Chlorate (CO^-₃), chlorite (CO^-₂) , bromate (BrO^-₃), and iodate (IO^-₃) can be measured in drinking water at the 1-ppb level with 1% precision by selected reaction monitoring. Chlorate and chlorite arise from ClO₂ used as a disinfectant. Bromate and iodate can be formed from Br^-or I^- when water is disinfected with ozone (O₃). For the highly selective measurement of chlorate, the negative ion selected by Q1 in Figure 21-26 is m/z 83 and the negative ion selected by Q3 is m/z 67. Explain how this measurement works and how it distinguishes CIO^-₃ from CIO^-₂, BrO^-₃ , and IO^-₃

Figure 21-6

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Collision gas (N2 or Ar) in + Quadrupole mass separator Cutaway view of Quadrupole mass separator Detector collision cell Q1 Q2 аз Mixture of Precursor ion Product ions Selected ion ions from (parent ion) (daughter ions) for monitoring chromatography column Octopole ion guide Quadrupole Entrance Exit Quadrupole mass filter mass filter lens lens Q1 Q2 Q3 Skimmer Lenses Quadrupole ion guide Нехарole Quadrupole ion guide Detector collision cell (b)