Calibration curve calculations problems.

support
Calibration curve calculations problems. monika lysakowska  2020-07-06
 

I have a problem calculating the calibration curve. The calculations Skyline does are different from my calculations in Excel.​I have entered all the appropriate values for settings and grids
and I got a good calibration curve. R square and intercept is identical to the calculations in the excel spreadsheet, slope differs by two decimal places (I think it is related to the Y-axis conversion). However, the calculated values by Skyline Quan differ slightly from heavy normalized to light values from the excel worksheet.

The data should match the normalized skyline. Currently they are about a percentage point off, which is substantial. It’s about 20% difference between the two. What can explain this?​

Regards,
Monika Lysakowska

 
 
Nick Shulman responded:  2020-07-06
Thank you for sending me your Skyline document and Excel spreadsheet.

It sounds like this is the graph which shows Excel calculating different numbers than Skyline:
https://skyline.ms/announcements/home/support/download.view?entityId=0941b06e-a1ca-1038-8aae-e465a393ee52&name=3.png

I am not sure where to find those numbers in your Excel spreadsheet but we will probably figure it out over email.
-- Nick
 
Nick Shulman responded:  2020-07-06
I think you are using the wrong equation in Excel to go from normalized area to concentration.

The equation that Skyline displays on the calibration curve goes from concentration to normalized area (i.e. "ratio to light").
So, when you have:
y = 0.83x + 0.0014
x is the concentration, and y is the normalized area

If you want to get the concentration from the normalized area, you need to solve for x, which is:
x = (y - 0.0014) / 0.83

-- Nick