Blank substraction of a recovery sample

Hello all,

I hope this question wasn´t asked before and I was too stupid to find it.

We are running a recovery sample (standards and internal standards in matrix and progressed the same as the samples) and control standards (standards and internal standards in solvent) with all our calibration and samples as quality control. For the control standards and the calibration we use the "accuracy" outlier to show us if the massurment is accurate enough, because our specification is a percentage range +/- 15% so 85-115%. For the Recovery sample we have other specifications: 60-120%. For that I found the "QC LCS Recovery"-outlier that uses the Info LCSA or LCSB and is shown in the "Matrix spike % Recovery" column (the red outlier in the picture below). There you dont have to use a range but min and max %. Because the recovery sample is prepared in the Matrix we want to substract the blank from the result. Our problem is that QC´s are not effected by the blank substraction. Is there any way to do so? Maybe the "Matrix spike recovery"-outlier could help but I could not make it work. I hope my question is clear and I hope someone can help me. 

 jjj

Thanks in advance and best regards

Simon Redlich

  • I forgot to mention that I use Agilent MassHunter Quantitative Analysis Version 10.1 Build 10.1.733.0 for QQQ. And that I know about the "Quantitate with Blank Subtraction" and "Quantitate with Blank Subtraction in Different Matrices" function of the software. But I could not figure out how to use one of them for my recovery sample as "QC"-type or "Matrix"-type.

  • Hello  ,

    Similar questions have been asked, but searching can be a bit touchy. I will combine the responses to previous requests here for everyone's benefit. 

    Regarding the matrix types and outliers -

    The various matrix sample types and matrix outliers are provided in quant for monitoring and reporting results for certain environmental analyses. There are EPA methods, for example, that require matrix spike recoveries. These values are only calculated for reporting purposes and are not used within quant to adjust final concentration results. 

    The calculations and their requirements are listed in the help and also in the data set manual, but it can be confusing if you have never set it up before. There is a series of videos installed with the Quant Supplemental material that give some good examples of how the various matrix outliers are used and what sample types and other settings need to be in place for calculation. If the videos are not installed there are installation instructions in this discussion.

    Regarding standard/QC blank correction - 

    The blank subtraction add-ins only work on samples. There is not a built in add-in that will correct the final concentration of other sample types.

    You could investigate the blank offset option for the calibration curve origin setting and see if this accomplishes what you need to do for correcting your standards. 

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