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The determination of the ozone concentration in the atmosphere is an urgent need but most current methods are limited by large-scale equipment or complex procedures. Herein, a gas–liquid chemiluminescence (GL-CL) assay based on a portable GL-CL detector platform was reported for the fast and sensitive online determination of ozone. Graphene quantum dots (GQDs) and Triton X-100 were employed to synergistically enhance the CL intensity of chromotropic acid (CA)–ozone. The increase was about seven-fold upon the addition of GQDs and Triton X-100. The potential enhancement mechanism was also investigated. The speculated CL enhancement mechanism was that GQDs could catalyze dissolved oxygen in the CA solution to produce more free radicals in the presence of UV-light, and these radicals converted CA into more active compounds that could react with ozone and emit photons. The free radicals, active compounds and luminophores were protected from water quenching by micelles produced by dissolving Triton X-100 in water and as a result, CL was markedly enhanced. Most importantly, the response time of the GL-CL detector platform towards ozone was less than 0.5 s. Based on this outcome, a GL-CL assay for detecting atmospheric ozone was successfully developed with a linear range from 0.1 to 150 ppbv and a detection limit of 0.02 ppbv. This work provides a rapid and sensitive method for the online measurement of ozone, and has great potential in environmental applications; the potential applications of GQDs and Triton X-100 in the field of GL-CL have also been highlighted.

In order to develop a novel detection method for the degree of polymerization (DP) of insulating papers, methanol was used as an indicator to explore the relationship between methanol concentration and DP in this paper. After extraction from oil, the methanol was oxidized and reacted with chromotropic acid to generate a purple-red compound. The spectral detection method was used to detect the concentration of methanol by absorbance, and then, the corresponding relationship between the concentration of methanol and the DP of insulating paper was established. Moreover, the detection methods based on furfural and methanol were compared. The results showed that methanol appeared during the initial aging period of the insulation paper, and the linear relationship between the methanol concentration and the DP of insulating paper was good. Compared with furfural, methanol was more sensitive to the change of DP in the early aging period, which proved that methanol could be used as a new type of indicator of insulating paper.

Oil-paper insulation in transformers plays an important role in the operation of power grid. At present, the aging (life assessment) of transformers are mainly conducted based upon the degree of polymerization, concentration of furfural, and the gas analysis of CO and CO2 in the transformer oil. However, these techniques lack sensitive response, especially in the early aging of oil-paper insulation. Methanol as a new indicator to evaluate the aging of insulating paper, is getting more and more attention. An evaluation method based on the measurement of methanol concentration using ultraviolet–visible spectrometer was proposed in this work. After the extraction from transformer oils, the methanol was oxidized using potassium permanganate. Then, chromotropic acid was used to react with the oxidation products (formaldehyde) to form a mauve clathrate, finally, the methanol content was measured using the spectroscopy. Different from traditional spectroscopy which calculate only by absorbance at the characteristic wavelength, this paper use the partial least squares method, obtain the relationship between the absorbance at selected regions and the concentration of methanol. The minimum detection limit for the proposed method was 10 ppb, whereas the correlation coefficient for the relationship between the absorbance and the concentration of methanol was as high as 0.99.

A novel detection scheme using chromatographic retention was proposed for paper-based analytical devices (PADs). Using a wax printer and an ink-jet printer, the PADs consisted of a straight-flow channel, a circular sample zone, and a band of brilliant green (BG) printed at the connection between the sample zone and the flow channel. When a constant volume of a sample solution was applied to the sample zone, the BG band formed a colored bar along the flow channel that marked the adsorption and desorption of the paper substrate according to the principles of chromatography. If the sample solution contained an anionic complex of boric acid with chromotropic acid, the anionic complex enhanced desorption of the BG from the paper substrate via the formation of an ion-pair with the BG, which resulted in an elongated colored bar. Fundamental equations for the retention behavior of the BG on the PADs were derived using a model based on chromatographic principles and ion-pairing formation. A retardation factor, Rf, was correlated with the concentration of boric acid contained in the sample solutions. To enhance the adsorption of the BG, 2,2,6,6-tetramethylpiperidine 1-oxyl was used to oxidize the paper substrate. The oxidized paper substrate shortened the colored bar of a blank solution and formed a clear boundary for the color. When the analytical conditions were optimized for pH and the concentration of chromotropic acid, the PAD permitted the measurement of boric acid for a concentration ranging from 0.3 to 3 mM. The proposed model was validated when the fitting curve was calculated using the derived equations, which resulted in good agreement with the experimental data.

A simple, accurate, and low-cost analytical procedure for methanol determination in sugarcane spirits (cachaca) employing analysis of digital images is presented. A portable system with cheap materials and lighting system to obtain images from a smartphone was built and an RGB system was used for analytical purposes. The reaction for determination of methanol in beverages consists in methanol oxidation to methanal, and consequent formation of a violet chromophore in the presence of chromotropic acid on heating in an oven at 80 °C for 15 min. From the system optimization, analytical curves that showed good linearity for the green channel (from RGB) was built, with regression coefficient (R 2) of 0.998. Relevant matrix effect in the samples was not verified, since the recovery percentage ranged from 83 to 110%. The results of methanol concentration in six cachaca samples obtained by the developed method were compared with using the spectrophotometric method with a confidence level of 95% (n = 3). The developed method has some economic and environmental benefits, since it has low reagent consumption with 800 μL per measured spot, as well as, it presents cheap and handle-easy devices, which encourages the quality control of this toxic and undesirable contaminant for smallholders and industries on production of sugar cane spirits.

A simple, accurate, and economical method has been proposed to measure formaldehyde in aqueous samples. The method is based on quantification of classical chromotropic acid – formaldehyde violet spots developed on TLC. Different parameters such as concentration of chromotropic and sulfuric acid, time of heating and order of application of reagents have been studied to find out the optimum working procedure. Spots have been quantified by scanning the spotted TLC and analyzing the image in computer with Visual Basic 6.0 based graphic application. The study consisted of developing an appropriate calibration line, analyzing artificial and real samples, and comparing the new method with a standard spectrophotometric method (NIOSH Method-3500, 1994). It has been concluded that the present method had the capability for measuring formaldehyde in aqueous samples at trace level with high precision and accuracy, particularly when dealing with turbid and small volume samples where the standard method failed.

A film of benzenesulfonamide azo dye has been prepared by spray pyrolysis method onto BK7 glass substrate with average thickness of 2.7 μm. This azo dye was derived from sulfamethoxazole and chromotropic acid by the Fox method. The optical constants (refractive index, n, extinction coefficient, k, dielectric constant, ɛ, optical, σopt, and electrical, σe, conductivities) were calculated for azo dye film by using spectrophotometer measurements of the absorption, transmittance and reflectance at normal incidence in the spectral range 300–900 nm. Third order nonlinear properties has been characterized by calculating the effective thermal nonlinear refractive index, n2, and thermo-optic coefficient, dn/dT, of the azo dye solution using thermal lens technique. Furthermore, the thermal lens effect was utilized to demonstrate all optical switching for the sample solution.

A non-toxic solid-phase test reagent for rapid determination of nitrite and nitrate was developed. Powdered reagent utilised azo- and diazo-components (p-nitroaniline and chromotropic acid, respectively), solid organic acid acidifier (malonic, maleic or oxalic acid), zinc dust (for nitrate determination), catalyst and masking agent. Effects of solid acidifier and the amount of Zn reducing agent were evaluated. The optimal reagent formulation was established in terms of dynamic range and response kinetics, and validated by parallel measurements in split samples using an accredited ion-chromatographic method. The optimal reagent contained malonic acid as acidifier and 1.0% of Zn reducing agent, and showed good sensitivity for the determination of nitrite (LOQ of 0.03 mg L−1) and nitrate (LOQ of 0.17 mg L−1), and fast analysis time of under 6 min. These reagents were shown to be stable for at least 3 months with RSD of

Polypyrrole nanofibers (PPy-NF) were prepared by an oxidative template assembly method and utilized for the fabrication of N-doped activated carbon nanofibers (N-AC-NF). Capacitor cells, containing N-AC-NF electrodes were used for capacitive dye removal (CDR) from aqueous solutions. It was found that CDR method can be used for the removal of triphenylmethane and chromotropic acid family dyes from aqueous solutions. The analysis of cyclic voltammetry, galvanostatic charge-discharge and impedance spectroscopy data, coupled with results of quartz crystal microbalance studies, provided an insight into the influence of chemical structure, size, charge-to mass ratio, concentration and redox-active ligands of the dyes on the capacitive behavior, dye removal efficiency, reversibility and cyclic stability of the cells. The CDR method offers advantages for the dyes of chromotropic acid family, due to larger voltage window, good capacitive behavior, improved cyclic stability and higher power-energy characteristics. It was found that charge storage mechanism is mainly attributed to double layer capacitance. CDR is a promising method for water purification, which offers advantages of energy saving and simple electrode regeneration.

Progress towards the development of a miniaturised microfluidic instrument for the direct measurement of nitrate in natural waters and wastewater using chromotropic acid is presented. For the first time, the chromotropic method for nitrate analysis has been transferred to a microfluidic chip configuration that can withstand the extremely acidic nature of the reagent within a field deployable platform. This simple method employs one reagent mixed in a 1 : 1 ratio with the sample to produce a yellow colour absorbing strongly at 430 nm. A stopped flow approach is used which, together with the very rapid kinetics and simple reagent stream, enables an uncomplicated microfluidic design and field deployable platform with a sample throughput of 9 samples per h, limits of detection of 0.70 mg L−1 NO3− and 0.31 mg L−1 NO3− for seawater samples, with a dynamic linear range from 0–80 mg L−1 NO3− and long-term reagent stability of up to 6 months. Validation was achieved by analysing split water samples by the analyser and ion chromatography, resulting in an excellent correlation co-efficient of 0.9969. The fully integrated sensing platform consists of a sample inlet with filter, storage units for chromotropic reagent and standards for self-calibration, pumping system which controls the transport and mixing of the sample, a microfluidic mixing and detection chip, and waste storage, all contained within a ruggedized, waterproof housing. The optical detection system consists of a LED light source with a photodiode detector, which enables sensitive detection of the coloured complex formed. The low cost of the platform coupled with integrated wireless communication makes it an ideal platform for in situ environmental monitoring.

The nonlinear optical properties of a new azo dye (1.8-Dihydroxy-naphthalin-3,6 disulfonic acid-[2-(4-azo)]-N-(2-pyrimiding)-benzene sulfonamide) in Dimethyl sulfoxide solvent were studied by Z-scan technique using cw diode laser at 532 nm. The nonlinear absorption coefficient and the nonlinear refractive index of the dye were calculated using the open aperture Z-scan and the closed aperture Z-scan techniques respectively. The sample showed a negative and large nonlinear refractive index value of $$-4.06\times 10^{-9}\,\hbox {cm}^{2}/\hbox {W}$$ , and reverse saturable absorption with high value of nonlinear absorption coefficient equal to $$1.37\times 10^{-4}\,\hbox {cm/W}$$ . Diffraction ring patterns were generated in the azo dye sample under cw laser beam irradiation together with optical limiting of the azo dye solution was demonstrated. These results indicate that the new dye is a promising candidate for applications in nonlinear optical devices.

We report a sensitive and selective method for determination of boron in uranium samples by spectrofluorimetry in synchronous derivative mode. This method is based on the complexation of non-fluorescent boron with fluorescent chromotropic acid to form fluorescent boron–chromotrope complex. The spectrum of native fluorescence of chromotropic acid seriously overlaps with that of the complex and hence, synchronous derivative mode was employed in which physical separation of excess ligand and complex is not necessary. With the optimized experimental and instrumental conditions, limit of detection obtained is 2 ng mL −1 . The linear concentration range is 5–100 ng mL −1 with regression coefficient better than 0.997. The precision is better than 5% at 10 ng mL −1 level and 3% at 50 ng mL −1 level ( n =9). Fluorescence quenching by residual matrix elements in the final sample solution is corrected by slope-ratio method. The method is validated with reference materials and successfully applied to the uranium nuclear fuels with the accuracy of ±10%. The proposed method reduces sample size requirement; thereby reducing load of uranium recovery from analytical waste in case of enriched uranium based samples.

A simple and low-cost assay for melamine is introduced that is making use of silver nanoparticles (AgNPs) functionalized with chromotropic acid (CTA). The surface of the AgNPs was capped with chromotropic acid which warrants the NPs to remain in stable and dispersed form. The presence of melamine induces the aggregation of the CTA-AgNPs due to the hydrogen bond interaction between CTA and melamine. This is accompanied by a color change from yellow to orange which can be observed with bare eyes. The method allows melamine to be quantified by absorptiometry with a linear response in the concentration range from 0.10 to 1.5 μM (R = 0.9996) and a detection limit of 36 nM which was much lower than the safe limits (20 μM in both the USA and EU, 8 μM for infant formula in China, 1.2 μM in the CAC review for melamine in liquid infant formula). The assay displays high selectivity to melamine over its structural analogs such as cyanuric acid, 2,4,6-trimethy-1,3,5-triazine, and phloroglucinol owing to the fact that only melamine can act as the hydrogen donor to form hydrogen bonds with the sulfo groups of the CTA-capped AgNPs. The method was successfully applied to the determination of melamine in spiked liquid milk and the average recovery was 99 %. Most amino acids and a high content of calcium do not interfere in this assay.

Covalent grafting of chromotropic acid (CA) moiety to a glassy carbon electrode was performed by electrochemical reduction of the corresponding diazonium cation generated in situ. Grafted electrodes were subjected to the electrochemical detection of multivalent cations using Fe(CN)6 3-/4- as an electrochemical probe molecule. In the absence of metal cations, redox reaction of the anionic probe was depressed by electrostatic repulsion between the probe and negatively charged CA moieties on the electrode surface. Binding of tetravalent cations such as Zr(IV) and Hf(IV) and trivalent cations such as Al(III) and lanthanide(III) to the CA moiety on the electrode surface resulted in an increase in the current intensity of the probe due to a decrease in electrostatic repulsion. Highly selective detection of the tetravalent cations was achieved in the micromolar concentration range at pH 1.0. © The Japan Society for Analytical Chemistry.

Background The US Centers for Disease Control and Prevention ensured adequate performance of the routine triglycerides methods used in Japan by a chromotropic acid reference measurement procedure used by the Centers for Disease Control and Prevention lipid standardization programme as a reference point. We examined standardized data to clarify the performance of routine triglycerides methods. Methods The two routine triglycerides methods were the fluorometric method of Kessler and Lederer and the enzymatic method. The methods were standardized using 495 Centers for Disease Control and Prevention reference pools with 98 different concentrations ranging between 0.37 and 5.15 mmol/L in 141 survey runs. The triglycerides criteria for laboratories which perform triglycerides analyses are used: accuracy, as bias ≤5% from the Centers for Disease Control and Prevention reference value and precision, as measured by CV, ≤5%. Results The correlation of the bias of both methods to the Centers for Disease Control and Prevention reference method was: y (%bias) = 0.516 × (Centers for Disease Control and Prevention reference value) −1.292 ( n = 495, R2 = 0.018). Triglycerides bias at medical decision points of 1.13, 1.69 and 2.26 mmol/L was −0.71%, −0.42% and −0.13%, respectively. For the combined precision, the equation y (CV) = −0.398 × (triglycerides value) + 1.797 ( n = 495, R2 = 0.081) was used. Precision was 1.35%, 1.12% and 0.90%, respectively. It was shown that triglycerides measurements at Osaka were stable for 36 years. Conclusions The epidemiologic laboratory in Japan met acceptable accuracy goals for 88.7% of all samples, and met acceptable precision goals for 97.8% of all samples measured through the Centers for Disease Control and Prevention lipid standardization programme and demonstrated stable results for an extended period of time.

In this work, a new, rapid and reliable method for the determination of boron in water samples by dispersive liquid-liquid microextraction based on the solidification of a floating organic drop (DLLME-SFO) prior to fluorescence spectra analysis was developed. As a result of its complexation with boric acid, the method relies on the enhancement of the fluorescence (λex = 350 nm, λem = 373 nm) of chromotropic acid. The influences of DLLME-SFO parameters, including the extraction solvent type and its volume, pH, the disperser solvent type and its volume, and salt effects were investigated. Under the optimized conditions, the limit of detection was 0.11 ng L(-1), with a preconcentration factor of 86 times. The calibration curve was linear in the range of 0-40 nM. The proposed method has also been successfully applied to analyze real water samples and the relative recoveries of water samples ranged from 86.9 to 93.2%.

A method for the on-line absorptiometric determination of trace amounts of boron in steels was developed using an anion-exchange column presorbed with chromotropic acid. The on-line reaction and separation were achieved by controlling the pH in order to accelerate the complex formation in the column by 2.7 and to stabilize the complex at pH 8 for the selective elution of a 1:2 complex and its detection at 350 nm. The effects from the iron matrix in the sample were effectively removed by using EDTA as a masking agent; a low limit for boron detection (3σ) of 0.04 µg g(-1) was obtained.

In acidic medium, thorium (IV) can react with a bisazo dye of chromotropic adds such as arsenazo HI (AA in), arsenazo M (AA M), chlorophosphonazo III (CPA III) and chlorosulphonphenol S (CSP S) to form an anionic chelate which further interacts with some proteins to produce a complex. This results in a significant enhancement of intensity of the resonance Rayleigh scattering (RRS) and the appearance of a new RRS spectrum. There are a few obvious RRS peaks in the range of 400–470 nm and the most intensive peak of them is located at 470 nm. The intensity of RRS is directly proportional to the concentration of protein in the range of 0—l.oμg-mL−1 for Th(IV)-CPA III system, 0–2.8 μg-mL−1 for Th(IV)-AA M system, 0–2.0 μg·mL−1 for Th(IV)-AA III system and 0–0.28 μg·mL−1 for Th(IV)-CSP S system, respectively. The detection limits for BSA (3s) are 10.7 ng·mL−1 for Th (IV)-CPA III, 6.3 ng·mL−1 for Th(IV)-CSP S, 13.6 ng·mL−1 for Th(IV)-AA III and 22.1 ng·mL−1 for Th(IV)-AA M, respectively. This new RRS method has high sensitivity and fairly good selectivity and can be applied to the direct determination of proteins in human serum with satisfactory results.

Two simple and highly sensitive spectrophotometric methods were developed for the quantitative determination of the drug sildenafil citrate (SC), Viagra, in pure form and in pharmaceutical formulations, through ion-associate formation reactions (method A) with mono-chromotropic acid azo dyes, chromotrope 2B (I) and chromotrope 2R (II) and ion-pair reactions (method B) with bi-chromotropic acid azo dyes, 3-phenylazo-6-o-carboxyphenylazo-chromotropic acid (III), bis-3,6-(o-hydroxyphenylazo)-chromotropic acid (IV), bis-3,6-(p-N,N-dimethylphenylazo)-chromotropic acid (V) and 3-phenylazo-6-o-hydroxyphenylazo-chromotorpic acid (VI). The reaction products, extractable in methylene chloride, were quantitatively measured at 540, 520, 540, 570, 600 and 575 nm using reagents, I–VI, respectively. The reaction conditions were studied and optimized. Beer's plots were linear in the concentration ranges 3.3–87.0, 3.3–96.0, 5.0–115.0, 2.5–125.0, 8.3–166.7 and 0.8–15.0 μg mL −1 with corresponding molar absorptivities 1.02 × 10 4 , 8.34 × 10 3 , 6.86 × 10 3 , 5.42 × 10 3 , 3.35 × 10 3 and 2.32 × 10 4 L mol −1 cm −1 using reagents I–VI, respectively. The limits of detection and Sandell's sensitivities were calculated. The methods were successfully applied to the analysis of commercial tablets (Vigoran) and the recovery study reveals that there is no interference from the common excipients that are present in tablets. Statistical comparison of the results was performed with regard to accuracy and precision using Student's t - and F -tests at 95% confidence level. There is no significant difference between the reported and proposed methods with regard to accuracy and precision.

A kinetic method has been developed for the spectrophotometric determination of subnanogram per milliliter levels of vanadium in the presence of large amounts of sodium chloride. The method is based on the catalytic effect of vanadium(V) on the oxidative coupling of N,N-diphenylhydrazine with chromotropic acid in the presence of bromate. In this reaction, chloride enhanced the catalysis of vanadium(V). Vanadium(IV) could be also determined because of its oxidation by bromate. By measuring the change in absorbance of the dye produced at a fixed time, vanadium(IV) and vanadium(V) in the range of 0.01–0.2 ng mL−1 could be determined. The relative standard deviation was 2.0% for ten determinations of 0.1 ng mL−1 vanadium(V). Interferences from diverse ions could be suppressed by the use of ethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic acid) as a masking agent. The method was successfully applied to the determination of vanadium(IV) and vanadium(V) in chloride-rich samples.

Three simple, rapid, and sensitive spectrophotometric methods for the determination of traces and ultratraces of tellurium(IV) were studied. These methods were based on either the oxidation of 4-bromophenylhydrazine (4-BPH) by tellurium in a basic medium and coupling with N-(1-naphthyl)ethylenediamine dihydrochloride (NEDA) to give a purple-colored product, the oxidation of 3-methyl-2-benzothazoline hydrazone hydrochloride (MBTH) by tellurium in a basic medium and coupling with chromotropic acid (CA) to yield a red-colored species, or the oxidation of 2,3-dimethoxystrychnidin-10-one (2,3-DMSO) by tellurium in an acidic medium to yield an orange-colored derivative. Beer’s law was obeyed in the range 1.0–25 μg/mL (purple-colored product), 0.7–20 μg/mL (red-colored species), and 0.3–15 μg/mL (orange-colored derivative). The reaction conditions and other analytical parameters were investigated to enhance the sensitivity of the proposed methods. The tolerance limit of various ions has been studied. The methods were applied to the analysis of tellurium in water samples (waste, river, lake, and spring), plant materials, soil samples, and telluride thin films. The results obtained were superior to those obtained using the reported method. The performances of the proposed methods were evaluated in terms of ‘t’-test and variance ratio ‘f’-test, which indicate the advances of the proposed methods over reported methods.

A method for solid phase extraction of trace metals such as Cd2+, Cr6+, Cu2+, Fe3+, Mn2+, Ni2+, Pb2+ and Zn2+ using nanometer-sized alumina coated with chromotropic acid prior to determination by inductively coupled plasma atomic emission spectrometry (ICP-AES) has been developed. Various influencing parameters on the separation and preconcentration of trace metals, pH, flow rate, sample volume, amount of adsorbent, concentration of eluent and sorption kinetics have been studied. The detection limits for Cd2+, Cr6+, Cu2+, Fe3+, Mn2+, Ni2+, Pb2+ and Zn2+ were found to be 0.14, 0.62, 0.22, 0.54, 0.27, 0.28, 0.53 and 0.38 ng ml− 1, respectively. The adsorption capacity of the solid phase adsorption material is 10.3, 11.3, 14.5, 16.4, 15.1, 11.7, 15.4 and 16.8 mg g− 1 for Cd2+, Cr6+, Cu2+, Fe3+, Mn2+, Ni2+, Pb2+ and Zn2+, respectively. The preconcentration factor was obtained in the range of 50–100 for all studied metal ions. Coexisting ions over a high concentration range have not shown any significant effects on the determination of aforesaid metal ions. The accuracy of the proposed method was tested by standard reference materials (NIST 1643e: water, NIST 1573a: tomato leaves and NIST 1568a rice flour) and natural waters and the results obtained were in good agreement with the certified values.

The interaction of aromatic sulfonates of azo and diazo components in diazotization and azocoupling reactions electrostatically immobilized on gelatin solidified gel was studied. It was found that, among the variety of the functional groups of the polymer (amino, hydroxy, and carboxy groups and guanidine, phenol, and sulfur-containing amino acid residues), some groups are capable of protonation and are responsible for the efficient electrostatic immobilization of aromatic sulfonates with amino and hydroxy groups. A sufficiently high capacity of the polymer gel causes the formation of a relatively large amount of immobilized compounds, which makes it possible to conduct different types of synthetic analytical reactions of the formation of azo dyes in these gelatin gels in the real-time mode. It was demonstrated that, in all cases, the rate-determining step is external diffusion. These effects were used for the preparation of irreversible sensing elements suitable for measurements of calibration functions using the fixed-time technique or the tangent method in the determination of nitrites in solutions.

We have previously reported basic data on the specificity of the color reaction of 3,4-methylenedioxymethamphetamine (MDMA) and related drugs with chromotropic acid (CTA) and sulfuric acid. In this communication, we report an extended line of experiments that optimized reaction conditions, and we describe the application of this method to screening for MDMA or 3,4-methylendioxyamphetamine (MDA) in seized tablets. The optimal concentration of CTA and optimal reaction time at room temperature were 1.0 mM and 30 min, respectively. Final concentrations of MDMA of less than 100 μM should be used to avoid nonspecific color development. The CTA-dependent color reaction was also studied using aqueous extracts from seized tablets containing MDMA or MDA. On the basis of our results, we conclude that the present procedure is useful for screening for MDMA and MDA in seized tablets.

The present work reports the first sequential injection (SI) method for the spectrophotometric determination of Ti(IV). The method is based upon the reaction of Ti(IV) with chromotropic acid (CA) in acidic medium to form a water-soluble complex (lambda(max)=420nm). The chemical and instrumental variables of the system that affected the reaction were studied. Selectivity was greatly enhanced using ascorbic acid. A linear calibration graph was obtained in the range 0.2-10.0mgl(-1) Ti(IV) at a sampling frequency of 24h(-1). The precision was satisfactory (s(r)=1.5% at 5.0mgl(-1) Ti(IV), n=12) and the 3sigma limit of detection, c(L), was 0.7mgl(-1) (n=10). The developed method proved to be adequately selective and was applied successfully to the analysis of real samples (dental implant and natural Moroccan phosphate rock) giving accurate results based on recovery studies (98-105%).

Two simple and sensitive spectrophotometric methods (M 1 and M 2 ) for the determination of mosapride in pure and in pharmaceutical preparations are described. These methods are based on the interaction of diazotized mosapride (MSP) couples with chromotropic acid (CTA) [M 1 ] in alkaline medium and diphenylamine (DPA) [M 2 ] in acidic medium. The resulting azo-dyes exhibit maximum absorption at 560 nm and at 540 nm for methods M 1 and M 2 , respectively. All variables were studied in order to optimize the reaction conditions. No interferences were observed from excipients, and the validity of the each method was tested against reference method.

Optimum conditions were found for the complexation of erbium(III) with sodium 2-(2,3-dimethyl-4-phenylazopyrazolone)naphthalene-1,8-dihydroxy-3,6-disulfonate in the presence and absence of cetylpyridinium chloride. The component ratios were 1:2 and 1:1:1 in the homo-and mixed-ligand complexes, respectively. The effect of foreign ions on complexation was studied. A procedure was developed for the photometric determination of erbium in a volcanogenic rock.

A simple, sensitive, and rapid flow-injection spectrophotometric method was developed for the determination of trace amounts of selenium(IV). The method is based on the oxidation reaction of 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) by selenium(IV) followed by the coupling reaction with chromotropic acid (4.5-dihydroxy naphthalene-2.7-disulphonic acid) in a basic medium (phosphate buffer, pH 10.5) to give a pink derivative with λmax 530 nm that is stable for more than 7 days at 35°C. The reaction and flow conditions of the full experimental design were optimized. A detection limit (2s) of 0.25 μg/L Se(IV) was obtained at a sampling rate of 10 samples per hour. Beer’s law is obeyed for a Se(IV) concentration range of 0.05–0.5 μg/mL at the wavelength of maximum absorption. The detailed study of various interference ions indicates that the method is highly selective. The method was successfully applied to the determination of traces of selenium(IV) in various water samples. The results obtained were in good agreement with those obtained by the reported methods at the 95% confidence level.

A chromotropic acid-functionalized polyurethane foam has been developed for use in an on-line preconcentration system for cobalt and nickel determination. The packing material was prepared by covalent coupling of chromotropic acid with the polyurethane foam through an azo group. Co and Ni ions were sorbed in the mini-column, from which they could be eluted directly to the nebulizer-burner system of a flame atomic absorption spectrometer. Elution of cobalt and nickel from the mini-column can be accomplished with 0.50 and 0.75 M HCl solutions, respectively. The enrichment factors obtained were 22 (Co) and 27 (Ni), for 60 s preconcentration time, and 57 (Co) and 59 (Ni), if a preconcentration time of 180 s was used. Under the optimum conditions, the proposed procedure allowed the determination of metals with detection limits of 0.43 (cobalt) and 0.52 microg/L (nickel), respectively, on using preconcentration periods of 180 s. The accuracy of the developed procedure was evaluated by analysis of the certified reference materials NIST 1515 Apple Leaves and NIST 1570a Spinach Leaves. The method was applied to the analysis of lettuce samples. The contents of cobalt in the samples analyzed varied from 0.75 to 0.98 microg/g. Nickel was not detected in the lettuce samples.

The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (λex. = 347 nm, λem. = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas-diffusion cell was thermostated at 40 °C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09–3.41 mg l− 1, while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (sr = 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l− 1 level, respectively). The developed method proved to be adequately selective and sensitive with 3σ limit of detection equal to cL = 0.03 mg l− 1. The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1–105.9%.

An agarose-based anion exchanger (Q-Sepharose) was loaded with chromotropic acid (CTA) and used for column preconcentration and determination of copper by flame AAS. Preliminary experiments indicated that a sample pH of 5.7-6.5 is best suited for accumulation of copper and a 2.5ml portion of a 0.02moll(-1) HCl solution can efficiently desorb the analyte from the column. An incomplete factorial design was used for optimization of five different variables that affect recovery of copper. The results indicated that ionic strength, pH and sample volume variables are the most important effects, respectively. Hence, these variables and their possible interactions were studied more carefully. In optimized conditions, the column could tolerate up to 0.18moll(-1) sodium nitrate in the matrix. A 5ml portion of a 0.02moll(-1) CTA was sufficient for loading of a 0.5ml column prior to preconcentration of copper from a 150ml sample solution. Matrix ions of Ca(2+), Mg(2+), Na(+) and K(+) and potentially interfering ions of Pb(2+), Ni(2+), Cd(2+), Co(2+), Zn(2+) and Mn(2+) with relatively high concentrations did not have any significant effect on the recovery of the analyte. A preconcentration factor of 60 and a detection limit of 1.0mugl(-1) was obtained for the determination of copper by the flame AAS method. A precision better than 2.5%, expressed as R.S.D., was also achieved. Application of the method to tap water and two different river water samples resulted in values well confirmed by direct determinations with ET-AAS.

Ozone has become the oxidant of choice for water disinfection, especially in large water treatment facilities. This paper describes a fast and sensitive method for the determination of ozone content by reaction with photoactivated chromotropic acid (CA, 4,5-dihydroxynaphthalene-2,7-disulfonic acid), which results in intense chemiluminescence (CL). Freshly ozonated water from a recirculating ozonizer/reservoir is injected into a carrier stream of deionized water in the flow-injection mode. This flow mixes with a stream of photoactivated CA solution in a spiral cell placed directly on top of an inexpensive miniature (8mm diameter active area) photomultiplier tube (PMT). Alkaline CA is photoactivated by passing it through a FEP-Teflon((R)) coil (residence time approximately 50s) wrapped around a 1W UV lamp emitting at 254nm; without photoactivation, the signal is approximately 70-fold lower. The S/N=3 limit of detection for aqueous ozone is 3mugl(-1) and good response slope is obtained up to an ozone concentration of 1.4mgl(-1), the highest that could be made in this study. The response obeyed a quadratic equation with r(2)=0.9984. No interference from permanganate ion is observed. The proposed system was applied to the monitoring of ozonation status of a playa lake water that exhibited significant ozone demand.

A novel, single and robust solid surface fluorescence-based sensing device assembled in a continuous flow system has been developed for the determination of trace amounts of aluminium in water samples. The proposed method is based on the transient immobilization of the target species on an appropriate active solid sensing zone (C18 silica gel). The target species was the fluorogenic chelate, formed as a result of the on-line complexation of Al(III) with chromotropic acid (CA) at pH 4.1. The fluorescence of the complex is continuously monitored at an emission wavelength of 390 nm upon excitation at 361 nm. The instrumental, chemical and flow-injection variables affecting the fluorescence signal were carefully investigated and optimized. After selecting the most suitable conditions, the sensing system was calibrated in the range 10–500 μg l−1, obtaining a detection limit of 2.6 μg l−1, and a R.S.D. of 2.2%, with a sampling frequency of 24 h−1. In addition, the selectivity of the proposed methodology was evaluated by performing interference studies with different cations and anions which could affect the analytical response. Finally, the proposed method, which meets the EU regulations regarding the aluminium content in drinking waters, was satisfactorily applied to different water samples, with recoveries between 97 and 105%. The simplicity, low cost and easy operation are the main advantages of the present procedure.

2,3-Dihydroxynaphthalene forms a strong chelate with titanium over the pH range 4 to 9. At pH 4–5, titanium is extracted into ethyl acetate along with iron, leaving behind V, Nb, Mo, and a host of elements present in complex matrices of rock samples. In the extract, titanium is easily separated from iron after raising the pH of the medium and re-extracting. The method is free from any interference. The sensitivity of the method is 3.2 × 104 L · mol−1 cm−1. The method has been applied to a number of diverse samples including rocks and minerals. The precision of the Ti method is excellent. This method has been compared with tiron, chromotropic acid, diantipyrilmethane (DAM) and other existing spectrophotometric methods used in the analysis of rocks, ores and minerals. The proposed method has definite advantages over most spectrophotometric methods in terms of sensitivity, selectivity, reproducibility and simplicity.

This work reports the application of a sequential-injection analysis (SIA) method for the determination of boron. The method relies on the enhancement of the fluorescence ( λ ex =313 nm, λ em =360 nm) of chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulphonic acid-CA) as a result of its complexation with boric acid (BA). Individual zones of the sample, the CA solution in a suitable buffer and a NaOH solution were aspirated in the holding coil of the SIA apparatus. As the zones were propelled towards the detector, zone penetration in the sample–CA interfaces occurred resulting in the formation of the strongly fluorescent BA–CA complex. The native fluorescence of the CA was quenched by the alkaline environment established as a result of the mixing at the CA–NaOH interface. The chemical and instrumental parameters affecting the fluorescence intensity were investigated and the influence of potential interferents was investigated. After selecting the most suitable conditions, the calibration plot for boron was linear in the range of 8–350 μg l −1 with a 3 σ limit of detection of 3 μg l −1 and a relative standard deviation of 2.7% at the 90 μg l −1 boron level ( n =8). Finally, the method was applied to the determination of boron in natural waters and pharmaceutical products with revoveries in the range of 96–106%.

In the present study, a spectrophotometric method for the determination of formaldehyde by using chromotropic acid was devised, in which the use of potentially hazardous and corrosive concentrated sulfuric acid was eliminated and advantageously replaced by a mixture of H 3 PO 4 and H 2 O 2 . The reaction between formaldehyde and chromotropic acid (CA) in a concentrated phosphoric acid medium was accelerate by irradiating the mixture with microwave energy for 35 s (1100 W), producing a violet–red compound ( λ max =570 nm). Beer's Law is obeyed in a concentration range of 0.8–4.8 mg l −1 of formaldehyde with a good correlation coefficient ( r =0.9968). The proposed method was applied in the analysis of formaldehyde in commercial disinfectants. Recoveries were within 98.0–100.4%, with standard deviations ranging from 0.03 to 0.13%.

A novel chromogenic reagent, 2-(2-sulfo-4-acetylphenylazo)-7-(2,4,6-trichlorophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid 1, was prepared by diazo coupling of 4-acetylaniline-2-sulfonic acid and 2,4,6-trichloroaniline to chromotropic acid through –N=N– groups. Based on this reagent, a simple, sensitive and selective spectrophotometric method was developed for the determination of lead. In 0.20 M phosphoric acid medium, lead reacts with 1 to form a 1:2 blue complex with an absorption maximum of 654 nm. Beer’s law is obeyed in the range of 0–0.6 mg L−1 of lead. The apparent molar absorptivity is 1.25 × 105 L mol−1 cm−1. The detection limit and quantification limit were found to be 0.63 µg L−1 and 2.1 µg L−1, respectively. The relative standard deviation for eleven replicate measurements was of 2.6%. The interference of foreign ions was also investigated. All the other foreign ions studied did not interfere with lead determination except for Ca(II) and Ba(II). The interference caused by Ca(II) and Ba(II) can be eliminated by prior extraction of lead with potassium iodide-methylisobutylketone (KI-MIBK). The proposed method was applied to the determination of lead in certified samples with satisfactory results.

Boron as boric acid was determined as a complex with chromotropic acid at pH 6.0 in an aqueous medium by fluorescence detection/flow-injection analysis. The complex was detected by measuring the fluorescence intensities (λ ex＝ 313 nm, λ em＝ 360 nm). EDTA was used as a buffer component with the role of a masking agent to metal ions. The background fluorescence of chromotropic acid could be decreased by mixing with 0.1 M ammonia water after complex formation, resulting in a stable baseline. The calibration graph was rectilinear over 10 －9 ～ 10 －6 mol dm －3 (M), and the detection limit was 5× 10 －10 M (S/N＝ 3). The reproducibility was 3.61％ (n＝10, with the peak height) at 6×10 －9 M of boron and sample throughput was 40 h －1 . Applications to river water, ion-exchanged water and distilled water could be achived without any pretreatments. For the analysis of ultrapurified water, an evaporation/preconcentration procedure was carried out, because the concentration was under the LOD and no reference water which could be used for the carrier solution or preparation of the reagent solutions.

Voltammetric behavior of titanium(IV) complexes with chromotropic acid, its azo-derivatives: 2-(4-sulfophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonic acid (SPANDS), chromotrope 2B, sulfonazo III and other azo-compounds: calmagite, tropeoline O and kalces was investigated at a hanging mercury drop electrode. These complexes strongly adsorb onto the electrode, thus can be determined by an adsorptive stripping voltammetry (optimal pH about 6). At pH about 3 reduction current enhancement for Ti-kalces complex was observed in the presence of chlorate ions. It is a rare example of a catalytic process with azo-compound as a complexing agent. Signal for Fe-calmagite complex reduction was also observed. Influence of foreign ions and the optimal conditions for titanium determination are described in detail. Additionally, a connection between obtained results and a structure of titanium complexes is discussed.

Optimal conditions were found for the sorption of lanthanum, terbium, and erbium complexes of some derivatives of chromotropic acid: Arsenazo II, Arsenazo III, Carboxyarsenazo, and Chlorophosphonazo III on Silochrom C-120 silica gel in the presence of tetrabutylammonium bromide (TBA). Diffuse reflection coefficients and molar coefficients of the chromaticity functions of the adsorbates were determined. It was demonstrated that the preconcentration of complexes on the solid matrix in the presence of TBA increases the sensitivity of the determination of rare-earth elements by a factor of 5–50 in comparison with solutions; the use of chromaticity characteristics further increases the sensitivity by 1.5–2 orders of magnitude.

The possibility of using three groups of azo compounds in chemical tests based on the principles of precipitation paper chromatography is considered. The first group consists of the reagents showing the highest affinity to cellulose (Congo Red, Brilliant Yellow, Stilbazo, Cadion IREA, Sulfarsazen, and Titan Yellow). These reagents are immobilized on paper and are not washed out of it in acidic, alkaline, and neutral solutions. The immobilization of the reagents results in a bathochromic shift of their absorption bands with respect to their solutions and enhances the acidic properties of the reagents. The second group comprises compounds that are immobilized on paper only in acidic solutions (mono- and bisazo derivatives of chromotropic acid: Arsenazo II, Arsenazo III, Orthanilic K, Sulfochlorophenol S, Chlorophosphonazo III, and Carboxyarsenazo). Their immobilization on paper does not lead to a shift in the absorption spectra and acidic properties. The third group consists of compounds that are immobilized on paper either in acidic or in alkaline solutions (Acid Chrome Dark Blue, Eriochrome Black T, Magneson KhS, and Eriochrome Blue Black R). They are absorbed by cellulose as free acids in acidic solutions and as sodium salts in alkaline solutions. Test procedures have been developed for the determination of acids; alkalis (0.1–100 mM); the total alkalinity of water (0.2–35 mM); the total acidity of water (0.2–20 mM); Cd, Al, and Pb (1–200 mg/L); Al, Th, U, and Zr (0.5–200 mg/L); and the total hardness of water (0.05–40 mM). The length of the colored zone in test strips laminated into a polymer film and contacting the test solution through a narrow edge is the analytical signal. The relative standard deviation does not exceed 30%; the analysis time is 10–15 min.

An electrochemical method for the determination of lead has been developed using overoxidized polypyrrole (OPPy) electrode doped with 2(2-pyridylazo)chromotropic acid anion (PACh 2� ). The PACh 2� acts both as a chelating agent and a counter anion within the polypyrrole matrix. In a typical assay, Pb 2� is accumulated on a solid electrode via the formation of a lead � /PACh complex at open circuit. The electrode containing the Pb 2� PACh 2� is then transferred to a 0.1 M acetate buffer where it is subjected to differential pulse anodic stripping voltammetry. The resulting stripping peak current was linearly related to the concentration of lead. The method has been optimized with respect to pH, concentration of chelating agent, accumulation time, reduction potential and time. The detection limit was found to be 10 ng ml � 1 with a linear range of 0 � /200 ng ml � 1 . The method has been validated for the determination of lead using spiked potable water at 25 ng ml � 1 . The average recovery was 93.4% with a relative standard deviation of 8.54%. # 2002 Elsevier Science B.V. All rights reserved.

The thiazolylazo compounds and their Co(II), Ni(II) and Cu(II) complexes of barbituric acid, uracil, thiouracil, citrazinic acid, chromotropic acid, gallic acid, pyrogallol and salicylic acid were prepared and characterized by 1H NMR, IR and the effect of pH on the electronic absorption spectra. The mode of ionization, the electronic transitions and the dissociation constants were discussed. The stoichiometries of the complexes were of 1:1, 2:1 and 3:2 (M:L). The copper complexes are of isotropic ESR spectra (except that of gallic acid which showed a complicated one) and are of magnetically diluted behaviour with orbital contribution. Detailed DTA data were obtained and discussed.

Four chelating matrices prepared by coupling Amberlite XAD-2 with chromotropic acid (AXAD-2-CA or 1), pyrocatechol (AXAD-2-PC or 2) and thiosalicylic acid (AXAD-2-TSA or 3) through azo spacer and impregnation of Amberlite XAD-7 with xylenol orange (AXAD-7-XO or 4) have been studied for enrichment of lead(II). All the four resins quantitatively sorb Pb(II) at pH 3.0-8.0 when the flow rate is maintained between 2 and 10 mlmin(-1). HNO(3) (0.5-4.0 M) instantaneously elutes Pb(II) from all the four chelating resins. The sorption capacity is in the range 16.0-186.0 mumolg(-1) and loading half time (t(1/2)) between 3.2 and 15.5 min. The tolerance limits of electrolytes (NaCl, NaBr, NaNO(3), Na(2)SO(4), Na(3)PO(4)) and cations (Ca and Mg) are reported. Phosphate interferes in the sorption with 3 and 4. The limit of detection and limit of quantification have been found to be in the ranges 2.44-7.87 and 2.76-8.64 ngml(-1), respectively. Lead has been determined in river (RSD approximately 2.6-12.8%) and tap (RSD approximately 1.8-7.2%) water samples.

A novel method of on-line absorptiometric determination for trace amounts of boron was developed based on the complexation with chromotropic acid presorbed on an anion-exchange column. On-line reaction and separation were achieved by controlling pH conditions in solutions to accelerate the 1:2 complex formation in the concentration process at pH 3 and to stabilize the complex in the separation process at pH 8. About 75% of the boron introduced into the stream was kinetically collected as the 1:2 complex on the column under the experimental conditions. The 1:2 complex was satisfactorily separated from excess reagent and matrix components by changing the concentration of NaClO4 in the eluent and its peak height on the chromatogram monitored at 350 nm was used for calibration. The sensitivity could be enhanced by increasing the sample amount introduced and the detection limits (3sigma) were 162 ng dm(-3) and 45 ng dm(-3) of boron, when 5.0 cm3 and 13.4 cm3 of the samples were used, respectively. The method has been successfully applied to the determination of boron in samples of river water, tap water and ion-exchanged water.