Spectrophotometric determination of iodate,iodide and acids by flow injection analysis

The production of iodine by reaction of iodate and iodide in acidic solution is used for the spectrophotometric determination of 1–6 × 10^?5 M iodate, 2–8 × 10^?3 M iodide, and ca. 10^?3 M acids. The sample is injected into a carrier stream containing the other two ions. The injection rate is ca. 100 h^?1.     

Structure of iodide ion arrays in iodinated nylon 6 and the chain orientation induced by iodine in nylon 6 films

Two species of iodide ions (I₃^? and I₅^?) are found in iodine—nylon 6 complexes. Orientation of I₅^? arrays (most likely I₂/I₃^? complex) along the polymer chain and I₃^? ions perpendicular to the chain axis in uniaxially drawn films and in films with planar orientation suggests that there is and intrinsic relation between the direction of iodide ion arrays and nylon 6 chains. When an unoriented film of nylon 6 in the amorphous or the α crystalline form is treated with an aqueous solution of iodine—potassium iodide, the I₃^? species in the resulting iodine—nylon complex lie in planes parallel to the surface of the film, and I₂/I₃^? units are oriented normal to the surface of the film. The γ form obtained by desorbing the iodine from this complex shows considerable uniaxial rientation with the nylon chains oriented perpendicular to the plane of the film; this orientation is maintained during the γ to α transition. It is proposed that the iodine-induced orientation of the nylon 6 chains is due to the nucleating effects of the iodide ion species as the iodine diffuses unidirectionally into the film.     

Exchange and decomposition reactions of isobutyl iodide with iodine

In the presence of elementary iodine, isobutyl iodide (2-methyl-1-iodopropane) undergoes isotopic exchange and also decomposes with production of additional iodine. Both reactions are approximately first order in isobutyl iodide and half order in iodine molecules. In degassed hexachlorobutadiene at 160°, the rate constants for exchange and decomposition are 7.5 × 10^?6 and 11.4 × 10^?6 (liter/mole)^1/2sec^?1, respectively. The decomposition is probably initiated by iodine atom abstraction of a β hydrogen atom, but comparison with rates for related compounds indicates that this hydrogen abstraction does not contribute significantly to the mechanism of exchange.     

Spectrophotometric and spectrofluorimetric determination of iodide by extraction of ICl−2 with rhodamine B

Iodide is determined after oxidation with nitrous acid in 5 M hydrochloric acid to ICl^?₂. The ion-pair formed with rhodamine B is extracted into toluene and measured spectrophotometrically (0.5–5 × 10^?5 M) or spectrofluorimetrically (1–10 × 10^?6 M). The relative standard deviations were 1.8% for the determination of 5 × 10^?6 M iodide (n = 5) by spectrofluorimetry and 2.3% (n = 50) for 1 × 10^?5 M iodide by spectrophotometry. Periodate, iodate and iodine responded exactly as iodide.     

Colorimetric Determination of Seleniumin Various Environmental Samples

A new reagent system using rhodamine‐B dye for the determination of selenium is described. The method is based on the reaction of selenium with acidified potassium iodide to liberate iodine. The liberated iodine bleaches the pink colour rhodamine‐B, which is measured at 555 nm. Beer's law is obeyed over the concentration range of 1–10 μg of selenium final solution volume of 25 mL (0.04–0.4 ppm) and the apparent molar absorptivity and Sandell's sensitivity was found to be 1.96× 10⁵ l mol^?1 cm^?1 and 0.0004 μg cm^?2, respectively. The method is simple, sensitive, and selective and is satisfactorily applied to micro‐level determination of selenium in various environmental and cosmetic samples.     

Electrochemistry of iodine and iodide in chloroaluminate melts

The electrochemical behavior of iodine and iodide has been studied in AlCl₃+NaCl mixtures with compositions ranging from NaCl saturated melts to AlCl₃+NaCl (63+37 mol %) at platinum and tungsten electrodes. Iodide is oxidized in two steps to iodine and I(I); a reduction wave to iodide and an oxidation wave to I(I) are obtained in iodine solutions. The equilibrium constant for the reaction, I^?+I(I)=I₂, is 6×10⁸ l mol^?1 in molten chloroaluminate melts at 175°C.     

Polyiodide composition in poly(vinyl acetate)-iodine-iodide complex

Polyiodide formed by complexation of poly(vinyl acetate) (PVAc) with iodine in the presence of iodide has been investigated by chemical analysis and resonance Raman spectrophotometry. When PVAc films were immersed in iodide-iodine aqueous solutions which had different ratios of iodide to iodine concentration [I^?]/[I₂], the complex films exhibited tremendous variations of swelling degree, despite the relatively small change in the amount of bound iodine. From a quantitative chemical analysis, the composition of polyiodide bound to PVAc was found to be 1.01 ± 0.035 in the molar ratio of iodide to iodine irrespective of the composition of the iodide-iodine aqueous solution ([I^?]/[I₂] = 2–500). The polyiodide formed in PVAc-iodine-iodide complex was therefore inferred to be (I₃^?)_n. Resonance Raman spectra obtained on PVAc-iodine-iodide complexes were also identical to those of the benzamide-iodine complex, in which the polyiodide consists of (I₃^?)_n, consistent with the result from chemical analysis.     

Microwave-assisted alkaline digestion combined with microwave-assisted distillation for the determination of iodide and total iodine in edible seaweed by catalytic spectrophotometry

Microwave energy has been novelty applied to speed up a tetramethylammonium hydroxide (TMAH) alkaline digestion of seaweed samples and to assist distillation of iodine from seaweed alkaline digests. Iodide in the alkaline digests from seaweed and distilled iodine, reduced back to iodine in a hydroxylamine hydrochloride solution, was determined by a catalytic spectrophotometric method based on the catalytic effect of iodide on the oxidation of As(III) by Ce(IV) in H₂SO₄/HCl medium (Sandell-Kolthoff reaction). The determination of iodide was directly performed in the alkaline digests, while total iodine was assessed by analyzing the hydroxylamine hydrochloride solution after the distillation process. Microwave-assisted alkaline digestion was performed using 7.5 mL of TMAH and irradiating samples at 670 W for two 5.5 min steps. Microwave-assisted distillation was carried out using 4.0 mL of the alkaline digest and 3 mL of a 2.2 M hydrochloric acid and 0.05% (m/v) sodium nitrite solution, with a microwave power at 670 W for two 90 s steps. The distillate (iodine vapor) was bubbled in 10 mL of a 500 μg mL⁻¹ hydroxylamine hydrochloride solution (accepting solution). The linear calibration ranges were 0.30-20.0 and 0.40-20.0 μg L⁻¹ for iodide determination and total iodine determination, respectively. The limit of detection was 9.2 μg g⁻¹ for iodide and 28.5 μg g⁻¹ for total iodine. Repeatability of the overall procedures, expressed as R.S.D. for 11 determinations, was 2.6% for 196.3 μg g⁻¹ of iodide measured after microwave-assisted alkaline digestion, and 5.8% for 954.3 μg g⁻¹ of total iodine by microwave-assisted alkaline digestion followed by microwave-assisted distillation. Finally, accuracy of the methods was assessed by analyzing the NIST-09 (Sargasso) certified reference material and the methods were applied to the determination of iodide and total iodine in different Atlantic edible seaweed samples with satisfactory results.     

The Photochemistry of Ch3I in Various Matrices at Low Temperature

The photodissociation of methyl iodide in various matrices at low temperature was studied. The observed Raman spectra excited by 514.5 nm laser radiation showed that there were two different photolytically produced iodine species isolated in the matrices after illumination by a medium pressure mercury lamp. One species which was dominant at lower iodine concentrations and exhibited a progression with an ωe of 201 cm^?1, belonged to the matrix isolated iodine monomer (I₂). The other species, which was dominant at higher iodine concentrations with an ω_e of approximately 180 cm^?1, belonged to the iodine aggregate ((I₂)_n). Five progressions of resonance Raman or resonance fluorescence of these two species were also observed in the other matrices. The iodine aggregate in the methyl iodide matrix at 77 K was formed in a crystalline structure, while the photolytically generated iodine aggregate from CH₃I/Ar (2/3) matrix at 10 K, after illumination with a mercury lamp, was in amorphous form. The rearrangement of photolytically produced iodine aggregate in methyl iodide matrix was observed as a function of the duration of illumination. Local heating effects of the laser radiation might induce the iodine monomer to aggregate in matrices. The photodissociation mechanism of methyl iodide in matrices is also proposed.     

Titrimetric determination of microgram amounts of lead by thiocyanate amplification after precipitation as lead hexathiocyanatochromate(III)

Lead (25–200 μg) is precipitated as Pb₃[Cr(SCN)₆]₂. The filtered precipitate is treated with 10% carbonate solution, and the thiocyanate dissolved is oxidized by iodine to sulphate at pH 8.2. After acidification, the excess of iodine is extracted into chloroform, and the iodide ion retained in the aqueous solution is amplified by bromine oxidation and subsequent treatment with more iodide. The method provides 152 iodine atoms for each original lead ion. Only Bi³⁺ and Cu²⁺ interfere seriously.     

Iodometric determination of milligram and microgram amounts of levocetirizine in pharmaceuticals

Four simple, selective and sensitive methods are described for the determination of levocetirizine dihydrochloride (LCT) in bulk drug and in tablets. The methods exploit the well-known analytical reaction between iodide and iodate in the presence of acid solution. Iodide present is oxidized by iodate in an amount equivalent to the HCl present in LCT to iodine and the liberated iodine is determined by four different procedures which inturn quantify LCT at varying detection range and sensitiveness. Two direct titrimetric procedures involve titration of iodine by thiosulphate either towards starch end point (method A) or potentiometrically (method B). Both the methods have a reaction stiochiometry of 1: 1 (LCT: liberated iodine) and have quantification ranges of 2–20 mg LCT for method A and method B. The liberated iodine is also measured spectrophotometrically at 350 nm (method C) or the iodine-starch complex measured at 570 nm (method D). In both the methods, the absorbance is found to be linearly dependent on the concentration of iodine which in turn is related to LCT concentration. The calibration curves are linear over 5–40 and 1.25–12.5 mg mL^?1 LCT for method C and method D, respectively. The calculated molar absorptivity and Sandel sensitivity values are 1.0 × 10⁴ L mol^?1 cm^?1 and 0.0435 mg cm^?2, respectively for method C, and their respective values for method D are 2.9 × 10⁴ L mol^?1 cm^?1 and 0.0156 mg cm^?2. The intra-day and inter-day accuracy and precision studies were carried according to the ICH guidelines. The method was successfully applied to the analysis of two brands of tablets LCT. The accuracy was also checked by placebo blank and synthetic mixture analyses besides recovery study via standard addition procedure.     

Jodometrische Titration von Perbromat (Bestimmung von BrO 4 − und BrO 3 − nebeneinander)

Perbromate is reduced to bromate by iodide in weakly alkaline solution (pH 7–9) at 100° C. The formation of iodine in the hot solution is prevented by addition of an excess of arsenite, which is finally titrated with a I₂-solution for the determination of BrO ₄ ^? . The total BrO ₃ ^? content is then determinated by titration of the acidified solution with thiosulphate. From both titrations the initial content of BrO ₃ ^? is obtained. Both methods are simple and accurate. A direct method for the determination of BrO ₃ ^? in solutions containing BrO ₄ ^? is also described.     

Field determination of iodide in water

A simple, fast and sensitive spectrophotometric method for the quantification of iodine and iodide in waters is described. Firstly iodide has been oxidised by sodium nitrite to iodine in HCl medium and the resulting I₂Cl^– has been preconcentrated into toluene. This can be subsequently determined in the extract with brilliant green. A ten-fold preconcentration is obtained, the molar absorptivity is (4.2×10⁴) I mol^–1 cm^–1 at 635 nm. A detection limit of 4 ng/ml iodide in water can be reached. The effect of common anions and cations have been investigated. The method has been applied to the determination fo free iodine, total iodine and iodide in river, pond and well water.     

Application of differential pulse polarography to the assay of ascorbic acid

A polarographic method for the determination of ascorbic acid in pharmaceutical preparations and fruit juices is described. The method is based on the oxidation of ascorbic acid by iodine, and the resulting iodide, after removal of excess iodine, is oxidized with bromine to iodate which is measured polarographically. The method enables analysis of solutions as dilute as 1.7 × 10^?6M ascorbic acid.     

Alternating current polarographic determination of microgram amounts of iodide ion by means of the catalytic oxidation of 1-amino-2-naphthol-4-sulfonic acid

The catalytic oxidation of 1-amino-2-naphthol-4-sulfonic, acid proceeds quickly with microgram amounts of iodide in the presence of sodium chlorate at pH between 1.3 and 2.0. The oxidation product shows a sensitive tensammetric wave at potentials of about +0.03 V vs. SCE (pH 1.75), so that the catalytic reaction was applied for the determination of microgram amounts of iodide ion. The most suitable conditions of the pH range, the concentration of ANS and sodium chlorate, reaction temperature and standing are 1.3–2.0, 3 × 10^?4M, 0.05 M, 50° C and 1 h respectively. Using the recommended procedure, iodide ion can be determined precisely in the concentration range 0.4–6.5 ng ml^?1 with a relative error of about 3%. Interference of foreign species and the application to the determination of total iodine in river and sea water are described.     

Optimization and validation of an ion‐pair RP‐HPLC‐UV method for the determination of total free iodine in rabbit plasma: application to a pharmacokinetic study

An ion‐pair reverse‐phase high performance liquid chromatographic method with UV–vis detection has been developed for the determination of total free iodine in rabbit plasma after vaginal administration of povidone–iodine (PVP‐I). Sample preparation was done by protein precipitation with acetonitrile in 96‐well format and aspirin was used as the internal standard. The 100 µL sodium thiosulfate solution (5 g L^?1) was added to 100 µL plasma sample before protein precipitation, to convert the total free iodine in plasma to iodide (I^?). Separation was performed on a C₁₈ column (200 × 4.6 mm i.d., 5 µm). The mobile phase consisting of a mixture of water phase (containing 10 mmol L^?1 18‐crown‐6 ether, 5 mmol L^?1 octylamine and 5 mmol L^?1 sodium dihydrogen phosphate, pH adjusted to 6.0 with phosphoric acid) and acetonitrile in the ratio 70:30 (v/v) was delivered isocraticly at a flow rate of 1.0 mL min^?1. The method was sensitive with a lower limit of quantification of 0.005 µg mL^?1, with good linearity (r² > 0.9990) over the linear range of 0.005–2 µg mL^?1. All the validation data, such as linearity, accuracy and precision, were within the required limits. The method was successfully applied to study the pharmacokinetic of PVP–I in rabbits after vaginal administration. Copyright © 2009 John Wiley & Sons, Ltd.     

Bis(2‐chloro‐N‐methyl­pyridinium) iodide triiodide

The title compound, 2C₆H₇ClN⁺·I^?·I₃^?, crystallizes with undulating layers of chains containing alternate iodide and triiodide anions formed from iodine and the heterocyclic iodide salt.     

Differential preconcentration of arsenic(III) and arsenic(V) with thionalide loaded on silica gel

2-Mercapto-N-2-naphtylacetamide (thionalide) on silica gel is used for differential preconcentration of μg l^?1 levels of arsenic(III) and arsenic(V) from aqueous solution. In batch experiments, arsenic(III) was quantitatively retained on the gel from solutions of pH 6.5–8.5, but arsenic(V) and organic arsenic compounds were not retained. The chelating capacity of the gel was 5.6 μmol g^?1 As(III) at pH 7.0. Arsenic retained on teh column was completely eluted with 25 ml of 0.01 M sodium borate in 0.01 M sodium hydroxide containing 10 mg l^?1 iodine (pH 10). The arsenic was determined by silver diethyldithiocarbamate spectrophotometry. Arsenic(V) was subsequently determined after reduction to arsenic(III) with sulphite and iodide. Arsenic(III) and arsenic(V) in sea water are shown to be < 0.12 and 1.6 μg l^?1, respectively.     

Determination of sulphur(II) compounds by flow injection analysis with application of the induced iodine/azide reaction

Sulphur(II) compounds that rapidly induce the iodine/azide reaction are determined by injection of 10-μl samples into an iodine/azide solution at a flow rate of 1.4 ml min^?1. Iodine consumption in the induced reaction is detected by biamperometry with platinum electrodes. The linear calibration ranges depend on the concentration of iodine in the iodine/azide solution pumped. The detection limit for thiosulphate, 2-mercapto-pyrimidine, 2-thiouracil, 2-thiobarbituric acid or 6-mercaptopurine is 0.1 mg l^?1 and for sulphide, cysteine, thiourea or glutathione is 0.2 mg l^?1 in the injected sample.     

Effect of styrene–acrylonitrile content on 0.5?M NaI/0.05?M I2 liquid electrolyte encapsulation for dye-sensitized solar cells

The effect of a gel polymer electrolyte (GPE) as the redox electrolyte used in dye-sensitized solar cells was studied. A GPE solution consisting of 0.5?M sodium iodide, 0.05?M iodine, and ethylene carbonate/propylene carbonate (1:1 w/w) binary solvents was mixed with increasing amounts of styrene–acrylonitrile (SAN). Bulk conductivity measurements show a decreasing trend from 4.54 to 0.83×10^?3?S?cm^?1 with increasing SAN content. The GPE exhibits Newtonian-like behavior and its viscosity increases from 0.041 to 1.093?Pa?s with increasing SAN content. A balance between conductivity (1.3?×?10^?3?S?cm^?1) and viscosity (1.4?Pa?s) is observed at 19?wt.% SAN. Fourier transform infrared spectroscopy detects elevated ring torsion at 706?cm^?1 upon the addition of SAN into the liquid electrolyte. This indicates that SAN does not bond with the liquid electrolyte. Finally, the potential stability window of 19?wt.% SAN, which ranges from ?1.68 to 1.38?V, proves its applicability in solar cells.