I
0
I
2
3 Time
4
5
6
7
%
I
1
I
l
l
, , , Pressure
(min)
Figure 1. NO peak from column preconditioned by Dietz method
0
[NO], 7.6%; span, 2 mV: attn, 2: system: Chromosorb 104-Molecular Sieve 5A
0
1
2
3
Time
5 (min)
4
6
Figure 2. NO peak from column preconditioned by modified Dietz
method An additional step was therefore added to the Dietz procedure. Following NO2 formation, the column was heated to 250 "C to desorb loosely-held NOz. Figure 2 shows that there is very little tailing for a sample having a concentration of 1.17% NO using a column pretreated in this manner. The full pretreatment procedure for conditioning Molecular Sieve 5A for NO analyses, to which we recommend adding step 6, is thus the following: 1) Activate the sieve by heating to 300 O C under vacuum for 20 hours to desorb all gases. 2) Break the vacuum at 300 O C with NO, maintaining a low NO flow for 1 hour to saturate the column. 3) Cool the column to 20 "C while continuing to saturate with NO for another hour. 4) Flush the column with He for % hour to remove all nonadsorbed NO. Add a stream of 0 2 at 25 "C to form NO:! on the active sites. 5) Raise the temperature to 100 OC while maintaining the 0 2 atmosphere and hold for l , hour to ensure that 0 2 and NO react. 6) Heat the column to 250 "C under a He atmosphere for 8 hours.
[NO], 1.17%; span, 0.50 mV; Attn, 1: system-Chromosorb Sieve SA
104-Molecular
LITERATURE CITED (1) R. N. Dietz, Anal. Chem., 40, 1576 (1968). (2) D. T. Clay and S.Lynn, Lawrence Berkeley Laboratory Report, No. 3059, University of California, Berkeley, CA. June 1974. (3) W. Joithe, A. T. Bell, and S. Lynn, I 8 EC, Proc. Des. Develop., 11, 434 (1972).
David T. Clay' Scott Lynn Department of Chemical Engineering University of California Berkeley, CA 94720
RECEIVEDfor review October 30, 1974. Accepted January 27, 1975. Present address, Weyerheuser Corp., Longview, WA 96822.
Rapid, Instrumental Neutron Activation Analysis for the Determination of Uranium in Environmental Matrices: Exchange of Comments Sir: Recently, Weaver ( I ) published a procedure for the determination of uranium in environmental matrices by neutron activation analysis. The author's procedure consists of a 4-hour thermal neutron irradiation and gamma spectrometry with a LEPD Ge(Li) detector after a decay period of 48 hours. The author claims the detection and measurement of the fission isotope 1331 (2'112 = 21 hr) by way of photopeaks at 14.4, 18.32, 21.40, 100.08, 106.80, and 1206
ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
109.32 keV. This is illustrated by gamma spectra obtained from an irradiated uranium standard and an irradiated coal sample. These spectra are, in fact, dominated by peaks in the proximity of the energies listed before. The decay scheme of 1331(2-4) does however not indicate transitions at energies lower than 150 keV. On the other hand is a Ge(Li) gamma spectrum of the isotope 239Np ( 2 ' 1 ~ 2 = 2.35 d) dominated by a photopeak at 106.13 keV
and by the following Pu-X rays:
L a , = 14.28 keV L cy2 = 14.08 keV L pi = 18.28 keV L p2 = 17.25 keV L y i = 21.40 keV
K CY, = 103.65 K CY^ = 99.45 K = 117.15 K p2 = 102.59
I t seems thus very likely that the photopeaks detected by Weaver are due to 239Nprather than 1331.This conclusion is confirmed by a calculation of the sensitivities for detection of both isotopes after the specified irradiation and cooling times. The decay rate of 239Np, produced by 23sU(n,y)239U(-P-(T1/2 = 23.5 min))239Np48 hours after the irradiation is a t least 20 times more intense than the (5). This calcudecay rate of 1331,produced by 235U(n,f)1331 lation was made on the assumption of a natural isotopic abundance for uranium as can be expected in environmental matrices. The author ( I ) determined by this procedure, uranium in orchard leaves, beef liver, sea water, ores, mud, and several coal-types. Since the same photopeaks were measured in standard and samples, the erroneous attribution of the photopeaks does not immediately imply errors in the analytical results. Correction for decay between counting standard and samples using the 21-hr half-life (1331)instead of the 2.35-d half-life (239Np)may, however, have led to small errors. The author's discussion about the possible 1331loss due to diffusion through the plastic irradiation vials seems not appropriate in the framework of the uranium determination.
LITERATURE CITED (1) J. N. Weaver, Anal. Chem., 46, 1292 (1974). (2) I. M. H. Pagden, G. J. Pearson, and J. M. Bewers, J. Radioanal. Chem., 8, 373 (1971).
(3) R . L. Heath in "Handbook of Chemistry and Physics" 52nd ed.. The Chemical Rubber Co., Cleveland. OH, 1972, 8-245. (4) M. Lederer, J. Hollander, and I. Perlman, "Table of Isotopes," 6th ed.. John Wiley and Sons, New York, NY, 1968. (5) 13.De Soete, R . Gijbels, and J. Hoste. "Neutron Activation Analysis," Interscience, New York, NY, 1972.
R. Dams Institute of Nuclear Sciences-R. Proeftuinstraat 86 B-9000 Gent, Belgium
U. G.
RECEIVEDfor review October 31, 1974. Accepted December 9,1974.
Sir: R. Dams is correct in his discussion of this paper (I). The X-ray and low energy gammas of 239Np were used in this work to determine the natural uranium content of environmental materials. The low energy photon detector (LEPD) was utilized for this purpose. The fission isotope 1331was measured after irradiation and solvent extraction in the coals as a check on the results of the above method as mentioned in the paper. A 21% Ge(Li) detector was utilized here to measure the 0.53-MeV gamma from 1331.There were no errors in half-life corrections to the data presented in Tables I and 11. Hence, the data are correct as presented. LITERATURE CITED (1) J. N. Weaver, Anal. Chem., 46, 1292 (1974).
Jack N. Weaver Nuclear Services Laboratory Nuclear Engineering Dept. North Carolina State University Raleigh, NC 27607 RECEIVEDDecember 9,1974. Accepted December 9,1974.
AIDS FOR ANALYTICAL CHEMISTS
Cyclic Multichannel Apparatus for Wireless Simultaneous Transmission of Conductivity Measurements Athos Bellomo, Alessandro De Robertis, Domenico De Marco, and Agatino Casale institute of Analytical Chemistry, University of Messina, Messina, ltaly
The development of cyclic monitors indicating pollution caused by industrial waste water is important for compliance with the laws on the matter. The importance of automatic, rapid, and reproducible measurements in this field is great because of the large number of samples to be analyzed and the length of time required for manual operations. The best system is that in which the detectors are able to feed the information directly into a recorder but, with this system, there are some difficulties when the distance between the detector and the monitor is great. We have produced a system for the cyclic control of pollution in either water or liquid on the basis of high frequency (HF) conductivity measurements in which the informa-
tion is wireless telecasted, thus allowing the simultaneous reception of information from other detectors. This apparatus may also be used when the noted electrochemical methods are not suitable. Therefore, it is our purpose, on the basis of the results obtained, to demonstrate how H F conductometry may be advantageously utilized in a monitor to obtain a new and versatile system for automatic electrochemical measurements. Parameters for Measuring Water Pollution. The conductivity of the water, now, is one of the most important and indicative variables measured and a new instrumental cyclic apparatus has been developed for its determination. Because of the suspended matter in water pollution, H F conductometry technique was considered to be more favorANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
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