favor of an increase of GeC14 (and presumably HCl also) in the vapor phase by the presence of calcium chloride in the liquid phase (1). Sodium chloride evidently produces a similar effect, and germanium may therefore be lost easily in the vapor initially evolved from boiling solutions containing sodium chloride, which escapes condensation when the HCl concentration in the liquid phase is as high as 6.1M (the constant-boiling
concentration for the HCl/H20 system in the absence of sodium chloride). Loss probably also occurs at lower HCl concentrations, depending upon the concentration of the sodium chloride present. LITERATURE CITED
(1) AlmBsy, A,, Barchnfalvi, F., NehBzvegyip. Kut. Int. KozlemBn. 1, 293-301 (1959); C . A . 54, 6236.f (1960).
( 2 ) Cluley, H. J., Analyst 76, 523-35
(1951). (3) Sandell, E. B., "Colorimetric Determination of Traces of Metals," 3rd ed., pp. 482-93, Interscience, New York, 1959. HUGHB. RAYNER
British Columbia Research Council, at the University of British Columbia, Vancouver 8, British Columbia, Canada.
Determination of Aluminum in Organo-Aluminum Compounds by X-Ray Fluorescence SIR: We have developed an x-ray fluorescence method for the determination of aluminum in organo-aluminum compounds. The method is applicable over the range from 0.05 to 10% and possibly even higher. The method has been developed especially for aluminum analysis of highly reactive pyrophoric compounds. Recent publications (1, 3) point u p the application of x-ray fluorescence to aluminum concentration determination. However, our method differs significantly from any previously reported, since i t applies to liquid systems which are highly reactive and require special handling techniques and equipment.
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I fGHR0MIUM WITH
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We used a General Electric XRD-3 x-ray instrument for this work. The original heat exchanger and line voltage stabilizer were replaced to make the instrument essentially equivalent to the XRD-5. The integral components of the instrument were: a General Electric S o . 2SPG power supply, a Hamner Model SX-R proportional counter preamplifier, a Hamner Model N302 nonoverload amplifier and pulse height discriminator, a General Electric No. 4SPG counter tube and helium tunnel assembly, a General Electric SPG electronic time register, a General Electric KO,BSPG scaler, a General Electric S o . BSPG rate meter, and a Machlett AEG-50-8 chromium target x-ray tube. Table 1. Comparison of Aluminum Analysis Data from X-Ray Fluorescence and Chemical Methods
Sample No.
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C D E
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Aluminum, % Chemical X-ray method 4.70 4.68 11.56 11.33 22.98 22.47 4.88 4.85 4.75 4.71 + O . 16 Mean error Relative error +1 .64%
ANALYTICAL CHEMISTRY
X AI Figure 1 . Plot of counts per second vs. AI for different target tubes
%
The procedure followed in setting the pulse height discriminator is that outlined by Miller (2). The electronic components were left on constantly. However, the x-ray source was usually turned off overnight. We found that a 30-minute warm-up period was advisable each morning before checking the pulse height discriminator settings. We have made a modification to the sample chamber of the XRD-3 which should be mentioned because it has certain advantages. The wall of the sample chamber adjacent to the x-ray tube was converted into a cooling panel. Small holes were drilled through the wall forming a water passage around the point of contact of the tube with the sample chamber. Tubing was connected to both ends of this passage. With this arrangement, tap water is circulated through the passageway a t all times so that the only heat to which the sample is exposed is that generated by the x-ray beam. The sample cells we used were made out of nylon by the Instrument Shop in our Research and Development Dept. After two years of operation we have seen no adverse effect of the x-ray beam on the nylon of the sample cell.
The general analytical procedure for determination of aluminum in organoaluminum compounds may be described as follows: prepare a stock solution containing approximately 60% triethylamine and 40% Stoddard solvent (dried over sodium). Place 20 ml. of this solution in a 50-ml. glass-stoppered graduated cylinder. Inject argon into the graduated cylinder through one hole of a two-hole rubber stopper. Purge a syringe with argon and then fill with the organo-aluminum compound to be analyzed, cap with a silicone rubber plug, and weigh. Transfer the sample from the syringe to the graduated cylinder containing the triethylamine solution. Recap the empty syringe and place the glass stopper on the graduated cylinder. Weigh the empty syringe and the graduated cylinder. The size of the sample is determined by the estimated aluminum content in the sample. For pure aluminum triethyl, the best sample size is approximately 4 ml. After thorough mixing, transfer the sample to the x-ray sample cell for analysis. Allow 1 minute after placing the sample cell into the x-ray beam for the helium atmosphere to reach pressure equilibrium. Register counts over a 400-second time period. For such counting intervals, the count level will usually be in excess of 50,000, giving a u value of less than 1.5% resulting from counting error. Total instrument time per sample is approximatcly 8 minutes. Considering calculation time, a sample may be analyzed for aluminum over wide concentration range in approximately 15 minutes. The accuracy of t h e method is shown by the data in Table I. DISCUSSION
The principal factors responsible for the successful application of x-ray fluorescence to the determination of lowlevel aluminum in pyrophoric organic systems were the availability of a chromium x-ray target tube, the modification of the sample chamber to provide sample cooling, and the use of sample cells fabricated out of nylon. Our first work on aluminum analysis was done with a tungsten target tube and without a pulse height discriminator. The background
count was very high and the net count extremely low. After installation of the pulse height discriminator into the system, we were successful in reducing the background count to a much lower level, but the sensitivity under these conditions was low. Fortunately, ai; this time the first chromium x-ray target tubes designed for use with General Electric equipment became available. Using this tube, we observed a 400% increase in aluminum sensitivity over that observed when using the tungiden target tube. By using the pulse height discriminator, we were able to hold the background count low and take rtdvantage of this
tremendous increase in sensitivity. Figure 1 emphasizes the great benefit gained by the combination of the pulse height discriminator and the chromium x-ray target tube for the determination of aluminum. Because of the nature of low molecular weight organo-aluminum compounds, we offer certain suggestions concerning their handling. Never expose the organo-aluminum compound to air or water. Always have an excess of complexing agent, in our case triethylamine, in the solution being analyzed by x-ray fluorescence. Otherwise, there nil1 be enough free aluminum trialkyl present in the sample to cause immediate deteri-
oration and rupture of the sample cell window. LITERATURE CITED
(1) Balk, E. R., Bronk, L. B., Pfeiffer, H. G., Kelbon, W. W., Winslow, E. H., Zemany, P. D., h A L . CHEM. 34, 1731-3 (1962). ( 2 ) Miller, D. C., Norelco Reptr. 4, N O .2, (1957’1.
( 3 j Smith, G. D., Maute, R. L., ANAL. CHEM.34, 1733-5 (196”). H. F. SMITH R. A. ROYER ilnalytical Research Section Research and Development Department Continental Oil Co. Ponca City, Okla.
Correction for Anomalous Fluorescence Peaks Caused by Grating Transmission Characteristics SIR: I n an earlier communication, the construction and calibration of a recording spectrofluoi ometer was described (4). During a study of fluorescence spectra using this instrument, an artifact appeared in some of the recorded spectra, the origin of which was traced to the grating of the analyzer monochromator. Because this type of behavior may be su5ciently general, Then using high precision gratings, it was felt that i t should be brought to the attention of other investigators in the field of analytical fluorescence. During studies on the fluorescence of 2-hydroxy-3-naphthoi(t acid, monosodium salt (I) we &-ere puzzled by a narrow band which appeared a t about 540 mp on the long wavelength side of the major fluorescent maximum of (I) as shown in Figure 1, curve -4. Because the relative intensity of this band, compared to the main band, did not change n ith purification, an impurity could not account for its presenve in the recorded spectrum. It was further puzzling to note that the wavelength maximum of this band did not show variations with solvent or p H as did other parts of the band. As a check, a variety of compounds having well characterized fluorescent spectra in this same region of the spectrum were run on the spectrofluorometer, and a siinilar shoulder at about 540 mp appeared in the recorded fluorescence spectra of these compoundq.
This led to the conclusion that the 540-mp band in (I) was caused by an instrumental anomaly, and was not a part of the fluorescence spectrum per se. The anomalous fluorescence maximum has been attributed to a “W-ood Anomaly” ( I ) of the high dispersion diffraction grating used in the monochromator (Bausch and Lomb, 500-mm. Llonochromator, having a 1200-linesper-mm. grating blazed for the near ultraviolet). The term “Wood ilnomaly” is used to refer to an anomalous and abrupt change in intensity of the spectral transmission properties of a diffraction grating at a particular m-avelrngth. This means that a monochromator containing such a grating will show a n abrupt maximum or minimum in its efficiency at certain wavelengths. The description of such anomalies by Palmer seems to be consistent with our observations (3).
80
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(Fluorescence intensity plotted in arbitrary units) A. Spectrum as recorded without correction: 6. Spectrum corrected for instrument response (using d a t a f r o n F ~ - J , J2- ~
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Figure 1. Fluorescerice spectra of 10-3M 2-hydroxy-3naphthoic acid, monosodium salt in 10% alcohol, 90% water
T o compensate for the \\-ood dnomaly of the grating, the combined monochromator and photomultiplier system was calibrated with a National Bureau of Standards lamp, certified to conform to the spectral irradiance of IC1 illuminant A (2, 5 ) . The resultant recording represented the spectral response of the analyzing monochromator-photomultiplier combination when corrected for changes in intensity of the source as a function of wavelength. This type of curve should be used Then correcting recorded fluorescence spectra. The spectral efficiency of the monochromator alone could be obtained from these data only by an independent calibration of the spectral response of the photomultiplier tube or b y use of an integrating screen. The procedure described above gave rise to the calibration curve shown in Figure 2. This curre represents the
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