Dear all

I was trying to calculate the drift in concentration from day to day basis as given in SW846 EPA but my calculation gives me negative answer.

can area of the standard can be taken for calculation?

I mean to say today i make new standard a suppose 1ppm(Single point cal)and inject and getan area.Then next day inject the same standard and get the area. From this can i use the formula

(First day area-2nd day/first day)*100

SW846 says
theoritical concentration -calculated concentration /theoritical concentration

please send me some suggestion