Measuring the Amount of the Analyte The amount of arsenic in each sample was determined by measuring intensity of the red color formd in the cuvetted with an instrument called a spectroph As shown Chapter spectrophotometer provides a num- ber called absorbance that is directly proportional to the to the concentra- ntensity, which is also propo onal ion of the species responsible for the color. To use absor bance for analytical purposes. a calibration curve must be generated by measuring the absorbance of several solutions hat contain known concentrations of analyte. The upper part of Figure 1F.2 shows that the color becomes more in tense as the arsenic content of the standards increases from 0 25 parts per million PP