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principios de analise instrumental 6ed skoog resolucoes

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(i) A spectral interference is encountered when the absorption or emission of a 
nonanalyte species overlaps a line being used for the determination of the analyte. 
 (j) A chemical interference is the result of any chemical process which decreases or 
increases the absorption or emission of the analyte. 
 (k) A radiation buffer is a substance added in excess to both sample and standards 
which swamps the effect of the sample matrix on the analyte emission or absorption. 
 (l) Doppler broadening arises because atoms moving toward or away from the 
monochromator give rise to absorption or emission lines at slightly different frequencies. 
9-2. The absorbance of Cr decreases with increasing flame height because chromium oxides 
are formed to a greater and greater extent as the Cr rises through the flame. The Ag 
absorbance increases as the silver becomes more atomized as it rises through the flame. 
Silver oxides are not readily formed. Magnesium exhibits a maximum as a result of the 
two above effects opposing each other. 
9-3. The electrothermal atomizer is a more efficient atomizer. It requires much less sample 
and keeps the atomic vapor in the beam for a longer time than does a flame. 
9-4. The continuum radiation from the D2 lamp is passed through the flame alternately with 
the hollow-cathode beam. Since the atomic lines are very narrow, the D2 lamp is mostly 
absorbed by the background, wherase the hollow-cathode radiation is absorbed by the 
atoms. By comparing the radiant power of the two beams, the atomic absorption can be 
corrected for any backbround absorption. 
9-5. Source modulation is employed to distinguish between atomic absorption (an ac signal) 
and flame emission (a dc signal). 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 3
9-6. The alcohol reduces the surface tension of the solution leading to smaller droplets. It 
may also add its heat of combustion to the flame leading to a slightly higher temperature 
compared to water which cools the flame. Alcohol also changes the viscosity of the 
solution which may increase the nebulizer uptake rate. All of these factors can lead to a 
great number of Ni atoms in the viewing region of the flame. 
9-7. At hih currents, more unexcited atoms are formed in the sputtering process. These atoms 
generally have less kinetic energy than the excited atoms. The Doppler broadening of 
their absorption lines is thus less than the broadening of the emission lines of the faster 
moving excited atoms. Hence, only the center of the line is attenuated by self-absorption. 
9-8. (1) Employ a higher temperature flame (oxyacetylene). (2) Use a solvent that contains 
ethanol or another organic substance. (3) Add a releasing agent, a protective agent, or an 
ionization suppressor. 
9-9. The population of excited atoms from which emission arises is very sensitive to the flame 
temperature and other conditions. The population of ground state atoms, from which 
absorption and fluorescence originate, is not as sensitive to these conditions since it is a 
much larger fraction of the total population. 
9-10. Nebulization: Aqueous solution containg MgCl2 is converted to an aqueous aerosol. 
 Desolvation. The solvent is evaporated leaving solid particles. 
 Volatilization. The remaining water is evaporated and the particles are vaporized. 
 Atomization. Mg atoms are produced 
 Excitation of Mg to Mg* 
 Ionization of Mg to Mg+ 
 Reaction of Mg to form MgOH and MgO 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 4
9-11. 5500 nm = = = = 2.5 10 = 1 
0.002 nm
R N Nλλ × ×Δ n 
 N = no. of blazes = 2.5 × 105 
 Size of grating = 
52.5 10 grooves
2400 grooves/mm
× = 104 mm 
9-12. The flame temperature at the four heights are estimated to be 1700, 1863, 1820, and 
1725 °C or 1973, 2136, 2092, and 1998 K. To obtain Ej in Equation 8-1, we use 
Equation 6-19. Then, 
 
34 8 1
19
9
6.626 10 J s 3.00 10 m s = = = 2.59 10 J
766.5 10 mj
hcE λ
− −
−
−
× × × ×× 
 Substituting into Equation 8-1 with the first temperature (1973 K) gives 
 
19
4
23 1
0
2.59 10 J = 3 exp = 2.2 10
1.38 10 J K 1973 K
jN
N
−
−
− −
⎛ ⎞×− ×⎜ ⎟× ×⎝ ⎠
 
 In the same way, we find 
 Height T Nj/N0 × 104 Ix/Iy 
(a) 2.0 1973 2.22 1.00 
(b) 3.0 2136 4.58 2.06 
(c) 4.0 2092 3.81 1.72 
(d) 5.0 1998 2.50 1.13 
 
9-13. (a) Sulfate ion forms complexes with Fe(III) that are not readily atomized. Thus, the 
concentration of iron atoms in the flame is less in the presence of sulfate ions. 
 (b) Sulfate interference could be overcome by (1) adding a releasing agent that forms 
more stable complexes with sulfate than does iron, (2) adding a protective agent, such as 
EDTA, that forms highly stable but volatile complexes with Fe(III), and (3) using a 
higher flame temperature (oxyacetylene or nitrous oxide-acetylene). 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 5
9-14. The energies of the 3p states can be obtained from the emission wavelengths shown in 
Figure 8-1. For Na, we will use an average wavelength of 5893 Å and for Mg+, 2800 Å. 
 For Na, the energy of the excited state is 
 
34 8 1
19
3 , 10
6.626 10 J s 3.00 10 m s = = 3.37 10 J
5893 Å 10 m/Åp Na
hcE λ
− −
−
−
× × ×= ×× 
 For Mg+ 
 +
34 8 1
19
103 ,Mg
6.626 10 J s 3.00 10 m s= = 7.10 10 J
2800 Å 10 m/Åp
E
− −
−
−
× × × ×× 
 (a) Substituting into Equation 8-1, gives at 2100 K 
 
19
5
23 1
0 Na
3.37 10 J = 3 exp = 2.67 10
1.38 10 J K 2100K
jN
N
−
−
− −
⎛ ⎞ ⎛ ⎞×− ×⎜ ⎟ ⎜ ⎟× ×⎝ ⎠⎝ ⎠
 
 
+
19
11
23 1
0 Mg
7.10 10 J = 3 exp = 6.87 10
1.38 10 J K 2100 K
jN
N
−
−
− −
⎛ ⎞ ⎛ ⎞×− ×⎜ ⎟ ⎜ ⎟× ×⎝ ⎠⎝ ⎠
 
 Proceeding in the same wave we obtain for Na and Mg+ 
 (b) Nj/N0 = 6.6 × 10–4 and 5.9 × 10–8 
 (c) Nj/N0 = 0.051 and 5.7 × 10–4 
9-15. The energy difference between the 3p and 3s states was shown in Solution 8-9 to be E = 
3.37 × 10-19 J. The energy difference between the 4s and 3p states E´ can be calculated 
from the wavelength of the emission lines at 1139 nm 
 
34 8 1
19
9
6.626 10 J s 3.00 10 m s = = 1.75 10 J
1139 nm 10 m/nm
E
− −
−
−
× × ×′ ×× 
 The energy difference between the 4s and 3s state is then 
 E′′ = 3.37 × 10–19 + 1.75 × 10–19 = 5.12 × 10–19 J 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 6
 (a) At 3000°C = 3273 K 
 
19
54
23 1
3
2 5.12 10 J = exp = 1.2 10
2 1.38 10 J K 3273
s
s
N
N
−
−
− −
⎛ ⎞×− ×⎜ ⎟× ×⎝ ⎠
 
 (b) At 9000°C = 9273 K, 
 
19
24
23 1
3
2 5.12 10 J = exp = 1.8 10
2 1.38 10 J K 9273
s
s
N
N
−
−
− −
⎛ ⎞×− ×⎜ ⎟× ×⎝ ⎠
 
9-16. The absorbances of the three standards are estimated to be 0.32, 0.18, and 0.09. The 
unknown absorbance was approximately 0.09. From a least-squares treatment of the 
data, the equation for the line is y = 1.5143x + 0.02. From the analysis, the concentration 
of the unknown is 0.046 ± 0.009 μg Pb/mL. 
9-17. During drying and ashing, volatile absorbing species may have been formed. In addition, 
particulate matter would appear as smoke during ashing, which would scatter source 
radiation and reduce its intensity. 
9-18. This behavior results from the formation of nonvolatile complexes between calcium and 
phosphate. The suppressions levels off after a stoichiometric amount of phosphate has 
been added. The interference can be reduced by adding a releasing agent which ties up 
the phosphate when added in excess. 
9-19. When an internal standard