Determination of, III

Supporting Information Available TGA curve, atomic coordinates, important bond distances and angles, hydrogen bonding interactions, and X-ray crystallographic information in CIF format for the structure determination of III. This material is available free of charge via the Internet at http //pubs.acs.org. 

Determination of III is based upon the different rate at which the coupled reaction to the first reduction step takes place for I and III (or II). Under the same experimental conditions, the voltammogram of I shows no anodic peak, while that of III still shows the reoxidation of remaining adsorbed 5,8-dihydroneopterin. This fact is exploited analytically, and this peak (Illia) is used for the joint determination of III and II, under the assumption that they behave exactly the same way. 

Alexiev A, Rubio S, Deyanova M, Stoyanova A, Sicilia D and Perez-Bendito D 1994 Improved catalytic photometric determination of iron (III) in cetylpyridinium premicellar aggregates Anal. Chim. Acta 295 211-19... 

The question of determination of the phase of a field (classical or quantal, as of a wave function) from the modulus (absolute value) of the field along a real parameter (for which alone experimental determination is possible) is known as the phase problem [28]. (True also in crystallography.) The reciprocal relations derived in Section III represent a formal scheme for the determination of phase given the modulus, and vice versa. The physical basis of these singular integral relations was described in [147] and in several companion articles in that volume a more recent account can be found in [148]. Thus, the reciprocal relations in the time domain provide, under certain conditions of analyticity, solutions to the phase problem. For electromagnetic fields, these were derived in [120,149,150] and reviewed in [28,148]. Matter or Schrodinger waves were... 

The chief uses of chromatographic adsorption include (i) resolution of mixtures into their components (Li) purification of substances (including technical products from their contaminants) (iii) determination of the homogeneity of chemical substances (iv) comparison of substances suspected of being identical (v) concentration of materials from dilute solutions (e.g., from a natural source) (vi) quantita tive separation of one or more constituents from a complex mixture and (vii) identi-1 ig- II, 16, 3. gcajjQij and control of technical products. For further details, the student is referred to specialised works on the subject. ... 

PRELIMINARY LABORATORY OPERATIONS III.l. DETERMINATION OF MELTING POINTS... 

Hydrolysis (or saponification) of n-butyl acetate. Boil 4-5 g. of n-butyl acetate (Section 111,95) with 50 ml. of 10 per cent, sodium hydroxide solution under reflux until the odour of the ester can no longer be detected (about 1 hour). Set the condenser for downward distiUation and coUect the first 10 ml. of distillate. Saturate it with potassium carbonate, aUow to stand for 5 minutes, and withdraw all the Uquid into a small pipette or dropper pipette. AUow the lower layer of carbonate solution to run slowly into a test-tube, and place the upper layer into a small test-tube or weighing bottle. Dry the alcohol with about one quarter of its buUr of anhydrous potassium carbonate. Remove the alcohol with a dropper pipette and divide it into two parts use one portion for the determination of the b.p. by the Siwoloboff method (Section 11,12) and convert the other portion into the 3 5-dinitrobenzoate (Section III, 27) and determine the m.p. 

Mehra, M. C. Rioux, J. An Analytical Chemistry Experiment in Simultaneous Spectrophotometric Determination of Fe(III) and Cu(II) with Hexacyanoruthenate(II) Reagent, /. Chem. Educ. 1982, 59, 688-689. 

The fermentation-derived food-grade product is sold in 50, 80, and 88% concentrations the other grades are available in 50 and 88% concentrations. The food-grade product meets the Vood Chemicals Codex III and the pharmaceutical grade meets the FCC and the United States Pharmacopoeia XK specifications (7). Other lactic acid derivatives such as salts and esters are also available in weU-estabhshed product specifications. Standard analytical methods such as titration and Hquid chromatography can be used to determine lactic acid, and other gravimetric and specific tests are used to detect impurities for the product specifications. A standard titration method neutralizes the acid with sodium hydroxide and then back-titrates the acid. An older standard quantitative method for determination of lactic acid was based on oxidation by potassium permanganate to acetaldehyde, which is absorbed in sodium bisulfite and titrated iodometricaHy. 

Significant distinction in rate constants of MDASA and TPASA oxidation reactions by periodate ions at the presence of individual catalysts allow to use them for differential determination of platinum metals in complex mixtures. The range of concentration rations iridium (IV) rhodium (III) is determined where sinergetic effect of concentration of one catalyst on the rate of oxidation MDASA and TPASA by periodate ions at the presence of another is not observed. Optimal conditions of iridium (IV) and rhodium (III) determination are established at theirs simultaneous presence. Indicative oxidation reactions of MDASA and TPASA are applied to differential determination of iridium (IV) and rhodium (III) in artificial mixtures and a complex industrial sample by the method of the proportional equations. 

On the basis of these reagents a procedure of determinations of Al(III), Cr(III), Hg(II), Cd(II), Pb(II) in deferent objects was develop and showed prospect in a subsequent investigation of these compounds. 

The optimal conditions for accelerating of investigated reaction by ions Fe(III) and Ag(I) ai e the following pH 5,0 (acetic buffer), Cj. . =l,6T0 M, CpMSA=4T0 M, Cpp =2-10 M. Under these conditions, factors of sensitivity for kinetic determination of metals mentioned above were established as a slope s tangent of the calibration curves that is a plot of reaction velocity (change of optical density of ferroin s solution for 4 minutes) versus analyte s concentration. Factors of sensitivity for determination of Mn(II), Fe(III), Ag(I), Pd(II), Co(II) ai-e 5,5-10" 1,1-10" 2,5-10" 2,0-10" 8,0-10", respectively. 

The results of investigation are taken as a principle of kinetic determination of trace amounts of Fe(III) and Ag(I) in different objects. 

It was found that sorbed palladium might catalyse reaction of Mn(III) reduction by Cf not only after it s removing from coal, but AC with palladium, Pd/AC, has also his own catalytic effect. On the base of dependence between characteristics of AC, chemical state of palladium on AC surface and catalytic action of Pd/AC in indicator reaction it might establish, that catalytic action concerns only to non-reduced or partly reduced palladium ions connected with chloride ions on coal surface. The presence or absence of catalytic action of Pd/AC in above-mentioned reaction may be proposed for determination of chemical state of palladium on AC surface. Catalytic effect was also used for palladium micro-amounts determination by soi ption-catalytic method. 

Consequent potentiometric titration of osmium(IV) and laithenium (IV) in their mixtures has been canied out in broad range of concentrations from 1 mkg to 200 mkg in samples of 20 ml. It has been shown the possibility of amperemetric determination of osmium(VI) in binary and triple systems with silver(I), platinum(IV), palladium(II), gold(III), founded on formation of corresponding compounds with dimerkaptotiopiron, having a different solubility. The deteriuination of Os(VI) is possible under tenfold - hundredfold excess of above mentioned metals. 

In this work, a method based on the reduction potential of ascorbic acid was developed for the sensitive detennination of trace of this compound. In this method ascorbic acid was added on the Cr(VI) solution to reduced that to Cr(III). Cr(III) produced in solution was quantitatively separated from the remainder of Cr(VI). The conditions were optimized for efficient extraction of Cr(III). The extracted Cr(III) was finally mineralized with nitric acid and sensitively analyzed by electro-thermal atomic absorption spectrometry. The determinations were carried out on a Varian AA-220 atomic absolution equipped with a GTA-110 graphite atomizer. The results obtained by this method were compared with those obtained by the other reported methods and it was cleared that the proposed method is more precise and able to determine the trace of ascorbic acid. Table shows the results obtained from the determination of ascorbic acid in two real samples by the proposed method and the spectrometric method based on reduction of Fe(III). 

Spectrophotometric methods based on an enhancement of the blue color produced on reduction of 12-molybdophosphate (arsenate) in the presence of antimony(III) are widely used for the determination of phosphoms(V) or arsenic(V). However, nature of heteropoly blue, their spectra, mechanism of the reaction are obscure. In addition, mixed POMs were shown as very efficient analytical forms for the determination of P(V) and As(V). 

Ln(II) in LnFj Ln(II) were determined after samples dissolution in H PO in the presence of a titrated solution of NFI VO, which excess was titrated with the Fe(II) salt. It was found that dissolution of the materials based on CeF CeFj in H PO does not change the oxidation state of cerium, thus phosphate complexes of Ce(III, IV) can be used for quantitative spectrophotometric determination of cerium valence forms. The contents of Ln(II, III) in Ln S LnS may be counted from results of the determination of total sulfur (determined gravimetric ally in BaSO form) and sum of the reducers - S and Ln(II) (determined by iodometric method). 

As the result of the performed investigations was offered to make direct photometric determination of Nd microgram quantities in the presence of 500-fold and 1100-fold quantities of Mo and Pb correspondingly. The rare earth determination procedure involves sample dissolution in HCI, molybdenum reduction to Mo (V) by hydrazine and lead and Mo (V) masking by EDTA. The maximal colour development of Nd-arsenazo III complex was obtained at pH 2,7-2,8. The optimal condition of Nd determination that was established permit to estimate Nd without separation in solution after sample decomposition. Relative standard deviations at determination of 5-20 p.g of Nd from 0,1 g PbMoO are 0,1-0,03. The received data allow to use the offered procedure for solving of wide circle of analytical problems. 

A simple, rapid and seleetive eleetroehemieal method is proposed as a novel and powerful analytieal teehnique for the solid phase determination of less than 4% antimony in lead-antimony alloys without any separation and ehemieal pretreatment. The proposed method is based on the surfaee antimony oxidation of Pb/Sb alloy to Sb(III) at the thin oxide layer of PbSOyPbO that is formed by oxidation of Pb and using linear sweep voltammetrie (LSV) teehnique. Determination was earried out in eoneentrate H SO solution. The influenee of reagent eoneentration and variable parameters was studied. The method has deteetion limit of 0.056% and maximum relative standard deviation of 4.26%. This method was applied for the determination of Sb in lead/aeid battery grids satisfaetory. 

The method of extraction of Ru(III) from thiocyanate solutions by water soluble extractants in the presence of ammonium sulfate as salting out agent followed by photometric determination of it in extract has been elaborated. 

Method of Rh(III) - Ru(III) separation and isolation them from rai e and nonferrous metals based on formation of different charged complexes with varied stability has been proposed. Possibility of sepai ation of Ru(III), Rh(III), Pd(II), Pt(II) by water-soluble extractants from concentrated thiocyanate solutions has been displayed. Accelerated procedures of extraction-photometric determination of Rh(III), Ru(III) in solutions and waste products, which ai e chai acterized by high selectivity, availability, usage of non-toxic extractants have been worked out. 

The possibility of preconcentration of selenium (IV) by coprecipitation with iron (III) hydroxide and lanthanum (III) hydroxide with subsequent determination by flame atomic absorption spectroscopy has been investigated also. The effect of nature and concentration of collector and interfering ions on precision accuracy and reproducibility of analytical signal A has been studied. Application of FefOH) as copreconcentrant leads to small relative error (less than 5%). S, is 0.1-0.2 for 5-100 p.g Se in the sample. Concentration factor is 6. The effect of concentration of hydrochloric acid on precision and accuracy of AAS determination of Se has been studied. The best results were obtained with HCl (1 1). 

SPECTROFLUORIMETRIC DETERMINATION OF OXYTETRACYCLINE AND CITRATE ION USING TERNARY COMPLEX WITH EUROPIUM(III)... 

The triplet-state energy level of oxytetracycline, the excitation maximum (412 nm), lifetimes of Eu-OxTc (58 p.s) and Eu-OxTc-Cit (158 p.s), were determined. A 25-fold luminescence enhancement at 615 nm occurs upon addition of citrate within a short 5-min incubation time at neutral pH. It s accompanied by a threefold increase of the luminescence decay time. The optimal conditions for determination of OxTc are equal concentrations of Eu(III) and citrate (C = T lO mol-E ), pH 7.2. Eor determination of citrate, the optimal conditions concentrations of Eu(HI) and OxTc are 1 0,5 (Cg = MO Huol-E-i, = 5-10-HuohE-i) at pH 7.2. 

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