contamination by W a n d this was removed by re-precipitation. was not so satisfactory as 12M HC104. The use of 16M "03 It reacted vigorously with tartaric and citric acids when V was present and tended to cause breakdown of the reagent. Conversion of Oxidized Sample to a Solution in TartaricPerchloric Acids. The use of HF was found essential to dissolve the oxidized sample completely after removing all but minor amounts of HClO?. Unfortunately, the precipitation of QPMo was inhibited by the presence of HF. Its effect could not be eliminated by complexing with borax because of the instability of fluoroboric acid in the boiling precipitation solution. The addition of excess of HBr t o the HF-tartaric acid mixture overcame the difficulty. Tartaric acid tended to char in the concluding stages of the evaporation with some breakdown of the W-Fe-tartaric acid complex. This was overcome by the addition of ethylene glycol. Precipitation of Quinoline Phosphomolybdate. Contamination o f the original QPMo precipitate by W, Nb, and Ta necessitated the use of solvent extraction and a re-precipitation for its elimination. The effect of different treatments of W-contaminated precipitates is shown in Table 11. The presence of Fe to form the stable W-Fe-tartaric acid complex was found essential to reduce W contamination to negligible proportions, as determined by x-ray fluorescent analysis. Contamination of the original precipitate by N b was considerable at the 3 level, but slight at the 1 level. Almost all N b remained on the sinter disk of the filter as a blue-gray residue after solvent extraction.
z
z
The impossibility of removing QPMo quantitatively from PTFE beaker walls without using solvent mixture made it necessary to use glass beakers for the initial precipitation. A volume of 200 ml was used for precipitation and acidity adjustment as specified in earlier work (3) was no longer necessary because of the presence of the large amounts of organic acids. Complete precipitation of QPMo was achieved only from boiling solutions. About 90 ml of QMoR was required t o start the first QPMo precipitation and 30 ml to complete it. About 45 ml of QMoR was required for the second precipitation of QPMo. Tartaric acid suppressed the formation of a partly insoluble complex between QMoR and ethylene glycol. Blank Determination. For the first QPMo precipitation the use of H N 0 3 instead of iron is specified to avoid an prevents the additional determination of P in iron. " 0 3 reduction of Mo by tartaric acid, which in turn suppresses For the re-precipitation the breakdown of QMoR by "03. of QPMo, 1 gram of Fe and 15 ml of 12M HC104 provided a reasonable margin for the suppression of M o reduction by tartaric acid. RECEIVED for review October 31, 1966. Accepted July 3, 1967. Published with permission of the Chief Scientist, Department of Supply, Australia.
(3) U. Fernlund and S. Zechner, 2. Anal. Chem., 146, 11I (1955).
Determination of Trace Elements in Chromatographic Paper by Neutron Activation and Gamma Spectrometry Peter Patek and Herbert Sorantin Institute of Chemistry, Reactor Centre, Seibersdorf, Austria
MANYE L E M ~ N T Sin various substances have been determined after separation on chromatographic paper by neutron activation. Only a few authors dealt with the impurities in the paper itself (1-3). Staerk and Knorr ( 4 ) made a quantitative assay of the sodium and chlorine content of Whatman No. 1, Schleicher Schull 2043a, and Schleicher-Schull white ribbon 5892 paper, and were able to show that only 10% of the mentioned impurities could be removed by chemical leaching. In one case a n additional uptake of the used reagents was noticed. Therefore, it is important to determine the trace elements in the paper before application. Whatman chromatographic paper No. 3 (185-200 mg/cmz) has a higher loading capacity and was used by us to separate trace elements from their matrix. Before identifying them by neutron activation, we were interested in the kind and amount of impurities in the paper itself, their distribution in different charges, and their influence on the degradation and loss of tensile strength during longer irradiations. -__.-__._____
(1) A. A. Renson, B. Maruo, R. J. Flipse, H. W. Jurow, and W. W. Miller, Proc. Second Intern. Conf: Peaceful Uses At. Energy, Geneca, 19-78, 24, 289 (1958). (2) A. G. Soulitis, ANAL.CHEM., 36, 811 (1964). (3) A. Dimitriadu, P. C . R. Turner, and T. R. Fraser, Nature, 198, 446 (1953). (4) H. Staerk and D. Knorr, Atomkernenergie, 6 , 408 (1961).
1458
ANALYTICAL CHEMISTRY
EXPERIMENTAL
Irradiations. For the detection of short-lived radionuclides, 10- to ZO-granl samples of paper were put into polyethylene containers and irradiated in the pneumatic rabbit system of the ASTRA reactor. The flux was 2 X 1 O I 2 neutrons/cm* second for thermal, and 2 X 1Olo neutrons/cm2 second for fast, neutrons. Longer irradiations were performed in a corner position of the reactor core a t a flux of 6 X 1013for thermal, and 6 x l O l a neutrons/cm2 second for fast, neutrons. In this position aluminum containers were used. All samples were wrapped in an additional layer of paper to avoid direct contact with the walls of the capsules. Counting Equipment. Gamma spectrometry was performed with a Harshaw 3- X 3-inch NaI crystal and a n Intertechnique 400 channel analyzer with multiscaler, tape recorder, x , y-writer, and a Packard printer. Standard Substances. Because no papers with known amounts of trace elements were available, solutions of different metals or salts were prepared and standardized by conventional methods. All chemicals were of analytical grade; for gold and aluminum, solutions of metals with 99.9975purity were used. For quantitative assays two strips of the same paper and size were taken. On one, a known amount of standard solution was applied and distributed by the addition of
’
I
Radionuclide “AI ”Br “Br
“C1 K6Mn S4Mn “CU
Half-life 2 . 3 minutes 17.6 minutes 36 hours 37 minutes 2.58 hours 278 12.8 15.4 2.7 12.0 84 7.5 27.8 60.0
Table I. Trace Elements in Chromatographic Paper Peak Counting Irradiation time Cooling time: at MeV time, minutes 3 minutes 20 minutes 1.78 5 1 hour
3 minutes 3 minutes
45 hours 20 minutes 2 hours
days
hours 1 hour 18 hours “Na hours 3 minutes 18 hours “8Au days 1 hour 4 days days 7 hours ... IroBa minutes ... ... I”Ba years ... ... “Cr days 7 hours 10 days ‘9Sb days 7 hours 10 days “SC 84 days 7 hours 10 days 76% 120 days 7 hours ... 65Z” 245 days 7 hours 10 days ”hAg 253 days 7 hours ... aco 5.27 years 7 hours 10 days * + = Element present, hut only confirmed qualitatively.
doubly-distilled water, and the paper was dried. Then both strips were irradiated in the same reactor position. Identification of Short-Lived Radionuclides. Irradiations of 0.5-3 minutes showed mainly the peaks of 56Mn, 16AI, 80Br, and WI. After cooling times of 18 minutes or longer, the lines at 0.51,0.84, 1.37, and 2.67 MeV became more significant and could he identified as 6‘Cu, &*Mn,and *“a. The peak at 0.170 MeV, which was partially covered by back-scattered energies, was estimated after decay and spectrum stripping measurements to be la9Ba. In longer-activated samples, only lsiAu could be detected as a new radionuclide after 17-hours irradiation, and 5.9-days cooling time. Later on it was possible to identify in the same sample 5Cr, ‘*‘Sb, 65Zn,and T o by decay of peaks, ratio of peak heights, or spectrum stripping of former spectra or spectra of irradiated standards. The half-lives of the radionuclides were checked by consecutively registered spectra; in the last ones the long-lived nuclides %e, “Sc, 54Mn,and >lo*Agcould be found. Quantitative determinations were performed by comparison of the peak areas of sample and standard. In a few cases spectrum stripping of peaks had t o be used. The decay of the activity was measured by multiscaler operation. The window was set at 1.78 + 0.18 MeV and the channels were shifted at an interval of 20 seconds. Comparison with the standard was made 5 minutes after the end of irradiation. No influence of dead time could be noticed. RESULTS AND DISCUSSION
The values found for the different trace elements are compiled in Table 1. To estimate the errors, it can be said that chemically prepared standards had an accuracy of better than f l % . Differences caused by irradiations could be assumed with f 5 %. Peak areas were generally determined with a relative error of &2%, whereas evaluation of peaks by spectrum stripping showed much greater deviation. No quantitative figures are therefore given in the latter case. The main difficulty was to maintain equal counting geometry for longer paper strips. The observed fluctuations in activity measurements were between 10 and 15 %.
0.6 0.78 1.6567 0.84 0.84 0.51 1.37 0.41
0.5 0.17 0.36 0.32 0.60 0.89 0.26 1.11
0.66 1.39
1
5 2
... 5 10 5
... ... ... 5 5 5
... 15
... 30
Method Multiscaler Peak area Peak area Peak area Peak area Spectrum stripping Peak area Peak area Peak area Spectrum stripping Peak area Spectrum stripping Peak area Peak area Peak area Spectrum stripping Peak area Spectrum stripping Peak area
Content, ppm 7
+* 6 0.2 7 9 0.003
++
+ 3 ++ 27 + 1 1
Figure 1. Autoradiogram of Whatman chromatographic paper No. 3 Irradiation = 15 minutes at 5 X loL2neutrons/ern2second Cooling time = 72 hours Exposure = Kodirex, 24 hours
Although for shorter paper strips the counting geometry was reproducible, differences of activity were observed. We assumed, therefore, that the trace elements are not distributed homogeneously. This fact could be confirmed by the autoradiogram (Figure 1). I t is therefore advisable to take greater paper samples, whenever possible, especially for blanks. After a thermal dose of 2.4 X IOLs neutrons/cma the paper became yellow and its tensile strength diminished by about 60 %.
If the applied doses were higher than 2 X 10’e neutrons/cm’, the paper lost its shape. Longer incore radiations converted the paper into a tarry mass. ACKNOWLEDGMENT The authors thank Hubert Bildstein for many helpful discussions. RECEIVED for review December 23, 1966. Accepted May 24, 1967.
VOL. 39, NO. 12, OCTOBER 1967
1459
