Nitrate levels in well water can be determined spectrophotometrically though a procedure that measures the intensity of absorbed light, at 410 nm, after the sample has been properly treated with phenoldisulfonic acid. An unknown sample of 25.0 mL of well water was analyzed, at 410 nm in a 1.00 cm cell, and found to have an absorbance value of 0.721. An identically treated 25.0 mL sample, to which 5.00 mL of 10.0 ppm nitrate concentration was added, provided an absorbance of 0.840. What is the concentration of nitrate in the original sample?

ppm nitrate = ______

Using Beer's Law calculate the value for (extinction coefficient) in units of ppm-1 cm:

= _____ ppm-1 cm

Assuming that the instrument used in this determination could reliably detect absorbance values down to 0.05 (and that no components other than the analyte had any appreciable absorbance) what would be the lower limit of detection?

________ M