10 mL of sample in a 40-mL volumetric flask, adds 4 mL of a reagent that will turn blue in the presence of orthophosphate, and dilutes the flask to 40 mL (i.e. adds deionized water up to the 40 mL fill line). After waiting for the color to develop, the analyst measures absorbance of the blue sample at 880 nm in a spectrophotometer and finds it to be 0.177 absorbance units.
Given the set of calibration standards in the table below, what is the total dissolved P concentration in the water sample, in mg/L?
P concentration Absorbance units
mg L$^{-1}$ (at 880 nm)
0 0.133
0.01 0.158
0.03 0.182
0.12 0.345
0.24 0.547
0.48 0.987
0.60 1.225
