Spectrophotometric earths

SPECTROPHOTOMETRIC DETERMINATION OF RARE EARTH ELEMENTS IN MONO CRYSTALS AND STARTING LEAD MOLYBDATE RAW MATERIAL... 

Atienza et al. [657] reviewed the applications of flow injection analysis coupled to spectrophotometry in the analysis of seawater. The method is based on the differing reaction rates of the metal complexes with 1,2-diaminocycl-ohexane-N, N, N, A/Metra-acetate at 25 °C. A slight excess of EDTA is added to the sample solution, the pH is adjusted to ensure complete formation of the complexes, and a large excess of 0.3 mM to 6 mM-Pb2+ in 0.5 M sodium acetate is then added. The rate of appearance of the Pbn-EDTA complex is followed spectrophotometrically, 3 to 6 stopped-flow reactions being run in succession. Because each of the alkaline-earth-metal complexes reacts at a different rate, variations of the time-scan indicates which ions are present. 

For identification, the same two tests as for aspirin itself were prescribed then (U.S.P. XII) and now (U.S.P. XIX) however, due to the pioneering work of Higuchi, Banes, Smith and Levine in the SO s,80 a test for non-aspirin salicylates was introduced using a siliceous earth column for separation from excipients and aspirin, and spectrophotometric finish at 306 nm. A limit of 0.3% is specified. 

As mentioned in the historical synopsis (Section 5.1), Levine121 perfected the compendial partition column procedure in which aspirin in chloroform is first trapped in an immobile phase of sodium bicarbonate on a column of siliceous earth (celite) then eluted with a solution of acetic acid in chloroform and measured spectrophotometrically. This has been also used for separation in combination products.80 For the determination of salicylic acid in presence of aspirin by this method, see Section 5.61. Ion exchange columns filled with strongly or weakly basic anion exchange resin in the acetate or chloride cycle have also been used for separation of aspirin in combination products. 122 123/l2lf This has also been adapted for a student experiment.125 A Sepha-dex-G25 column has been used for the separation of aspirin from salicylic acid.126... 

Ion chromatography is a convenient method for simultaneous determination of alkali, alkaline earth and ammonium ion concentrations in solution. The identity of the analytes is set by the retention times and quantation is carried out by a detector. Conductivity is frequently used, after chemical suppression of the eluate, by which chloride counterions were exchanged by hydroxide. UVV spectrophotometric measurement of hydroxide ions at 200 nm was proposed as an alternative method to suppressed conductivity. Both methods... 

The United States Pharmacopoeia 23 [11] and Indonesian Pharmacopoeia IV [9] describe the assay of benzoic acid and salicylic acid in ointments. Two chromatographic columns (20 x 2.5 cm) are used to effect the separation. One transfers a mixture of 1 g siliceous earth and 0.5 mL diluted phosphoric acid (3 in 10) to the first column (A), then packs above this a mixture of 4 g siliceous earth and ferric chloride-urea reagent. A mixture of 4 g siliceous earth and 2mL of sodium bicarbonate solution (1 in 12) is packed into the second column (B). For analysis, column A is mounted directly above column B. The sample solution is inserted onto column A, allowed to pass into the column, and then washed with 2-40 mL of chloroform. Benzoic acid can be eluted from column B by using a 3 in 100 solution of glacial acetic acid in chloroform. The benzoic acid content then can be determined by a spectrophotometric method such as that described earlier (section 4.5). 

Among chromenes, only the spiropyrans and their heterocyclic derivatives have found a wide practical application as photochromic substances.5 6,7-Chromenediols have been proposed as analytical reagents for the spectrophotometric assay of rare earth cations.279 Chromenes with structure and activity similar to those of hashish constituents have been prepared.280 A number of chromenes, mostly with aryl substituents in positions 2,3, and 4 have been patented as biologically active substances.126,280 290... 

Alkali earths Ca, Mg Sulphonated poly (styrene- divinyl benzene) 0.12M hcio4 Ions coupled with Arsenazo 1 pH10 in post column reaction Spectrophotometric at 590nm [16,17]... 

Colour. The colour of fully-refined oils is less intense than non-refined oils. Acid and alkaline treatment, and the use of bleaching earths, would all be expected to affect the colour of the oil. The method used could be spectrophotometric or colorimetric. 

The merocyanine form of numerous BIPS compounds in solution complex with many transition and rare-earth metal ions. The complexation between 6-nitro-8-methoxyBIPS and several ions was studied by spectrophotometric, luminescent, stopped-flow, and nanosecond laser flash photolysis techniques. The absorption maximum of the dye, 580 nm, is shifted to the 480-500 nm region, and the relatively weak fluorescence shows a similar hypsochromic shift. The kinetics of the complexation involved a fast reaction between the components, followed by a slow equilibrium of the complex to its most stable isomer. The photoreactions of the complexes include formation of a short-lived triplet state (lifetime about 2 x 10 5 s,... 

Spectrophotometric method of analysis of rare earth elements. 61... 

Spectrophotometric analysis of rare earths with organic reagents. 

Spectrophotometric methods of analysis of rare earths are given in Tables 1.34 and 1.35. 

The complexes Mg(N03)2 terpy 2H20, Ca(SCN)2 2terpy H20, and Ba(SCN)2 terpyH20 have been reported, but are of unknown structure (455). ESR studies of the terpy radical anion obtained from the reaction of terpy with alkaline earth metals (Mg, Ca, Sr, or Ba) have indicated that a significant interaction occurs between the anion and the cation (79). Spectrophotometric measurements have indicated that magnesium sulfate forms a 1 1 complex with terpy in water, with K = 5.858 + 0.023 mol (185,186). 

A. J.W. O Laughlm, Chemical spectrophotometric and polarographic methods 341 37B. S.R. Taylor, Trace element analysis of rare earth elements by spark source mass spectroscopy 359... 

Use of the three-column system shown in Fig. 2 has been examined to judge its potential for rare earth separations. The purities of Sm, Eu, and Gd that were obtained from the mixed Sm-Eu-Gd sample used for this basic study were Sm20j 99.5%. EUjOj 99.99%, Gd203 99.5%. The composition of the natural Sm-Eu-Gd sample separated in this study was Nd 13%. Tb 4.5%, Sm 25%, Eu 4.8%, Gd 27.0%, and the other RE elements 25%. Gd and Eu alternatively labeled with Gd-(153, 159) and Eu-(152, 154) were used to determine the displacement curves of these two elements while the displacement curve of Sm was determined by using a spectrophotometric method. 

Until Arsenazo I and related reagents were introduced into spectrophotometric analysis, there were no sensitive reagents for such elements as Th, Zr, Hf, U, and rare earths. 

The Xylenol Orange method has been recommended for spectrophotometric determination of Sc. Numerous azo reagents have also been proposed for scandium. Some methods enable scandium to be determined in the presence of rare-earth elements. 

Poluektov, N. S., Kononenko, L. I. Spectrophotometric Methods of Determining Individuel Rare Earth Elements, Kiev, Naukova Dumka, 1968... 

Formation constants of 3d metal ions with A-m-tolyl-p-substituted benzohydroxamic acids and of rare earths with thenoylhydroxamic acid have been determined. Formation constants of proton and metal complexes of iV-phenyl-2-thenoyl- and A-p-tolyl-2-thenoyl-hydroxamic acids have also been determined. In addition, study has been made of the mixed ligand complexes involving nicotine- and isonicotino-hydroxamic acids. A method of extraction and spectrophotometric determination of vanadium with chlorophenylmethylbenzohydroxamic acid has also been published. It may be mentioned that hydroxamic acids (in particular, the A-phenylbenzohydroxamic acid) have been widely used as analytical reagents for metal ions. Solvent extraction of titanium by benzo- or salicyl-hydroxamic acid in the presence of trioctylamine in the form of coloured complexes has been reported. A-w-Tolyl-p-methoxybenzohydroxamic acid has been used for extraction and spectrophotometric determination of Mo and W from hydrochloric acid media containing thiocyanate. 

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