Question

The detection limit for caffeine analysis must be calculated. Eight absorbancereadings from a blank solution are 0.1239, 0.1098, 0.1182, 0.1150, 0.1219, 0.1251, 0.1199,and 0.1099. The slope of a calibration curve is 0.59 /mM. What is the detection limit?

Answer 1

detection limit = 3X STANDRD DEVIATION / SLOPE OF THE CALIBRATION LINE

for calculating standard deviaton, first mean of sample need to be calculated which is (0.1239 +0.1098+ 0.1182 +0.1150 + 0.1219 + 0.1251 +0.1199 + 0.1099)/8 =0.117963

take differences of each sample from Arithmetic mean needs to be taken

the values are

they are (absorbance of particular point -average)

0.006038
-0.00806
0.000338
-0.00286
0.004038
0.007237
0.001238
-0.00796

Their squares

3.64514E-05

6.50039E-05

1.13906E-07

8.19391E-06

1.63014E-05

5.23814E-05

1.53141E-06

6.34014E-05 take the quare of averages give

0.000243379

Standard deviation= sqrt* {0.000243379/(N-1)} where N= number of samples

Srandad deviation= 0.00589

deteaction limt= 3*0.00589/0.59=0.029949 mM