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4. The following data were found in a determination of chromium in water. The protocol was to run a blank, the sample, and then the sample with two standard-addition spikes. Three replicate runs were made for each sample. Incidently, this was all done automatically using a computer-controlled instrument. The significantly different responses to the spikes were caused by the other matrix components. Solution Blank Sample 1 Addition 1 Addition 2 Blank Sample 2 Addition 1 Addition 2 Blank Sample 3 Addition 1 Addition 2 Conc. Cr (ng mL") 0.000 +2.000 +4.000 0.000 +2.000 +4.000 0.000 +2.000 +4.000 # 1 0.005 0.054 0.000 0.537 0.001 0.086 Instrument readings #2 0.179 0.305 0.666 0.790 0.214 0.341 0.009 0.058 0.000 0.548 0.003 0.083 0.191 0.310 0.659 0.784 0.213 0.350 # 3 0.005 0.058 0.000 0.531 0.000 0.078 0.188 0.318 0.667 0.805 0.212 0.337 Calculate the concentrations of Cr in the three samples, based on the means of the measured values for each sample and the standard additions. Make the blank correction if necessary.