Of the mildew-resistant textiles analyzed, the fabric containing the smallest amount had a copper %quine linolate content of 0.041 f 0.005% (the average and average deviation for five determinations). To find out whether the method was applicable to other metal quinolinolates, zinc 8-quinolinolate was analyzed. The conditions for titrating zinc with EDTA and murexide differed slightly from those used for copper. Ethyl alcohol was added to the solution being titrated and a pH range of 6 to 7 was found desirable. The chromatograms were airdried from 24 to 48 hours prior to titration. Paper dried for short periods of time reduced this
PH.
Zinc 8-quinolinolate dissociated quantitatively using the HC1-butanol solvent. The zinc appeared a t Rf 0.8 and the 8-quinolinol a t Rf 0.7. All of the zinc was contained in the Rf 0.8 ring. It is also possible to determine whethcr any interferences-i.e., zinc or other metals-are present in the solution by titrating prior to dissociating the chelate. Zinc 8-quinolinolate can be identified by color reactions of the Rf 0.8 ring
-
Table 111. Copper 8 Quinolinolate Content of a 1-Gram Sample of Treated Textiles Using Two Methods
Spectrophotometric
Chromatotitrimetric (PAN indicator)
Cloth, webbing (water repellent and mildew reaietant) 0.006 Gram 0 005 0.008
0.006 0.006 Av. 0.006
Cotton duck fire, water, weather, and m’ dew resietant) 0.002 0.002
d
0.003
0.002 0.002 0.002 Av. 0.002
Cotton thread (mildew resietant) 0.008 0.007 0.007 0.008
0.007 0.007 Av. 0.007
for zinc, such aa the pink color with dithiaone and the ultraviolet fluoresence of the 8quinolinol ring at Rf 0.7. Table I lists the results of analysia of chloroform solution of zinc and copper 8quinolinolatea. LITERATURE CITED
(I) Darbey, A., Am. Dywtufl Reptr. 42,
453 1953). (2),,F era1 S Scation . CCCD-950, Dyeing anrMtertreatmg Proceeeea for Cotton Fabrics,” September 30, 1959. (3) Hill, C. H., ct al., ANAL. CHEM.28, 1688 (1956). (4) Hollingahead, ,F. 0.W. “Oxine and Ita Derivatives Vol. I, butterworth’s Scientsc Pubdcation, London, 1954. ( 5 ) Miles, T. D., Delasanta, A. C., Am. Dyestuf Reptt. 48, 31-2 (1969). (6) Rose, A., Hutchinson, A., Witt, H., Sharkey, 1. R., Zbid., 45,3624 1956). (7) Siu, R. G. H. “Microbial ecomgroeition of Cefiuloee with S ecial eferences to Cotton Textiles,” %einhold, New York, 1951. ( 8 ) Welcher, F. J., “The Analytical Us? of Eth lenediaminetetraacetic Acld Van doatrand. Princeton. N. j,. 1958.
e6
b
RECEIVEDfor review October 5 . Accepted February 20, 1961. divlaon of Anal ice1 C h e e t r y , 137th Meeting, ACS, Cceland, Ohio, April 1960.
Effect of Take-Off Angle on Electron Probe Calibration L. S. BlRKS
and R. E. SEEBOLD U. S. Naval Research laboratory, Washington 25, D. C.
b The effect of take-off angle on calibration curves for quantitative electron probe analysis is illustrated using the Ni-Fe and Ni-Cr systems and takeoff angles from 6 to 90 degrees. In both the Ni-Fe and Ni-Cr systems, there is strong matrix absorption of NiKa radiation ond the Ni calibration curve is sensitive to take-off angle. Low take-off angles lead to the greatest deviation from linearity in the x-ray intensity vs. composition curve. For FeKa or CrKa’radiation, the matrix absorption by Ni is about the same as the self-absorption of the element for its own radiation. There is little effect of take-off angle on Fe and Cr calibration. With careful specimen preparation, precision of a few per cent of the amount present was obtained in the Ni-Cr system for take-off angles from 6 to 45 degrees and for electron energies of 20 to 45 k.e.v. Poor specimen preparation with local inclinations of 5 degrees to the average surface leads to errors as large as 10 to 15% of the amount present in the Ni calibration.
Q
ANALYSIS with the electron probe requires calibration curves relating measured x-ray intensity to per cent composition. These curve8 are similar in appearance to those used in fluorescent x-ray spectroscopy and may be obtained from a series of known composition standards provided the standards are solids, homogeneous on a 1-micron size scale, and with a smooth surface. For electron excitation they may also be obtained by calculation techniques (1) that make use of the mass absorption coefficients, excitation efficiencies (g), and a single standard such as 100% of the element to be calibrated. One of the important parameters that affect the calibration curves is the take-off angle for x-rays-i.e., the angle between the emerging x-rays and the specimen surface. For small take-off angles, the path length for emerging radiation is increased and the x-ray intensity is reduced according to the usual x-ray absorption law. Calibration curves a t various take-off angles are most easily compared if one plots UANTITATIVE
relative rather than absolute x-ray intensity. By relative intensity we mean: the characteristic intensity from an element a t an intermediate composition divided by the characteristic intensity from a 100% standard of the same element at the same take& angle. Thus all calibration curves pass through the same zero and 100% end points. In the present paper, the Ni-Fe and Ni-Cr systems were chosen for study because the strong absorption of NiKa radiation by Fe or Cr leads to very nonlinear calibration curves and illustrates the effect of take-off angle dramatically. EXPERIMENTAL RESULTS
Calibration curves were prepared for the Ni-Fe and Ni-Cr systems a t takeoff angles of 6, 20, and 90 degrees using the calculation technique (1) and 100% standards. All of the curves are plotted in terms of relative x-ray intensity as explained in the introduction. Nickel-Iron. Figure 1 shows the results for the Ni-Fe system. The different character of the Ni and Fe VOL 33, NO. 6, M A Y 1961
687
100
+
Fe
of the FeKa curves, the relative intensity is greater than the linear relation to composition because of strong secondary fluorescence excitation by NiKa radiation. Measuremente of relative NiKa and FeKa intensities were made at °ree take& angle in the electron probe on a known specimen containing 64% Ni, 15% Fe, and 17% Cr. The presence of Cr precluded use of the calibration curvea of Figure 1, but recalculation with allowance for the Cr gave measured values of 63.3% Ni and 15.3% Fe. As expected, the Ni intensity is appreciably less than the corresponding weight per cent. Nickel Chromium. Calibration curves for the Ni-Cr system are shown in Figure 2. They are'similar to the Ni-Fe curves but with less deviation from linearity because NiKa radiation is not absorbed as strongly by Cr as by Fe, and CrKa radiation
0
weight percent
-
Figure 1. Calibration curves for Ni-Fe system at take-off angles of 6 O , 20°, and 90" Operating voltage 2 5 k.e.v. Cross In center marks 50% intensity-50% poaitlon point
com-
curves is explained as follows. h i K a radiation ia more strongly absorbed by Fe than by Ni itself; therefore, the NiKa intensity a t intermediate compositions is reduced relative to the intensity from the 100% standard and the curves fall below the linear relation to composition. The lower the take-off angle, the longer the path length and the greater the reduction in relative intensity. Thus the curve for Gdegree t a k e d angle is reduced more than the one for 90 degrees. F d L radiation, on the other hand, is absorbed about equally by Fe and Ni. The increased path length a t low take-off angle alters the intensity for the intermediate compositions and that from the 100yo standard by about the same amount, leaving the relative intensity unaffected and making the curves nearly the same for all take-off angles. For all
Table
I.
... 100
weight
-
Cr percent
0
Figure 2. Calibration curves for Ni-Cr system at take-off angles of 6O, 20°, and 90" Operating voltage 2 5 k.e.v.
Calculated and Observed Relative X-Ray Intensities for Nickel Specimen: 78.1% Ni; 20.070 Cr; 1.570 Si
K.E.V. 20 6" 12' 18' 30" 45"
25
30
30
-
45
Calcd.
Obsd.
Calcd.
Obsd. Calcd. Obsd. Calcd. Obsd
Calcd. Obsd.
68.8 72.8 75.0 75.8 76.6
67.2 75.0 77.0 76.4 70.6
66.1 72.0 73.0 75.1 76.1
67.1 72.2 73.6 74.7 75.0
54.8 63.3 67.1 72.4 74.5
61.2 69.1 72.0 74.0 75.5
62.6 67.4 72.0 76.4 76.4
59.2 66.6 71.0 73.4 79.1
56.7 64.2 68.8 71.3
0
weight
50
percent
100
Figure 3. Calibration curves for Ni in Ni-Cr system at take-off angles of 6' and 90" Operating voltagea 2 0 and 45 k.e.v.
is not lis strongly enhanced as was FeKa. The effect of primary electron energy on calibration was also considered for the Ni-Cr system and Figure 3 shows the curves for NiKa a t 20 and 45 k.e.v. for take-off angles of 6 and 90 degrees. At the higher voltage, the electrons penetrate deeper into the specimen and the path length for emerging radiation is increased. Thus the relative Nia intensity is less at 45 than a t 20 k.e.v. Measured and calculated relative intensities were compared for a 78.1% Ni, 20.0y0 Cr, 1.5% Si specimen at take-off angles of 6, 12, 18, 30, and 45 degrees and for electron energies of 20, 25, 30, 36, 45 k.e.v. These angles and voltages cover the usual operating conditions for most of the present electron probes. Results are shown for Ni in Table I and for Cr in Table 11. The variation of relative intensity with take-off angle is appreciably greater a t the higher voltage for both Ni and Cr. The calculated intensities in Table I each represent 78 weight 7 0 Ni. The observed weight per cent is found simply by multiplying the 78% times the observed/calculated intensity ratio. Using all the data in Table I, the average observed weight per cent for Ni is 77.5% with a relative standard deviation uNi% = 2.4% of the amount present. For Cr the data for Table I1 give 19.9% with a relative standard deviation of 6% of the amount present. DISCUSSION
Table II.
Calculated and Observed Relative X-Ray Intensities for Chromium Specimen: 78.1% Ni; 20.0% Cr; 1 .5y0 Si
K.E.V. 20 6" 12" 18" 30' 45"
688
25
30
36
45
Calcd. Obsd. Calcd. Obsd. Calcd. Obsd.
Calcd.
Obsd.
Calcd.
Obsd;
19.1 18.9 19.4 21.6 22.5
19.0 20.5 21.4 22.2 22.5
17.5 20.3 20.7 21.7 25.3
18.3 19.8 20.7 21.7 22.1
17.9 19.9 20.7 21.8 25.5
21.2 21.9 22.3 22.6 22.8
19.2 20.2 20.7 21.8 23.8
20.4 21.7 22.0 22.5 22.8
19.0 20.1 20.5 22.4 21.8
ANALYTICAL CHEMISTRY
19.7 21.1 21.8 22.3 22.5
Figures 1, 2, and 3 show that calibration curves can be either sensitive or insensitive to take-off angle. The criterion is not the absolute value of matrix absorption coefficient but rather the relative value compared with the selfabsorption coefficient of an element for its own radiation. In the Ni-Fe system the absorption coefficient of Fe for NiKa is 6.9 times greater than the
self-absorption coefficient of Ni. Therefore, the Ni calibration curve i s sensitive to take-off angle-via., path length. For FeKa, however, the absorption coefficient in Ni is only 1.2 times the self-absorption coefficient in Fe, and so the Fe calibration is insensitive to take-off angle. When calibration is sensitive to takeoff angle, it will also be sensitive to electron energy because higher energy electrons will penetrate deeper into the specimen and increase the path length for emerging radiation in the same way as decreasing the take-off angle. Thus in Figure 3 i t can be seen that low electron energies lead to better linearity and are to be preferred. From Tables I and I1 for carefully prepared specimens, the agreement between calculated and measured values is about the same at low take-off angles and at high. Theoretically, the greater absolute x-ray intensity at high takeoff angles should lead to better precision because of the nature of x-ray statistics.
However, the present state of the art in electron probe analysis haa not reached the refinement where statistical considerations are the limiting factors in precision; when it does reach that refinement, a longer counting time st low take-off angles will partially compensate for a lower absolute intensity. For improperly prepared specimens where there are local inclinations to the average surface, one can wtimate the possible errors that would occur at various take-off angles. Assuming a °ree local inclination to the average surface, the actual take-off angle would be 11 degrees but the 6degree calibration curve would be used for estimating composition. In the Ni-Fe system, this would lead to an error of 10 to 15% of the amount present in the 10 to 50% Ni range. The same Wegree local inclination would lead to an error of less than 5% of the amount present a t a 20-degree take-off angle and to negligible errors a t take-off angles of 30 degrees or greater. Experience has in-
dicated that local inclinations as large as 5 degrees are unlikely to occur with carefully prepared Specimens except at the junction of very hard and very soft phases. X-ray intensity across a constant composition zone ordinarily does not vary by more than 1% of the amount present even a t a 6degree take-off angle. Aa a final point, it should be stressed again that calibration curves of about the same precision can be prepared for a wide range of take-off angles and operating voltages provided the specimen is prepared properly, but no adjustment in operating conditions can compensate for poor specimen preparation. LITERATURE CITED
(1) Rirks, L. S. J . A p p l . Phya. (in press). (2) Birks, L. k., SpecttodLim. AI% (in prese).
RECEIVED for review December 1, 1 9 8 . Accepted January 10, 1961.
Correlation of an Infrared Absorption Band in the 10- to 11 -Micron Region with the 3-Substituted Phenoxy Group HOWARD J. SLOANE' Chemical Physics Research Laboratory, The Dow Chemical Co., Midland, Mich.
b An intense absorption band in the 10.2- to 1 1.3-micron region appears to b e characteristic of many 3-subThe stituted phenoxy compounds. band has been of diagnostic value in this laboratory and is discussed for several types of structures. The analytical utility of the relationship depends also on the absence of a strong band from this region of the spectra of isomeric phenoxy compounds which are not substituted in the 3position; this appears to be so for the compounds studied. Most 3-halophenOXY compounds exhibit this band even upon.further ring substitution.
E
of the infrared spectra of a variety of mate= containing the structure X - 0 - u , where XAMINATION
v '
1
X is H or phenyl and Y is halo, oxy, or alkyl, has shown that in nearly every case an intense absorption band is observed in the region of 10.2 to Present address, Beckman Instru-
ments, Inc., Fullerton, Calif.
11.3 microns. In general, the band is present whether or not there are other substituents on the phenyl ring, except in the few cases noted below. Study of the spectra of isomcric compounds which are not substituted meta to the oxygen atom reveals that ordinarily there is no intense band in this region. EXPERIMENTAL
Most of the infrared spectra used in this study, including those illustrated in Figure 1, were obtained on a doublebeam spectrometer equipped with sodium chloride optics and designed and built in this laboratory (8). When possible, compounds were scanned as 10% w./v. carbon tetrachloride and carbon disulfide solutions in 0.1-mm. cells. If solubility limitations precluded solution work, spectra were obtained as Nujol mulls. RESULTS A N D DISCUSSION
In Table I are recorded the wavelength positions of this prominent and persistent absorption for a variety of
3-substituted phenoxy compounds. The table has been arranged to some extent by compound type, since for several families of compounds the band is reasonably constant within each group. The 3-halophenols of group A show a strong absorption in the range of 10.80 to 11.28 microns in the case of the chloro compounds, and in the region of 11.05 to 11.67 microns for the bromophenols. The parent 3-halophenols absorb at considerably longer wave lengths than the median positions, however. Diphenyl ethers, chlorinated ia the 3position (group D), show this absorption in the narrow range of 10.80 to 10.99 microns. Many of the higher substituted derivatives of 3-halophenols and diphenyl ethers (groups A and D) up to and including most trisubstituted phenols exhibit this absorption. The higher substituted compounds (group B), comprised of 2,4,5-tri, tetra-, and penta- halogenated phenols, however, are not so consistent; bands are observed which are at shorter wave lengths than those of group A or are of diminished intensity. The simple 3-alkyl phenols (group VOL. 33, NO. 6, M A Y 1961
689
