Fo(D) Std
/
BCR-I
I
',
1pA
':
I
4 '
%L---
Reproducibility. Total iron concentrations were generally reproducible to f1.5% or better. The reproducibility of ferrous and ferric concentrations obviously depends on the concentration ratio of two species. However, in these samples where the ratio lies within the range 1:3 to 3:1, better than f3% could be obtained. Limitations. The greatest limitation to the present method is that it is applicable only to samples amenable to the reported dissolution procedure. Thus refractory materials, such as chromite, would not be suitable. In principle, any sample for which the standard dichromate titration (1, 2 ) procedure can be used to determine the ferrous content, can be subjected to the polarographic method to provide information on the ferrous, ferric, and total iron content. The additional information gained and the advantages of the instrumental method of analysis can therefore be appreciated. Data for the USGS Standard Rocks only are reported in this paper to validate the method. However, presently, work on a wide array of other samples has been commenced or is contemplated, and it is certainly applicable to a considerable number of determinations.
-0'35 -0.15 +0'05 LITERATURE CITED
Volt v5 Ag/AgCI Figure 4. AC polarograms for a standard ([Fe(lll)] = 1.00 X 10-3M)
and a USGS Rock Standard
L. Shapiro and W. Brannock, U.S. Geol. Surv. Bull, 1144A, A48 (1962). L. C. Peck, U.S. Geol. Surv. Bull., 1170 89(1964). L. E. Reicker and J. J. Fahey, U.S. Geol. Surv. Bull., 1144 B (1962). J. L. Bouvier, J. G. Sen. Gupta, and S. Abbey, Geol. Surv. Can., Paper 72-31 _ .(19721. - -, (5) J. J. Lingane, J. Amer. Cbem. Soc., 68, 2448 (1946). 161 L. Meites. Anal. Cbem.. 20. 895 11948). i7j M. Pinta, '"Dekction and Determination of Traces Elements," israel Program for Scientific Translations, Jerusalem, 1966, pp 434-437. ( 8 ) L. Cernatescu, R. Ralea, G. Burlacu, M. Furnica, 0. Bot, and M. Radu, Bull, Stiintif, Sect, Stiln. Tech. Cbim., 6, 185 (1954). (9) I. M. Issa, R. N. Issa. and I. F. Hewaidy. Cbemisf-Analyst, 47, 88 (1958). (10) G. L. Bien and E. D. Goldberg. Anal. Cbem., 26, 97 (1956). (11) B. Rehak. Hutn. Listy, 5, 432 (1957). (12) E. P. Parry and D. P. Anderson, Anal. Cbem., 45, 458 (1973). (13) A. M: Bopd, Anal. Cbem., 45, 2026 (1973). (14) A. M. Bond, V. Biskupsky, and D. A. Wark, Anal. Cbem., 46, 1551 (1974). (15) S. C. Creason and D. E. Smith, Anal. Cbem., 45, 2401 (1973). (16) F. Van Der Pol, M. Sluyters-Rehback, and J. H. Sluyters, J. Nectroanal. Cbem., 45, 277 (1973). (17) D. E. Glover and D. E. Smith, Anal. Cbem., 44, 1140 (1972). (18) D. E. Glover and D. E. Smith, Anal. Cbem., 45, 1869 (1973). (19) A. M. Bond and J. R. Thackeray, Cbem. Instrum., 4, 299 (1972). (20) K. Yamashita and H. Imai, Bull. Cbem. Soc. Jap., 41, 1339 (1968). (21) F. J. Flanagan, Geocblm. Cosmocbim. Acta, 37, 1189 (1973). (22) F. J. Flanagan, Geocbim. Cosmocbim. Acta, 33, 81 (1969). (1) (2) (3) (4)
\
rate of (100 f 1)% was found. With ferrous ion, as shown in Figure 2, a very small ferric contribution was sometimes observed, and a recovery rate of (99 f 1.5)%was found for this species. Standard Rocks. Table I shows data obtained on five standard rocks, along with average values obtained via other methods (21 ) and the range of values reported in the literature (22). T h e polarographic results lie well within the range of published data and generally within f2% of the average values compiled from all available data. Figure 3 shows typical dc polarograms of three of the samples, and Figure 4 gives ac polarograms of a standard solution and a sample. Considering that the ferrous, ferric, and total iron were all obtained from the one experimental approach, compared with other methods where two or even three experiments are required, the ease and convenience of the proposed method can be appreciated.
RECEIVEDfor review August 2, 1974. Accepted September 20, 1974.
Relative Photoelectron Signal Intensities Obtained with a Magnesium X-Ray Source Herve Berthou and Christian K. Jplrgensen Departement de Chimie minerale et analytique, Universite de Geneve, 12 11 Geneva 4, Switzerland
X-Ray photoelectron spectroscopy has often been used for quantitative (or semiquantitative) analysis of metallic or alloyed samples. Since people use either an aluminum or a magnesium X-ray source, the relative photoelectron signal Intensities of 76 elements are compared for both sources. Dlfferences arise though the same intensity behavior Is observed. Further on, the relative reproducibility is much better with a high-intensity magneslum source (10 to 15 % ) 482
than with aluminum (20 to 30%). The intensity variation cannot be straightforwardly correlated with the 233-eV dlfference between the photon energies 1486.6 and 1253.6 eV. In a few cases, a kind of sharing due to secondary processes such as shake-up or multiplet splitting might explain the discrepancies from the values expected using the ratios of theoretlcal photolonization cross-sections.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, M A R C H 1975
T a b l e I. Relative Photoelectron S i g n a l Intensities Obtained with a Magnesium X-Ray Source for Elements from Lithium to Arsenic (Values Previously Obtained w i t h a n Aluminum X-Ray Source Are in P a r e n t h e s e s ) Ele ment
Li
Be C
N 0
0.03 (0.02) 0.09 (0.07) 0.25 (0.27) 0.4 (0.4) 0.6 (0.6) 1.0 (1.0) 2.0 15% (2.0)
...
...
...
...
...
.,.
...
0.009
...
...
...
...
0.013
...
...
*..
0.015 (0.01) 0.021 (0.02) 0.14 (0.08) 0.14 + 15% (0.10) 0.22 (0.18) 0. 52 0.43 (0.3) 0.46 (0.35) 0.'54 (0.42) 1.0 (0.9) 1.35 (0.8) 1.5 1.2 (0.9) 1.4 20% (0.9) 1.3 40%
...
...
...
...
...
...
...
...
...
...
*..
...
...
...
...
... ...
.. .
...
...
*..
0.05
0.07
...
0.04 (0.04) 0.10 (0.08) 0.08 (0.06)
0.04 (0-05) 0.21 (0.12) 0.20 (0.12) 0.23 0.17 (0.11) 0.16 i 20% (0.11) 0.2 i: 40% (0.'18) 0.3 (0.15) 0.32 (0.25) 0.5 (0.28) 0.56 (0.37) 0.62 + 20% (0.4) 0.7 (0.3) 0.57 i 40%
...
Si
P
... ...
S
...
...
c1
...
K
...
0.28 (0.25) 0.5
Ca
...
...
sc Ti
... ...
... ...
V
...
...
(3)
...
...
...
Fe
co
...
0.09
Ni
...
...
c u (1)
...
...
CU(II)
...
...
Zn
...
Ga
...
...
Ge
...
...
As
...
15%
* *
Cr Mn
3d
...
...
Mg
*
3p
...
A1
Na
3s
...
e . .
0.03 (0.02) 0.045 (0.04) 0.24 (0.13) 0.19 (0.15) 0.20 (0.22) 0.36 0.23
F
2P
2s
Is
(1.1) 1.15 (1.0)
*.. ...
... ...
... ...
1.15 (1.8) 1.2 (2.1) 1.15 (1.7) 1.9 (3.0)
0.25 (0.07) 0.23 0.25
...
1.9 (1.5) 2.2 (3.2) 2.1 (4 1
0.4 0.45
...
0.2
(4 1
...
..
(3 1
X-ray photoelectron spectroscopy has generally been used for studing chemical bonding and the chemical influence of ligands on a central atom ( I , 2 ) . However, one aspect of this technique has often been underestimatednamely, its capability to give quantitative (or a t least, semiquantitative) results. C. D. Wagner has been the first ( 3 )t o
0.6 (0.45) 0.3 (0.4) 0.33 (0.38)
...
...
... ...
0.09 (0.03) 0.08 (0.06) 0.09 (0.1) 0.26 (0.08) 0.46 20% (0.15) 0.33 (0.12) 0.4 + 40% (0.25) 0.6 (0.4) 0.3 (0.4) 0.45 (0.48)
*
demonstrate that X-ray photoelectron spectroscopy can be a method for quantitative analysis. Nowadays, people turn their attention on such results in view of application in metallic surface studies ( 4 , 5 ) complex chemistry (6), in catalysis ( 7 ) , or in adsorption of alkaline metals on phosphates (8). On the other hand, theoretical calculations of pho-
A N A L Y T I C A L CHEMISTRY, VOL. 47, NO. 3, M A R C H 1975
483
Table 11. Intensity Ratios between the Relative Intensities Obtained with Magnesium a n d Aluminum X-Ray Sources for t h e S a m e Elemental Shell (Photoionization Cross-section Ratios for 1253.6- a n d 1486.6-eV Photons. Calculated from Nefedov et al. ( 9 ) , Are Given in Parentheses) Element
Li Be C
N 0 F Na Mg A1 P S
c1 K Ca Ti
V Cr Mn
Fe co Ni
CU(1) CU(II) Zn Ga
Ge As
Is
1.5 (1.72) 1.3 (1.67) 0.93 (1.63) 1.0 (1.61) 1.0 (1.59) 1.0 (1.57) 1.0 (1.53)
. . . .
. . . .
. . . .
... . . . . . .
... ... . . .
. . . .
. . . .
. . . .
...
. . .
. . . . . . . . . . . .
2s
2P
...
. . . ... ...
...
...
...
1.5 (1.56) 1.1 (1.55) 1.85 1.51) 1.3 (1.48) 0.91 (1.47)
1.5 (13 4 ) 1.1 (1.82) 1.75 (1.79) 1.4 (1.77) 1.22 (1.75) 1.43 (1.71) 1.33 (1.7) 1.38 (1.69) 1.11 (1.66) 1.69 (1.65) 1.33 1.56 1.18 1.15 0.64 0.57 0.68 0.63 1.27 0.69 0.52
...
*..
... ... ...
...
... *.. ... ... ... . . . ... ... . . . . . . ... ...
... ...
* . .
...
toionization cross-sections for 1486.6- and 1253.6-eV photons have recently been published and compared with experimental results for elements with 2 = 3 to 92 (9-11). Independently of Wagner, we also measured the photoelectron signal intensities in hundreds of stoichiometric compounds (containing 77 elements) which we analyzed with an aluminum source ( 1) and resumed in a subsequent paper ( 1 2 ) . Our results agreed well with those of Wagner. As we now use a magnesium X-ray source, such intensity measurements were repeated and we found differences. The most striking example arises with the Cs3d5/2 signal decreasing to about half its previous value. On the other hand, 4f photoelectron signal relative intensities are enhanced, such as for hafnium 4f7/2 by about 60% (13).Comparison will be made with theoretical results. EXPERIMENTAL Our measurements are made with a Varian IEE-15 photoelectron spectrometer. A retarding potential is applied to the samples to keep the energy of emitted photoelectrons entering the analyzer constant at 36 eV. A high intensity magnesium X-ray source is run at 11000 V and 0.15 A. With these standard settings, the resolution (defined as the presence of two distinct maxima in the superposition of two Gaussian signals with the same one-sided half-width d and same height, occurring ( I ) for a distance above 1.70 6 of the two component maxima) is close to 1 eV and the value of 2 6 is 1.3 eV and 1.2 eV for metallic gold 4f7/2 and for metallic silver 3d5/2, respectively. Each region up to ten was scanned one after the other, whereas a small intensity decrease may be observed during measurements, because of hydrocarbon contamination. We circumvented this problem by scanning the regions sequentially--i.e., a few scans per region repeated 25, 50, or 100 times. Powdered samples are generally stuck onto an one-sided Scotch tape (600P, No. 15, 3M Company) consisting of polymerized CH2 groups. Programs are run between 60 to 100 minutes. As done previously, we determined the relative intensities of the strongest signals of a given element in comparison with the fluorine 1s signal. In the following, we use the colloquial name Wagner 484
35
. . . .
. . . .
. . . .
...
...
. . . .
.. . ..
..
1.o (1.43) 1.25 (1.42) 1.33 (1.41)
...
. . . ...
... * . . 3.57
... . . .
... ... ...
3d
3P
...
... ...
... 1
.
.
...
. . .
. . . .
...
...
0.8 (1.67) 1.75 (1.63) 1.67 (1.61) 1.54 1.45 1.11 2 .o 1.28 1.78 1.51 1.55 2.33
... 1.33 0.75 0.88
. . . .
. . . .
... ... ...
* . .
...
3 .o 1.42 0.92 3.25 3.06 2.75 1.6 1.5 0.75 0.94
= w for this unit of intensity. In practice, we established a set of secondary standards such as nitrogen Is, oxygen Is, sulfur 2 ~ 3 1 2or chlorine 2 ~ 3 1 2 .When a large number of compounds with or without fluorine are compared, a consistent set (within 10 to 15%reproducibility) of intensities can be established. Actually, the reproducibility mentioned above is better than the 20 to 30% previously obtained with the aluminum X-ray source. This fact might be correlated to the much higher electronic density around the samples when bombarded with 1253.6-eV photons coming from the high intensity source. When metallic or alloyed samples are analyzed, the reproducibility becomes better than 2%. Relative intensities given in Tables I-V refer to photoelectron signals with j = 1 + %, when resolved. The intensity ratio ( 1 + 1)/1 between the signals for j = 1 + K (at lower ionization energy) and j = 1 - is generally respected. Nevertheless, this latter rule is not observed for elements such as calcium, scandium, titanium, and vanadium u-here the 2 ~ 3 1 2signal is much higher by about three times than the 2~112(for which the full width is only marginally broader than the 2p3/2), and for heavy elements when the 4p level is considered. For measuring photoelectron signals, we only consider the signal height at maximum in pulses per second and then, normalized it by comparison with the reference signal height(s) of known intensity. If we were to consider the area under the curves, equivalent to the height at maximum multiplied by the full width, the disagreement previously observed for the 2p and 4p levels is less pronounced but still exists. For analytical purposes, the area is far less suitable because of the mildly undulating background. Finally, the results given through Tables I-V are reproducible within 10% (unless quoted). Figures 1 and 2 resume the relative intensities given as a function of the atomic number 2 for the Is, 2s, 2~312,3s, 3d5/2, 4s, 4~312, 4d5/2, 4f7/2, 5p3/2 and 5d shells of elements with Z = 3 to 92. Whereas results given by W. J. Carter et al. ( I 1 ) predict a smooth exponentially-like increase for Is, 2s, 2p, 3d, 4d, and 4f shells with the atomic number, our results show variations and something like steps in a staircase for 2p, 3d, and 4f shells while increasing dramatically with 2. Discontinuities in intensity appear between Z = 17 and 20 for 2p and 3p shells (less pronounced in the latter case) and between 2 = 28 and 31 (also true for 3s and 3d shells). Later on, discontinuities also appear between 37 and 39 and between 47 and 50 for the 3d and 3p shells. Generally, discontinuities ap-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, MARCH 1975
-32 Figure 1. Relative intensities of Is, 2.5,2p, 3s, 3p, 3d, and 4p photoelectron signals as a function of the atomic number Z(the left-hand higher scale refers to the Is, 2p, and 3d relative intensities)
Table 111. Relative Photoelectron Signal Intensities Obtained with a Magnesium X-Ray Source for Elements from Selenium to Barium (Values Previously Obtained with an Aluminum X-Ray Source Are in Parentheses) Element
s'.
Se
...
Br
0.2
Rb
0.2
Sr
...
Y
...
Zr
...
N?J
...
Mo Ru
0.07
Rh
0.075
...
0.31 (0.5) 0.5 (0.5) 0.6 (0.7) 0.75 (0.8) 1.05 f 20% (0.85) 0.6
0.5
(0.8)
(12 )
0.55 (0.8) 0.6 0.47 (0.8) 0.4
1.35 i 30% (1.2) 1.6 2 .o (1 3 ) 1.9 (2.1) 2.15 (1-9) 2.45 (2.5) 3.35 (3 .O) 4.5 i 15% (4.0) 3.95 25% (5 .O) 5.35 (6 - 0 ) 4.5 i 3 5 % (4.0) 3.9 (4.0) 4.05 (6.5) 3.9 (5.5)
(1.1) Pd
0.05
Ag.
0.03
Cd
0.05
In
...
0.5 (0.6) 0.4 (0.8) 0.6 (1.O) 0.75
Sn
0.1
0.88
sb
.
I
3d
3P
.
0.65
Te
. . .
0.43
I
...
0.31
Cs
...
...
Ba
...
...
(0 5) 0.6 (0.55) 0.66 (0.6) 1.72 f 30% (0.8) 1.3 + 20% (0.9) 1.5
*
4s
...
...
0.11 (0.08)
...
... ...
4d
4P
...
0.18 i 255% (0 S O ) 0.23 (0.2) 0.55 i 50%
...
...
...
...
...
...
...
...
...
...
...
...
...
0.1? 0.16
... ...
...
(0.2) 0.18 (0.2) 0.10 i 40% (0.2 1 0.18 0.21 (0.14) 0.16 (0 2 ) 0.085 (0.1) 0.09 (0.1) 0.095 , (0.1) 0.095
0.15
...
0.2 i 50% (0.2) 0.28 i 25% (0.2) 0.3 i 20% (0.35) 0.63 i 25% (0.5) 0.95 f 1 5 % (0.7) 0.9 45%
0.135
(0.8) 1.1 2 5 %
*..
... ... 0.065 0.04 0.05 0.04 0.055
0.115 0.115
0.09
...
...
...
0.65
...
...
5P
...
* *
(1 .O) 0.93 i 50% (0.7) 0.75 i 20% (0.6) 0.71 (1.3) 1.1 I1 5 % ( 1 3)
... ... ...
... ...
...
... ... 0.06 (0.05) 0.10 0.14 i 20% (0.15)
______
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, M A R C H 1975
485
Table IV. Relative Photoelectron Signal Intensities Obtained with a Magnesium X-Ray Source for the Lanthanides (Values Previously Obtained with an Aluminum X-Ray Source Are in Parentheses) Element
3d
4d
La
3.35 i 25% (2) 2.4 i 15% (2 ) 1.8 i 25% (21 2.2 * 20q (3) 2.2 (2.3) 2.2 (2.2)
1.33 z 40% (1.O) 0.65 i 2 0 5 (0.5) 0.71 i 2 5 % (0.4) 0.73 * 20% (05) 0.62 * 1 5 5
Ce Pr Nd Sin Eu
*..
Gd
DY
... ...
Ho
...
Er
...
Tm
...
Yb
...
Lu
...
jP e
.
.
* 203 0.23 * 3 5 5
0.11
0.25 (0.1)
0 -09
(0 .O 7) 0.17
0.18 (0.06) 0.29 i 3 0 % (0.15) 0.35
0.85
02 2 0.21 (0.15) 0.24 -t 15q (0.1) 0.33 0.22 (0 .O 7) 0.31
(0.2)
0.98 (0.8) 0.83 0.46 f: 40% (0.4) 0.72 (0.25) 0.99 i 3 0 q (0.5) 0.95 (0.4) 0.7 + 25'7, (0 5) 1.3 (0.5)
(3 Tb
41
...
0.48 (0.3) 0.57 024
(02) 0.34 (0.25) 0.58 (0.3) 0.75 (0.35) 0.97 (0.5) 2.34 i 3 0 ' i ; ( 3 ) (0.75)
0.34 (0.15) 0.17
*
0.28 3 5 5 (0.2 5) 0.45 i 25';
Table V. Relative Photoelectron Signal Intensities Obtained with a Magnesium X-Ray Source for Elements from Hafnium to Uranium (Values Previously Obtained with an Aluminum X-Ray Source Are in Parentheses) Element
...
Ta
...
w
...
Re
0.3
os
0.25 (0.3) 0.25 (0.5) 0.2 (03 ) 0.25 (0.35) 0.3
Ir Pt Au Hg
0.25
Pb
...
Th
U
486
0.85 (0.8) 0.71 (1 .O) 0.6 0.6 (0.8)
T1
Bi
4d
4P
Hf
... . . .
...
0.8 (1.O) 0.85 (1.2)
0.6 (0.9) 0.65 (0.9) 0.6 (0.8) 0.63 (1.O) 0.55
* 40%
(0.9)
0.72 + 20%
(1 .O) 0.84 i 3 0 8 (12) 0.7 i 30% (1.3)
4f
1.45 (0.9) 1.7 (1.4) 1.7 2.1 * 15°C (1.8) 2.65 (1.3) 2.6 (1.8) 2.5 (1.8) 2.5 (2 2) 2.5 (2.4) 3.1 (2.5) 3.9 * 20% (3 2) 4.3 i 30% (3.5) 6.8 i 30% (7) 3.1 (7)
ANALYTICAL CHEMISTRY, VOL. 47, NO. 3, MARCH 1975
5s
...
0.2
...
0.23
...
0.2
...
0.26
0.15
...
0.07 (0.05)
...
5d
SP
...
...
...
...
...
...
* . . ...
0.12
...
0.17 (0.3)
...
0.20 (0 2 5 ) 0.25 (0.4) 0.21 (0.3) 0.22
...
...
...
(0.25)
0.1
0 .l
...
...
...
...
... ...
0.48 (0.4) 0.45 (0.5) 0.55 (0.5) 0.9
...
6P
...
i 20%
* 25%
(1.O) 0.41 (0.9)
... ... ... 0.23 0.05 U5f 0.11
LO
50
KO
7c
BC
90
-2
Figure 2. Relativelntensities of 4d, 4f, 5p, and 5d photoelectron signals as a function of the atomic number Z (the right-hand higher
scale refers to the 4f relative intensities)
pearing in different shells are seen roughly within the same gaps. On the other hand, 2s, 3s, 3p, 4s, 4p, 4d, and 5p intensities seem to scatter around a mean value instead of increasing smoothly with 2 as predicted. For these last^ shells, it is noted that their intensities are quite low.
RESULTS AND DISCUSSION Elements from Lithium to Arsenic. T h e relative intensities of photoelectron signals obtained with a magnesium X-ray source are resumed for elements from 2 = 3 to 33 in Table I and compared with those obtained with aluminum (quoted in parentheses through Tables). Whereas Is and 2s signal intensities are roughly equivalent for both sources, the 2p intensities show an increase from carbon to chromium and a decrease for the subsequent elements. On the other hand, they remain almost constant for manganese, iron, cobalt, and nickel, and again increase from copper to gallium, while for aluminum photons the increase was the general trend. This step appearing from manganese to nickel might be explained by a kind of intensity sharing because, for these elements, the 2p signals are accompanied by satellite structure due to shake-up or shake-off process (14, 1 5 ) or to multiplet splitting (interelectronic repulsion) ( 1 ) when the ground state has positive total spin quantum number S. As also shown in Table I, the 3s, 3p, and 3d signal intensities are generally enhanced when using magnesium instead of aluminum photons, but their variations follow the same trend in both cases. Theorists concentrate interest on the Is signal increasing strongly from Z = 3 to 11 as a function of Z , O.OO2(2 - 1 ) 3 w. They argue that the intensities are proportional to the X-ray absorption cross-section (9, 1 0 ) . For s and p electrons, it can be approximated by the absorption edge going as (-3rd) power of the photon energy (as suggested by Kramers ( 1 2 ) ) whereas higher 1- values correspond to delayed maxima above 100-eV photon energy. Quite generally, t h e transition elements show intensities 2 to 10 times lower than expected from interpolation between the surrounding elements or by extrapolation. As seen from data given by Nefedov et al. (91, the ratios between the total photoionization cross-sections for 1253.6and 1486.6-eV photon energies decrease slowly from lithium to calcium for the Is, 2s, 2p, and 3p shells and vary from about 1.7 to 1.4. Hence, we could expect a much larger difference between relative intensities with both sources. However, this predicted increase does not agree well with our experimental results, as seen in Table I1 (figures in parentheses refer to Nefedov data). T h e increase is much less
with the exception of calcium where the agreement is good enough. I t is noted that the magnesium X-ray source does not make so much difference between copper(1) and copper(I1) 2p signals as aluminum, but this difference appears to a larger extent for the 3p and 3d shells. Elements from Selenium to Barium. Table I11 gives the relative intensities of the 3s, 3p, 3d, 4s, 4p, 4d, and 5p shells for elements from 2 = 34 to 56. On the whole, there is not so much change when using aluminum or magnesium for these shells, with the exception of the last seven elements. In general, when considering s shells, their intensities are very low and their maximum lies around 0.1 w. As mentioned above, the most surprising difference appears with the cesium 3d5,z intensity decreasing by 40% when using magnesium. Whereas we noticed two maxima for antimony 3 d 5 ~and cesium 3d5/2 with a minimum for tellurium and iodine, the second has disappeared to give one maximum followed by several elements (Te, I, Cs, Ba) of almost similar intensities. This behavior also appears for the 4d shell. Elements from Lanthanum to Lutetium. The relative intensities of the 3d, 4d, 4f, and 5p shells of the lanthanides are resumed in Table IV. In this table, figures giving poor accuracy are quoted. T h e reason is that we find a big discrepancy when comparing the intensities measured for fluorides and oxides. Actually, a factor of two generally appears between both species. We attempted to explain this anomalous behavior by the fact that lanthanide oxides might be quite sensitive t o water vapor by forming on the surface (the photoelectrons leave from the first 30 A) hydroxides of the type M(OH)s instead of M203. So far, figures given in Table IV take into account such formation and, hence, are the average results of fluorides, hydroxides (?), and complexes such as NaX2MClG where X is Cs, Rb, or T1. Nevertheless, 3d shell intensities are roughly equivalent, with the exception of lanthanum. In this series, the largest differences appear in the 4d, 4f, and 5p shell intensities which are well enhanced when using a magnesium source. Elements from Hafnium to Uranium. Table V resumes the relative intensities of the 4p, 4d, 4f, 5s, 5p, 5d, and 6p shells of elements from Z = 72 t o 92. While the 4p or 5d shell intensities remain almost constant from rhenium to thallium and the 4d shell intensities are decreased when using a magnesium source, the 4f signals as mentioned beforehand are well enhanced and stay almost constant from osmium to mercury. T h e last two elements show a quite different behavior when using a magnesium source. Whereas the thorium 4f and 5d shell intensities are quite comparable to those obtained with an aluminum source, the uranium 4d, 4f, and 5d shells decrease by 46, 56, and 54%, respectively, when considering the results obtained with magnesium. This rapid jump from thorium to uranium is not a t all understood since there is only 233-eV difference between both photon energies (this is also true for cesium 3d). One may expect that the satellite structure observed in certain uranium compounds ( I ) contributes to this anomalous low intensity.
CONCLUSION Our results are to some extent offered for comparison with other models of photoelectron spectrometers, since it is not evident that our intensities relative to fluorine Is do not contain specific properties of the Varian IEE-15 apparatus. Nevertheless, the few results given in literature ( 4 , 1 1 ) suggest that roughly the same relative intensities would be obtained in general, with the probable exception ANALYTICAL CHEMISTRY, VOL. 47, NO. 3 , M A R C H 1975
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of very high ionization energies (just below t h e photon energy) where the discrimination from small escape width of electrons having low kinetic energy also introduces a serious problem of vertical sample inhomogeneity.
(8) C. K. Jgrgensen, L. Bakenc, and H. Berthou, Chimia, 27, 384 (1973). (9) V. I. Nefedov, N. P. Sergushin, J. M. Band, and M. B. Trzhaskovskaya, J. Nectron Spectrosc., 2, 383 (1973), (for Z = 1 to 20). (10) J. J. h a n g and F. 0. Ellison, Chem. Phys. Lett., 25, 43 (1974). (for 2 = 1 to 10). (11) W. J. Carter, G. K. Schweitzer, and T. A. Carlson. Proc. lnte. Conf. Electron Spectrosc., Namur (1974), in press (for Z = 3 to 92). (12) C. K. Jqkgensen and H. Berthou, Chem. Soc. Faraday Discuss., 54, 269 (1973). (13) C. D. Wagner, private communication. (14) C. S.Fadiey, Chem. Phys. Lett., 25, 225 (1974). (15) T. A. Carlson, J. C. Carver, L. J. Saethre. F. Garcia Santibanez, and G. A. Vernon, Proc. lnt. Conf. Nectron Spectrosc., Namur (1974) in press.
LITERATURE CITED C. K. J0rgensen and H. Berthou, Mar. Fys. Medd. Danske Vid. Selskab, 38, NO. 15 (1972). K. Siegbahn, C. Nordling, G. Johansson, J. Hedman, P. F. Heden, K. Hamrin.. U. Gelius. T. Beromark. L. 0.Werme. R. Manne. and Y. Baer. “ESCA Applied Free M%iecules,” North-Holiand Publishing Company; Amsterdam, 1969. C. D. Wagner, Anal. Chem., 44, 1050 (1972). P. E. Larson, Anal. Chem., 44, 1678 (1972). R. M. Friedman, J. Hudis, M. L. Perlman. and R. E. Watson, Phys. Rev. B 8, 2433 (1973). L. E. Cox and D. M. Hercules, J. Nectron Spectrosc.. 1, 193 (1973). R. M. Friedman, R. I. Declerk-Grimee, and J. J. Fripiat, Proc. lnt. Conf. Nectron Spectrosc. Namur (1974), in press. ~
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RECEIVED for review July 1, 1974. Accepted October 3, 1974. Grant (2-323-70) from the Swiss National Science Foundation permitted the purchase of the photoelectron instrument.
Determination of Nanogram Quantities of Carbonyl Compounds Using Twin Cell Potential Sweep Voltammetry Badar K. Afghan, Achut
V. Kulkarni,’
and James F. Ryan
Analytical Methods Research Section, Canada Centre for Inland Waters, P.O. Box 5050, Burlington, Ontario, Canada L7R 4A6
Twin cell potential sweep voltammetry is used to determine and differentiate various classes of carbonyl compounds in natural waters and industrial effluents. A systematic study of polarographic behavior of these compounds in various media, such as alkaline medium, citrate buffer, and in the presence of various amines, is reported. It is possible to detect and distinguish various classes of carbonyl compounds using the above media. Individual carbonyl compounds can also be determined down to 0.25 pg/liter without any separation or preconcentration of the sample. The above method is applied to determine various carbonyl compounds in natural waters and industrial effluents.
The determination of “carbonyl compounds” in natural waters and industrial effluents is of considerable interest ( I ). In this paper, t h e term “carbonyl compounds” is used in a collective sense to describe those aldehydes and ketones which are known for their strong taste, odor, corrosive and related problems. In our laboratory a preliminary survey of various samples ranging from drinking waters to industrial effluents was carried out to obtain information concerning the nature and levels of these compounds. This survey indicates that formaldehyde and related compounds d o occur in considerable quantities in some pharmaceutical, chemical, petroleum, and industrial effluents. Levels as high as 50 mg/ liter, in terms of formaldehyde equivalent concentrations, are found in som-e industrial waters ( 2 ) . Although the methods used in our preliminary investigations give reasonably accurate results for relatively clean waters, they are not suitable for industrial effluents and receiving waters ( 2 ) .The fluorometric procedure was too specific for formaldehyde alone, and the colorimetric method Permanent address, Analytical Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay, 400085, India. 488
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gave very high molar extinction coefficients for the unknown compounds present in these effluents. Although the colorimetric procedure was relatively more reactive to carbonyl compounds, it did not react with most common aldehydes such as benzaldehyde, vanillin, furfural, etc. Therefore, work was initiated to develop a method which would react with as many commonly occurring carbonyl compounds as possible and which would more accurately determine the total carbonyl content of all samples. The majority of carbonyl compounds condense with a wide variety of amines to produce >C=N- compounds and water ( 3 ) . Resultant products such as imines, substituted hydrazone, oximes, and semicarbazones are also known to reduce at the dropping mercury electrodes ( 4 , 5 ) . Furthermore, these addition products reduce a t a dropping mercury electrode (DME) involving the same number of electrons regardless of t h e nature of the carbonyl compounds (6-8). Similar values for the diffusion current constants ( I ) for some aldehydes with semicarbazide have already been reported (9). Therefore, it should be possible to obtain the same order of current for similar concentrations for different carbonyl compounds and, hence, use this approach for the determination of total carbonyl content in a sample. T h e use of semicarbazone for the determination of carbonyl compounds has been reported in t h e literature (9, IO);however, earlier workers used conventional d c polarography in conjunction with preconcentration and separation steps to determine these compounds. It is possible to increase the sensitivity by at least 2-3 orders of magnitude if the reduction of semicarbazones or other azomethine derivatives is monitored by twin cell potential sweep voltammetry. In our laboratories, higher sensitivities can be achieved using a twin cell set-up since it eliminates all of the nonfaradaic and faradaic currents not relevant t o analysis (11-15). In addition to the increase in sensitivity, this tech-
ANALYTiCAL CHEMISTRY, VOL. 47, NO. 3, MARCH 1975
