Selective preconcentration and determination of iodine species in milk samples using polymer inclusion sorbent

A method to determine low levels of iodine species namely I⁻ and IO₃⁻ in aqueous samples was developed and applied to milk and milk powder samples. It is based on selective preconcentration of I⁻ in polymer inclusion sorbent (PIS) and neutron activation analysis (NAA) of I⁻ sorbed in PIS. The PIS was found to be highly selective for I⁻ in presence of IO₃⁻ and other anions commonly present in the milk samples. In order to preconcentrate total I⁻ + IO₃⁻ content in the PIS, IO₃⁻ was reduced to I⁻ using a mixture of acetic acid and ascorbic acid. It was found that total iodine content in milk could be determined with epithermal neutron activation analysis (ENAA). A scheme was developed to determine I⁻, IO₃⁻ and total iodine. The developed method was applied to milk reference materials (NIST SRM-1549 and IAEA-RM-153 milk powder) and a commercially available milk powder. The scheme for estimation of iodine in different forms was validated by using reference material NIST SRM-1549.     

A new resonance scattering spectral method for the determination of trace amounts of iodate with rhodamine 6G

Under the conditions of 0.04 mol L⁻¹ HCl-8.0 × 10⁻⁴ mol L⁻¹ KI, there is a fluorescence peak at 540 nm and a synchronous fluorescence peak at 540 nm for rhodamine 6G (RhG). When there is IO₃⁻, it reacts with exceed I⁻ to form I₃⁻. And I₃⁻ and RhG combine into ion association particles. The particles exhibit three resonance scattering peaks at 320, 400 and 595 nm. And there is fluorescence quenching at 540 nm. Iodine concentration is proportional to the intensity of the resonance scattering intensity at 400 nm in the range of 1.0-20 × 10⁻⁷ mol L⁻¹. And a new resonance scattering spectral (RSS) method has been described for the determination of IO₃⁻ in salt samples. The spectral results have been verified that the formation of (RhG-I₃)_n association particles and solid-liquid interfaces are the main factor that cause the fluorescence quenching and resonance scattering effects.     

Boron-dipyrromethene based specific chemodosimeter for fluoride ion

3,5-Bis(trimethylsilylethynyl)-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene [BODIPY(CCTMS)₂] has been synthesized by coupling of 3,5-dibromo-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene with trimethylsilylacetylene under pd(0) coupling conditions. The BODIPY(CCTMS)₂ was used as a selective colourimetric and fluorescent chemodosimeter for fluoride ion, following the F⁻ ion induced cleavage of trimethylsilyl group, the protecting group of ethyne functionality by monitoring the changes in UV-vis and fluorescence properties. The dosimeter BODIPY(CCTMS)₂ display clear changes in colour, absorption and emission bands selectively for F⁻ ion over other anions such as Cl⁻, Br⁻, I⁻, ClO₄⁻ and HPO₄²⁻.     

Comparative study of the vicinal functionalization of olefins with 2:1 bromide/bromate and iodide/iodate reagents

A comparative evaluation was made on the syntheses of vicinal halohydrins, halo methyl ethers, and halo acetates from olefins using 2:1 Br⁻/BrO₃⁻ and I⁻/IO₃⁻ reagents. In many cases both reagents afforded products selectively in high yields. The highest halogen atom efficiencies attained were 97% and 93% for Br⁻/BrO₃⁻ and I⁻/IO₃⁻, respectively. Of the two reagents, I⁻/IO₃⁻ was established to be the preferred reagent for vicinal functionalization of linear alkenes and also for halo acetate preparation. However, only Br⁻/BrO₃⁻ was effective for vicinal functionalization of trans-stilbene and chalcones.     

Silver nanoplates-based colorimetric iodide recognition and sensing using sodium thiosulfate as a sensitizer

A colorimetric method for the recognition and sensing of iodide ions (I⁻) has been developed by utilizing the reactions between triangular silver nanoplates (TAg-NPs) and I⁻ in the presence of sodium thiosulfate (Na₂S₂O₃). Specifically, I⁻ together with Na₂S₂O₃ can induce protection of TAg-NPs owing to the formation of insoluble AgI, as confirmed by the high-resolution transmission electron microscopy (HRTEM). In the absence of Na₂S₂O₃, the etching reactions on TAg-NPs were observed not only by I⁻ but also other halides ions. The Na₂S₂O₃ plays as a sensitizer in this system, which improved the selectivity and sensitivity. The desired colorimetric detection can be achieved by measuring the change of the absorption peak wavelength corresponding to localized surface plasmon resonance (LSPR) with UV–vis spectrophotometer or recognized by naked eye observation. The results show that the shift of the maximum absorption wavelength (Δλ) of the TAg-NPs/Na₂S₂O₃/I⁻ mixture was proportional to the concentration of I⁻ in the range 1.0 × 10⁻⁹–1.0 × 10⁻⁶ mol L⁻¹. Moreover, no other ions besides I⁻ can induce an eye discernible color change as low as 1.0 × 10⁻⁷ mol L⁻¹. Finally, this method was successfully applied for I⁻ determination in kelp samples.     

A colorimetric assay for measuring iodide using Au@Ag core–shell nanoparticles coupled with Cu

Au@Ag core–shell nanoparticles (NPs) were synthesized and coupled with copper ion (Cu²⁺) for the colorimetric sensing of iodide ion (I⁻). This assay relies on the fact that the absorption spectra and the color of metallic core–shell NPs are sensitive to their chemical ingredient and dimensional core-to-shell ratio. When I⁻ was added to the Au@Ag core–shell NPs-Cu²⁺ system/solution, Cu²⁺ can oxidize I⁻ into iodine (I₂), which can further oxidize silver shells to form silver iodide (AgI). The generated Au@AgI core–shell NPs led to color changes from yellow to purple, which was utilized for the colorimetric sensing of I⁻. The assay only took 10 min with a lowest detectable concentration of 0.5 μM, and it exhibited excellent selectivity for I⁻ over other common anions tested. Furthermore, Au@Ag core–shell NPs-Cu²⁺ was embedded into agarose gels as inexpensive and portable “test strips”, which were successfully used for the semi-quantitation of I⁻ in dried kelps.     

Chemical modification of poly(vinyl chloride) by nucleophilic substitution

The reaction of poly(vinyl chloride) (PVC) in nucleophile (Nu)/ethylene glycol (EG) or Nu/N,N-dimethylformamide (DMF) solution was found to result in the substitution of Cl in PVC with Nu from solution, in addition to the straight elimination of HCl, both of which led to the dechlorination of PVC. Examined Nu⁻ were I⁻, SCN⁻, OH⁻, N₃⁻, and the phthalimide anion. For the Nu/EG solution, elimination was favoured over substitution for all Nu⁻. The ratio of substitution to dechlorination was notable, descending in the order OH⁻ > SCN⁻ = N₃⁻ > phthalimide anion > I⁻. For the Nu/DMF solution, the ratio of substitution to dechlorination was high, in the order SCN⁻ > N₃⁻ > I⁻ > phthalimide anion. In both cases, the orders of the ratios were similar to those of the nucleophilic reactivity constant, I⁻ > SCN⁻ > N₃⁻ > phthalimide anion, except for I⁻. The low ratio for I⁻ was attributable to the elimination of HI after the substitution of Cl in PVC with I in solution, because I⁻ is a strong nucleophile, as well as an excellent leaving group. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution, the ratio of substitution to dechlorination was higher for I⁻, SCN⁻, N₃⁻, and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG.     

Spectrophotometric analysis of iodide oxidation by chlorine in highly mineralized solutions

A spectrophotometric method for determining the concentrations of various iodine compounds (I⁻: initial compound, I₃⁻: under-oxidized iodine form, I₂ and I₂Cl⁻: target iodine forms and ICl₂⁻: over-oxidized iodine form) in their joint presence has been developed in order to study iodine processing from underground brines in Turkmenistan which are characterized by considerably higher mineralization and lower iodide content compared than those in Japan and USA. It was found that solutions with constant iodine concentrations and variable chloride concentrations had an isosbestic point at 474 nm with a molar absorbtivity of I₂ plus I₂Cl⁻ of 610.2 l mol⁻¹ cm⁻¹, while the absorbance of other iodine forms at this wavelength was negligible. This allowed us to use an absorbance at 474 nm for calculating the iodine concentration in solutions of variable chloride concentration. For calculating concentrations of other iodine compounds, absorbances at other wavelengths were used: 225 nm (I⁻ and ICl₂⁻), 248 nm (I₂Cl⁻) and 350 nm (I₃⁻). Beer’s law was valid for all iodine compounds in solutions with constant salt concentrations at all wavelengths. The authors have also developed a detailed algorithm for calculating the concentrations of the various iodine forms in their joint presence. The method was applied to solutions with various chloride concentrations and additions of microcomponents of natural solutions (bromide and iron ions, naphthenic acid and hydrogen sulfide). The overall precision for calculating the concentrations of various iodine compounds was <5% for solutions with an oxidant excess of <2-fold, and with chloride concentrations of <5 mol l⁻¹.     

Syntheses and investigation of the effects of position and nature of substituent on the spectral,electrochemical and spectroelectrochemical properties of new cobalt phthalocyanine complexes

The syntheses of new cobalt phthalocyanine (CoPc) complexes, tetra-substituted with diethylaminoethanethio at the peripheral (complex 3a) and non-peripheral (complex 3b) positions, and with benzylmercapto at the non-peripheral position (complex 5), are reported. The effects of the nature and position of substituent on the spectral, electrochemical and spectroelectrochemical properties of these complexes are investigated. Solution electrochemistry of complex 3a showed three distinctly resolved redox processes attributed to Co^IIIPc⁻²/Co^IIPc⁻² (E_½ = +0.64 V versus Ag|AgCl), Co^IIPc⁻²/Co^IPc⁻² (E_½ = −0.24 V versus Ag|AgCl) and Co^IPc⁻²/Co^IPc⁻³ (E_½ = −1.26 V versus Ag|AgCl) species. No ring oxidation was observed in complex 3a. Complex 3b showed both ring-based oxidation, attributed to Co^IIIPc⁻¹/Co^IIIPc⁻² species (E_p = +0.86 V versus Ag|AgCl), and ring-based reduction associated with Co^IPc⁻²/Co^IPc⁻³ species (E_½ = −1.46 V versus Ag|AgCl), with the normal metal-based redox processes in CoPc complexes: Co^IIIPc⁻²/Co^IIPc⁻² (E_p = +0.41 V versus Ag|AgCl) and Co^IIPc⁻²/Co^IPc⁻² (E_½ = −0.38 V versus Ag|AgCl). Solution electrochemistry of complex 5 showed the same type and number of species observed in complex 3a: Co^IIIPc⁻²/Co^IIPc⁻² (E_p = +0.59 V versus Ag|AgCl), Co^IIPc⁻²/Co^IPc⁻² (E_½ = −0.26 V versus Ag|AgCl) and Co^IPc⁻²/Co^IPc⁻³ (E_½ = −1.39 V versus Ag|AgCl) species. These processes were confirmed using spectroelectrochemistry.     

A flow injection analysis system for monitoring silver (I) ion and iodine residuals in recycled water from recovery systems used for spaceflight

A laboratory-built flow injection analyzer is reported for monitoring the drinking water disinfectants silver (I) ion and iodine in water produced from NASA's water recovery system. This analyzer uses spectrophotometric detection with a custom made 10 cm optical flow cell. Optimization and interference studies are discussed for the silver (I) ion configuration. Subsequent results using the silver (I) configuration with minor modifications and alternative reagents gave promising results for iodine determinations as well. The estimated MDL values for Ag⁺ and I₂ are 52 μg L⁻¹ Ag⁺ and 2 μg L⁻¹ I₂; the mean percent recoveries were 104% and 96.2% for Ag⁺ and I₂ respectfully; and percent relative standard deviations were estimated at 1.4% for Ag⁺ and 5.7% for I₂. The agreement of this potentially multifunctional analyzer to reference methods for each respective water disinfectant is measured using Bland–Altman analysis as well as more traditional estimates.     

A novel dichromate-sensitive fluorescent nano-chemosensor using new functionalized SBA-15

A novel fluorescence nano-chemosensor for Cr₂O₇²⁻ anion has been developed by assembly of fluorescent aluminum complex of 8-hydroxyquinoline (AlQ_x) within the channels of modified SBA-15. SBA-SPS-AlQ_x shows a fluorescence emission at 486 nm. The observed remarkable fluorescence of SBA-SPS-AlQ_x quenches in presence of Cr₂O₇²⁻ anion. The results showed that this fluorescent nano-material can be a useful chemo-sensor for determination of dichromate anions in aqueous solutions. The linear detecting range of fluorescent nano-chemosensor for Cr₂O₇²⁻ anion was 0.16–2.9 μmol L⁻¹. The lowest limit of detection (LDL) was also found to be 0.2 ng mL⁻¹ in aqueous solutions. SBA-SPS-AlQ_x showed selectively and sensitively fluorescent quenching response toward Cr₂O₇²⁻ ion in comparison with I₃⁻, NO₃⁻, CN⁻, CO₃²⁻, Br⁻, Cl⁻, F⁻, H₂PO₄⁻ and SO₄²⁻ ions, which was because of the higher stability of its inorganic complex with dichromate ion.     

A novel and selective spectral method for the determination of trace chlorine in water basing on the resonance scattering effect of rhodamine B-I(3) association nanoparticles

In Na₂HPO₄-citric acid buffer solution, Cl₂ can oxidize I⁻ to form I₂ and then it reacts with excess I⁻ to form I₃⁻. The I₃⁻ combines respectively with rhodamine dyes, including rhodamine B (RhB), butyl rhodamine B (b-RhB), rhodamine 6G (RhG) and rhodamine S (RhS), to form association particles which give stronger resonance scattering (RS) effect at 400 nm. The RS intensity of the RhB, b-RhB, RhG and RhS systems is proportional to chlorine concentrations in the range of 0.008-1.74, 0.019-1.33, 0.021-2.11 and 0.019-2.04 μg/mL Cl₂, respectively. The detection limits of the systems were 0.0020, 0.0048, 0.0063 and 0.0017 μg/mL, respectively. In them, the RhB system has good stability and high sensitivity, and has been applied to the analysis of chlorine in drinking water, with satisfactory results which is in agreement with that of the methyl orange (MO) spectrophotometry.     

Sequential injection analysis for automation of the Winkler methodology, with real-time SIMPLEX optimization and shipboard application

A multipurpose analyzer system based on sequential injection analysis (SIA) for the determination of dissolved oxygen (DO) in seawater is presented. Three operation modes were established and successfully applied onboard during a research cruise in the Southern ocean: 1st, in-line execution of the entire Winkler method including precipitation of manganese (II) hydroxide, fixation of DO, precipitate dissolution by confluent acidification, and spectrophotometric quantification of the generated iodine/tri-iodide (I₂/I₃⁻), 2nd, spectrophotometric quantification of I₂/I₃⁻ in samples prepared according the classical Winkler protocol, and 3rd, accurate batch-wise titration of I₂/I₃⁻ with thiosulfate using one syringe pump of the analyzer as automatic burette.In the first mode, the zone stacking principle was applied to achieve high dispersion of the reagent solutions in the sample zone. Spectrophotometric detection was done at the isobestic wavelength 466 nm of I₂/I₃⁻. Highly reduced consumption of reagents and sample compared to the classical Winkler protocol, linear response up to 16 mg L⁻¹ DO, and an injection frequency of 30 per hour were achieved. It is noteworthy that for the offline protocol, sample metering and quantification with a potentiometric titrator lasts in general over 5 min without counting sample fixation, incubation, and glassware cleaning. The modified SIMPLEX methodology was used for the simultaneous optimization of four volumetric and two chemical variables. Vertex calculation and consequent application including in-line preparation of one reagent was carried out in real-time using the software AutoAnalysis. The analytical system featured high signal stability, robustness, and a repeatability of 3% RSD (1st mode) and 0.8% (2nd mode) during shipboard application.     

Protonation of carbonate in aqueous tetraalkylammonium salts at 25 degrees C

Protonation constants of carbonate were determined in tetramethylammonium chloride (Me₄NCl_aq 0.1 ≤ I/mol kg⁻¹ ≤ 4) and tetraethylammonium iodide (Et₄NI_aq 0.1 ≤ I/mol kg⁻¹ ≤ 1) by potentiometric ([H⁺]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaCl_aq (0.1 ≤ I/mol kg⁻¹ ≤ 6) were also critically analysed. Both protonation constants of carbonate follow the trend Et₄NI > Me₄NCl > NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electrolytes was also evaluated.     

Zirconium(IV)-porphyrins as novel ionophores for fluoride-selective polymeric membrane electrodes

The feasibility of using Zr(IV)-porphyrins as novel ionophores for preparing anion-selective polymeric membrane electrodes is examined. Electrodes constructed using o-nitrophenyl octyl ether plasticized poly(vinyl chloride) membranes containing Zr(IV)-octaethylporphyrin (OEP) dichloride (Zr(IV)[OEP]Cl₂) or Zr(IV)-tetraphenylporphyrin (TPP) dichloride (Zr(IV)[TPP]Cl₂) were found to exhibit enhanced potentiometric selectivity toward fluoride compared to electrodes based on a typical anion-exchanger (e.g. tridodecylmethylammonium chloride). At pH 5.5, the electrodes displayed the following selectivity sequences: ClO₄⁻ > SCN⁻ > I⁻ > F⁻ > NO₃⁻ > Br⁻ > NO₂⁻ > Cl⁻ and F⁻ > ClO₄⁻ > SCN⁻ > I⁻ > NO₂⁻ > NO₃⁻ > Br⁻ > Cl⁻ for membranes doped with Zr(IV)[OEP]Cl₂) and Zr(IV)[TPP]Cl₂, respectively. Both ionophores are shown to operate via a charged carrier mechanism, with 10 mol% of lipophilic tetraphenylborate derivative in the membrane phase required to achieve optimal selectivity. Electrodes prepared with both metalloporphyrin species display super-Nernstian response toward fluoride with slopes typically greater than −100 mV per decade. It is shown, via UV-VIS spectroscopy of the membrane phase, that this behavior occurs due to spontaneous formation of hydroxide ion bridged porphyrin dimers in the membrane in the presence of the lipophilic anionic additive. The dimers are easily converted to monomeric species upon increasing the concentration of fluoride in the sample solution. Decreasing the pH of sample buffer background solution (from pH 5.5 to pH 3) decreases the lower detection limit (DL) of the electrode response toward fluoride (by two-order of magnitude) and improves the electrodes’ selectivity.     

Crystal Structures and Ionic Conductivities of Ternary Derivatives of the Silver and Copper Monohalides: I. Superionic Phases of Stoichiometry MA4I5:RbAg4I5, KAg4I5, and KCu4I5

The superionic properties of the compounds RbAg₄I₅, KAg₄I₅ and KCu₄I₅ have been investigated by powder neutron diffraction and complex impedance spectroscopy. RbAg₄I₅ and KAg₄I₅ have room-temperature ionic conductivities of σ=0.21(6) and 0.08(5) Ω⁻¹ cm⁻¹, respectively, which increase gradually on increasing temperature. KCu₄I₅ is only stable in the temperature range between 515(5) K and its melting point of 605 K, and its ionic conductivity is σ=0.61(8) Ω⁻¹ cm⁻¹, at T=540 K. At lower temperatures, KCu₄I₅ disproportionates into KI+4CuI and the ionic conductivity falls by over three orders of magnitude. Least-squares refinements of the powder neutron diffraction data for RbAg₄I₅ at ambient temperature confirm the reported structure (space group P4₁32, Z=4, a=11.23934(3) Å), though with some differences in the preferred locations of the mobile Ag⁺. KAg₄I₅ and KCu₄I₅ are found to adopt the same basic structure as RbAg₄I₅, with the I− forming a β-Mn-type sublattice, with the K⁺ located in a distorted octahedral environment and the Ag⁺(Cu⁺) predominantly distributed over two sites which are tetrahedrally co-ordinated to I⁻. The implications for the conduction mechanism within these compounds are discussed, using a novel maximum entropy difference Fourier technique to map the distribution of the Ag⁺(Cu⁺) within the unit cell.     

Fluoride-induced intermolecular excimer formation of bispyrenyl thioureas linked by polyethylene glycol chains

New bispyrenyl thioureas linked by polyethylene glycol (PEG) chains, L1-L3, and methoxy benzene pyrene thiourea, L4, were synthesized. Upon binding with F⁻ in CHCl₃, L1-L3 exhibited strong excimer emission bands (I_E) and weak monomer emission bands (I_M), while L4 displayed the same intensity of both bands. However, little or no change was observed in fluorescence spectra of L1 upon adding OH⁻, AcO⁻, BzO⁻, H₂PO₄⁻, Cl⁻, Br⁻, and I⁻. Therefore, only F⁻ induced the pyrene excimer formation. Job’s plots showed 1/1 or 2/2 complexation of L1 with F⁻. Ratios of I_E/I_M of L1·F⁻ complex were dependent on the concentration of L1, implying that the dimerization of L1 proceeded via the intermolecular excimer formation. Among L1-L4, L1 possessed the highest binding constant and sensitivity toward F⁻ implying the importance of the linking PEG chain. L1 was demonstrated to be an excellent probe for F⁻ in CHCl₃ with the detection limit as low as 46.2 μg/L.     

Increasing the sensitivity of the spectrophotometric determinations of the oxygen content in YBCO superconducting samples using the I3-starch compound

The conditions for formation of the I₃⁻-starch compound and measuring its absorbance have been found, and a spectrophotometric method has been developed for the determination of the oxygen content in YBa₂Cu₃O_y superconducting bulk samples. The method involves the following stages: a decomposition of the sample in an acid medium in the presence of iodide ions under inert atmosphere; formation of a complex between Cu(II) and glycine; binding the I₃⁻-complex with a starch and the absorbance measurement of the colored I₃⁻-starch compound. The coefficient of the active oxygen is calculated by the ratio of the absorbances of two solutions and the method does not require both calibration and precise measuring sample mass. The accuracy of the results is confirmed applying the comparative spectrophotometric method that uses the yellow I₃⁻-complex. The precision of the results evaluated by the relative standard deviation is 2%. The developed method is sensitive and allows a sample mass about 2 mg to be used. The analysis is rapid and requires a simple and inexpensive apparatus. Thus the new method would be useful for an express analytical control of the oxygen content of YBCO-superconducting materials produced for the electronics.     

Color response of tri-armed azo host colorimetric sensors and test kit for fluoride

Five new chromogenic tripodal receptors (2a-e) containing electron withdrawing and donating groups appended to the azophenol moiety were synthesized, characterized, and their chromogenic behaviors toward various anions were investigated. These tripodal receptors showed a distinct color change only when treated with fluoride ions in CH₃CN solution. Yet, other anions such as Cl⁻, Br⁻, I⁻, NO₃⁻, ClO₄⁻, AcO⁻, HSO₄⁻, and H₂PO₄⁻ could not cause any color change. Thus, the receptors 2a-e can be used as a colorimetric chemosensor for the determination of fluoride ion. In addition, ¹H NMR experiments were carried out to explore the nature of interaction between tripodal receptors and fluoride. Finally, analytical application and the use of test strip of the receptor 2b to detect fluoride was also reported.     

2, 2′-Dihydroxyazobenzene-based fluorescent system for the colorimetric ‘turn-on’ sensing of cyanide

2, 2′-Dihydroxyazobenzene (DHAB) demonstrated high sensitivity and low selectivity toward three anions: CN⁻, CO₃²⁻, and HCO₃⁻. In the presence of Cu(II), complex DHAB-Cu(II) could give rise to enhanced fluorescence intensity by about 45-fold at 590 nm and visible red-to-reddish orange color change upon the addition of cyanide by utilizing an indirect method, while no changes were observed in the presence of other anions, including F⁻, Cl⁻, Br⁻, I⁻, H₂PO₄⁻, CH₃COO⁻, NO₃⁻, CO₃²⁻ and HCO₃⁻, and SO₄²⁻, making the DHAB-Cu(II) complex a selective and sensitive cyanide chemosensor.