Characterization of indigo carmine with surface‐enhanced resonance Raman spectroscopy (SERRS) using silver colloids and island films,and theoretical calculations

The application of resonance Raman (RR) and surface‐enhanced resonance Raman (SERR) spectroscopies to the qualitative and semiquantitative analysis of the artificial dye indigo carmine has been examined using sodium‐citrate‐reduced silver colloid and island films with various roughnesses. Additional, the Raman spectrum of the solid state and density functional theory (DFT) calculations helped to a better understanding of the fully optimized geometry and of the vibrational wavenumbers of the dye. A strong chemical interaction of indigo carmine with the silver colloidal particles was observed mainly at very low concentration of 0.03 × 10⁻⁹ M and with silver film surfaces at a concentration of 10⁻⁴ M . The indigo carmine orientation possibilities while going to different metallic substrates are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Square Wave Electroanalysis at Generator–Collector Gold–Gold Double Hemisphere Junctions

Gold–gold double‐hemisphere junction electrodes with an inter‐electrode gap of typically 1 µm are employed for generator–collector square wave voltammetry. Electrochemical data are recorded as a function of both generator and collector potential to give three‐dimensional response “maps”. At sufficiently low frequencies, close‐to‐steady‐state conditions for the collector response are achieved and peak responses complementary to those for the generator electrode are recorded. Due to localised interelectrode gap diffusion (fast) as opposed to peripheral diffusion (slow), information about reaction products and intermediates can be obtained. Local pH gradient effects provide additional “fingerprint” information beneficial for future application in analytical detection.     

Voltammetric Determination of Indigo Carmine and Amaranth on a Silver-Based Mercury Film Electrode

Abstract

The voltammetric behavior of indigo carmine and amaranth on silver-based mercury film electrodes was studied. At pH 4, reduction current peaks were observed at potential ?0.11 V (indigo carmine) and ?0.24 V (amaranth), respectively. The system showed a linear response to both of the food colorants in a concentration range of 0 to 100 ng/ml. Detected at different reduction potentials, indigo carmine and amaranth could be determined separately without interfering with each other. This method demonstrated a better reproducibility and longer life time than the existing techniques.     

流动注射催化动力学光度法测定碘离子

Based on catalysis of I- on the decolor reaction between potassium bromate and indigo carmine in the acid medium,and combined with flow injection analysis,a new flow-injection catalytic kinetic spectrophotometric method was found for determination of iodide in sample.The experimental results show that the determination is carried out at temperature of 80℃ and the concentration of H_2SO_4,KBrO_3,and indigo carmine is 1.2 mol/L,1.8×10~(-2) mol/L and 1.0×10~(-4) mol/L respectively,the linear range for the method is 0.50～1.8 mg/L.The detection limit is 0.0022 mg/L.The relative standard deviation is 1.92%.The proposed method was applied to the determination of iodide in troche successfully.The recovery was between 99.2% and 103.6%.     

On the interpretation of the Raman spectra of Maya Blue: a review on the literature data

The Raman spectroscopy of Maya Blue (MB), a nanostructured organic–inorganic hybrid material, has received considerable attention. A re‐evaluation of the Raman literature data for indigo dye, genuine MB samples and model specimens obtained by the binding of indigo to phyllosilicate clays, such as palygorskite and sepiolite, using chemometric analysis of normalised spectra is reported. Available data present features in support of the following ideas: (1) dehydroindigo accompanies indigo in MB; (2) different topological isomers, i.e. dye molecules attached to different coordinative sites of the palygorskite framework, are involved in MB; and (3) different procedures were probably used for preparing MB in ancient Mesoamerican civilisations. Copyright © 2010 John Wiley & Sons, Ltd.     

FT‐Raman spectroscopy—a rapid and reliable quantification protocol for the determination of natural indigo dye in Polygonum tinctorium

In the recent years, Raman and IR spectroscopies have attracted increasing attention as fast, non‐invasive and widely applicable alternative analytical approaches for a variety of materials. Vibrational spectroscopy has been used in the analysis of herbal products, dyes and sensitive art objects, besides complex and aqueous biomaterials such as biopolymers or mammalian tissue. Compared to conventional analytical methods based on high‐performance liquid chromatography (HPLC) or gas chromatography, which often involves extensive and time‐consuming sample preparation, Raman or IR spectroscopy can avoid these procedures. The present work introduces a fast and reliable quantification method for the determination of naturally occurring indigo dye in dyer's knotweed (Polygonum tinctorium) based on Fourier transform (FT) Raman spectroscopy. The results were validated by HPLC‐UV, and the merits and drawbacks of the present method are elaborated. Besides the qualitative aspects of signal assignment and comparison to appropriate attenuated total reflectance Fourier transform infrared (ATR‐FT‐IR) measurements, the Raman spectrum of dihydro indigo, an important intermediate in the indigo dying process, is presented for the first time and discussed with regard to its spectroscopic behaviour. Copyright © 2010 John Wiley & Sons, Ltd.     

Removal of textile dye mixtures by using modified Mg–Al–Cl layered double hydroxide (LDH)

The removal of Indigo Carmin (IC) and Congo Red (CR) dye mixtures using layered double hydroxide (LDH) (modified with sodium dodecyl sulfate (SDS)) has been studied. In the experimental context of this study, LDH was synthesized under a nitrogen atmosphere at room temperature using the coprecipitation method and characterized by Fourier transform infrared specroscopy (FTIR), X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX) and scanning electron microscopy (SEM) analyses. Contact time, temperature, and initial dye concentration on the adsorption process have been investigated. Results show that the maximum removal of IC and CR was obtained as about 50% and 95%, respectively. The isothermal data were fitted to Langmuir, Freundlich, and Temkin adsorption isotherms. Elovich and other kinetic model equations were applied. Adsorption depended on the starting naphthalene concentration at investigated various temperatures (298, 308, and 318?K) significantly.     

基于红色碳量子点的荧光法快速检测饮料中的胭脂红

该研究以红色碳量子点为荧光探针,建立了一种饮料中胭脂红的荧光快速检测方法,以满足食品着色剂胭脂红的检测需求。首先以对苯二胺为碳源,于180 ℃水热反应合成红色碳量子点(RCDs)。研究发现所制备的RCDs的荧光发射峰与胭脂红的紫外可见吸收峰明显重叠,且两者之间存在内滤效应。基于内滤效应机理,建立了一种对胭脂红定量检测的荧光快速检测方法。结果表明：在0.5~50 μg·mL-1范围内胭脂红的浓度与RCDs的荧光强度比值呈线性相关,线性方程为IF0/IF=0.059c+0.979,相关系数(r2)为0.978,检出限为0.397 μg·mL-1,3个加标水平下的回收率为93.1%~101%,相对标准偏差(RSD)为0.97%~2.1%。该方法具有快速、灵敏度高及稳定性好的特点,可用于实际饮料样品中胭脂红的检测。     

Isomeric Diruthenium Complexes Bridged by Deprotonated Indigo in cis and trans Configuration

The doubly deprotonated form L^2? of indigo=H₂L can bind two [Ru(acac)₂] complex fragments in the cis ( 1 ) and trans configuration ( 2 ), as evidenced from crystal structure analysis. While the latter type of N,O; N ^’ ,O ^’ coordination has been observed earlier, for example, with [Ru(bpy)₂]²⁺, leading to two equivalent six‐membered ring chelates, the cis arrangement in 1 is observed here for the first time in a dinuclear complex, producing one five‐membered ring chelate with N,N ^’ coordination and one seven‐membered chelate with O,O ^’ coordination. The different structures of the isomers result in differing electrochemical and spectroelectrochemical (EPR, UV‐Vis‐NIR) responses for various accessible charge states 1 ⁿ and 2 ⁿ, n=–, 0, +, 2+. The associated electronic structures were analyzed by DFT (structures, spin density) and TD‐DFT calculations (electronic transitions), revealing mainly metal‐based reduction but largely indigo ligand‐based oxidation of both neutral precursors.     

Metal Complexes of Indigo and of Some Related Ligands

While the first coordination compounds of indigo were reported over 100 years ago, a systematic study of the coordination chemistry of this important dye and also its structural “relatives” remained silent for over half a century. Only in the last two decades of the 20th century research on this topic started again keeps on growing ever since. It could be established, mainly by X-ray crystallography, but also by many other modern spectroscopic techniques, that deprotonated indigo, and its deprotonated oxidized and reduced forms act as mono- and bidentate chelate ligands in metal complexes