Cerium , fluorescence

Several instmmental methods are available for quantitative estimation of from moderate to trace amounts of cerium in other materials. X-ray fluorescence is widely available, versatile, and suitable for deterrninations of Ce, and any other Ln, at percent levels and lower in minerals and purer materials. The uv-excited visible luminescence of cerium is characteristic and can be used to estimate Ce content, at ppm levels, in a nonluminescing host. X-ray excited optical luminescence (15), a technique especially appropriate for Ln elements including cerium, rehes on emissions in the visible, and also measures ppm values. Atomic emission spectrometry is appHcable to most lanthanides, including Ce (16). The precise lines used for quantitative measurement must be chosen with care, but once set-up the technique is suitable for routine analyses. 

The ESR spectrum of the pyridazine radical anion, generated by the action of sodium or potassium, has been reported, and oxidation of 6-hydroxypyridazin-3(2//)-one with cerium(IV) sulfate in sulfuric acid results in an intense ESR spectrum (79TL2821). The self-diffusion coefficient and activation energy, the half-wave potential (-2.16 eV) magnetic susceptibility and room temperature fluorescence in-solution (Amax = 23 800cm life time 2.6 X 10 s) are reported. 

Fluorescent lamp coatings, ethylene oxide polymers in, 10 688-689 Fluorescent lamps, mercury in, 16 41 Fluorescent lighting phosphors, cerium application, 5 688-689 Fluorescent photo-induced electron transfer (PET) sensor, 24 54 Fluorescent pigments, for inks, 14 318 Fluorescent probes, 11 150 16 388 modified-base oligonucleotides as, 17 633-634... 

Cerium magnesium aluminate is a highly efficient green phosphor (lmax. = 541 nm), which is used in trichromatic fluorescent lamps. The high quantum yield of 65 % is effected by the energy transfer from the sensitizer, Ce3 +, to the activator, Tb3 +. ... 

Natural teeth exhibit blue-white fluorescence in the long-wavelength UV [5.435]-[5.437]. Luminescent pigments are used to imitate this phenomena in artificial teeth. They are added to the ceramic paste at a concentration of 0.3-0.5 wt%. Yttrium silicates doped with cerium, terbium, and manganese give the best results [5.438]. The excitation maximum of these phosphors is in the range 325-370 nm. The fluorescence color of the teeth can be varied by changing the concentration of activators. 

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 oxidation detector for the fluorimetric analysis of carbohydrates in effluents from liquid chromatography columns provides a sensitive method of analysis in blood and urine [110]. The principle involves the reduction of cerium(IV) to cerium(III) by oxidizable compounds such as organic acids and many carbohydrates. The fluorescence... 

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. 

The COMOSS has also been fabricated on a PDMS chip for CEC separation of FITC-labeled peptides (Figure 6.25). However, in the CEC separation of a mixture of rhodamine and fluorescein, a broad rhodamine peak was obtained, but fluorescein did not have this problem. This was possibly because the neutral rhodamine had diffused into the PDMS substrate, as illustrated in the fluorescent image in Figure 6.26 [360]. In another report, CEC separation of a peptide mixture was performed on a PDMS chip after cerium(IV)-catalyzed polymerization of the stationary phase within the channels [646]. 

Lee and Field [318] have discussed a technique of post-column fluorescence detection of nitrite, nitrate, thiosulphate and iodide anions by high performance liquid chromatography. These anions react with cerium(IV) to produce fluorescent species in a post-column packed bed reactor. 

A kinetic-fluorimetric method for the determination of choline and acetylcholine by oxidation with cerium (IV) was reported by Lunar et al. [47]. To sample solutions containing 0.017-1.OmM choline and/or acetylcholine were successively added 6M H2S04 (5mL) and 7.1 mM Ce(IV) solution (0.35 mL), the mixture diluted to 10 mL with water, and the solution heated to 80° C for 2 min. A portion of the solution was transferred to a cell maintained at 20 0.1°C, and after 1 min the Ce(III) fluorescence intensity was measured at 360 nm (excitation at 260 nm) as a function of time. 

Isomerism.—In an interesting series of memoirs, Levj 3 has shown that certain hydrated platinocyanides, notably those of barium and calcium, exist in two modifications, having the same chemical composition and crystalline form, but exhibiting a remarkable difference in their optical characters, differing in colour and in the intensity of their fluorescence. The barium and calcium salts show this most distinctly, and the cerium salt only to a small extent. Other platinocyanides do not show this at all. 

Cerium Platinocyanide,6 Cej[Pt(CN)4]3,18H20, yields fluorescent crystals in two varieties, namely, yellow a-crystals and greenish yellow (3-crystals, analogous to the two calcium isomerides.5... 

Figure 5 shows the effect of the dopant cerium on the spectral power distribution (SPD) of a typical cool-white fluorescent lamp. This dopant has been useful in reducing UV emissions from the emissions of household quartz, halogen, and other lamps, particularly the desktop variety. 

Figure 5 Comparison of 32 watt, T8 4100 K, SP 41, fluorescent lamps of the same type doped with various amounts or cerium. A = Oppb, B = 250 ppb, and C = 500 ppb Source From Ref. 8.

Cerium is an essential component in several of the new generation of phosphors in tricolor lamps that have made possible more efficient and more compact fluorescent lighting (31). 

While the type of available eluent depends upon the detection method being applied in anion exchange chromatography, a corresponding classification is not necessary in cation exchange chromatography. For the separation of alkali metals, ammonium, and small aliphatic amines, mineral acids such as hydrochloric or nitric acid are typically used as eluents, independent of whether the subsequent conductivity detection is performed with or without chemical suppression. The concentration range lies between 0.002 mol/L and 0.04 mol/L. Bachmann et al. [141] employed cerium(III) nitrate in very low concentrations as the eluent for the indirect fluorescence detection of alkali metals. 

A further derivatization technique for forming fluorophors has been described by Lee and Fields [37]. They reacted oxidizable inorganic anions such as nitrite, thiosulfate, and iodide with cerium(IV), thereby forming fluorescing cerium(III) according to Eqs. (190), (191), and (192)... 

Cerium(III) may be detected at an excitation wavelength of 247 nm and an emission wavelength of 350 nm. To stabilize the cerium(IV) reagent, it is prepared in sulfuric acid of the concentration c = 0.5 mol/L. The addition of sodium bismutate serves to oxidize possible cerium(III) traces in the reagent to keep the residual fluorescence as low as possible. 

For the reaction of the column effluent with the cerium(IV) reagent, instead of a simple injection loop, Fields et al. used a solid-bed reactor with a volume of 2.8 mL. This relatively large volume is necessary to allow the required reaction time of at least two minutes for the oxidation of nitrite ions with cerium(IV). While the reaction of nitrite ions with cerium(IV) is comparatively slow, the maximum fluorescence yield with iodide is obtained in less than ten seconds. On the other hand, the reaction kinetics with thiosulfate appears to be completely different. As seen in the respective diagram in Fig. 6-21, this reaction is characterized by a fast rise of the fluorescence yield within a short time, which increases as the reaction product from Eq. (191), tetrathionate, also reacts slowly with cerium(IV). 

Fig. 6-21. Time dependence of the fluorescence yield for the reaction of nitrite, thiosulfate, and iodide with cerium(lV) (taken from [37]).

Fig. 6-22. Analysis of nitrite, thiosulfate, and iodide upon application of fluorescence detection after derivatization with cerium(IV). — Separator column Vydac 302 IC eluent 0.001 mol/L KHP + 0.01 mol/L Na2S04 pH 5.5 with Na2B407 flow rate 1 mL/min detection fluorescence after reaction with cerium(IV) injection volume 100 pL solute concentrations 0.5 ppm nitrite, 1.1 ppm thiosulfate, and 1.5 ppm iodide (taken from [37]).

Fig. 6-23. Analysis of monovalent cations with indirect fluorescence detection. — Separator column 100 mm x 3.2 mm I.D. ION-210 eluent 10-5 mol/L cerium(III) sulfate flow rate 1 mL/min detection indirect fluorescence injection volume 20 gL solute concentrations 0.16 ppm sodium (1), 0.15 ppm ammonium (2), 0.21 ppm potassium (3), 0.71 ppm rubidium (4), and 1.2 ppm cesium (5) (taken from [41]).

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