Differential pulse polarographic peak potentials

Differential Pulse Polarographic Peak Potentials at the Dropping Mercury Electrode (18,19)... 

Methods A - UV absorbance at x nm E - potentiometry with a glass electrode Ei/2 - d.c. polarographic half-wave potentials of wave n Ep - differential pulse polarographic peak potential of wave 1 ... 

Betso and McLean [11] have described a differential pulse polarographic method for the determination of acrylamide and acrylic acid in polyacrylamide. A measurement of the acrylamide electrochemical reduction peak current is used to quantify the acrylamide concentration. The differential pulse polarographic technique also yields a well-defined acrylamide reduction peak at 2.0 V versus SCA (reduction potential), suitable for qualitatively detecting the presence of acrylamide. The procedure involves extraction of the acrylamide monomer from the polyacrylamide, treatment of the extracted solution on mixed resin to remove interfering cationic and anionic species, and polarographic reduction in an 80/20 v/v) methanol/water solvent with tetra-n-butylammonium hydroxide as the supporting electrolyte. The detection limit of acrylamide monomer by this technique is less than 1 ppm. 

Eletrochemical detection has been used for the detection of synthetic dyes. Fogg et al. (226) described a method for the qualitative and quantitative determination of several synthetic dyes using polarographic detection. The system was a stationary mercury drop electrode operated in the differential-pulse mode. Ashkenazi et al. (131) used fast-scan square-wave voltammetry for the polarographic detection of five synthetic dyes. The voltametric mode was observed to be much faster than the differential-pulse method. Another advantage is that the experimental measurement produces, in addition to the peak current, the redox potential of the dye, which can serve to identify the analyte further. 

With the differential pulse polarography [245], the antibiotics can be determined at low concentration, if necessary, at the ppm or even sub-ppm level. Tetracycline hydrochloride is determined in aqueous acetate buffer pH 4 (detection limit 0.1 ppm), but for the analysis of chlortetracycline hydrochloride, oxytetracycline hydrochloride and free tetracycline, a non-aqueous medium must be used. Streptomycin sulphate is analysed in alkaline solution, trace quantities of zinc being masked by Na2EDTA, and the detection limit is 1 ppm. A determination in blood serum or urine is also possible but the peak potentials are shifted here to more negative values. The polarographic determination is preceded by ultrafiltration. Penicillin G potassium and ampicillin must be first functionalised by nitrosation. The authors also recommend an analysis of mixtures which is however demonstrated only with chloramphenicol and tetracycline, at 2.4 and 4.2 ppm, respectively. 

Figure 23-19 Voltammogram for a differential pulse polarography experiment. Here At = ig, - is, (see Figure 23-18). The peak potential, Epeak is closely related to the polarographic half-wave potential.

Polarographic reduction studied both by d.c. and differential pulse polarography and linear sweep voltammetry are discussed in detail elsewhere , in particular with respect to pH-dependence of limiting currents and half-wave and peak potentials. The results can be summarized as follows. 

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