Chromatography Forum

In plotting a standard curve in EXCEL is the use of
1. time-scale in line graphs
2.scatter graphs
ok or a simple line graph should be used. What will be the problem, if any, if we use the above two?

You should use XY (Scatter) standard type > sub-type: scatter-compares pairs of value. After the graphic is done, right click on the point and choose Add Trendline...
Choose type Linear and click OK. You will get the calib curve.

Thankyou for your response. I wanted to confirm a little thing.

With doubling the concentration we should ideally get doubling of the areaas well. But I am getting areas like 8231, 16372, 40854, 105707, 220384, 465781. With these values I am getting a r2 value of 0.9994. Is it correct?

Sometimes I don't even bother plotting the line out - I use linest() (an array function meaning you have to select a 2 column by 4 row output area, then ^shift-Enter) after selecting Ys, Xs, true,true. It gives the slope, intercept, r² and standard errors.

Thankyou DR. What you are telling is a line graph. I wanted to confirm whether my readings are correct or not. In a line graph I get a
r2=0.7 and in a scatter R2=0.9994. With doubling in concentration I should get a doubling in area also, but they are not. Still I am getting a nice r2 value.

At the higher concetrations, you get a nice doubling of the peak areas. At the low concentrations, the peak areas increase with a factor that is larger than 2.

Consider that the integration parameters that you are using may be set too high and cut off the bottom of the peaks at the low concentrations. This will give you exactly the pattern that you observe.

Hi sonal,
I couldn't find out how can you have the value r2=0.7 in line graph. I tried your value you have and got both R2 in scatter =0.9994 and r2 in line graph=0.999355, did I make mistake somewhere? Could you please clarify it for me, I really want to have more experience in this field? Thank you!

You must have plotted the graph in time scale (go to chart options- axes-time scale)