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MassHunter Calculations are off for ICP-MS.

andrewb602

Just wondering how I can fix calculations done on Masshunter? I have a spreadsheet that automatically calculates the ppm of samples, which should match up with masshunter. but doesn't. The first excel sheet is just an exported table from MassHunter. As you can see, The verification standard (although failing) and the drift standard both match up with their respective concentrations (they are off by a bit but still close). The second excel sheet, I have changed the total dilution on masshunter, which should give the correct concentration of 200 Hg [He], however, this is not the case. The third excel sheet I attached is a training method we used, and when inputting the numbers into the spreadsheet, matches with that on masshunter.The concentration from graph, ug found, and ug/serving in the first yellow spreadsheet should match up with the second green spreadsheet (which is from masshunter), but they don't. 
The third green spreadsheet (again from Masshunter) matches up with the second yellow spreadsheet, which tells me that Masshunter calculations are wrong. *Changing the total dilution column in masshunter should give the same results in the yellow spreadsheet (see 4th and 5th picture). As you can see in the 5th and 6th picture, the ug/serving (ppm) matches with the concentration (ppb) from masshunter at 2.24 ppb.

  • 0

    Hello, what samples are you comparing stating the calculations are off?  The only samples that show a change in Total dil are 2003 and 2008. sample 2003 shows 0.127ppb, multiplied by your dilution factor gives 0.244ppb which is what that table shows.  2008 shows 0.057ppb, multiplied by the 2.0 factor gives 0.114 which again matches the first spreadsheet.

    How are you calculating your results in Excel?  Are you using the 3 decimal slope in the calibration window to calculate concentration? 

    As those exported tables show a Ratio column, you are using internal standards.  The software calculates a ratio for each replicate and then averages the replicates.  The ratio is cps analyte mass/cps ISTD mass.  When you export the data and allow Excel to use more decimal places, calculations will match much better than if you use the 3 decimal slope listed in the software. 

    In the example below for Be9.  The software shows a slope of 0.0035.  If you use this to calculate concentration the result is 49.867 not the 49.998 listed by the software.

    When you export the Calibration Summary, the slope is actually 0.003490886.  

    If you then take the ratio for the current sample 0.174542769 and use "a" above for slope and "b (blank)" above for the offset the calculated concentration will match what is calculated.

  • 0 in reply to Tom Herzog

    The first spreadsheet is masshunter without the total dilution column changed. The results of sample 2003 from the first spreadsheet are inputted into the second spreadsheet, which should give the same concentration as shown in the third spreadsheet (when masshunter's total dilution is changed to the respective values). But this isn't the case for sample 2003.

    To show that it should match up, the training method given to us is used on the 4th, 5th, and 6th spreadsheets.
    In the 4th spreadsheet, total dilution in masshunter remains unchanged, so we input the values from the 4th spreadsheet (masshunter) into the yellow boxes in spreadsheet #5 (I also apologize for not changing the sample ID in spreadsheet 5, but we are looking at Andrew spiked coffee sample NOT 2003). In the 5th spreadsheet, the ug/serving (ppm) is 0.002235, which, when the total dilution is changed on masshunter (spreadsheet 6), the concentration for Andrew spiked coffee is 2.24 ppb, which matches.

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