The recently developed instruments include the cathode-ray polarograph, the square-wave polarograph and the Cambridge Univector polarograph unit. These instruments have been tested to obtain information on their relative merits and details of the results obtained are described. The tests included the following aspects : (i) sensitivity for reversible and irreversible reductions a t the dropping-mercury electrode, (ii) resolution for elements with half-wave potential values very close together, (iii) effects of the reduction of a major constituent a t a more positive potenti.al on the determination of a minor constituent, and (iv) speed of applicatjon, reproducibility and usefulness in analytical chemistry. DESPITE statements about the relative merits of high-sensitivity derivative polarographs,l y 2 no comparative study of their behaviour has been made.L4 series of solutions has, therefore, been examined by using three polarographs that are more sensitive than those hitherto available commercially. These instruments are-(a) the Univector unit, manufactured by Cambridge Instrument Co. Ltd., (6) the Mervyn -Harwell square-wave pclarograph, manufactured by Mervyn Instruments, and (c) the single-sweep cathode-ray polarograph, manufactured by Southern InstrumentsLtd.These will be referred to as CU, SWP and CKP, respectively, in this paper.
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