# Plotting graph - On Microsoft Excel for protein quantitation (Aug/24/2006 )

Hi everybody,

I'm using Microsoft Excel to plot BSA calibration curve through Bradford assay. I use the Add Trendline function to get the value of R square as well as the y=mx+c equation in the linear curve. However I was confused over whether I should set the intercept at zero or not. I guess it should be set to zero. Please help me over this problem.

Thank you in advance.

Best Regards,

Rigie

-rigien-

QUOTE (rigien @ Aug 24 2006, 02:56 PM)

Hi everybody,

I'm using Microsoft Excel to plot BSA calibration curve through Bradford assay. I use the Add Trendline function to get the value of R square as well as the y=mx+c equation in the linear curve. However I was confused over whether I should set the intercept at zero or not. I guess it should be set to zero. Please help me over this problem.

Thank you in advance.

Best Regards,

Rigie

I'm using Microsoft Excel to plot BSA calibration curve through Bradford assay. I use the Add Trendline function to get the value of R square as well as the y=mx+c equation in the linear curve. However I was confused over whether I should set the intercept at zero or not. I guess it should be set to zero. Please help me over this problem.

Thank you in advance.

Best Regards,

Rigie

Hi Rigie,

Linear regression fitting allows the following from a theoretical point of view:

1) If you plot your data after blank substraction it is assumed that the intercept is zero. Then you should force the line to go through the point (0,0)

2) Otherwise, the intercept should be the blank's mean, provided you did the protein assay with duplicate or, best, triplicate samples.

Hope this helps you decide. Best regards,

Gerardo

-Gerardo-

QUOTE (Gerardo @ Aug 24 2006, 01:41 PM)

1) If you plot your data after blank substraction it is assumed that the intercept is zero. Then you should force the line to go through the point (0,0)

or if you zero your spectrophotometer against a zero standard.

-mdfenko-

Thank you two for the speedy response. Badly needed that.

Best Regards,

Rigie

-rigien-