Cells, concentration amalgam with transference

This chapter is concerned with the determination of activity coefficients with the aid of various types of concentration cells, and with the comparison of such activity coefficients with the predictions of the Debye-Hiickel theory, developed in the previous chapter. The types of cells discussed are (a) cells without transference, including those containing amalgam electrodes, (b) cells with transference, and (c) cells without transference containing mixtures of electrolytes. 

Hg CV-AFS state with stannous chloride or sodium tetrahydroborate the vapor generated is collected on an amalgamation surface/ Au or Pt. The concentrated mercury is revolatilized by rapid heating of the amalgamation surface and transferred to the absorption cell for measurement at 253.7 nm Hg is chemically reduced to the elemental and waste waters Applicable to 0.001-10 pg L-1 in tap, rain, 111... 

Amalgam Cells.—If the electrolyte in the concentration cell without transference is a salt of an alkali metal, e.g., potassium chloride, it is necessary to set up some form of reversible alkali metal electrode. This is achieved by dissolving the metal in mercury, thus forming a dilute alkali metal amalgam which is attacked much less vigorously by water than is the metal in the pure state." The amalgam nevertheless reactia with water to some extent, and also with traces of oxygen that may be... 

The use of a sodium amalgam electrode [Na(Hg)/NaC104(s)] in DMF has been reported [205] and a similar lithium amalgam electrode has been employed in DMSO [207]. The potential of the cell, Li(Hg)/Li Cr (DMSO), has been measured for LiCl concentrations from 0.01 to 1.0 M and the Nernst relation was verified within 1 mV the Li(Hg) electrode obeys the Tafel equation with the transfer coefficient a = 0.5 over... 

As with hydride generation, the evolved mercury vapor can either be transferred directly to the optical cell for measurement or trapped for later release. As the mercury is normally liberated slowly from solution over a period of 1-2 min, low intensity signals are generated consequently, vapor trapping is frequently used to improve concentration detection limits for solution analysis. Enhanced separation and concentration of mercury is usually achieved by amalgamation on a noble metal trap, from which it is subsequently thermally desorbed (at 500-700°C). 

---