Barker square-wave polarography

Die Empfindlichkeit der Square-wave-Polarographie ist nach Anga-ben von Barker (18) fiir reversible Vorgange etwa 4 10-8 m, fur... 

G. C. Barker, Square-Wave and Pulse Polarography, in Progr. Polarogr. 2 (1962) 411. 

It is possible to exploit the difference in the time-dependencies of y(pro-portionalto /1 /6) and ic (proportional to f 1/3) to separate the two (J. N. Butler M. L. Meehan, J. Phys. Chem. 69 (1965) 4051), and thereby to push back the lower limit somewhat. However, instrumental refinements such as square wave polarography (G. C. Barker I. L. fenkins, Analyst 77 (1952) 685) and, pulse polarography (G. C. Barker A.W. Gardner, Z.Anal. Chem. 173 (1960) 79) are much more efficient in doing so, and are therefore the methods of choice for concentrations between 10-5 and 10 7 M. 

G. C. BARKER (1915-2000) and I. L. JENKINS introduce square-wave polarography (1952) Analyst 77 685... 

The first voltammetric method was polarography. Electrolysis at a dropping mercury electrode was first described by Heyrovsky in 1922, and the first po-larograph constructed by Heyrovsky and Shikita in 1925. Heyrovsky was awarded the Nobel Prize in 1959. Further developments of the method are linked with the names of Matheson and Nichols (oscillo-polarography), Heyrovsky (derivative polarography), and Barker (square wave and pulse polarography). 

G. Barker [1958] Square-Wave Polarography. III. Single Drop Polarography, Anal. Chim. Acta 18,... 

G. Barker, R. Faircloth, and A. Gardner [1958] Use of Faradaic Rectification for the Study of Rapid Electrode Processes, IV. Theoretical Aspects of Square Wave Polarography, Nature 181, 247-248. 

Reverse pulse methods Application of pulse methods Alternating current and square-wave techniques Principles of alternating current polarography Basic relationships for the AC processes Improved ACP techniques Applications of AC polarography Tensammetry and detection of surface-active substances Square-wave polarography (Barker s method)... 

Barker GC, Jenkins IL (1952) Square-wave polarography. Analyst 77 685-6%... 

The method of potentiostatic pulses is sometimes combined with the DME (called pulse polarography). hi this case the pulse frequency should match the drop frequency, where each pulse is used at a definite time in the drop life, hi Barker s method, large pulse amphrndes are used. Other versions of the potentiostatic pulse technique are square-wave and staircase voltammetry here smaU-amphtude pulses are used. 

Since its introduction, the technique has been associated with important applications in many branches of chemistry a principal example is in analytical chemistry, including that of organic substances. The method provides a simple technique for the detection and estimation of electroreducible ions and compounds present in solution at very small concentrations. The sensitivity of conventional polarography allows the measurement of concentrations of various ions to approximately 10 mol liter. Several procedures have been developed to extend the analytical range, notably the compensation method and the square wave polarographic technique introduced by Barker and Jenkins. " ... 

Originally (in the technique introduced by Barker [89] in 1952) the square-wave potential was applied to the DME with constant modulation frequency (225 Hz) and slow scan rate of the voltage ramp (about 2 mV s" ). The current response was recorded at the end of each drop life in a short period of time ( 2 ms). This method could be treated by the steady-state theory in an analogous way to the derivative and differential pulse polarography. It has attained considerable attention for reversible electrode processes due to its applicability especially in trace analysis [90]. 

Because Barker in this period confined his work to studies at the dme, he focused on and attempted to solve problems peculiar to that electrode. One of those problems is capillary noise or capillary response . These terms refer to the current required to charge the interface between mercury and the film of solution which penetrates some distance into the capillary. Charge must be supplied when the potential is changed, but also the interface itself is unstable, so that the charging current varies from drop to drop. In order to understand the reasoning which led Barker to normal and differential pulse polarography, it is useful to describe in more detail the operation of his square-wave instrument. 

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