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principios de analise instrumental 6ed skoog resolucoes

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is used, the ratio of intensity of the analyte line to that of the 
internal standard is plotted as a function of the analyte concentration (see Figure 1-12). If 
the internal standard and the analyte species are influenced in the same way by variation 
in the aspiration rate and the flame temperature, and if the internal standard is present at 
approximately the same concentration in the standards and the unknown, the intensity 
ratio should be independent of these variables. 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 7
9-20. Setting up two equations in two unknowns 
 0.599 = 0.450m + b 
 0.396 = 0.250m + b 
 Subtracting the second equation from the first gives 
 0.203 = 0.200 m 
 or the slope m = 0.203/0.200 = 1.015 
 Then using this value in the first equation gives 
 b = 0.599 – 0.450 × 1.015 = 0.14225 
 The unknown Pb concentration is then x = (0.444 – 0.14225)/1.015 = 0.297 ppm Pb 
9-21. In the spreadsheet below we first calculate the equation for the line in cells B10 and B11. 
 y = 0.920 x + 3.180 
 The mean readings for the samples and blanks are calculated in cells D7:G7, and the 
mean Na concentrations in cell D8:G8. These values are uncorrected for the blank. The 
blank corrections are made in Cells B14:D14. These are then converted to %Na2O in 
cells B15:D15 by the following equation 
 22 6
conc. Na O in μg/mL 100.0 mL %Na O = 100% 
1.0 g 10 μg/g
× ×× 
 The error analysis shows the calculations of the 4 standard deviations by the equations in 
Appendix 1, Section a1-D2. Since the final result is obtained by subtracting the blank 
reading, the standard deviations must be calculated from the difference in cells E24:G24 
by 2d A = + s s s
2
bl where sA is the standard deviation for the concentration of A and sbl is 
the standard deviation of the blank. These are then converted to absolute and relative 
standard deviations of %Na2O in cells E25:G26. 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 8
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 
 
8
 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 9
 
Principles of Instrumental Analysis, 6th ed. Chapter 9
 
 
 
9
9-22. 
 
 
Skoog/Holler/Crouch Chapter 10
Principles of Instrumental Analysis, 6th ed. Instructor’s Manual
 
 
 1 
CHAPTER 10 
10-1. An internal standard is a substance that responds to uncontrollable variables in a similar 
way as the analyte. It is introduced into or is present in both standards and samples in a 
fixed amount. The ratio of the analyte signal to the internal standard signal then serves as 
the analytical reading. 
10-2. Flame atomic absorption requires a separate lamp for each element, which is not 
convenient when multiple elements are to be determined. 
10-3. The temperature of a high-voltage spark is so high (~40,000 K) that most atoms present 
become ionized. In a lower temperature arc (~4000 K) only the lighter elements are 
ionized to any significant exten. In a plasma, the high concentration of electrons 
suppresses extensive ionization of the analyte. 
10-4. D–1 = (2d cosβ)/nf (Equation 7-16) 
 (a) 
7
1
3
1 mm 10 Å2 cos 63 26
120 grooves mm = = 2.9 Å/mm
30 0.85 m 10 mm/m
D−
′× × ×
× ×
D
 
 (b) 
7
1
3
1 mm 10 Å2 cos 63 26
120 grooves mm = = 0.97 Å/mm
90 0.85 m 10 mm/m
D−
′× × ×
× ×
D
 
10-5. In the presence of air and with graphite electrodes, strong cyanogens (CN) bands render 
the wavelength region of 350 to 420 nm of little use. By excluding nitrogen with an inert 
gas, the intensities of these bands are greatly reduced making possible detection of 
several elements with lines in this region. 
10-6. By Nebulization, by electrothermal vaporization, and by laser ablation. 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 10
 
 2
10-7. The advantages of the ICP over the DCP are higher sensitivity for several elements and 
freedom from some interferences and maintainence problems. No electrodes need to be 
replaced in the ICP, whereas in the DCP, the graphite electrodes must be replaced every 
few hours. Advantages of the DCP include lower argon consumption and simpler and 
less expensive equipment. 
10-8. Ionization interferences are less severe in the ICP than in flame emission because argon 
plasmas have a high concentration of electrons (from ionization of the argon) which 
represses ionization of the analyte. 
10-9. Advantages of plasma sources include: 
1. Lower interferences 
2. Emission spectra for many elements can be obtained with one set of excitation 
conditions. 
3. Spectra can be obtained for elements that tend to form refractory compounds. 
4. Plasma sources usually have a linearity range that covers several decades in 
concentration. 
10-10. The internal standard method is often used in preparing ICP calibration curves to 
compensate for random instrumental errors that arise from fluctuations in the output of 
the plasma source. 
 
 
Skoog/Holler/Crouch Chapter 11
Principles of Instrumental Analysis, 6th ed. Instructor’s Manual
 
 
 1 
CHAPTER 11 
11-1. Three types of mass spectrometers are used in atomic mass spectrometry: (1) quadrupole 
mass analyzers, (2) time-of-flight mass spectrometers, and (3) double-focusing mass 
spectrometers. The quadrupole mass spectrometer separates ions of different mass based 
on selective filtering of ions during their passage through four parallel rods that serve as 
electrodes. One pair of rods is attached to a positive dc voltage and the other to a 
negative dc voltage. In addition, variable radio frequency ac voltages that are 180° out of 
phase are applied to each pair of rods . The ions to be separated are then accelerated 
between the rods. Only ions having a limited range of m/z values are able to pass through 
the rods. All others are annihilated by stiking the rods. By varying the dc and ac 
voltages simultaneously, separation of ions of different masses occurs. 
 In the time-of-flight mass spectrometer, ions are accelerated periodically into a field-free 
drift tube. Their velocity in the tube is determined by their mass-to-charge ratio so that 
they arrive at a detector at different times depending on their mass 
 In a double-focusing mass spectrometer, ions are accelerated into a curved electrostatic 
field and then into an electromagnetic field. The lightest ions are deflected to a greater 
extent than are heavier ions, and thus are dispersed on a plane where they are detected. 
11-2. The ICP torch in an ICPMS instrument causes atomization and ionization of the species 
which can then be separated by the mass spectrometer. 
11-3. The ordinate (y-axis ) in a mass spectrum is usually the relative abundances or intensities 
of the ions. The abscissa (x-axis) is usually the mass-to-charge ratio. 
 
 
Principles of Instrumental Analysis, 6th ed. Chapter 11
 
 2
11-4. ICPMS has become an important tool for elemental analysis because of its high 
sensitivity, its high degree of selectivity, and its good precision for determining many 
elements in the periodic table. 
11-5. The interface consists of a water-cooled metal cone with a tiny orifice in its center. The 
region behind the cone is maintained at a pressure of about 1 torr by pumping. The hot 
gases from the ICP impinge on the cone, and a fraction of these gases pass through the 
orifice where they are cooled by expansion. A fraction of the cooled gas then passes 
through a second orifice into a region that is maintained at the pressure of the mass 
spectrometer. Here, the positive