Mechanism and functions of Mervyn-Harwall Square Wave Polarograph Mark lll are reviewed with 14 figures, which show the general features and characteristics of the instrument. Frequency of the square wave superposed on D.C. potential is 225 c/s, the amplitude of which can be selected between 2 and 32mV peak to peak. Capacity current in the electrode response is primarily limited to some extent by diodes and next, after amplification, eliminated by a diodes-gate circuit which opens for 100, u sec. at the latter end of each square wave life. The gate circuit is followed via a gain-selector and amplifier by a phase sensitive detector, which changes A.C. response into D.C. response fed into the polarogram recorder. When recording “Strobe Polarogram, ” the electrode potential can be set automatically at a definite potential near ECM (ca. -0.5V) for some time-interval before and after the fall of each drop, so that the drop-time may be kept constant at any potential. The time-delay for the strobe polarogram is 2 sec. after the fall of the preceding drop. D.C. potential sweep is generated by a electronical circuit which has not been used in the conventional polarographs. The proportionality of the wave heights to the square wave amplitudes is fairly beautifull up to 16mV (Fig. 11), and further it is found by Fig. 12 that the wave heights can also be proportionality selected by the gain control. The experience of the author in a few experiments so far has shown that the maximum sensitivity in practice seems to be about 10^-7M in the case of lead or cadmium in chrolide medium, because of the irregular deflection of the recorder-pen, which might be due to the noise caused by the capillary or the electronical circuit or some other reasons.

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In polarography there are many methods to have been studied to increase the sensitivity.Among them the square wave polarography, studied by Dr.Barker, is recognized to be the most available. The remarkable features of square wave polarography are (1) to use the usual dropping mercury electrode, (2) to need no special pretreatment and (3) to be operated with the same procedure as in the ordinary polarography. The high-sensitive polarograph studied by us, based upon Barker's square wave polarography, is composed of the generator of the square wave voltage applied to the cell, the generator of the gating signal and the current amplifier. The generation of square wave signal may be attained with the clipping as shown in Fig. 1 or with multivibrator as shown in Fig. 2. We obtained the square wave signal from the flip-flop circuit as shown in Fig. 3, which was driven by the input pulses. The pulses were generated by the decatron counting circuit driven with the crystal oscillator. In the decatron counting circuit there was used the double pulse decatron, whose poles are arranged as shown in Fig. 4. The output of the power amplifier with ha.gh4idelity of the square wave signal was applied to the cell. The gating pulses were also derived from the same decatron circuit and in the same way the gating signal were obtained by the flip-flop circuit. The current-amplifier was composed of the pre-amplifier, the gating circuit and the main amplifier. In the preamplifier the transister amplifier was used. In the gating circuit the pentode amplifier was used, whose pedestal was compensated with the balancing circuit as shown in Fig. 5. As the main amplifier, the three-stage frequency selective amplifier was used, so that the remaining pedestal from the gating circuit and the A.C. signal caused by gating the D.C. signal might be eliminated. The frequency selective amplifier was the cathode follower amplifier as shown in Fig. 7, whose negative feed-back circuit was Twin-T network as shown in Fig. 6. In the polarographic circuit, as shown in Fig. 8. the D.C. potential was applied to the anode through the choke coil and the square wave voltage through the condenser. The cathode of the cell was grounded through the resister, whose potential drop signal was given to the pre-amplifier. In the above mentioned circuit of polarograph, the terminals of the D.C. potential applier, the square wave voltage generator and the resister, with which the current signal was obtained, were all grounded, so the noise was kept minimum. With this polarograph the reversible depolarizes such as Cd- or Pb-ion of 2×10^-7 mol/l can be detectable. It seems that the factor limiting the sensitivity of detection is the series-resisters connected with the cell and the most noticeable resister is the capillary of the dropping mercury electrode

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In the analytical applications of the polarographic method, it is desirable to eliminate the effect of the double layer capacity. Assuming that the auxiliary electrode of the polarographic cell is not polarized and the resistance of solution is very small, it can be considered a simple electrical equivalent circuit for the cell. The equivalent circuit consists of a resistance R_x and capacitance C_x in parallel, and the conductivity 1/R_x is propotional to the concentration of bulk solution. Such being the considerations, a new A.C. bridge polarograph has been introduced in this paper. The conductivity 1/R_x was measured independently of the capacitance component C_x by a means of detecting 6he phase difference between a current i_c flows through the capacitance component C_x and the superimposed AC. voltage. At the same time, the variations of the C_x was recorded automatically. The principle of the polarograph was discussed, and the electrical characteristics and a few of the actual applications are presented here.

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Scope and limitation of square wave (S.w.) polarogaphic method of analysis, in constrast with those of d.c. and a.c. polarographic methods, have been investigated. Procedures for the analysis of metallic impurities in non-ferrous metals by s.w. polarographic method have been developed. The procedures have been applied in practice. The results and some comments on the method were given. By s.w. polarographic method Bi(lll), Sb(lll), Cu(ll), Pb(ll) + Sn(ll, lV) and Cd(ll) gave separated waves, repectively, from 1 N HCL base solution (each 30γ mg/100 ml), while the d.c. polarographic waves of Bi, Sb and Cu and a.c. polarographic waves of Bi and Sb overlapped each other. (each 0.2mg/100m1) The lowest concentration levels for the quantitative analysis of the metals from the state base solution were 50γ/100ml, 30-50γ/100rnl and 20 to 10γ or less/100ml by d.c., a.c., and s.w. polarographic method, respectively. The lowest relative cocentration levels for the determination of Zn in the presence of Cd were ca. 2%, 0.025% and 0.002% relative by d.c., a.c., and s.w. polarographic method, respectively. The change of wave height of s.w. polarograms of Cu and Zn from 0.45 N HCLO (50r/100ml) with the change of the distance between d.m.e. and anode (5-20 mm) was negligibly small. The temperature coefficients of the wave height were generally smaller or even negative. Best results were generally obtained when the dissolved oxygen was removed before electrloysis. The wave heights were very sensitive to the change of droptime. The determination procedures of Pb and Cu (0.0018-0.0027%) in electrolytic tin, Pb and Cu (0.0004-0.0009%) in high pure selenium, and Bi and Pd (0.0001-0.0006%) in electrolytic silber were established. The results obtained by these methods showed a good agreement with those by the dithizone method and d.c. polarographic method. The s.w. polarographic method has several advantages, i.e., it requires less skill in comparison with the dithizone method and smaller amount of the sample, ease of chemical pre-treatment, and shorter time for analysis in comparison with the d.c. polarographic method.

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