NO and NO₂ are involved in important biological processes.  For example, NO is involved in blood pressure regulation, immune response, and neurotransmission; NO₂ is a strong oxidizing and nitrating agent.  Nitrous acid can, under certain conditions, serve as a source for both. Two spectroscopic probes, ABTS and TMPD, were chosen to study the mechanism of the reaction with NO₂ and one of the probes in an O₂ free environment at 25^oC.  Except under certain conditions, both reactions followed the rate law, rate = (k₁+k₂[H⁺])[HNO₂]², where k₁ = 10.9 M^-1s^-1 and k₂ = 175 M^-1s^-1.  This result is fully consistent with the known HNO₂ disproportionation to yield NO and NO₂. This reaction is followed by a fast and kinetically invisible reaction with NO₂ and one of the spectroscopic probes.  A reaction with water soluble tri-aryl phosphine was also studied.  The reaction is first order in tri-aryl phosphine and second order in NO and has a rate constant of k = 5 x 10⁶ M^-2s^-1.  This reaction has allowed us to identify NO as the unreacted product of HNO₂ with the spectroscopic probes.  This reaction has great potential as an analytical test for NO, which is otherwise difficult to detect because of weak spectroscopic features and low reactivity.