Pulse polarography

Polarography

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Pulse polarography^[1] It is a polarographic method. At a certain time in the late growth period of each mercury drop on the dropping mercury electrode, a square wave voltage is superimposed on the linearly changing DC voltage, and the electrolytic current is recorded in the late single cycle period of the square wave voltage. It is one of the most sensitive polarographic methods. The concentration of the supporting electrolyte used can be very thin. If a three electrode device is used, it can also be measured in the solution without supporting electrolyte.

Chinese name: Pulse polarography
Methods: A new method of polarographic analysis

Mass of front discharge: 50 000∶1
Advantages: High sensitivity

catalog

Pulse polarography

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Polarography is one of the most sensitive polarographic methods. It is several times more sensitive than square wave polarography, and the concentration of supporting electrolyte used is also lower than square wave polarography (as low as 0.02mol/dm three ）。 There are two kinds of pulse polarography: conventional pulse polarography and differential pulse polarography. There are differences in the way of applying voltage between the two, and the polarographic patterns are also different. The way in which the differential pulse pole increases the voltage is similar to the square wave polarography, and the polarographic wave obtained is also similar. The difference between differential pulse polarography and square wave polarography is that at a certain time of a mercury drop, only one square wave voltage is applied, Δ E is 2-100 millivolts, and the square wave voltage lasts for a relatively long time, some as long as 40-80 milliseconds. Only one reduction current is measured on a mercury drop; Square wave polarography adds many square waves to a mercury drop, and each square wave lasts for a short time. The current is measured twice in a cycle, including both oxidation current and reduction current. The capillary noise current is fully attenuated by pulse polarography and voltage, thus improving the sensitivity. Pulse polarography can detect 10 -9 G/ml (1 ppb) of cadmium. Good resolution. The difference between the two peaks is 25 millivolts. The front polarographic current has little effect on the rear current.

classification

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According to the form of applying pulse current and the way of current measurement,

1. Conventional pulse polarography

2. Differential pulse polarography

Conventional pulse polarography

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The conventional pulse polarography is to use time to control synchronization on an initial potential Ui without electrode reaction. At the later stage of mercury droplet survival, a rectangular pulse voltage with gradually increasing amplitude is sequentially superimposed. A current measurement is carried out 20 ms before each pulse disappears to obtain i-E polarography.

Differential pulse polarography

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Differential pulse polarography is to apply a slowly changing DC voltage to the mercury drop electrode, and then use Time controller Control, synchronously superimpose a rectangular pulse voltage with equal amplitude at the later stage of each mercury drop's survival, measure the current difference 20 ms before the pulse voltage is added and 20 ms before the pulse voltage disappears, and obtain the polarogram.