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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 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.

Chromotropic acid has been covalently linked with the benzene ring of Amberlite XAD-2, through an –NN– group, to design a new polymer matrix. Elemental analyses, thermogravimetric analyses and infrared spectra were used to characterize the resulting functionalized Amberlite XAD-2. It was used for the separation and preconcentration of CdII, CoII, CuII, NiII, FeIII and ZnII prior to their determination by flame atomic absorption spectrometry. The optimum pH values for quantitative sorption are 5.0–6.0, 4.0–4.5, 4.5–5.5, 4.0–5.0, 5.0–6.5 and 5.5–7.0 for CdII, CoII, CuII, FeIlI, NiII and ZnII, respectively. All these metal ions can be desorbed with 2 mol l–1 HCl or HNO3 (recovery, 96–100%). The sorption capacity of the resin is 9.35, 3.84, 8.50, 3.24, 6.07 and 9.65 mg g–1 of resin for Cd, Co, Cu, Ni, Fe and Zn, respectively. Tolerance limits for electrolytes NaCl, NaBr, NaNO3, Na2SO4 and Na3PO4 on the sorption of these metal ions are reported. NaNO3, Na2SO4 and Na3PO4 are tolerable up to a concentration level of a few millimoles in the sorption of 0.1 mg l–1 Cd. Similarly, NaNO3 with Cu (0.1 mg l–1) and Na3PO4 with Fe (0.1 mg l–1) interfere when their concentration exceeds a few millimoles. The enrichment of all of these metal ions is quantitative in the presence of 0.1 mol l–1 of MgII and CaII. The preconcentration factors are found to be 100, 150, 100, 120, 200 and 200 for Cd, Co, Cu, Fe, Ni and Zn (concentration level, 5–10 µg l–1), respectively, and their respective t1/2 values are 2.6, 4.3, 2.9, 5.8, 3.4 and 2.4 min. The simultaneous determination of Cd, Co, Cu, Fe, Ni and Zn is possible. The method was applied to the determination of these six metal ions in river water samples (RSD < 7.8%). Cobalt contents of pharmaceutical samples (vitamin tablets) were preconcentrated by the present chelating resin and estimated by flame atomic absorption spectrometry, with RSD < 1.1%.

The authors prepared colloidal dispersions consisting of polyaniline, dopant (perchlorate, benzenesulfonate or polystyrene sulfonate) and surfactant stabiliser [poly(vinyl alcohol)]. The dispersions took up anionic analytes in their oxidised forms and ejected the anions on deprotonation or reduction. Thus, uptake and release were controlled externally by varying the redox potential and/or pH in solution. Organic anions such as chromotropic acid anion and anthraquinone sulfonates were taken up quantitatively into the oxidised dispersion particles and concentrated 250–1000 times. Although the uptake of these anions was quantitative, ejection from the deprotonated or reduced forms was not so. In order to achieve high ejection efficiency, we prepared a dispersion of doping polystyrene sulfonate to introduce immobile negative charge. As a result, the recovery of chromotropic acid increased up to 100% at the cost of uptake capacity. Competitive interactions of the negative charge and targeted anion with the cationic sites in polyaniline were confirmed by electrochemical and electron spin resonance measurements and were responsible for the increase in the recovery. Electrochemical ejection of chromotropic acid was found to be quantitative when methyl viologen was present in solution as an electron mediator.

The catalytic effect of vanadium(v) on the oxidation of chromotropic acid by bromate ion was studied with a view to developing a method for the determination of vanadium(v) in atmospheric aerosols. By monitoring the reaction thermometrically and using the initial-rate method, vanadium was determined over a very favourable linear concentration range (0–50 ppb) with a relative standard deviation of 8.9%. The proposed method is interference-free and can readily be used for the determination of vanadium in atmospheric aerosols. The results obtained were compared with those provided by two techniques frequently used for the same purpose: electrothermal atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry.

A flow-injection system for the spectrophotometric determination of titanium in rocks using chromotropic acid as the colour-forming reagent is described. Sample decomposition involving the use of metaborate was investigated. In addition, the optimization of chemical and physical variables and a study of interfering ions was also carried out. Standard rock samples from the United States Geological Survey and Geological Survey of Japan were used to assess the accuracy of the method. With a solution sampling frequency of 80 h–1, the system yields precise results (relative standard deviation

A spectrophotometric method has been developed for the quantitative determination of aqueous hexamethylenetetramine (HMT) alone, in the presence of large amounts of formaldehyde, and in the presence of urine. The method is based on the perchloric acid hydrolysis of HMT to formaldehyde, oxidation of formaldehyde by hydrous silver(I) oxide, and oxidation of silver(O) with iron(III) in the presence of FerroZine. Optimum conditions were developed and HMT was determined over the range from 3 × 10–7 to 3.3 × 10–6 mol dm–3. The method developed is approximately 7.5 times more sensitive than the chromotropic acid method.

Micro-amounts of titanium(IV) were determined spectrophotometrically using a flow injection manifold and chromotropic acid as a complexing reagent. The various experimental conditions were optimized for the determination of titanium(IV) at 443 nm. Linear calibration was achieved over a titanium concentration range of 5 × 10–5–4.7 × 10–4 mol dm–3. The limit of detection of the proposed method was 25 ng. The method was applied to the determination of titanium in bauxite.

A rapid and sensitive thermometric method for the determination of trace amounts of vanadium(V) based on its catalytic effect on the rate of oxidation of chromotropic acid by bromate in acidic solution is proposed. The reaction rate was obtained graphically from the temperature-time curve. Using the given concentrations of reactants, the extent of oxidation of chromotropic acid is proportional to the concentration of vanadium(V) present. Concentrations in the range 1.2–130 p.p.b. can be determined. The relative standard deviation for 50 p.p.b. of vanadium(V) was 2.2%. As other ions at a 500-fold excess do not interfere, the method has been applied to determine vanadium(V) in petroleum derivatives.

A bisazoic derivative of chromotropic acid has been synthesised on the basis of a study of functional analytical groups in the determination of palladium(II). The reagent thus obtained gives a very sensitive reaction with palladium(II), which enables between 0·1 and 4 µg of palladium per ml to be determined, both alone and in the presence of some other elements. Palladium(II) combines with the reagent in the ratio 1:2, and the instability constant of the compound is 2·89 × 10–7.

Two flow injection (Fl) methods, conventional and stopped-flow, are described for the determination of formaldehyde based on its reaction with pararosaniline in the presence of sulphite ion followed by spectrophotometric detection at 570 nm. The calibration graphs are linear over the ranges 2.0–50 and 0.2–10 µg ml–1 of formaldehyde for conventional and stopped-flow Fl, respectively. The coefficient of variation was 6.3% at the 0.6 µg ml–1 level in the stopped-flow mode, the detection limit being 0.1 µg ml–1 of formaldehyde. Sampling rates of 41 and 18 samples h–1 were achieved in the conventional and stopped-flow modes, respectively, this being a major advantage of these methods. The effect of several organic and inorganic species was studied and only low relative molecular mass aldehydes were found to interfere. The stopped-flow method was applied to the determination of formaldehyde in air in work environments and its accuracy was confirmed by comparing the results with those obtained using the standard chromotropic acid method.

The determination of boron with chromotropic acid has been studied using high-performance liquid chromatography (HPLC). The anionic complex formed between boric acid and chromotropic acid in an aqueous solution was injected on to an anion-exchange column (TSK gel IC-Anion PW, 5 cm × 4.6 mm i.d.) and detected at 350 nm. The complex formation between boric acid and chromotropic acid was enhanced in the presence of octyltrimethylammonium chloride, resulting in higher sensitivity. The calibration graph was rectilinear up to 1.0 µg of boron. The proposed method was applied satisfactorily to the determination of boron in waters and in commercially available chemicals.

Ethanol and xylene vapours were found to interfere with the determination of formaldehyde vapour by the chromotropic acid method, whether water or a mixture of chromotropic and sulphuric acids were used as the scrubbing solution. The interference can be removed by a porous polymer sorbent, Tenax GC. Thus, with a Tenax GC pre-trap, the chromotropic acid method can be applied to the determination of formaldehyde vapour in clinical laboratories where alcohol and xylene vapours are often encountered. The advantages of selecting chromotropic-sulphuric acid instead of water as the scrubbing solution are discussed.

A simple method for removing the excess of co-extracted reagent in the ion-association extraction of metal complex anions with quaternary ammonium salts has been applied successfully to the spectrophotometric determination of boron at the parts per 109 level in river water with 1,8-dihydroxynaphthalene 4-sulphonic acid (DHNS) and tetradecyldimethylbenzylammonium chloride (zephiramine). The procedure using DHNS described here greatly improves the previous method using chromotropic acid. Acetate buffer (pH 3.8), EDTA and DHNS are added to the sample solution (less than 50 ml) and the pH of the resulting solution is adjusted to 10.2. Then sodium chloride is added and the mixture is shaken with 5 ml of a 2 × 10–3M solution of zephiramine in 1,2-dichloroethane (DCE). The organic phase is washed once with 10 ml of a back-washing solution (1.0 M in sodium chloride, pH 10.2) and the absorbance of the organic phase is measured in a quartz cell. The boron complex with DHNS is extracted quantitatively into DCE and its apparent molar absorptivity in DCE is 2.4 × 104 l mol–1 cm–1 at 341 nm. The detection limit and precision achieved with the method are 1 µg l–1 and 5%, respectively. EDTA allows most interferences caused by metals to be suppressed, and other sources of bias due to the effect of co-extractable anions are almost eliminated by adding relatively large amounts of sodium chloride to the extraction system. Parts per 109 amounts of boron present as boric acid in river water are determined spectrophotometrically, and the results obtained are successfully compared with those obtained by the methylene blue method.

A comparative study of the determination of nitrates in calcareous soils by the chromotropic acid, phenoldisulphonic acid and nitrate ion-selective electrode methods was investigated, using 0.02 N copper(II) sulphate solution as extractant, which, in addition to being a preservative for nitrates, helps filtration and eleminates interference by hydrogen carbonates in the ion-selective electrode method. Silver sulphate, which had no effect on either procedure, can be added to the extractant for the precipitation of chlorides.Nitrate in soil suspensions was determined by the ion-selective electrode method. Nitrites if present were eliminated by acidifying the extract with 1 N sulphuric acid containing sulphamic acid.To avoid reaction between soluble organic matter and sulphuric acid in the chromotropic acid method, reagents were added in two steps with continuous cooling. Nitrites were eliminated as in the ion-selective electrode method.Both methods were faster than the phenoldisulphonic acid method and gave identical results; the correlation coefficient was 0.999 8.

A catalytic reaction rate method is described for the determination of trace amounts of CuII. The method is based on the CuII-catalysed oxidation of chromotropic acid (the disodium salt of 4,5-dihydroxynaphthalene-2,7-disulphonic acid) by hydrogen peroxide. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance at 430 nm. A detailed study of the kinetic characteristics of the above reaction has been carried out and the proposed method allows the determination of CuII in the range 12.7–190.6 ng ml–1; the precision and accuracy were found to be within 1–2%. The method has been successfully applied to the determination of copper in tap and sea water samples and in biological materials.

A method of removing the excess of reagent extracted into an organic phase in the solvent extraction of metal complex anions with quaternary ammonium salts was applied to the solvent extraction of the boron complex anion formed with chromotropic acid (1,8-dihydroxynaphthalene-3,6-disulphonic acid) by using zephiramine (tetradecyldimethylbenzylammonium chloride). EDTA, chromotropic acid, zephiramine and buffer (pH 3.5) are added to the sample solution, which is then shaken with 1,2-dichloroethane. The organic phase is washed twice with a back-washing solution (0.6 M in sodium chloride, pH 9.2) and the absorbance of the organic phase measured in a quartz cell. The boron complex is extracted quantitatively into the 1,2-dichloroethane and its apparent molar absorptivity in 1,2-dichloroethane is 1.4 × 104 l mol–1 cm–1 at 351 nm. Micro and trace amounts of boron in natural waters are determined spectrophotometrically.

A simple and sensitive catalytic method is proposed for the determination of FeIII; the method is based on the catalytic effect of FeIII on the oxidation of chromotropic acid (the disodium salt of 4,5-dihydroxynaphthalene-2,7-disulphonic acid) by hydrogen peroxide. The reaction was followed spectrophotometrically by measuring the rate of change in the absorbance of the coloured product at 440 nm. Micro-amounts of FeIII(11.2–167.6 ng ml–1) can be determined with good accuracy and reproducibility. The influence of foreign ions on the accuracy of the results was investigated and the method was found to be adequately selective and has been satisfactorily applied to the determination of FeIII in tap and sea water samples and in biological materials.

Contrary to previous reports ethanol has been found to interfere with the colorimetric determination of formaldehyde and glycollic acid with 1,8-dihydroxynaphthalene-3,6-disulphonic acid (chromotropic acid) or 2,7-dihydroxynaphthalene in concentrated sulphuric acid. The effect is greater for glycollic acid than for formaldehyde. The mechanism for these observations is given.