Chromogenic Agent Research Articles

Direct colorimetric detection of copper(II) ions in sampling using diffusive gradients in thin-films

A novel binding phase was developed for use in diffusive gradients in thin-film (DGT) sampling for Cu(II) by employing methylthymol blue as a chelating and chromogenic agent. Methylthymol blue was adsorbed onto beads of Dowex 1 × 8 resin (200–400 mesh) and the resin beads were then immobilised onto an adhesive disc. Analysis of exposed binding discs by either UV–vis spectrophotometry or computer imaging densitometry provided robust quantification of adsorbed Cu(II) in the 0.2–1 μg cm −2 range, allowing detection at μg L −1 concentrations in the test solution (ca. 17 μg L −1 for a 24 h deployment), and in good agreement with established DGT theory. The method was shown to be a potential replacement for binding phases based on Chelex 100 where a colorimetric response to a specific metal is desired.

The case for the use of unrefined natural reagents in analytical chemistry—A green chemical perspective

An important part of the Green Chemistry philosophy is the need to develop and adopt green analytical techniques and procedures. These include the reduction of reagent and solvent usage, the minimization of solid, liquid and gaseous materials produced by analytical processes, the replacement of reagents and solvents of high occupational or environmental toxicity with much more innocuous materials, and the reduction of energy use in analytical processes. One aspect that has received little attention in this context is the use of unrefined natural reagents derived from plant and animal tissues or microbial cells. Crude plant extracts may contain chemical compounds that enable their use as indicators in acid–base or redox titrations, or as chromogenic or fluorogenic agents. Enzymes extracted from plants may be used directly in soluble form, or incorporated in biosensors or solid phase reactors, for analytical measurements, or as a means of removing interferences or performing speciation studies. The use of natural reagents in conjunction with a flow injection system can confer a number of advantages. The enhanced kinetic control that flow analysis offers may assist in avoiding undesirable side reactions that would otherwise occur using unpurified reagents. The lifetime of natural reagents may be prolonged when used in a flow analysis system because their exposure to light or air can be controlled. Any changes in response that do occur may be readily corrected by regular standard checking and recalibration. This article reviews the use of natural reagents with an emphasis on flow-based analytical systems, and makes the case for further research in this latent area of green analytical chemistry.

Spectroscopic, structure and DFT studies of copper(II) and palladium(II) complexes of pyridine-2-carboxaldehyde-2-pyridylhydrazone: A chromogenic agent for palladium(II)

A heterocyclic hydrazone ligand, pyridine-2-carboxaldehyde-2-pyridylhydrazone, HL, 1, was investigated as a new chromogenic agent for selective detection of Pd 2+. The ligand HL, 1, undergoes 1:1 complexation with Pd 2+ and Cu 2+ to form complexes [Pd(L)Cl], 1a and [Cu(HL)Cl 2], 1b respectively. The complex 1a gives a characteristic absorption peak at 536 nm with distinct reddish-pink coloration. The change in color can easily be distinguished from other metal complexes by the naked eye. No obvious interference was observed in the presence of other metal ions (Na +, K +, Mg 2+, Ca 2+, Al 3+, Mn 2+, Fe 3+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Cd 2+, Sn 2+, Hg 2+, Pb 2+). The association constants, K ass (UV–Vis), were found to be 5.52 ± 0.004 × 10 4 for 1a and 4.94 ± 0.006 × 10 4 for 1b at 298 K. On excitation at 295 nm, the ligand HL, 1 strongly emits at 372 nm due to an intraligand 1(π–π ∗) transition. Upon complexation the emission peaks are blue shifted ( λ ex 295 nm, λ em 358 nm for 1a and λ ex 295 nm, λ em 367 nm for 1b) along with a quenching ( F/ F 0 0.32 for 1a and 0.88 for 1b) in the emission intensity. DFT and TDDFT calculations were highly consistent with the spectroscopic behavior of the ligand and complexes. The molecular structure of the complex 1b has been determined by single crystal X-ray diffraction studies.

Color Stability of Different Denture Teeth Materials against Various Staining Agents

The purpose of this in vitro study was to evaluate the color stability of two brands of porcelain teeth and three brands of acrylic denture teeth. Samples were immersed into three staining drinks as test groups and distilled water as a control. Color measurements of teeth were performed by using a spectrophotometer. Before immersion, the initial color value of each tooth was recorded. Color change values were determined after 1 day, 1 week, 2 weeks, and 4 weeks of immersion. Color differences were characterized using the CIE L*a*b* color space. The color stability of all teeth was significantly affected by the immersion period (p<0.0001). Instant coffee was found to be the most chromogenic agent among the solutions tested (p<0.0001). Among the materials tested, porcelain was found to be more resistant to discoloration. It was concluded that acrylic teeth showed a higher degree of color change and that the amount of color change for each group increased proportionally with time.

Preparation of data base for the determination and estimation of high explosives and a comparative study of different methods of estimation of RDX

Analysis of post explosion residues containing high explosive and quick disposal of cases require a suitable analytical data base in the laboratory for the rapid detection and estimation of explosives In the residues. GC-MS is found to be appropriate for the separation, detection and estimation of explosives and a suitable data base for the detection and estimation of high explosives is presented. RDX has been found to be one of the main constituents of the explosives. Depending on the availability of RDX in the post explosion residues, suitable analytical method Is needed for its detection and estimation. A comparative study of the different methods of detection and quantitation of RDX using UV-Vis, FTIR, GC-MS, HPLC and HPTLC instruments has been made for proper selection of the analytical method. The range of detection and estimation of RDX is 100 μg - 1 ng or less depending on the method used. Two chromogenic agents tryptophan and chromotropic acid used for the detection of CH 2 O and RDX (which decompose to 3CH 2 Ο in presence of strong H 2 SO 4 ) were examined for the quantitation of CH 2 O and traces of RDX. Formaldehyde in presence of H 2 SO 4 and traces of FeCl 3 solution reacts with tryptophan to form a red colored complex with absorption maximum at 451 nm. Similarly, CH 2 O (RDX) reacts with chromotropic acid in 16 N H 2 SO 4 to form a blue-violet colored complex with an absorption maximum at 577 nm. However, CH 2 O can be completely converted into the complex with large excess of tryptophan or chromotropic acid and the extinction coefficients of the complex are utilized for the quantitation of CH 2 O or RDX. The stability constant of the complex at 298 K between CH 2 O and chromotropic acid has been determined.

A cleaner and simple spectrophotometric micro-fluidic procedure for copper determination using nitroso-R salt as chromogenic agent

A cleaner and simple spectrophotometric method using microflow analysis (μFA) was performed. It consisted of a T-junction with microcoil on a polymethyl methacrylate (PMMA) chip which was fabricated by laser ablation and a molded polydimethylsiloxane (PDMS) as top plate. The fabricated PMMA chip was integrated with light emitting diode (LED) as light source and spectrometer as detector. The proposed device was applied to determining copper in water samples using nitroso-R salt as chromogenic reagent at 495 nm. It was found that the proposed μFA system was with less reagents and samples consumption with tiny waste generation. The relative standard deviation (R.S.D.) was less than 2% ( n = 11) with the percentage recovery of 98.0 ± 1.7% ( n = 7). The linear range for determination of copper in water samples was over the range of 0.05–3.0 μg mL −1 with a correlation coefficient ( r 2) of 0.999. The limit of detection (3 σ) was 47 ng mL −1 with a sample throughput of 30 h −1.

Application of Boron as the Chromogenic Agent in Spectrophotometry I. A Novel Fading Spectrophotometric Method for the Determination of Aminomethylbenzoic Acid with Boric Acid

AbstractIt is the first time that boron has been used as a chromogenic agent to determine aminomethylbenzoic acid (PAMBA) by the fading spectrophotometric method in this paper. The study indicates that at pH 10.00 the absorbance of PAMBA decreases when boric acid (BA) is added to the solution. A simple, rapid, sensitive and reliable novel method based on the product of PAMBA and BA is obtained. The stoichiometric ratio of the product is 1:2. Beer's law is obeyed in the range of PAMBA concentrations of 0.13 ˜ 38.40 μg/mL at a wavelength of 242 nm (ε242 is 8.1 × 104 L/mol/cm). The equation of linear regression is A = ‐0.06635 – 0.02914C (× 10−5 M), with a linear correlation coefficient of 0.9974. The detection limit is 0.12 μg/mL and RSD 0.11%. The method is successfully applied to the determination of PAMBA in pharmaceutical samples, and average recoveries from pharmaceutical samples and urine samples were between 98.4 ˜ 102.5%. The other components in these samples do not interfere with the determination by the proposed method.

Absorption spectroscopic and FTIR studies on EDA complexes between TNT (2,4,6-trinitrotoluene) with amines in DMSO and determination of the vertical electron affinity of TNT

TNT (2,4,6-trinitrotoluene) formed deep red 1:1 CT complexes with chromogenic agents like isopropylamine, ethylenediamine, bis(3-aminopropyl)amine and tetraethylenepentamine in DMSO. The complexes were also observed in solvents like methanol, acetone, etc. when the amines were present in large excess. The isopropylamine, complex showed three absorption peaks (at 378, 532 and 629 nm) whereas higher amines showed four peaks (at 370, 463, 532 and 629 nm). The peak at 463 nm vanished rapidly. The peak of the complexes near 530 nm required about 8–10 min to develop and the complexes were stable for about an hour but the peak slowly shifted towards 500 nm and the complexes were found to be stable for more than 24 h. The evidence of complex formation was obtained from distinct spots in HPTLC plates and from the shifts in frequencies and formation of new peaks in FTIR spectra. The peaks near 460 nm (transient) and 530 nm may be due to Janovsky reaction but could not be established. The extinction coefficients of the complexes were determined directly which enabled the accurate determination of the association constants K DA with TNT and amines in stoichiometric ratios. The results were verified using iterative method. The quantfication of TNT was made using ɛ value of the complex with ethylenediamine. The vertical electron affinity ( E A) of TNT was calculated using the method suggested by Mulliken.

Determination of formaldehyde in foodstuffs by flow injection spectrophotometry using phloroglucinol as chromogenic agent

A spectrophotometric method for the determination of formaldehyde in foodstuffs was described by using phloroglucinol as the chromogenic agent. The reaction between formaldehyde and phloroglucinol could occur rapidly at room temperature under mild conditions. The spectrophotometric measurements were conducted at 474 nm of an unstable intermediate orange product of the reaction, which greatly increased the sample throughput. Flow injection technique was used to control the merging and reaction timing of the reagents and sample. A detection limit (3 σ) of 0.023 μg ml −1 was achieved. The relative standard deviation was 0.29% for the determination of 7 μg ml −1 formaldehyde ( n = 11). The proposed method was applied to the analyses of formaldehyde in several preserved foodstuffs and the results were in good agreement with those obtained by a standard method.

Mercury speciation by CE: A review

CE methods for the speciation of inorganic and organomercury compounds are reviewed. Sample preparation, separation conditions and detection modes are discussed. Efficient separation and sensitive determination of mercury species by CE typically involves complexation with various thiols, chromogenic and other chelating agents; however, some methods do not require complexation. Spectrophotometric detection based on UV-visible absorption is by far the most commonly used. Hyphenated techniques, such as CE/inductively coupled plasma (ICP)-MS, hydride generation coupled to ICP-MS or atomic fluorescence spectrometry and CE/atomic absorption spectrometry are gaining popularity due to their high sensitivity and selectivity. Last, but not least, the potential and applications of electrochemical methods for detection of separated mercury species are outlined.

Monocyclic and dicyclic hydrocarbons: structural requirements for proximal giant axonopathy

The chromogenic and neurotoxic gamma-diketone 1,2-diacetylbenzene (1,2-DAB), but not its isomer 1,3-DAB, induces blue discoloration of tissues and urine, clustering of axonal microtubules and proximal neurofilament-filled axonal swellings in rodents. The remarkable chromogenic property of 1,2-DAB, a monocyclic aromatic hydrocarbon, arises from reaction with lysine residues of proteins and formation of dimeric and polymeric derivatives. Tetralin, a dicyclic solvent structurally related to acetyl ethyl tetramethyl tetralin, a chromogenic and neurotoxic agent, reportedly induces excretion of green urine, and causes neurological disturbances in humans. Monocyclic aromatic 1,2,4-triethylbenzene (1,2,4-TEB), but not its isomer 1,3,5-TEB, is also reportedly chromogenic and induces neurophysiological deficits in rodents consistent with axonal neuropathy, but without neuropathological confirmation. We treated 12-week-old C57Bl/6 mice by gavage with 300, 600, or 900 mg/kg/day 1,2,4-TEB, or equivalent doses of 1,3,5-TEB, 3 days/week, for up to 12 weeks, or intraperitoneally with 400 mg/kg/day tetralin, or 50 or 100 mg/kg/day of its alpha-tetralol analogue, 5 days/week, for up to 5 weeks. Animals treated with 1,2,4-TEB, but not 1,3,5-TEB, tetralin or alpha-tetralol, developed hind limb weakness, excreted greenish urine, and showed 1,2-DAB-like neuropathology. These findings support the hypothesis that 1,2-spaced ethyl (or acetyl) moieties on a benzene ring of hydrocarbons are required for hydrocarbons to induce chromogenic changes and proximal giant neurofilamentous axonopathy. Key molecular targets of these compounds likely reside in the axon where they serve to maintain normal cytoskeletal organization.

Factorial design for optimization of flow-injection preconcentration procedure for copper(II) determination in natural waters, using 2-aminomethylpyridine grafted silica gel as adsorbent and spectrophotometric detection

The 2-aminomethylpyridine anchored silica gel (AMPSG) was successfully used as a sorbent in a simple spectrophotometric flow system for Cu2+ preconcentration in natural water samples, using sodium diethyldithiocarbamate as chromogenic agent (460 nm). The system was optimized using a full factorial design 25 to determine better analytical conditions to determine copper in the natural water samples such as those from river, tap, stream, spring, well, waste, synthetic brackish water and a water reference material (NIST-1640). The better conditions used were: 180 s loading; 30 s elution; 30 s regeneration of the column; loading flow rate 6.6 mL min−1; buffer solution for the preconcentration and regeneration of the column-acetate buffer pH 5.75; elution flow rate 1.6 mL min−1; eluent composition 0.20 mol L−1 HNO3. Under these conditions, the preconcentration factor obtained was 77, and the detection limit achieved was 3.0 ng mL−1. The recovery of spiked water samples ranged from 95.2 to 104.7%.

The Synthesis of 7-Substituted-3-dinitrostyryl Cephalosporins and Their Ability for Detecting Extended Spectrum β-Lactamases (ESBLs)

We synthesized 7-substituted-3-(2,4-dinitrostyryl)cephalosporin derivatives which were Nitrocefin analogs, for detecting extended spectrum beta-lactamase (ESBL) specifically. HMRZ-86 which has carboxypropyloxyimino group on 7-aminothiazolacetamide substituent were not hydrolyzed by class A, C and D beta-lactamases, but it was hydrolyzed by ESBL and metallo beta-lactamase (class B), then its color changed from yellow to red. The hydrolysis of metallo beta-lactamase was inhibited by adding sodium mercapto acetic acid (SMA). Therefore HMRZ-86 is a useful chromogenic agent to detect ESBL specifically.

Direct Microspectrophotometric Determination of Bismuth in Silver with Semi-Xylenol Orange

75–300 ng of bismuth in a sample mass of 20 mg of silver can be determined spectrophotometrically in a nitric acid medium (0.18 mol L−1) with Semi-Xylenol Orange as chromogenic agent. Its selectivity is realized by using less toxic reagents in very small amounts to mask some of the interfering impurity cationic species while the matrix effect is negligible. The conditional formation constant of the colored chelate formed was found to be lg K′f=3.1. It exhibits a maximum at 540 nm with a molar absorptivity of 4.2×104 L mo1−1 cm−1. The linear regression equation for this determination is A=0.022+0.0018 C, where C stands for the concentration of Bi (ng per 0.5 mL) with a correlation coefficient γ of 0.9873. The RSD at the level of 200 ng of Bi (n=10) was found to be 5%.

Spectrophotometric determination of propranolol in formulations via oxidative coupling with 3-methylbenzothiazoline-2-one hydrazone

A simple spectrophotometric method has been developed for the determination of propranolol hydrochloride in pure as well as in dosage forms. The method is based on the oxidative coupling reaction with 3-methylbenzothiazoline-2-one hydrazone. A mixture of an acidic solution of the chromogenic agent and the drug upon treatment with ceric ammonium sulfate produces an orange color peaking at 496 nm. The absorbance–calibration plot was linear over the range 1–10 μg/ml with minimum detectability ( S/ N=2) of 0.1 μg/ml (3.38×10 −7 M). The molar absorbitivity was 3.195×10 3 l/mol/cm with correlation coefficient ( n=10) of 0.9999. The different experimental parameters affecting the development and stability of the color were carefully studied and optimized. The proposed method was applied successfully to the determination of propranolol in its dosage forms. A proposal of the reaction pathway was presented.

Spectrophotometric Determination of Cefepime Hydrochloride, Cefoperazone Sodium, Ceftazidime Pentahydrate. Cefuroxime Sodium and Etamsylate Using Ammonium Molybdate

A simple, rapid and sensitive spectrophotometric method has been developed for the quantitative determination of five drugs of pharmaceutical interest; cefepime HCI , cefoperazone Na , ceftazidime pentahydrate , cefuroxime Na and etamsylate in pure form as well as in pharmaceuticals. The method is based on the reduction of the chromogenic agent , ammonium molybdate (Mo6+), to molybdenum blue (Mo5+) by the examined drugs in sulphuric acid medium and by aid of heating in boiling water bath. The resulting "blue coloured" product possess a characteristic λmax at 695-716 nm. Beers law is obeyed over the concentration range of 2-70 μg ml-1 with molar absorpitivities ranging from 2.704×10-3–24.14×10-3 L.mol-1.cm-1 and Sandell sensitivities ranging from 1.03x10-3–5.4x10-3 μg cm-2. The proposed method has been applied successfully for the determination of the examined drugs both in pure form and in pharmaceutical formulations. The accuracy and precision of the proposed method are comparable with those of the reported methods .

DETERMINATION OF COBALT IN FOODS BY β-CYCLODEXTRIN POLYMER PHASE SPECTROPHOTOMETRY USING 2-(5-BROMO-2-PYRIDYLAZO)-5-DIETHYLAMINOPHENOL

ABSTRACT The chromogenic agent, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) was included/adsorbed on β-cyclodextrin polymer (β-CDP) to form the modified polymer of inclusion of 5-Br-PADAP (β-CDP-5-Br-PADAP). The modified polymer can adsorb cobalt to form a colored complex and the maximum absorbance of 5-Br-PADAP-cobalt complex on β-CDP was measured at 588 nm. The optimum conditions for the adsorption of cobalt on β-CDP-5-Br-PADAP were: pH of 8.0, temperature of 25°C, and shaking time of 40 min for 25 ml of sample solution and 60 min for 200 ml of sample solution. The working range of the calibration graph was 0.1−1.6 µg of cobalt. The interferences from nickel, zinc, copper, chromium, manganese, lead and iron, which form colored species with 5-Br-PADAP in the polymer phase, were investigated. The method was applied satisfactorily for the determination of cobalt in laver (a kind of edible alga).

Determination of Manganese (II) in Foodstuffs by β-Cyclodextrin Polymer Phase Spectrophotometry with 1-(2-Pyridylazo)-2-naphthol

The chromogenic agent, 1-(2-pyridylazo)-2-naphthol (PAN) was included in g -Cyclodextrin polymer ( g -CDP) and the modified polymer of inclusion of PAN ( g -CDP-PAN) was obtained. Based on the fact that g -CDP-PAN can adsorb Mn (II) in solution to form Mn (II)-PAN complex, a sensitive and selective solid phase spectrophotometric method for the determination of trace amounts of Mn (II) has been developed. The maximum absorbance of Mn (II)-PAN complex in g -CDP was at 514 nm. The working range of the calibration graph was 2-12 w g of Mn (II). The interference of molybdenum, lead, cobalt, chromium, iron, nickel, zinc, tin, cadmium, and copper that form colored species with PAN in the polymer phase was investigated. The method was applied to the determination of Mn (II) in black rice and tea samples. A new method for the determination of trace amounts of manganese by polymer phase spectrophotometry is described. Manganese reacted with 1-(2-pyridylazo)-2-naphthol (PAN) that was included in a g -cyclodextrin polymer. The absorbance of the colored polymer, packed into a 5 mm quartz cell, was determined directly at 514 nm. The proposed method was applied to the determination of manganese in black rice and tea samples.

MICRODETERMINATION OF ZINC(II) IN ALLOYS AND ORES BY VISIBLE SPECTROPHOTOMETRIC TECHNIQUE USING 2,3-DICHLORO-6- (2-HYDROXYNAPHTHYLAZO)- QUINOXALINE IN PRESENCE OF MIXED SURFACTANTS

ABSTRACT A new spectrophotometric method for the microdetermination of zinc is proposed. The method is based on complexation reaction of zinc(II) with the chromogenic agent 2,3-dichloro-6-(2-hydroxynaphthylazo)quinoxaline in the presence of cetyltrimethylammonium bromide (CTAB) and nonyl phenoxy polyetho-xyethanol (OP) in slightly basic medium containing 20% (v/v) ethanol. Under certain experimental conditions, Beer's law is obeyed over the range 0.02–0.80 µg ml−1 of Zn2+ with molar absorptivity of 1.06 × 105 l mol−1 cm−1 and Sandell sensitivity of 0.62 ng cm−2. The limits of detection and quantification as well as the regression equation are also calculated. The relative standard deviation for ten determinations for sample containing 0.5 µg ml−1 was found to be 1.15%. As compared with other methods, our method is highly sensitive and selective because of the complex has high, and sharp absorption band at 616 nm. In addition, the present method is simple and rapid, no heating, no extraction or standing is needed. The proposed method has been applied successfully to the spectrophotometric determination of trace amounts of zinc in some alloys and ore samples.

4-Aminoantipyrine spectrophotometric method of phenol analysis: Study of the reaction products via liquid chromatography with diode-array and mass spectrometric detection

The synthesis of new pyrazolone molecules and their application as chromogenic agents in phenol analysis by the 4-aminoantipyrine method has been described by our group in previous published papers. A fully detailed mechanism is given therein based on experimental and theoretical data. In this paper, the study of the reaction products and by-products via liquid chromatography with diode array and mass spectrometric detection is presented, sorting out the spectrophotometric determination of phenols.