An electromagnetic vibrator for electrodes used in polarography and amperometric titrations

ANALYTICA

200

AN

ELECTROMAGNETIC POLAROGRAPHY

VIBRATOR AND

A.

Ihpavlmettt

CHIMICA

of Clternislry.

ACTA

FOR

AMPEROMETRIC

J.

VOL.

ELECTRODES

13 (1955)

USED

IN

TITRATIONS

LINDSEY

Siv John

Cass

College,

London

( ExgZaud)

Vibrating electrodes have been used in polarographic and amperometric determinations for several years and the devices employed to produce the necessary motion have varied considerably. Moving coil1 and moving iron2 (reed) loudspeaker units, cam-driven lever vibrators and clectromagnctic vibrators3 of the “massage” machine type have all been used. In the last mentioned publication the essential conditions for stable diffusion currents were established. An electromagnetic vibrator of this type moves the electrode in approximately one direction, but may be disturbed and vibrate in other modes as well. The path of the clectrocle in its electrolyte may thus be altered and so cause difficulty in measuring accurately the amplitude of vibration. Also at the lower speeds of vibration, the ditfusion current may change with change in the mode of vibration. However, such a vibrator has the advantages of being light and portable and gives a suitable amplitude of vibration when used on the a.‘~. mains for which it is designed. The description which follows is of an electromagnetic vibrator designed with a centring guide to constrain the motion to one direction only. ‘rile ch2ctromlgnct is rigidly fixed Within the cylindrical brass housing h and is COnnCCtCCl to ihc current supply via the plug B on the top. A soft iron armature is hold by strong flat spiral springs ncross the magnet and vibrates as the field changes. The electrode support is a brass rod screwed on to the nrmaturc and sliding freely in a collar which may bc central by means of three large nuts G. The clcctrocle thus moves vertically up and down,

Figs. I and 2 are sectional drawings showing constructional details and Fig. 3 gives extra detail of the armature springs. These drawings with their legends should be selfexplanatory and sufficient guide for construction of the apparatus. The electrode, brcpared as dcscribcd prcviously3~4~ 6 is screwed into ihe holder and the current supplied to the electromagnet adjustcd’by means of a “Variac” transformer to give a suitable amplitude of vibration. The amplitude is conveniently measured by focussing a microscope on a brightly illuminated #bubble ot air in the glass stem of the electrode. The conditions of vibration arc more surely reproduced with this instrumento than with other types of apl~aratns.7~8 The author wishes to acknowledge the assistance of Mr. K. Gus in constructinfi the instrument. Ru~eretrces

p. 302

ELECTROMAGNETIC

VIBRATOR

Scale drawing showing construction of tlw clectromagnctic vibrator. A, cylindrical brass housing, B, mains plug, C, soft iron armaturc. D. laminated elcctromagnot with coil of about 8000 turns No, 36 S.W.G. cnamelletl copper wire. E, electrode support of brass rod, 17, brass collar, G, control knobs for ccntring the clcctrode support, I-i, flat spiral springs of brass.

Details of the construction of an elcctromagnctic vibrator for micro-clcctrotles arc given. Tlrc d&&n embodies a ccntring guide which constrains the vibration in one tlircction only. The instrument is suitable for polsrography and ampcrometric titrations. RESUME Des d&tails dc construction tl’un vrbratcur 4lectromagn6tiquc pour microdlectrodcs sent donnbs. Ix dispositif pcmact lcs vibrations rlaas uno direction sculemcnt. Cet apparcil convicnt h tics titrations l~olarogra.phiques et anip&roni&riqucs. ZUSARIMENFASSUNG Es sind 15inzcllreitcn gcgcben ilbcr clic Konstruktion eincs clektromugnctischen Vibrators fur AMikroclektroden. Das Dispositiv erlaubt Vibrationen in nur einer liichtung. Dicscr Apparat cignet sich fllr polerographische und ampcrometrische’ Titrationen. ‘Rcferonces

p.

202

VOL.

13 (r955)