ANALYTICAL CHEMISTRY, VOL. 50, NO. 4, APRIL 1978
analytical emission lines for a n unknown sample. With the sample being aspirated, the auxiliary needle may be used to introduce a standard solution of the desired element(s). In this way, spectral interference effects a t a particular wavelength can be studied. This scheme would also be helpful in organic sample analysis where cheaper and more convenient aqueous standards could be introduced through the auxiliary needle to locate and evaluate spectral lines. One disadvantage of the dual sampling scheme is that the precision is degraded by a factor of 2 compared t o single sample aspiration. In a study to show the additivity of t h e signals from each of two sample needles, a 1pg/mL solution of Sr was used. The results are shown in Figure 2. I t can be seen that the nebulization ratio for needles A and B is approximately 1:2. The composite signal, d , is equal to the sum of the individual signals corrected for t h e background (blank) level. T h e peak-to-peak noise seen on the signals also appears to be additive, with the relative noise being essentially constant a t 2-3% RSD.
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In conclusion, this design has been shown t o offer simple and rugged operation, with the capability for precise positioning of the glass needles. T h e nebulizer requires less machine work than other designs and should be less expensive to manufacture. The absence of metals provides a measure of safety from corrosion by highly acidic samples. Finally, the multiple sampling capability may prove useful in specialized areas of analysis.
LITERATURE CITED (1) R N. Kniseley, H. Amenson. C. C. Butler, and V. A. Fassel, Appl. Spectrosc., 28, 285 (1974). (2) K. W. Olson, W. J. Haas, Jr., and V. A. Fassel, Anal. Chem., 49,632 11977\ , , ” . .,. (3) K. Ohls, ICP Inform. News/., 2, 357 (1977). (4) C. C. Wohlers, ICPInform. News/., 3, 37 (1977).
RECEIVED November 14, 1977. Accepted January 13, 1978. Research sponsored by the Department of Energy under contract with the Union Carbide Corporation.
Dropping Mercury Electrode for Polarography in Glass-Corroding Media Hugues Menard and Francine LeBlond-Routhler Department of Chemistry, University of Sherbrooke, Sherbrooke, Quebec, Canada J IK 2R 1
During the past few years, a section of analytical chemistry dealing with polarography in glass-corroding media seems to have attracted many workers. This is due to the construction of capillaries protected by polychlorotrifluoroethylene (KEL-F) or polytetrafluoroethylene (Teflon). With these capillaries, polarographic measurements can be made directly in hydrofluoric acid or concentrated sodium hydroxide solutions that are used as solvents for metallic samples containing silicates, thus eliminating stages of evaporation and redissolution which were previously necessary to protect the glass capillaries b u t could also lead to systematic errors. Techniques of constructing those capillaries inert t o corrosive solvents have been summarized by Bond and co-workers (1,2),who also add that all the techniques are extremely hard to p u t into practice and that the chances of success are few. I t must also be said t h a t enormous work has been accomplished by Raaen (3-11) eight to fifteen years ago and by Clifford and Balog (12) concerning the construction and use of a capillary inert in hydrofluoric acid which made possible the study of some redox, reactions especially of metal ions in glass-corroding media. Devynck (13) recently studied the polarography of antimony in hydrofluoric acid. But, u p to now, it seems t h a t all techniques for t h e construction of capillaries require a certain dexterity and could be said to be almost an art. From the analytical point of view, the availability of a simple technique in making such capillaries would be of great concern for all interested laboratories. We present here a method of constructing a polyethylene capillary for use in solutions extremely corrosive to glass.
EXPERIMENTAL Construction of a Capillary. A “Sargent-Welch Scientific Company” capillary C 2-5 s No drop-time S-29419) is cut into 5-cm lengths. One end of the 5-cm long capillary is immersed in a melted polyethylene bath (for example, in a beaker filled with granulous polyethylene heated at 200 “C). Then, when it is removed slowly, a mass (Figure la) of polyethylene adheres very well to the glass but does not penetrate into the glass capillary. 0003-2700/78/0350-0687$01 .OO/O
Just before the polyethylene chills, a mild pressure of nitrogen is applied at the other end of the capillary so as t o form a 1- to 2-mm diam. bubble (Figure Ib). When the polyethylene is well chilled, it is tooled to get a more adequate form so that it can be inserted into a polarographic cell (Figure IC).The polyethylene on the glass capillary must be at least 2-mm thick so as to maintain a good mechanical resistance. Then, with a No. 80 drill (0.0343-cm diam.) revolving at 17 000 turns/min (Dumore Hi Speed sensitive drill No. 8226), a hole is drilled into the bubble (Figure Id). The minimum length between the bubble and the end of the polyethylene capillary is 0.5 to 1 cm. The drop time of the mercury drop will depend on the length of the glass capillary and also the orifice diameter of the polyethylene capillary. The glass capillary should be kept as short as possible, that is, 5 cm. Also, the form of the orifice of the polyethylene capillary should be modified; this can be done by using a needle point. The main purpose of the use and construction of the capillary is to eliminate any defect from dead volume that could trap air bubbles in the portion between the two capillaries. m, (Fisher Reagents. Stock solutions of bismuth trioxide, Scientific Co.) are prepared from commercial HF 48% by volume m, (J. T. Baker (Allied Chemical). Bismuth trichloride, Chemical Co.) is prepared from sodium hydroxide (Anachemia Chemicals Ltd.) with twice-distilled water. Apparatus. A model 174 A polarograph (Princeton Applied Research) was used with a three-electrode system. The saturated calomel reference electrode was separated from the test solution by a porous Teflon junction.
RESULTS AND DISCUSSION We selected polyethylene for several reasons. Polyethylene is know ( 1 4 ) to be inert to hydrofluoric acid at room temperature and to have mechanical properties comparable with those of Teflon. Also, it is not toxic and can be manipulated without any danger. We noticed that it sticks to glass but does not penetrate into the capillary; this was not the case when we tried other polyolefins such as polypropylene for example. Figure 2 is an x-ray photograph of two capillaries filled with mercury. We note that the mercury completely fills the junction of the two capillaries and that the capillaries work well even though the bubble is spherical. T h e drill doesn’t
c 1978 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 4, APRIL 1978
o
b
C
d
Figure 1. Sketches of the capillary-fabrication steps after: (a) it is taken out slowly of the polyethylene bath: (bj a miM pressure of nitrogen has been applied; (c) being worked up for the polarographic cell; (dj having been bored with a drill
Figure 4. (a)Classical polarogram of lov3mBi3+in 48% commercial HF; (b) differential pulse polarogram, same conditions Figure 2. X-ray of two capillaries filled with mercury
Figure 4 gives the classical and the differential pulse porn Bi3+ in 48% commercial HF. The shapes larograms of of the two curves demonstrate that this capillary can be used in media extremely corrosive to glass. A polarogram of acetonitrile in anhydrous HF recorded in the laboratories of the National Institute of Science and Nuclear Techniques in Saclay (15)confirms the efficiency of the capillary.
ACKNOWLEDGMENT The authors thank Miss Charest for her technical assistance in radiology. And, most of all, sincere thanks to F. Kimmerle for his interest and good discussions. LITERATURE CITED
m Bi3+ in NaOH 10 M; (b) Figure 3. (a) Classical polarogram of differential pulse polarogram, same conditions
reach the inferior part of the bubble due to the fact that there is no air in this cavity. m Bi3+ in Figure 3 shows the classical polarogram of a 10 rn NaOH solution. To demonstrate the good performance of the polyethylene capillary, a differential pulse polarogram is superposed, which indicates adequately the reproducibility of the mercury drops.
(1) A. M. Bond. T. A. O'Donnell. and A. B. Wauoh. J . Nectfoanal. Chem., 39, 137 (1972) (2) A. M. Bond and T A. O'Donnell, Anal. Chem , 44, 590 (1972). (3) H. P. Raaen, Anal. Chem., 34, 1714 (1962). (41 H. P. Raaen. Anal. Chem.. 36. 2420 (1964). (5j H. P. Raaen, Anal. Chem.; 37; 677 (1965).' (6) H. P. Raaen, Anal. Chem., 37, 1355 (1965). (7) H. P.Raaen, "Analysis Instrumentation 1965", Plenum Press, New York. N.Y., 1966, p 219. (8) H. P. Raaen, Chem. Insfrum., 1, 287 (1969). (9) H. P. Raaen, Anal. Chim. Acta, 44, 205 (1969). (10) H. P. Raaen, Anal. Chim. Acta, 48, 427 (1969). (11) W. L. Belew and H. P. Raaen, J . Necfroanal. Chem., 8, 475 (1964). (12) A. F. Clifford and G. Balog. Nucl. Sci. Absrr., 5 , 694 (1951). (13) J. Devynck, H. MOnard, G. Comarmond, and B.TrOmilbn, Can. J. Chem.. in press. (14) P. P. Coppola and R. C. Hughes, Anal. Chem., 24, 768 (1952). (15) J. Devynck, personal communication, May 1977.
RECEIVED for review November 29,1977. Accepted January 27, 1978. Support of this work by the National Research Council of Canada is gratefully acknowledged.
