schematic are stabilization trimmers and are nominally 20 pf. Exact values are dependent upon the details of wiring practice used in circuit construction and should be experimentally chosen for optimum high-frequency stability. Some operational precautions are required when using a device with these energy levels. Although the output is short-circuit-proof with respect to ground, a short circuit of the output to the other power supply terminals could cause destruction of the output stage. The input stage of the booster exhibits quite high input impedance (approximately 100 Kohms) and will tolerate input voltages of +15 volts; inputs in excess of this range can destroy the input stage of the booster. The booster itself will normally be operated by an operational amplifier (i.e., an inexpensive 741 type for synthetic work) in a DeFord ( 2 , 3 potentiostat configuration; ~~
(2) D. E. Smith, CRC Crit. Rev. A n d . Chem.,2,247 (1971),
under these conditions, it is conceivable that touching reference and auxiliary electrode leads when the potentiostat is at high voltage may damage the follower. Personal safety precautions should, of course, be taken as the circuit can pose a shock hazard (130 V). Our standard operating procedure includes turning offthe booster power supply whenever sample or leads are changed; thus far, no difficultieshave arisen. RECEIVED for review July 3, 1972. Accepted October 6, 1972. Part of this work was conducted under the auspices of the Air Force Office of Scientific Research, USAF(ASFC), AF-AFOSR-69-1625, and by the U.N.C. Materials Research Center under Contract DAHC-15-67-C0223 with the Advanced Research Projects Agency.
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(3) A. A. Pilla, in “Applications of Computers to Analytical Chemistry,” H. Mark, Jr., J. S. Mattson, and H. C. MacDonald, Ed., Vol. 2, Dekker, New York
Filter Unit for Ion Exchange Resin-Loaded Papers K. A. H. Hooton and M. L. Parsons Department of Chemistry, Arizona State University, Tempe, Ariz. 85281
Tm USE OF ION EXCHANGE resin-loaded filter papers has become established as a concentration technique employed in X-ray fluorescence and neutron activation analysis ( I , 2). Filtration of the sample through the resin-loaded paper disks has to be repeated a number of times before all the cations or anions have been exchanged because of the thinness of the paper ( ~ 0 . mm) 3 and consequent short length of theimpregnated ion exchange “column.” Various types of filter units have been used by workers in the field. Campbell and coworkers (3, 4 ) described two versions of their filtration apparatus for a 35-mm diameter disk where a polyethylene cap with a 30-mm diameter hole was sealed into a filter funnel, the disk held in the cap by a vial with the bottom cut off. Hayden (5) used a disposable unit in which a 25.4-mm resin-loaded disk was placed in the cap (with 22.2mm hole) of a polyethylene bottle cut off at the shoulder. The top section of the bottle, which acted as a funnel, screwed into the cap containing the disk and the bottom section of the bottle was used to collect the filtrate. Bergmann and coworkers (6) mounted a 14-mm resinloaded disk in a Teflon (Du Pont) holder clamped in an aluminum-glass pipe coupler. The inlet side of the coupler was sealed to a 25-ml capacity funnel and the outlet side to a Teflon stopcock. Hakkila et al. (7)used a 23.8-mm disk in a filter unit consisting of a 125-ml Erlenmeyer flask with a glass (1) W. J. Campbell, E. F. Spano, and T. E. ween,
ANAL. LHEM..
38,987(1966). (2) D. E. Becknell, R. H. Marsh, and W. Allie, Jr., ibid,,43, 1230 ,1(1.11\ \L,,L).
(3) E. F. Spano, T. E. Green, and W. J. Campbell, US.Bur. Mines Rept. h e s t , 6308(1963). (4) E. F. Spano, T. E. Green, and W. 3. Campbell, ibid., 6565 (1964). ( 5 ) J. A. Hayden, Talonra,14,721 (1967).
(6) J. G. Bergmann, C. H. Ehrhardt, L. Granatelli, and J. L. Janik, ANAL.C H E M . ,1258 ~ ~ ,(1967). (7) E. A. Hakkila, R. G. Hurley, iind G. R. Waterbury, ibid., 41, 665(1969).
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450
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Figure 1. Lexan disk holder chimney clamped over a modified Hirsch funnel. Tackett (8) seated a 32-mm resin-loaded disk in a machined Plexiglas (Norton Co.) block and held the disk in place with a Plexiglas tube which fitted snugly into the block. Malissa and Marr (9) clamped 5-mm disks between two rubber washers and two glass plates, one plate fused to a funnel and the other plate fused to an outlet tube. AU of the filter units described above passed the sample unidirectionally through the disk a number of times until cation or anion exchange was complete. However, due to the nature of the ion exchange resin-loaded disk, filtration can be performed through the disk in one direction and back through in the reverse direction, the cycle being repeated an adequate number of times until all the cations or anions have been exchanged. Using this principle, we have constructed a number of the following filter units for 50-mm resin-loaded disks giving an active filtration area of 29-mm diameter for use in a Philips PW1410 vacuum X-ray spectrometer. (8) S. L.Tackett,ibid.,43,972(1971). (9) H. Malissa and I. L. Marr, Mikrorhim. Acta, 1971,241.
VOL. 45, NO. 2, FEBRUARY 1973
The filter unit is illustrated in Figures 1 and 2. The twopiece paper disk holder (Figure 1) was machined out of 6.35mm thick Lexan. Two screw-cap 250-1111 polycarbonate Erlenmeyer flasks (Nalgene Cat. No. 4108-0250) were each drilled with one 1.32-mm hole (No. 55 drill) at the 130-ml level on a smooth area of the flask away from the graduations and other raised markings. The tops of the flasks required smoothing flat with fine emery paper placed on a flat surface. Two rubber washers, which were fitted between the tops of the flasks and the disk holder, were cut from 0.9-mm thick rubber to 32-mm 0.d. and 29.5-mm i.d. A sample or standard solution of up to 100 ml was measured into one of the flasks, the flask screwed into one side of a No. 40 pinch type ball-and-socket clamp and the second flask screwed into the opposite side of the clamp. The resinloaded disk, presoaked in demineralized water, was placed in the bottom section of the disk holder and the top section fitted. After the two rubber washers were fitted into opposite sides of the disk holder, the holder was inserted between the two Erlenmeyer flasks and the tops of the flasks were seated on the rubber washers in the recesses in the holder. By rotating the flasks, the two air holes in the flasks were located one above the other when the apparatus was standing on the bench. The locking screw of the clamp was tightened to hold the assembly of flasks and disk holder together. To filter the sample, the filter unit was inverted, care being taken to avoid loss of sample through the air hole. To assist filtration, a very slight suction from an aspirator filter pump was applied to the lower air hole, contact being made with the flask by a piece of thick-walled rubber tubing. By slight tilting of the flask and occasional removal of the suction, loss of filtrate through the lower air hole was avoided easily. For field use, suction may be applied from a hand operated vacuum pump (Edmund Scientific, Cat. No. 71301). By inverting the filter unit and repeating the above procedure, the
I 32.77 .dia.
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I
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I
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Figure 2. Assembled filter unit
sample was again filtered through the disk. Repeated filtrations are rapidly performed with this filter unit, seven or eight filtrations having been found sufficient to complete the ion exchange reaction. For good sealing between the suction tubing and the flask, the hole was drilled as described earlier on a smooth area of the flask. Because of the reduced sample handling and greater convenience of operation, together with the ability to be modified for use with other size disks and active filtration areas, this filter unit is considered to be an improvement on the previously described units.
RECEIVED for review October 6, 1972. Accepted November 7, 1972. From a thesis to be submitted by K.A.H.H. to the Graduate Faculty of Arizona State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry.
Signal Generator for Electrochemical Analysis of Mixtures of Electroactive Species G. I. Connor and G. H. Boehme Division of Sciences, Electronics Engineering Group
C. J. Johnson and K. H. Pool Department of Chemistry, Washington State University, Pullman, Wash. 99163 THE EXTENSION OF POLAROGRAPHY to stationary electrode voltammetry (SEV) and cyclic voltammetry has placed a demand of improved versatility on the linear voltage ramp with time. Consequently, several signal generators have been reported recently that offer a multitude of ramp rates and controlled switching potential and hold time (1-5). While these signal generators offer versatility in the analysis of the reduction as well as the oxidation of an electroactive species, they lack the ability to adequately analyze many mixtures of electroactive species. With mixtures, the prob___ (1) J. L. Huntington and D. G. Davis, Chem. Znsrr~m.,2, 83 (1969). (2) R. L. Meyers and I. Shain, ibid.,p 203. (3) J. S. Springer, ANAL.CHEM.,42 (8), 22A (1970). (4) R . H. Bull and G. C. Bull, ibid.,43, 1342 (1971). (5) Chia-Yu Li. Donald Ferrier, and R. R. Schroder, Cliem. Imfrum., 3, 333 (1972).
lems of distortion or concealment of one current peak by the current peak of another electroactive species becomes a serious problem for the electroanalyst. Jones and Perone (6) have discussed this problem in some detail and have developed a computerized fast sweep derivative polarographic method which incorporated timed holds after each reduction of an electroactive species. The timed holds allow sufficient decay between current peaks to analyze mixtures of electroactive species. Using this technique, concentration ratios 1OOO:l of one electroactive species over another could be determined. Farwell and Geer (7) have reported the use of timed holds for the resolution of mixtures of electroactive __ (6) D. 0. Jones and S. P. Perone, ANAL.CHEM., 42, 11 51 (1970). (7) S. 0. Farwell and R. 0. Geer, Abstracts 26th Northwest Regional Meeting of the American Chemical Society, Bozeman, Mont., June 1971, No. 25.
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