and by the following Pu-X rays:

L a, = 14.28 keV K CY, = 103.65 L cy2 = 14.08 keV L pi = 18.28 keV K = 117.15 L p2 = 17.25 keV K p2 = 102.59

K CY^ = 99.45

L y i = 21.40 keV

I t seems thus very likely that the photopeaks detected by Weaver are due to 239Np rather than 1331. This conclusion is confirmed by a calculation of the sensitivities for detec- tion 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))239Np 48 hours after the irradiation is a t least 20 times more intense than the decay rate of 1331, produced by 235U(n,f)1331 (5). This calcu- lation was made on the assumption of a natural isotopic abundance for uranium as can be expected in environmen- tal matrices.

The author ( I ) determined by this procedure, uranium in orchard leaves, beef liver, sea water, ores, mud, and sev- eral 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 ana- lytical results. Correction for decay between counting stan- dard 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 1331 loss due to diffusion through the plastic irradiation vials seems not appropriate in the framework of the uranium determina- tion.

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

(4) M. Lederer, J. Hollander, and I. Perlman, "Table of Isotopes," 6th ed..

(5) 13. De Soete, R. Gijbels, and J. Hoste. "Neutron Activation Analysis," In-

R. Dams

Chemical Rubber Co., Cleveland. OH, 1972, 8-245.

John Wiley and Sons, New York, NY, 1968.

terscience, New York, NY, 1972.

Institute of Nuclear Sciences-R. U. G. Proeftuinstraat 86 B-9000 Gent, Belgium

RECEIVED for review October 31, 1974. Accepted Decem- ber 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 en- vironmental materials. The low energy photon detector (LEPD) was utilized for this purpose. The fission isotope 1331 was 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 util- ized 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).

Nuclear Services Laboratory Nuclear Engineering Dept. North Carolina State University Raleigh, NC 27607

RECEIVED December 9,1974. Accepted December 9,1974.

Jack N. Weaver

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 compli- ance 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 direct- ly into a recorder but, with this system, there are some dif- ficulties when the distance between the detector and the monitor is great.

We have produced a system for the cyclic control of pol- lution in either water or liquid on the basis of high frequen- cy (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 electro- chemical methods are not suitable. Therefore, it is our pur- pose, 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 auto- matic electrochemical measurements.

Parameters for Measuring Water Pollution. The con- ductivity 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 favor-

ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975 * 1207

M O N I T O R

HF amplifier Frequency Voltage +

B 7-- - -g- C 1 --

\I paratively wide range for a very long time and does not re- quire the use of reactives and, consequently, of standard-

Figure 2. Schematic of the signal generator circuit

T r k i s t o r s Tl = B C 140 TI, T, = BFW 10 T4 = 2N 3819 T5 = B C 108/B T,, T, , T8 = 2N 914 T$ = 2N 3866

Inductances LI = 24 turns CuL 6 0.4 mni -

stand d 6 mm, tapped at 10th turn

L,, 4, LS, L:, L,. L12, L14,

L,, L,, L~~ = 40 PH

LIS, LIB, Lis = VK 200 Philips

Lis, LIS = 10 PH Li7 = 3 turns CuL o 1 mm section 10 mm L,, = 4 tu rns Ag 0 1 mm section 10 mni

D,, D, = BZY 88 C6V1

C< = 20 p F

Diodes

Condensers (25 WV)

C,, C,, C,, C , , , C,,, C l j , Cia = 4.7 nF c,. c, = 100 pF

= 56 p F = 15 p F = 3.3 nF = 100 nF

= 2.2 nF = 12 p F

c,,, c,1, CZZ C,, C25

c23

c 33

c3, Other

c 2 5 c 2 t , c30, c32, c34

c31, c 3 5 , c3S, c 4 0 , c41, c42

C,7, C,,, C,,, C,, variable

B = Battery S = Switch M = Connection to cell Z = BNC coaxial plus

= 120 pF = 470 pF = 47 n F = 150 p F = 33 p F = 39 p F = l O p F = 22 p F - 1 nF

= 4 30 p F = 10 n F

= 20 p F

1208 ANALYTICAL CHEMISTRY, VOL. 47, NO. 7 , JUNE 1975

12 v

Figure 3. Schematic of the monitor

Resis tances ( j W, tolerance 5%) = 820 R = 2.2 kn

R1, R,, R 6 0

R63 Potent iometers

PI = 100 kR P, = 25 k 0 P, = 1 kfi

T rans i s to r s Ti T,

= 82 kR = 68 k!2 = 120 kR = 4 7 kR = 820 k R L 270 k n = 1 2 M R = 1 0 M R = 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:, TIE = BFW 10

Dj, D,, D,, D; = A A 119 D2, D3 = BB 105/B D5: DE, Ds = 1N 757/A

ci = 4 . 7 p F c2 = 33 p F

CE, c1i = 12 p F cr, ci1 = 3.9 pF 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 PF C,,, Cd5, CS7, C,, = 6.8 nF Cz1 = 2 n F

c 3 2 = 22 n F

Diodes

Condensers (16 W . V .

C,. C,, C j , C13 = 1.2 nF

= 0.8 + 6.8 p F

C2ir C28 = 300 p F

c 2 E = 5.6 p F c 2 5 = 1.75 n F

c2r. c31 = 27 nF c 2 4 = 2.5 n F

C4,, CS1 = 58 n F C34, C,,, Cd: = 1 0 PF c38, = 68 p F

e393 cjz = 500 ilF C3;% CA2, C,,, CBD = 100 nF

c 4 G , c 4 4 = 20 n F c:i, CS, = 1.5 nF c43 = 5 nF c49, C,S = 20 PF C 56 = 1 0 n F c59 = 470 nF

L1 = 4 t u rns CuL 0 0.3 mni stand 4 7 nini L2 = L, overexposed to L, L3, L: = 4 tu rns CuL 6 0.3 nini stand ri 4 mm L, = L, = LIT = VK 200 Philips L5 = 9 tu rns CuL 6 0.3 nim stand 6 7 nini L, = 15 tu rns CuL o 0.3 mm stand 6 7 nim LI,, L I I , LIZ, LIS, LI,, J-15, Lt, = 10 MHz I F

Inductances

t r ans fo rmers L, = light 12 V, 0.1 A

being in direct contact with the liquid, is the same as used in oscil- lometry (1-6). An alteration of the conductivity due to the varia- tion of the ionic concentration varies the cell response, conse- quently 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

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 func- tion 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 1209

A = Aer ia l

B = Batter ies

C = Oscillator and separator

D = Multipliers and

c i rcui ts

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

(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 oscil- lating 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 cir- cuit allow the cyclic excursion of the frequency by means of the discharge phase of the condenser C55. A flip-flop circuit (IO) peri- odically supplies the charge of ‘255. The signal at 10 MHz, ampli- fied by T3, Tq, T5 is taken in direct current by De and D7 and ap- plied 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 con- verter.

The electronic commutator Tg, T ~ o , T11 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 re- corded peak step by step.

The whole apparatus is in a solid state except for the Perkin- Elmer Model 165 recorder.

This system, which can be programmed for more channels, is a typical example of a new instrumental method for remote indica- tion 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 se- lected 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.

Figure 5. Recording of standard conductivities

The time required for a complete scanning in the actual opera- tional 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 detector- remote 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 “im- mersible” with alternate plates (4). The cell is also preserved from impacts by a protector.

DISCUSSION Calibration of the System. The realization of an auto-

matic system of analysis generally requires that the electro- chemical properties of the substance under examination are to 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 ob- tained 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 the oscillating circuit and thus regulating the circuits of the monitor and detector, it is possible to cover the conductivity range suitable for the measurements which one intends to carry out. In any case, the oscillator works in the ascendent part of the concentra- tion curve ( 5 ) to obtain a high sensitivity response.

The calibration curve of Figure 5 is sufficiently regular in the conductivity range investigated. Table I shows a num- ber of measurements.

The low frequency measurements were made by means of two different conductometric bridges. Differences in re- sults obtained from the two LF bridges were not smaller on the average than those obtained in the comparison between the two LF bridges and the method described.

T o evaluate the precision of the apparatus, the conduc- tivity was measured in a steric condition and in movement. The movement of the flowing liquid has no influence on the markings of the detector keeping within high reproducibili- ty limits.

Application of Remote Control. The above-mentioned

1210 ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975

Table I. Values Obtained by Cyclic and Manual Processes LF X values

S a m p l e No No proof Average X cycl ic I appar.'

1 4 1697 1690 2 6 1737 1740 3 7 1834 1830 4 5 1894 1895 5 4 1961 1960 6 4 2024 2030 7 5 2102 21 00 8 5 2175 2175 9 7 2270 2265 10 5 2302 2300 1 1 4 2399 2395 12 3 2475 2475 13 5 2589 2595 14 6 2682 2685 15 5 2822 2825 16 6 2883 2885 17 5 2975 2980 18 3 3308 3305

a Halosis conductometric bridge. Jones L & N conductometric bridge.

11 appar. b

1702 1737 1835 1897 1964 2021. 2100 2178 2270 2306 2400 2478 2590 2679 2816 2881 2975 3311

Std dev

12,5 13,5 9,6 9,2

6,3

11,2 8,2 6,8 5,4 7,6

8,7 9,1

12,l

13,l

11,6

15,5

12,3

23,O

Variation coefficient

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

instrumental method is suitable for checking the constancy of the composition of flowing liquids in order to control the salinity of nutrition tanks of culture and checking of pollu- tion (PCP).

This system of monitors informs simultaneously at a dis- tance about the conductivity variations occurring in a liq- uid system, amplitude and duration of these variations, and the return to the standard conditions.

In continuous daily controls, the recorded information in a cyclic analysis is undoubtedly to be preferred to the sub- jective interpretation of the operator.

CONCLUSIONS The described apparatus, adaptable to 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 lat- ter 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 FM broadcast band. Anyway, the broadcast frequency may be selected according to the frequency allowed.

We hope, by means of this method, to make a useful con- tribution to automatic research on signalizing the pollution for the continuous transmission of the conductivity mea- surements.

The method presented to measure the conductivity of

water is suitable to illustrate one of the many applications of the H F technique in the branch of electrochemical auto- matic analytical chemistry.

ACKNOWLEDGMENT We thank C. D'Arrigo for his helpful collaboration.

LITERATURE CITED (1) K. Cruse and R. Huber, "Hochfrequenztitration", Monographien, Ange-

(2) E. Pungor, "Oscillometry and Conductometry", Pergamon Press, Elms-

(3) D. Dobos. "Electronic Electrochemical Measurements". Terra Ed., Bu-

(4) A. Bellomo and G. D'Amore, Affi Soc. Peloritana Sci. Fis. Mat. Mat., 5 ,

(5) A. De Robertis, A. Casale, D. De Marco. and A. Bellomo, Ani Soc. Pelo-

(6) A. De Robertis, A. Casale, D. De Marco. and A. Bellomo. Affi Soc. Pelo-

(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).

wandte Chemie No 69, Verlag Chemie, Weinheim, 1957.

ford, NY, 1965.

dapest, 1966.

119 (1959).

ritana Sci. Fis. Mat. Mat., 18, 65 (1972).

ritana Sci. Fis. Mat. Mat., 18, 81 (1972).

(10) J. Millman and C. Halkias. "Electronic Devices and Circuits", McGraw-

(1 1) 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 the 4th Congres- so della SocietA Italiana di Biologia Marina, Lipari, 18-20 May 1972. Supported by the Consiglio Nazionale delle Ri- cerche-Roma.

Hill Book Co., Tokyo, 1967.

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 the stationary phase is deposited, rather irreproducibly, from a slug of so- lution passing slowly through the column. We find tha t

more even coatings of the desired thickness can be pro- duced by filling the column with a solution of the calculat- ed amount of stationary phase in benzene, freezing the so- lution, and evaporating the solvent in vacuo. Uniform coat-

ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975 * 1211