and by the following P u - 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 t h a t the photopeaks detected by Weaver are due t o 239Nprather than 1331. This conclusion is confirmed by a calculation of t h e 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. T h e 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 t o small errors. T h e author's discussion about the possible 1331loss due t o diffusion through the plastic irradiation vials seems not appropriate in t h e 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). T h e X-ray and low energy gammas of 239Np were used in this work t o determine the natural uranium content of environmental materials. T h e low energy photon detector (LEPD) was utilized for this purpose. T h e 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 t o 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
T h e development of cyclic monitors indicating pollution caused by industrial waste water is important for compliance with the laws on the matter. T h e importance of automatic, rapid, and reproducible measurements in this field is great because of the large number of samples t o be analyzed and the length of time required for manual operations. The best system is t h a t in which the detectors are able t o 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 ( H F ) 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, t o demonstrate how H F conductometry may be advantageously utilized in a monitor t o 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 t o be more favorANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
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\I
M O N I T O R Voltage
+
HF amplifier
Frequency
paratively wide range for a very long time and does not require the use of reactives and, consequently, of standard-
7----gC
1 -- B
Figure 2. Schematic of the signal generator circuit
Trkistors Lis, LIS = 10 PH Tl = B C 140 Li7 = 3 turns CuL o 1 mm section 10 mm TI,T, = BFW 10 L,, = 4 t u r n s Ag 0 1 m m section 10 mni T4 = 2N 3819 Diodes T5 = B C 108/B D,,D, = BZY 88 C6V1 T,, T , , T8= 2N 914 Condensers (25 W V ) T$ = 2N 3866 = 20 p F C< Inductances C,, C,, C,, C , , , C,,, C l j , Cia = 4.7 n F LI = 24 turns CuL 6 0.4 mni c,. c, = 100 p F stand d 6 m m , tapped at = 56 p F 10th turn = 15 p F L,, 4, LS, L:, L,. L12, L14, = 3.3 nF LIS, LIB, Lis = VK 200 = 100 nF Philips = 12 p F = 2.2 n F L,, L,, L~~ = 40 PH
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ANALYTICAL CHEMISTRY, VOL. 47, NO. 7 , JUNE 1975
c,,, c,1, CZZ C,, C25 c25 c2t,
c30,
c32,
c34
c23 c31,
c35,
c3S,
c40,
c 33
C,7, C,,, C,,, C,
c41,
c42
variable
c3,
Other B = Battery S = Switch M = Connection to cell Z = BNC coaxial plus
= 120 p F = 470 p F = 47 n F = 150 p F = 33 p F = 39 p F = lOpF = 22 p F - 1 nF = 20 p F = 4 30 p F = 10 n F
12 v
Figure 3. Schematic of the monitor
Resistances ( jW, tolerance 5%) = 820 R R1, R,, R 6 0 = 2.2 k n
R63
Potentiometers PI = 100 kR P, = 25 k 0 P, = 1 kfi Transistors Ti T,
= 82 kR = 68 k!2 = 120 k R = 47 kR = 820 k R L 270 k n = 12MR = 10MR = 2.2 M n = 4.7 kl2 = 220 k n = 3.3 kR
= A F 124 = A F 125 = A F 116
TIS, Ti6 = BC 108/C TI:, T I E = BFW 1 0 Diodes Dj, D,, D,, D; = A A 119 D2, D3 = BB 105/B D5: DE,Ds = 1N 757/A Condensers (16 W . V . ci = 4.7 p F c2 = 33 p F C,. C,, C j , C13 = 1.2 nF CE, c1i = 12 p F cr, ci1 = 3.9 pF = 0.8 + 6.8 p F c , , e15 c,, cin = 1 nF c12. c36 = 470 p F c16 = 8.2 pF c1: = 120 p F C!, = 2.2 n F CI,, C22, C,o = 220 P F C,,, Cd5, CS7, C,, = 6.8 n F = 2 nF Cz1 c32 = 22 n F C2ir C28 = 300 p F c25 = 1.75 n F c2E = 5.6 p F
being in direct contact with the liquid, is the same as used in oscillometry (1-6). An alteration of the conductivity due to the variation of the ionic concentration varies the cell response, consequently causing a frequency displacement of the oscillating circuit to which it is connected (7-9). The signal generator circuit, Tz and T3 (Figure 2), works at a frequency of 5.8 MHz and is coupled, through the isolation stage Tr, to the multiplier circuits Ts, T7 to
c2r. c31
= 27 n F = 2.5 n F C4,, CS1 = 58 n F C34, C,,, Cd: = 1 0 PF c38, = 68 p F C3;%C A 2 ,C,,, C B D= 100 nF e393 cjz = 500 ilF c4G, c44 = 20 n F c:i, CS, = 1.5 nF c43 = 5 nF c49, C,S = 20 PF C 56 = 10 nF c59 = 470 n F Inductances L1 = 4 t u r n s CuL 0 0.3 mni stand 4 7 nini L2 = L, overexposed to L, L3, L: = 4 t u r n s CuL 6 0.3 nini stand ri 4 mm L, = L, = LIT = VK 200 Philips L5 = 9 t u r n s CuL 6 0.3 nim stand 6 7 nini L, = 15 t u r n s CuL o 0.3 m m stand 6 7 nim LI,, L I I , L I Z , LIS, LI,, J-15, Lt, = 10 MHz I F transformers L, = light 12 V, 0.1 A c24
obtain the frequency of 104 MHz. Such a signal, amplified by 2’8, pilots T g which irradiates a power of about 500 mW through the antenna circuit. A signal at 1,600 Hz generated by Tj is applied to the oscillating circuit as a “marker”. The emitted frequency may vary, as a function with the water conductivity, within 1 MHz, thus establishing the limits of 103.5 and 104.5 MHz. ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
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A = Aerial B = Batteries C = Oscillator and separator circuits
D = Multipliers and HF rmplifler circuits F = Cold plate of the
G = Hot p l a t e of the
H = Protectton
shield of
the cell
I = Temperature compensator
l
Figure 5. Recording of standard conductivities
(Y
I I
t Flguro 4. Diagram of the detector and the cell
The thermistors R3 and Rg, in direct contact with the liquid under examination, allow the thermal compensation of the oscillating circuit. R2 and Rs values were selected in order to obtain the desired compensation range. The apparatus is powered by means of batteries which ensure a sufficient independence t o avoid an interruption of the apparatus which, closed in a water-tight container, is thermoisolated. The possibility of using solar cells would permit an unlimited operation of the system. Figure 3 is the electrical schematic of the monitor. The signal at 104 MHz is amplified by T1 and afterwards converted by Tz at 10 MHz. The varicap diodes Dz and Ds inserted in the conversion circuit allow the cyclic excursion of the frequency by means of the discharge phase of the condenser C55. A flip-flop circuit (IO)periodically supplies the charge of ‘255. The signal at 10 MHz, amplified by T3, Tq, T5 is taken in direct current by De and D7 and applied to the direct current amplifiers T12, T13, Ti4 that drive the electronic commutator Tg, Tlo, T11 (11). The same discharge potential of C55 unbalances the differential amplifier T17, TIS which supplies the synchronous scanning signal to the recorder by the frequency metric investigation of the converter. The electronic commutator Tg, T ~ oT,11 balances the differential amplifier again when the receiver presents the direct current value due to the signal coming out from the detector to the integrating network C38, C36, R24. The selection circuit Te, T7, T g inserts the recording only during the discharge phase of condenser C55 in order to avoid the presence of spurious peaks. The light L,, inserted by T i g , Tzo, marks the recorded peak step by step. The whole apparatus is in a solid state except for the PerkinElmer Model 165 recorder. This system, which can be programmed for more channels, is a typical example of a new instrumental method for remote indication of the variations signaled by more detectors dipped in a liquid on a multichannel recorder. The monitor, in a multichannel system, gives the answer of every cell. This is possible since the signal of every detector is selected by the receiver because of its frequency “marker” value. The expansion range of every channel is 100 units on the chart of the recorder. This expansion corresponds to a pre-calibrating conductivity range. 1210
ANALYTICAL CHEMISTRY, VOL. 47,
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The time required for a complete scanning in the actual operational conditions is 45 seconds which is sufficient to give complete information. The speed of the chart of the recorder is 5 mm/min. This system may be used for the “Pollution Control Purpose (PCP)” because of its simplicity. It if is necessary, the detectorremote recorder may be provided with an alarm signal to indicate toxic conditions in the water or liquid under examination. Cell. Figure 4 shows the size of the detector and the detailed scheme of the cell formed by a tube in which the upper part is firmly fixed to the base of the detector and it is of the type “immersible” with alternate plates (4).The cell is also preserved from impacts by a protector.
DISCUSSION Calibration of the System. T h e realization of a n automatic system of analysis generally requires t h a t the electrochemical properties of t h e substance under examination are t o be determined by a conventional method, For this purpose, a number of measurements were made with the above-described method and were compared with those obtained with the low-frequency conductometric method. For the calibration, a number of solutions of NaCl in a x range between 1.5 X and 3.5 X wLS were used. In Figure 5, the curves of a series of standards are reported. By varying the frequency of t h e oscillating circuit and thus regulating the circuits of the monitor and detector, it is possible t o cover the conductivity range suitable for t h e measurements which one intends t o carry out. I n any case, t h e oscillator works in the ascendent part of the concentration curve ( 5 )t o obtain a high sensitivity response. T h e calibration curve of Figure 5 is sufficiently regular in t h e conductivity range investigated. Table I shows a number of measurements. T h e low frequency measurements were made by means of two different conductometric bridges. Differences in results obtained from t h e two LF bridges were not smaller on the average than those obtained in t h e comparison between the two LF bridges and the method described. T o evaluate the precision of the apparatus, t h e conductivity was measured in a steric condition and in movement. T h e movement of t h e flowing liquid has no influence on t h e markings of the detector keeping within high reproducibility limits. Application of Remote Control. T h e above-mentioned
Table I. Values Obtained by Cyclic and Manual Processes LF X
a
values
Sample No
No proof
Average X c y c l i c
I appar.'
11 appar. b
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
4 6 7 5 4 4 5 5 7 5 4 3 5 6 5 6 5 3
1697 1737 1834 1894 1961 2024 2102 2175 2270 2302 2399 2475 2589 2682 2822 2883 2975 3308
1690 1740 1830 1895 1960 2030 21 00 2175 2265 2300 2395 2475 2595 2685 2825 2885 2980 3305
1702 1737 1835 1897 1964 2021. 2100 2178 2270 2306 2400 2478 2590 2679 2816 2881 2975 3311
Std dev
Variation coefficient
12,5 13,5 9,6 9,2 13,l 6,3 11,6 11,2 8,2 6,8 5,4 7,6 15,5 8,7 9,1 12,3 12,l 23,O
0,737 0,777 0,523 0,486 0,668 0,311 0,552 0,515 0,361 0,295 0,225 0,307 0,599 0,324 0,322 0,427 0,407 0.695
Halosis conductometric bridge. Jones L & N conductometric bridge.
instrumental method is suitable for checking the constancy of the composition of flowing liquids in order t o control t h e salinity of nutrition tanks of culture and checking of pollution (PCP). This system of monitors informs simultaneously at a distance about the conductivity variations occurring in a liquid system, amplitude and duration of these variations, and the return t o the standard conditions. In continuous daily controls, the recorded information in a cyclic analysis is undoubtedly t o be preferred t o the subjective interpretation of the operator.
CONCLUSIONS T h e described apparatus, adaptable t o more channels, is suitable for remote monitoring of the ionic pollution in water (PCP). A good reproducibility and agreement with manual methods are obtained but, with respect to the latter ones, the time and personnel required is less. The broadcast frequency used by us for transmission is legal in our country although it is in the middle of the F M broadcast band. Anyway, the broadcast frequency may be selected according t o the frequency allowed. We hope, by means of this method, t o make a useful contribution t o automatic research on signalizing the pollution for the continuous transmission of the conductivity measurements. T h e method presented t o measure the conductivity of
water is suitable t o illustrate one of t h e many applications of t h e H F technique in the branch of electrochemical automatic analytical chemistry.
ACKNOWLEDGMENT We thank C. D'Arrigo for his helpful collaboration.
LITERATURE CITED (1) K. Cruse and R. Huber, "Hochfrequenztitration", Monographien, Angewandte Chemie No 69, Verlag Chemie, Weinheim, 1957. (2) E. Pungor, "Oscillometry and Conductometry", Pergamon Press, Elmsford, NY, 1965. (3) D. Dobos. "Electronic Electrochemical Measurements". Terra Ed., Budapest, 1966. (4) A. Bellomo and G. D'Amore, Affi Soc. Peloritana Sci. Fis. Mat. Mat., 5 , 119 (1959). (5) A. De Robertis, A. Casale, D. De Marco. and A. Bellomo, Ani Soc. Peloritana Sci. Fis. Mat. Mat., 18, 65 (1972). (6)A. De Robertis, A. Casale, D. De Marco. and A. Bellomo. Affi Soc. Peloritana Sci. Fis. Mat. Mat., 18, 81 (1972). (7) F. Oehme, J. Necfroanal. Chern., 1, 181 (1959). (8) C. N. Reilley and N. H. McCurdy, Jr., Anal. Chem., 25, 86 (1953). (9) G. B. Blake, Analyst(London),75, 689 (1950). (10) J. Millman and C. Halkias. "Electronic Devices and Circuits", McGrawHill Book Co., Tokyo, 1967. (11) B. Ridge, Electronic Circuit Design Handbook, €€€Magazine, 1970.
Received for review April 17, 1973. Accepted February 19, 1974. The present paper was presented a t t h e 4th Congresso della SocietA Italiana di Biologia Marina, Lipari, 18-20 May 1972. Supported by the Consiglio Nazionale delle Ricerche-Roma.
Freeze-Dry Method for Coating Capillary Columns Ian T. Harrison Institute of Organic Chemistry, Syntex Research, Stanford lndusfrial Park, Palo Alto, CA 94304
Capillary columns for gas chromatography are usually coated by the dynamic method ( 1 ) in which t h e stationary phase is deposited, rather irreproducibly, from a slug of solution passing slowly through the column. We find t h a t
more even coatings of the desired thickness can be produced by filling the column with a solution of the calculated amount of stationary phase in benzene, freezing the solution, and evaporating the solvent in vacuo. Uniform coatANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
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