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    It is unlikely that a change to Empower 2 is responsible unless the instrument method has also changed.

    Do you know if the instrument control software (ICOPS/ICS) or firmware was changed concurrently with the upgrade to E2 ?

    That seems to me a more likely culprit.

    I would recommend the default Needle Overfill Flush (~ 15 uL, if memory serves).  Simply remove the check mark from the box. 

    The thought here is that if sample loss is occurring due to adsorption in the needle, the larger overfill flush volume provides a better opportunity to saturate any active sites responsible for adsorption.

    Let the Community know how you make out.

    Regards,

    Rich

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