Detection limit. In spectrophotometry, we measure the concentration of analyte by its absorbance of light. A lowconcentration
sample was prepared, and nine replicate measurements
gave absorbances of 0.004 7, 0.005 4, 0.006 2,
0.006 0, 0.004 6, 0.005 6, 0.005 2, 0.004 4, and 0.005 8 in a
1.000-cm cell. Nine reagent blanks gave values of 0.000 6,
0.001 2, 0.002 2, 0.000 5, 0.001 6, 0.000 8, 0.001 7, 0.001 0,
and 0.001 1.
(a) Find the absorbance detection limit with Equation 5-2.
(b) The calibration curve is a graph of absorbance versus
concentration in a cell with a pathlength of 1.000 em. Absorbance
is a dimensionless quantity. The slope of the calibration
curve is m = 2.24 X 104 M-1• Find the concentration detection
limit with Equation 5-4.