Cerium Detection

To verify that the quantity of leached salt was dependent on the area exposed to the pure water, a test was conducted in which only half the surface area was exposed. The results presented in Fig. 10.11 show that the amount of cerium is limited by the sample area exposed to the solution. With an assumed density of the coating material of 1.5 g/cm, the amount of cerium provided by the coating material could be calculated. The results of this calculation have been related to the maximum concentration of cerium detected by ICP in Table 10.3. The fraction of detected material was in the vicinity of about 50% in all cases. No dominant influence of agitation could be concluded from these data. 

Table 10.3 Fraction of cerium detected reiative to the amount of cerium provided by the coating material...

B. Self-indicating reagents. This is well illustrated by potassium permanganate, one drop of which will impart a visible pink coloration to several hundred millilitres of solution, even in the presence of slightly coloured ions, such as iron(III). The colours of cerium(IV) sulphate and of iodine solutions have also been employed in the detection of end points, but the colour change is not so marked as for potassium permanganate here, however, sensitive internal... 

M sulphuric acid at 25 °C is 1.43 0.05 volts. It can be used only in acid solution, best in 0.5M or higher concentrations as the solution is neutralised, cerium(IV) hydroxide [hydrated cerium(IV) oxide] or basic salts precipitate. The solution has an intense yellow colour, and in hot solutions which are not too dilute the end point may be detected without an indicator this procedure, however, necessitates the application of a blank correction, and it is therefore preferable to add a suitable indicator. 

Procedure (copper in crystallised copper sulphate). Weigh out accurately about 3.1 g of copper sulphate crystals, dissolve in water, and make up to 250 mL in a graduated flask. Shake well. Pipette 50 mL of this solution into a small beaker, add an equal volume of ca AM hydrochloric acid. Pass this solution through a silver reductor at the rate of 25 mL min i, and collect the filtrate in a 500 mL conical flask charged with 20 mL 0.5M iron(III) ammonium sulphate solution (prepared by dissolving the appropriate quantity of the analytical grade iron(III) salt in 0.5M sulphuric acid). Wash the reductor column with six 25 mL portions of 2M hydrochloric acid. Add 1 drop of ferroin indicator or 0.5 mL N-phenylanthranilic acid, and titrate with 0.1 M cerium(IV) sulphate solution. The end point is sharp, and the colour imparted by the Cu2+ ions does not interfere with the detection of the equivalence point. 

Bachmartn, K., Boden, J., and Haumann, I., Indirect fluorimetric detection of alkali and alkaline earth metal ions in capillary zone electrophoresis with cerium (III) as carrier electrolyte, /. Chromatogr., 626, 259, 1992. 

Methods for determination of thiol drugs (i.e., captopril [21-25], penicillamine [26-28], hydrochlorothiazide [24, 25, 29, 30], and tiopronin [31, 32]) have been developed. These methods are based on CL from a cerium (IV) oxidation system sensitized by adequate fluorophores such as quinine and rhodamine B. By using HPLC-coupled CL-flow-injection analysis method, tiopronin and its metabolite 2-mercaptopropionic acid in human urine were sensitively determined with the detection limits of 0.8 and 1 pM, respectively [32],... 

Similar to the discovery of many other elements, cerium was detected simultaneously by several different scientists. In 1803 the Swedish chemist Jons Jakob Berzehus (1770—1848)... 

Cerium may be analyzed in solution by AA or ICP techniques. The metal or its compounds are digested in nitric acid, diluted appropriately prior to analysis. Also, it may be measured by ICP/MS at a still lower detection level (low ppt). The metal may be analyzed nondestructively by x-ray techniques. 

Cerium in Plants and Animals. Professor Alfonso Cossa, finding the rare earths of the ceria series to be present in many apatites, and realizing the close association in nature between these earths and calcium and phosphorus, tested for them and detected their presence in bone (66). He also detected them in the ash of barley, beech wood, and tobacco. With the aid of C. Schiapparelli and G. Peroni of the University of Turin, he demonstrated their presence in human urine (66, 67, 68). 

Secondly, we studied the oxidation of oxalate by cerium(IV) in sulfuric acid. This reaction is analagous to the classical manganese (111) oxalate reaction studied by H. Taube and also by F. Duke. Indeed, it proceeds through an intermediate containing one or more oxalates per cerium. This decomposes to give cerium(III) and other products. The point I want to raise is that we have been able to detect free radicals in this reaction, using EPR experiments and a flow system. So far, it has not been possible to say whether the radical is the oxalate or CO2 radical, both of which have been proposed in other studies. 

In separate experiments it was observed that the addition of lanthanum(III) or alumi-num(III) at similar and somewhat higher concentration levels to the cerium(III) had no detectable effect on the reaction rate. 

Amino acids have been detected fluorimetrically after ion-exchange chromatography by monitoring the fluorescent derivatives produced on treatment with o-phthalaldehyde and 2-mercaptoethanol [57]. An Aminco-Bowman fluoromicrophotometer was used for the detection. An advantage of this technique is that only 2 min were required at room temperature for formation of the products, thus avoiding the lengthy reaction coils of the ninhydrin and cerium(IV) systems. 

The cerium(IV) oxidation reaction of many organic acids provides a sensitive and selective method for HPLC analysis of these compounds [116,117]. The oxidation of specific classes of organic compounds with cerium(lV), and the effects on the reaction of temperature, acidity, anion and catalyst, have been studied extensively [118-120]. The reaction produces cerium(HI) which is fluorescent and can be measured spectrofluori-metrically. The method has been applied successfully to the post-column reaction and detection of nmole amounts of organic acids by HPLC. 

Fig.4.56. Comparison of UV detection with the cerium oxidation system for some organic acids. (From ref. 117 with permission of Marcel Dekker, New York.)...

Fig.4.71. Separation of some chlorophenols by cerium(IV) oxidation and fluorimetric detection. Column Corasil-C, 0.61 m X 4.83 mm I.D. Gradient elution from water to 36% acetonitrile-64% water. Peaks 1 = phenol (18.4 ppb) 2 = o-chlorophenol (22.S ppb) 3 = p-chlorophenol (20.2 ppb) 4 2,4-dichlorophenol (52.2 ppb) 5 = 2,4,6-trichlorophenol (42.6 ppb) S = solvent.

The HPLC analysis of phenols and related pollutants of the environment may be made by use of the cerium(IV) oxidation technique mentioned earlier (Section 4.2.1.6.2) [195]. The limits of detection of many phenols are ca. 0.4 ppb (parts per 109) in environmental samples. The detector shows good linearity in the region 10-230 ppb of phenol. 

RELATIVE RESPONSE OF PHENOLS WITH CERIUM(IV) SULFATE-FLUORIMETRIC DETECTION [195]... 

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