minutes, the per cent recovery in the order given was 99.7, 99.5, and 99.7. Next, a series of experiments was run in which the mole ratio of Ph4AsCl to perchlorate was varied. l-sing 25 ml. of 0.02M ammonium perchlorate mixed with 5 ml. of concentrated hydrochloric acid, the volume of 0.02M Ph4AsC1 added was varied from 30 to 50 ml. (mole ratio of 1.2-2.0 to 1). Ten to 15 minutes were allowed for coagulation and the precipitate was filtered, washed with water saturated with Ph4AsC104, and dried as before. The per cent recovery ranged from 99.3 to 99.8. Because the final volume of the solution containing the precipitate was different in each of these experiments, another series was set up using various volumes of 0.05.11 Ph4hsC1, each of which was diluted to 50 ml. before being added to the ammonium perchlorate-hydrochloric acid solution. The results of these experiments are given in Table I. Table I shows that, with 0.006M perchlorate ion and 0.8M hydrogen ion,
the optimum concentration of Ph4AsC1 is 0.012 to 0.016M (molar ratio of 2.02.5 to 1). With less than a 2 : l ratio, slightly low results were obtained, which were probably caused by incomplete precipitation. With a ratio of 5:1, high results were obtained, probably because of absorption of the reagent. The data from Table I using the optimum mole ratio (aliquots 3 through 8 ) , combined with the results from two other experiments using 50 ml. of 0.02M Ph4AsC1, give an average recovery of 99.80/, with a standard deviation of 0.18. ?;either chlorate nor bromate interfere in the analysis when present up to O.4yGin ammonium perchlorate. The interference of other ions was not determined. However, Willard and Smith (8) found that the reagent would precipitate perrhenate, permanganate, periodate, tungstate, molybdate, chromate, iodide, bromide, and the chloride complexes of mercuric, stannic, cadmium, and zinc ions.
LITERATURE CITED
( 1 ) Alley, B. J., Dykes, H. W. H., ANAL.CHEM.36, 1124 (1964). ( 2 ) Burns, E. A,, Muraca, R. F., Zbid., 32, 1316 (1960). ( 3 ) Greenhalgh, It., Riley, J. P., J . Marine Biol. Assoc. United Kingdom 41, 175 (1961). C.A. 55, 27714b (1961). ( 4 ) Haight, G. P., ANAL.CHEM.25, 642 (1953). ( 5 ) Ribaudo, C., "Methods of Analyzing
Polysulfide-Perchlorate Propellants," Tech. Rept. 2334, Samuel Feltman Ammunition Laboratories, Picatinny Arsenal, Dover, N. J., September 19.56. (6) Sjolemma, B., Z . dnorg. Chem. 42, 127 11904). ( 7 ) Willard,'H. H., Perkins, L. R., ANAL. CHEM.25, 1634 (1953). (8) Willard, H . H., Smith, G. M., IND. ENG.CHEM.,ANAL.ED. 11, 186 (1939). ( 9 ) Willard, H. H., ThomDson. J. J., Ibid., 2, 272 (1930).
DONALD J. GLOVER J. M. ROSEN Organic Chemistry Division Chemistry Research Department U. S. Naval Ordnance Laboratory White Oak, Silver Spring, Md. 20910
An Improved Portable Fluorescent X-Ray Instrument Using Radioisotope Excitation Sources SIR: Karttunen et al. (2) recently described a portable fluorescent x-ray instrument utilizing the radioisotope tritium absorbed in zirconium to excite the K-x radiation of elements 2 = 16 to 35. This particular radioisotope was chosen because it most efficiently excited the elements of most interest to them, the components of meteorites. This paper demonstrates that the radioisotope promethium-147 in a n aluminum matrix and emitting bremsstrahlung radiation is a more universal excitation source for fluorescent x-rays covering the elemental range 2 = 19 through 92. A krypton-methane sealed proportional counter is used for detection and resolution. The apparatus weighs approximately 10 Ib. and occupies a volume of 1/2 cubic foot.
and it is a n excellent excitation source for t h e generation of fluorescent x-rays in elements requiring 3 to 12 k.e.v. This radioactive source is used to excite the characteristic fluorescent x-rays of elements in the range 2 = 16 to 35 and 2 = 45 to 82. I n the lighter
L
16000
14000
E,
(Pm"'/AI
F
elements the K-x radiation is generated while in the heavier elements the L-x radiation is excited. The bremsstrahlung emitted from the radioisotope promethium-147 when in an aluminum matrix is an excellent excitation source for fluorescent x-rays
SOURCE)
I O O O O ~
c w
c
EXPERIMENTAL
Apparatus. T h e portable fluorescent x-ray instrument mentioned above is used for t h e collection of data. The apparatus consists of only two major pieces, a nickel-cadmium battery powered transistorized power supplgrecorder, and a sealed proportional counter for detection and resolution, plus the small radioisotope excitation source. Sources. T h e tritium/zirconium bremsstrahlung sourcp has been fully described in the previous publication,
4000
2 000
1 Au I i Bi 2 20 2223
U
2
VOL. 37, NO. 2, FEBRUARY 1965
307
One should be forewarned of the intense krypton escape peak occurring with the spectrum of elements 2 = 40 to 50, but this does not cause any difficulty. Electronics. The single channel analyzer circuit which is based o n the Chalk River discriminator circuit by Goulding and Robinson (1) has been further modified. Because the single channel analyzer is sensitive to pulses of only a few millivolts (50 to 60), great care must be taken to provide very stable supply voltages. The negative ll/z volt dry cell battery supply has been replaced with a mercury battery shunted by a 50-pfd., &volt capacitor. The positive 12-volt power supply is now stabilized by a 12-volt zener diode. Different voltages than the above can be used satisfactorily with the single channel analyzer, but the proper selection must be made to prevent oscillation or reduce sensitivity. Procedure. The usual sample preparation procedures of x-ray spectrometry are used. T h e sample can be nearly any material with the only criteria t h a t the source-samplecounter distances are regulated and t h a t the surface area being examined is also limited to the same identical size as the standards. The Rustrak recorder on the portable x-ray unit merely draws a curve; the height of the peak corresponds to the amount of the element present. A more sophisticated method of x-ray quanta accumulation and presentation is to use a miniaturized multichannel analyzer which furnishes a digital record of the events detected in the proportional counter.
SAMPLE EXCITED BY Prn"'/AI
t
RCL-256 CHANNEL ANALYZER
NI
n
L
Pb
I
RUSTRAK RECORDER ce 4 0 2 %
~
c
I
1
I
\ I
ENERGYSAMPLE EXCITED BY H'IZr NI
R C L - 2 5 6 CHANNEL ANALYZER
Ca 4 0 2 %
I
l
t
1
1
l ENERGY-
Figure 2. Spectrums of the same sample excited b y both the H3/Zr and Pm'*'/AI sources
in all elements in the range 2 = 19 to 92. The promethium-147, with a halflife of 2.6 years and a maximum beta energy of 223 k.e.v., is mixed with aluminum powder and compressed into a disk 0.5 em. in diameter X 1 mm. thick and covered a t the front with a 0.005-cm. thick aluminum foil and a t the back with 3 mm. of lead. An activity of about 55 mc. furnishes adequate photon intensity. The photon output is approximately 2 x 105 photons per second. Since the photons from this source are more energetic than those from the H3/Zr source, it is possible to excite the K-x radiation in elements 2 = 17 to approximately 55. The excitation of L-x radiation is then more efficient and is used in the elements 2 = 56 to 92. In fact, in the 2 range 50 to 60 both K-x and L-x radiation are excited in the elements. This does not cause any problems in the analytical application. For the excitation of the characteristic fluorescent x-rays of the rare earth elements, both sources are good though the H3/Zr source is slightly more efficient and furnishes higher fluorescent intensities. The peak-tobackground ratio is also somewhat better for the rare earth elements using the H3/Zr source. Figure 1 illustrates the elemental range for the excitation of K-x radiation and L-x radiation using the Pm14'/Al source. The chart shows the elements and compounds tested. Figure 2 depicts the analytical curves for the same sample using first the H3/Zr excitation source and then the Pml"/Al source. It is interesting to note the difference in curves due to the excitation efficiency. The sample was a mixture containing 49.38% G O z , 20.97% N O , and 29.65y0 PbO. 308
e
ANALYTICAL CHEMISTRY
Detection. A proportional counter is used for detection because of its inherent desirable feature of energy sensitivity or discrimination. The LND-450 BK model used is a small, rugged proportional counter designed for the detection of low energy electrons and gamma or x-rays. The gas-fill, 90% krypton-lOyO methane, is at atmospheric pressure, and the 2-mil thick beryllium window does not seriously lessen the intensity of longer wavelengths of interest (K and Ca).
4000 3500
1
RESULTS A N D DISCUSSION
I t should be restated that the only difference between this portable fluorescent x-ray instrument and a con-
-- K I
-
.. .. .... K2 ----- K3 - K4 ,
Ni
-.-
,
CEO* NiO PbO ---
4 0 . 2 0 % Ce 16.39% Ni 49.50 11.20
57.13 64.84 BACKGROUND
8.12 4.14
27.52 % Pb 23.08 18.04 13.97
A
3000
E, > k
2500
VI
2000 I-
z 1500 1000
500
io Figure 3. Typical set of curves from a group of standard ternary mixtures using the Pm14'/AI source
Table 1.
Typical Powders and Alloys Analyzed with the Pm147/AI Source
RCL-256 channel analyzer,
Sample composition Representative powders Synthetic mixtures ( 1 ) Zr02 25.66y0 Zn SnO 5 7 . 5 8 Sn ( 2 ) Ce02 57.13%,Ce NiO 8 . 1 2 Ni PbO 18.04 Pb
NBS portland cement #lo14 Si02 19.495% CaO 6 3 . 3 6 Fee02 2 . 5 0 Typical alloy NBS 1204 Cr
Ni
Mo
12.75y0 70.6 4.28
peak height Found Deviation, 7,
Miniaturized apparatus (Rustrak recorder). peak height Found Deviation, yo
26.34 55.99 57.14 8.12 17.49
+2.65 -2.76 0.0 0.0 -3.05
27.5 58.1 58.1 8.6 16.9
63 39 2.47
:
+o. 05 -1.20
63.1 2.6
-0.4 +4.0
12.82 69.31 4.19
+0.55 -1.83 -2.10
11.9 70.4 4.1
-6.7 -0.3 -4.2
...
+7.2 +0.9 f1.7 +5.9 -6.3 ...
ides from t h e following: COO, NiO, ZrO,, SnO, CeO,, a n d PbO. Figure 3 depicts a typical set of curves obtained from a group of standard 'ternary mixtures. The NBS cements analyzed were portland cements 1011, 1014, and 1016. It is possible to analyze the cements only for the CaO and FetOa content. The alloys analyzed were the NBS series 1190, 1203, 1205, and 1204. The results are shown in Table I. The samples were analyzed both with a multichannel analyzer, and with the miniaturized single channel analyzer and Rustrak recorder. LITERATURE CITED
(1) Goulding, F. S., Robinson, L. B., At. Energy Comm. Ltd., AECL 767, CREL 778 (January 1959). (2) Karttunen, J. O., Evans, H. B.,
Henderson, D. L., Markovich, P. J., Niemann, R. L., ANAL. CHEM. 36,
ventional fluorescent x-ray unit is that a radioisotope source replaces the x-ray tube, and that the proportional counter not only detects the characteristic radiation but also resolves the radiation, thereby eliminating the need for a dispersive crystal. The finite resolution of the detector rauses some difficulty in situations where
the components are separated by one atomic number. I n such cases, peak shift, selective filtration, or unfolding techniques, etc., must be used. I n cases where A 2 2 2, the conventional straightforward analytical procedures are used. Applications. T h e powder mixtures analyzed quantitatively include ox-
1277-1282 (1964).
JOHN 0. KARTTUNEN DALEJ. HENDERSON
Chemistry Division Argonne National Laboratory Argonne, Ill. 60440 Work performed under auspices of U. S. Atomic Energy Commission.
Possible Errors in Interpreting Results of Two Channel Gas Chromatography SIR: In some recent developments in the field of two channel gas chromatography (1,%'),acertain assumption has been made that is not warranted and could give misleading results. This assumption is that two peaks from the same column in two different detectors that vary in retention times by even a few seconds can be positively stated to represent two different components. This situation is best illustrated in peaks B and I31 in the figure from Reference ( 2 ) . There is, however, at least one possible case where this assumption will not be true. Let us assume that the detector represented by the upper curve is sensitive to two Components h and R having overlapping peaks, while the lower detector is sensitive to only component A. This situation is illustrated in Figure 1. Keulemans (3) has shown that, the effect of a n unresolved impurity on a peak can shift the retention time of the
peak maximum. This effect will be to shift the maximum of the peak in the
upper curve but not in the lower. As a result, we now observe only C in the upper curve and A in the lower and the two have different retention times. If, observing this result, we applied the above assumption, we would conclude that C and A must represent different substances while they, in fact, represent the same major component. Considering the complexity of the natural materials now being investigated by two channel chromatography and the widely varying sensitivities of different detector systems, the possibilities for errors of this type should be kept in mind. LITERATURE CITED
( 1 ) Oaks, D.
A (observed)
Figure 1 . Situation where one detector is sensitive to two components (upper curves), while other detector is sensitive only to component A (lower curve)
M.,Hartrnann, H., Dimick, K. P., ANAL.CHEM.36, 1560 (1964). ( 2 ) Ibid., No. 10, 36, 82A (1964). ( 3 ) Ettre, L. S., Ibid., No. 8, 31A (1964). C. L. TEITELBAUM Coty, Div. Chas. Pfizer & Co., Inc. 423 West 55th St. S e w York, N. Y. 10019 VOL. 37, NO. 2, FEBRUARY 1965
309
