Here is an extremely sensitive method for measuring nitrite (NO2 ) down to 1 nM in

Chapter 19, Problem 19-25

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Here is an extremely sensitive method for measuring nitrite (NO2 ) down to 1 nM in natural waters. The water sample is treated Total reflection 1 2 1 2 90 45 Power out Power in 10/(dB/m)/10 with sulfanilamide and N-(1-naphthylethylenediamine) in acid solution to produce a colored product with a molar absorptivity of 4.5 104 M1 cm1 at 540 nm. The colored solution is pumped into a 4.5-meter-long, coiled Teflon tube whose fluorocarbon wall has a refractive index of 1.29. The aqueous solution inside the tube has a refractive index near 1.33. The colored solution is pumped through the coiled tube. An optical fiber delivers white light into one end of the tube, and an optical fiber at the other end leads to a polychromator and detector. Long-pathlength spectrometer. [Adapted from W. Yao, R. H. Byrne, and R. D. Waterbury, Determination of Nanomolar Concentrations of Nitrite and Nitrate Using Long Path Length Absorbance Spectroscopy, Environ. Sci. Technol. 1998, 32, 2646.] (a) Explain the purpose of the coiled Teflon tube and explain how it functions. (b) What is the critical angle of incidence for total internal reflection at the Teflon/water interface? (c) What is the predicted absorbance of a 1.0-nM solution of colored reagent? 19-2