Why Doesn't the Recalculated Concentration in Excel Fit the Calculated Concentration in Analyst?


Date: 11/29/2017
Categories: QTRAP Systems , Triple Quad Systems , Analyst Software

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For research use only. Not for use in diagnostic procedures.


Issue Description

Analyst is using more significant figures for the peak area and the regression equation than what is visible within the results table. If you use only the visible significant figures out of Analyst in Excel, you will have not the same results as in Analyst for the calculated concentration. This article will explain how to change the significant figures in Analyst for peak area, how to copy this information into Excel and which formula you need to calculate the results in Excel.

How to Change the Regression Equation Significant Figures is already an article with an embedded video.


Resolution

Changing Significant Figures in the Table Settings

First, you need to open the Table Settings to change the significant figures in Analyst. Analyst will always use all significant figures, even if you only see three significant figures.
To adjust the number of significant figures, right click and then select Table Settings -> Edit
 
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Next click on the Columns and Edit.
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Under Analyte, change the Significant Figures to 10 for Analyte Peak Area and uncheck the Scientific Notification.
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Do the same for Internal Standard, if you use one. IS Peak Area to 10 for Significant Figures and uncheck the Scientific Notification. Please also check the Show for IS Concentration.
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Also change the Precision for the Calculated Concentration under Record to 10.
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Than click OK and Done on the next Window.

Copy the Needed Information into Excel

Make sure the columns for Analyte Peak Area, IS peak Area, Analyte Concentration, IS Concentration and Calculated Concentration are visible.
Now you can copy the whole table for one analyte out of the Analyst results table into Excel by highlighting the whole table and pressing ctrl+c together. Paste the table into Excel with ctrl+v.
 
Refer to the Article How Do I Change the Significant Figures of Regression Equation in Analyst to change the significant figures for the Equation to 12. You can find it on https://sciex.com under Support -> SCIEXNow -> Knowledge Base Articles.
 
After reopening Analyst, the following information appears in the Calibration Pane:
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In Excel, use the following formula:
Analyte calc. Concentration = IS Concentration * ((Analyte Peak Area/(IS Peak Area * a))-b/a)
to recalculate the results from Analyst.

Please add this as usual in Excel.
 
NOTE: If you use weighting, the last figures could be a bit different.