UV-Visible and Infrared Spectroscopic Methods in Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 219

16. Perform the following calculation: (a) A ¼ 0:012, %T ¼ ?;(b)T ¼ 95%, A ¼ ?; (c) wave-
length ¼ 350 nm, wave number ¼ ? cm 1 ; (d)Wave number ¼ 4000 cm 1 , frequency ¼?
hertz.
17. For the following compound formaldehyde:

H
H

C O

(a) Draw the electronic structure that shows all the sharing and nonsharing bonds,
(b) Indicate the types of molecular orbitals in formaldehyde?
18. The absorbance of a 2-cm sample cell of a 10 ppm solution is 0.43, what would be
the absorbance of a 1-cm cell of 15 ppm solution of the same chemical under the same
condition?
19. A 2-cm cell of 0.003% (w/v, i.e., 0.003 g/100 mL) solution of C 12 H 17 NO 3 (MW¼
223:3) has a l max of 280 nm with an absorbance of 0.92. What is the absorbance of
the same chemical when the concentration is 0.005% using 1 cm cell under the same
wavelength? Report e in 1/CM cm).
20. The molar absorptivities (e) of two compounds A and B were measured with pure
samples at two wavelengths. From these data in the following table, determine the
concentration (in M) of A and B in the mixture. The absorbance of a mixture of A and B
in a 1.0 cm cell was determined to be 0.886 at 277 nm and 0.552 at 437 nm.

e at 437 nm (M 1 /cm 1 )

e at 277 nm (1/M/cm)

Chemical A 14,780 5112

Chemical B 2377 10,996

21. Draw a schematic diagram of the following: (a) UV-VIS spectrometer and (b) FTIR
spectrometer.
22. From the following methods, do a literature/internet search (Hint: NEMI database and
APHA's standard method topic), give a list of methods that use only ''UV''
spectrometry (i.e., not to include visible spectrometry). (a) EPA 100-600 series
methods, (b) APHA's 4000 series methods for inorganic nonmetallic constituents
23. Which one of the following IR instruments cannot record spectrum: (a) FTIR, (b) DIR,
or (c) NDIR? Explain why?
24. Explain: (a) Why in situ atmospheric CO 2 can be monitored by IR? (b) Why in situ
atmospheric (stratospheric) O 3 can be measured by UV?
25. Explain: (a) Why O 2 and N 2 will not affect the monitoring of CO in auto emission using
IR? (b) Why a long cell is needed to monitor trace organic compounds using IR?