a 25.0 ml aliquot of an aqueous quinine solution was diluted to 50.0 ml and found to have an absorbance of 0.528 at 348 nm when measured in a 1.00 cm cell. a second 25.0 ml aliquot was spiked with 10.00 ml of a 23.4 ppm quinine standard. after dilution to 50.0 ml, this solution had an absorbance of 0.610 at 348 nm in the same 1.00 cm cell. calculate the concentration of quinine in the sample in ppm.