Reverse flow injection spectrophotometric determination of iron(III) using chlortetracycline reagent

A simple reversed flow injection colourimetric procedure for determining iron(III) was proposed. It is based on the reaction between iron(III) with chlortetracycline, resulting in an intense yellow complex with a suitable absorption at 435 nm. A 200 μl chlortetracycline reagent solution was injected into the phosphate buffer stream (flow rate 2.0 ml min⁻¹) which was then merged with iron(III) standard or sample in dilute nitric acid stream (flow rate 1.5 ml min⁻¹). Optimum conditions for determining iron(III) were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 0.5–20.0 μg ml⁻¹. The detection limit (3σ) and the quantification limit (10σ) were 0.10 and 0.82 μg ml⁻¹, respectively. The relatives standard deviation of the proposed method calculated from 12 replicate injections of 2.0 and 10.0 μg ml⁻¹ iron(III) were 0.43 and 0.59%, respectively. The sample throughput was 60 h⁻¹. The proposed method has been satisfactorily applied to the determination of iron(III) in natural waters.     

Efficiency and mechanism of new poly(acryl-phenylamidrazone phenylhydrazide) chelating fiber for adsorbing trace Ga, In, Bi, V and Ti from solution

A new po1y(acrylphenylamidrazone phenylhydrazide) chelating fiber is synthesized from polyacrylonitrile fiber and used for preconcentration and separation of trace Ga(III), In(III), Bi(III), V(V) and Ti(IV) from solution (5–50 ng ml⁻¹ Ti(IV) or V(V) and 50–500 ng ml⁻¹ Ga(III), In (III) or Bi(III) in 1000–100 ml of solution can be enriched quantitatively by 0.15 g of fiber at a 4 ml min⁻¹ flow rate in the pH range 5–7 with recoveries >95%). These ions can be desorbed quantitatively with 20 ml of 4 M hydrochloric acid at 2 ml min⁻¹ from the fiber column. When the fiber which had been treated with concentrated hydrochloric acid and washed with distilled water until neutral was reused eight times, the recoveries of the above ions by enrichment were still >95%. Two-hundred-fold to 10 000-fold excesses of Cu(II), Zn(II), Ca(II), Mn(II), Cr(III), Fe(III), Ba(II) and Al(III) caused little interference in the determination of these ions by inductively coupled plasma-atomic emission spectrometers (ICP-AES). The relative standard deviations for enrichment and determination of 50 ng ml⁻¹ Ga, In or Bi and 10 ng ml⁻¹ V or Ti are in the range 1.2–2.7%. The contents of these ions in real solution samples determined by this method were in agreement with the certified values of the samples with average errors <3.7%.     

Determination of As(III) and total inorganic arsenic by flow injection hydride generation atomic absorption spectrometry

A simple procedure was developed for the direct determination of As(III) and As(V) in water samples by flow injection hydride generation atomic absorption spectrometry (FI–HG–AAS), without pre-reduction of As(V). The flow injection system was operated in the merging zones configuration, where sample and NaBH₄ are simultaneously injected into two carrier streams, HCl and H₂O, respectively. Sample and reagent injected volumes were of 250 μl and flow rate of 3.6 ml min⁻¹ for hydrochloric acid and de-ionised water. The NaBH₄ concentration was maintained at 0.1% (w/v), it would be possible to perform arsine selective generation from As(III) and on-line arsine generation with 3.0% (w/v) NaBH₄ to obtain total arsenic concentration. As(V) was calculated as the difference between total As and As(III). Both procedures were tolerant to potential interference. So, interference such as Fe(III), Cu(II), Ni(II), Sb(III), Sn(II) and Se(IV) could, at an As(III) level of 0.1 mg l⁻¹, be tolerated at a weight excess of 5000, 5000, 500, 100, 10 and 5 times, respectively. With the proposed procedure, detection limits of 0.3 ng ml⁻¹ for As(III) and 0.5 ng ml⁻¹ for As(V) were achieved. The relative standard deviations were of 2.3% for 0.1 mg l⁻¹ As(III) and 2.0% for 0.1 mg l⁻¹ As(V). A sampling rate of about 120 determinations per hour was achieved, requiring 30 ml of NaBH₄ and waste generation in order of 450 ml. The method was shown to be satisfactory for determination of traces arsenic in water samples. The assay of a certified drinking water sample was 81.7±1.7 μg l⁻¹ (certified value 80.0±0.5 μg l⁻¹).     

A flow-injection renewable surface sensor for the fluorimetric determination of vanadium(V) with Alizarin Red S

Vanadium(V) is determined by a simple bead injection spectroscopy–flow-injection analysis (BIS–FIA) system with spectrofluorimetric detection using a commercially available flow cell (Hellma 176-QS). The 500 μl of a homogeneous bead suspension of an anionic resin (Sephadex QAE A-25) previously loaded with the fluorogenic reagent 1,2-dihydroxyanthraquinone-3-sulfonic acid (Alizarin Red S) was injected to fill the flow cell. Next, V(V) is injected into the carrier and reacts with the immobilized reagent on the active solid support placed in the flow cell to form a fluorescent chelate in the absence of surfactant agents. The complex is so strongly retained on the beads that the regeneration of the solid support becomes extraordinarily difficult, so needing the renovation of the sensing surface which is achieved by means of bead injection. At the end of the analysis, beads are automatically discarded from the flow cell and transported out of the system by reversing the flow.

The measurement of fluorescence is continuously performed at an excitation wavelength of 521 nm and an emission wavelength of 617 nm. Using a low sample volume of 800 μl, the analytical signal showed a very good linearity in the range 2–60 ng ml⁻¹, with a detection limit of 0.45 ng ml⁻¹ and a R.S.D. (%) of 4.22 for 50 ng ml⁻¹ of V(V) concentration (n = 10). The sensor showed both a good selectivity, which could also be increased by the addition of EDTA and F⁻ as masking agents, and applicability to the determination of V(V) in waters, physiological samples (serum and urine) and mussel tissues.     

Development and application of a capillary electrophoresis-electrochemiluminescent method for the analysis of enrofloxacin and its metabolite ciprofloxacin in milk

Enrofloxacin (ENR) is a fluoroquinolone developed exclusively for the use in veterinary practice for the treatment of respiratory and gastrointestinal infections, and ciprofloxacin (CIP) is its main active metabolite. Their contents are regulated by the EU Council Regulation no. 2377/90 in animal edible tissues. We developed a sensitive and rapid method for the determination of ENR and CIP by capillary electrophoresis (CE) with electrochemiluminescence (ECL) detection. The method is based on the detection of aliphatic tertiary or secondary amino moieties in ENR and CIP with end-column tris(2,2-bipyridyl)ruthenium(II) electrochemiluminescence. Parameters that affect separation and detection were optimized. Under the optimized conditions, the calibration functions were linear in the range of 0.03–1 μg ml⁻¹ for ENR and 0.05–1.2 μg ml⁻¹ for CIP. The detection limits of ENR and CIR were 10 ng ml⁻¹ and 15 ng ml⁻¹, respectively, based on the signal-to-noise ratio of 3. The relative standard derivations of the peak height and the migration time for ENR and CIP were less than 4.13%. The developed method was successfully applied to determine ENR and CIP in milk with a solid-phase extraction procedure.     

Spectral studies on the interaction of Amido black 10B with DNA in the presence of cetyltrimethylammonium bromide

The interaction of Amido black 10B (AB) with DNA in basic medium was studied in the presence of cetyltrimethylammonium bromide (CTMAB) based on the measurements of resonance light scattering (RLS), UV–vis, CD spectra, and RLS imaging. The interaction has been proved to give a ternary complex of CTMAB–DNA–AB in Britton–Robinson buffer of pH 11.55, which exhibits strong negative Cotton effect at 233.3 nm and 642.8 nm, and strong RLS signals characterized at 469 nm. Experiments showed that the enhanced RLS intensities (ΔI_RLS) against the mixture of AB and CTMAB are proportional to the concentration of fish sperm DNA (fsDNA) and calf thymus DNA (ctDNA), respectively over the range of 0.03–1.0 and 0.05–1.5 μg ml⁻¹, with the limits of determination (3σ) of 7.3 ng ml⁻¹ for fsDNA and 7.0 ng ml⁻¹ for ctDNA.     

High-performance liquid chromatographic assay of phosphate and organophosphorus pesticides using a post-column photochemical reaction and fluorimetric detection

A sensitive method for the post-column reaction detection of organophosphorus pesticides is described. The method relies on photolysis of the organocompounds by irradiation with a low-pressure mercury lamp (main spectral line, 254 nm) in the presence of peroxydisulfate. The resultant orthophosphate was reacted with molybdate to form molybdophosphoric acid, which subsequently reacted with thiamine to generate thiochrome. Finally, the fluorescence intensity of thiochrome was measured at 440 nm with excitation at 375 nm. Factors affecting the rate of these reactions were optimized so that its contribution to the total band-broadening was negligible.

This detection system was used for the determination of phosphate, acephate and methamidophos, which were separated on an ODS column by isocratic reversed phase chromatography with acetonitrile–water as the mobile phase. A linear relationship between analyte concentration and peak area was obtained within the range 0.016–7.0 μg ml⁻¹ with correlation coefficients greater than 0.9995 and detection limits between 4 and 12 ng ml⁻¹. Intra- and inter-day precision values of about 1.2% R.S.D. (n = 10) and 2.1% R.S.D. (n = 30), respectively, were obtained.

Pesticide residues below ng ml⁻¹ levels could be determined in environmental waters when a preconcentration device was coupled on-line with the HPLC system. Detection limits as low as 0.01 ng ml⁻¹ were achieved for only 250 ml of sample. In the analyses of vegetables and grains, the detection limit was about 1 μg kg⁻¹.     

Application of a new resin functionalised with 6-mercaptopurine for mercury and silver determination in environmental samples by atomic absorption spectrometry

Polystyrene–divinylbenzene (8%) has been functionalised by coupling it through an ---N=N--- group with 6-mercaptopurine. The resulting chelating resin has been characterised by using elemental analysis, thermogravimetric analysis and infrared spectra. The resin is highly selective for Hg(II) and Ag(I) and has been used for preconcentrating Hg(II) and Ag(I) prior to their determination by atomic absorption spectrometry. The maximum sorption capacity for Hg(II) and Ag(I) was found to be 1.74 and 0.52 mmol g⁻¹, respectively, over the pH range 5.5–6.0. The calibration range for Hg(II) was linear up to 10 ng ml⁻¹ with a 3σ detection limit of 0.02 ng ml⁻¹; the calibration range for Ag(I) was linear up to 5 μg ml⁻¹ with a detection limit of 29 ng ml⁻¹. The recoveries of the metals were found to be 99.7±3.8 and 101.3±4.1% at the 95% confidence level for both Hg(II) and Ag(I). In column operation, it has been observed that Hg(II) and Ag(I) in trace quantities can be selectively separated from geological, medicinal and environmental samples.     

Supported liquid membranes for the determination of vanillin in food samples with amperometric detection

A supported liquid membrane system has been developed for the extraction of vanillin from food samples. A porous PTFE membrane is impregnated with an organic solvent, which forms a barrier between two aqueous phases. The analyte is extracted from a donor phase into the hydrophobic membrane and then back extracted into a second aqueous solution, the acceptor. The determination (100–1400 μg ml⁻¹ vanillin) was performed using a PVC-graphite composite electrode versus Ag/AgCl/3MKCl at +0.850 V placed in a wall-jet flow cell as amperometric detector. The solid sample is directly placed in the membrane unit without any treatment, and the analyte was extracted from the sample, passes through the membrane and conduced to the flow cell by the acceptor stream. The limit of detection (3σ) was 44 μg ml⁻¹. The method was applied to the determination of vanillin (9–606 μg g⁻¹) in food samples.     

Effect of pH on the characteristics of potassium permanganate–luminol CL reaction in the presence of trace aluminum(III) and its analytical application

At pHs ≥ 11.45, trace Al was found to enhance the CL from luminol–KMnO₄ system. However, at pHs ≤ 10.42, it was found to inhibit strongly the CL from luminol–KMnO₄ system. The effect of pH, luminol and potassium permanganate concentrations on the kinetic characteristics of CL system was investigated in the presence of trace Al. On this basis, a flow injection inhibition chemiluminescence method was established for the determination of trace Al in this study. Under optimized conditions, the CL decreased linearly with Al(III) concentration in the range of 8–500 μg L⁻¹ and the detection limit (3σ) of 2 μg L⁻¹. The relative standard deviation (R.S.D.) is 3.6% for 100 μg L⁻¹ Al(III) (n = 11). The method has been applied to the determination of trace Al in real water samples with satisfactory results without the pretreatment of samples. The results given by the proposed method are in good agreement with those given by ICP-AES detection method.     

HPLC determination of Vitamin D(3) and its metabolite in human plasma with on-line sample cleanup

A HPLC method with automated column switching and UV-diode array detection is described for the simultaneous determination of Vitamin D₃ and 25-hydroxyvitamin D₃ (25-OH-D₃) in a sample of human plasma. The system uses a BioTrap precolumn for the on-line sample cleanup. A sample of 1 ml of human plasma was treated with 2 ml of a mixture of ethanol–acetonitrile (2:1 (v/v)). Following centrifugation, the supernatant was evaporated to dryness under a stream of dry and pure nitrogen. The residue was reconstituted in 250 μL of a solution of methanol 5 mmol l⁻¹ phosphate buffer, pH 6.5 (4:1 (v/v)), and a 200 μl aliquot of this solution was injected onto the BioTrap precolumn. After washing during 5 min with a mobile phase constituted by a solution of 6% acetonitrile in 5 mmol l⁻¹ phosphate buffer, pH 6.5 (extraction mobile phase), the retained analytes were then transferred to the analytical column in the backflush mode. The analytical separation was then performed by reverse-phase chromatography in the gradient elution mode with the solvents A and B (Solvent A: acetonitrile–phosphate buffer 5 mmol l⁻¹, pH 6.5; 20:80 (v/v); solvent B: methanol–acetonitrile–tetrahydrofuran, 65:20:15 (v/v)). The compounds of interest were detected at 265 nm. The method was linear in the range 3.0–32.0 ng ml⁻¹ with a limit of quantification of 3.0 ng ml⁻¹. Quantitative recoveries from spiked plasma samples were between 91.0 and 98.0%. In all cases, the coefficient of variation (CV) of the intra-day and inter-day-assay precision was ≤2.80%. The proposed method permitted the simultaneous determination of Vitamin D₃ and 25-OH-D₃ in 16 min, with an adequate precision and sensitivity. However, the overlap of the sample cleanup step with the analysis increases the sampling frequency to five samples h⁻¹. The method was successfully applied for the determination of Vitamin D₃ and 25-OH-D₃ in plasma from 46 female volunteers, ranging from 50 to 94 years old. Vitamin D₃ and 25-OH-D₃ concentrations in plasma were found from 4.30–40.70 ng ml⁻¹ (19.74 ± 9.48 ng ml⁻¹) and 3.1–36.52 ng ml⁻¹ (7.13 ± 7.80 ng ml⁻¹), respectively. These results were in good agreement with data published by other authors.     

Ultrasensitive assays of trans- and cis-β-carotenes in vegetable oils by high-performance liquid chromatography–thermal lens detection

The fact that β-carotene might be the protective factor against various cancers, suggests the need for a rapid reliable assay for this potential marker. We have proposed the method for selective, precise and simple profiling of carotenoids as well as for simultaneous ultrasensitive assaying of trans-β-carotene (TBC) and cis-β-carotene(s) (CBC) in five vegetable oils. The oil samples diluted 20 or 100 times were directly injected and analysed by means of the isocratic non-aqueous reversed-phase high-performance liquid chromatography (HPLC) combined with ultrasensitive thermal lens detection (TLS).

Elution of TBC was followed by CBC; both were identified and determined in olive, safflower, sesame, wheat germ and linseed oil by standard addition method. The presence of lutein/zeaxanthin, some xanthophyll and/or early eluting carotene may be also presumed in the aforementioned oils. The examined oils showed different and characteristic carotenoid/carotene profiles and characteristic TBC-to-CBC ratios. Both analytes were selectively detected in the presence of palmitic, oleic, linoleic, linolenic and stearic acid, β-sitosterol and --tocopherol. This extends applicability of the method to other vegetable oils as well.

Favourable analytical performances (high sensitivity, low limits of detection (LODs) and wide linearity span) enabled the direct analyses of highly diluted oils. This resulted in several major benefits of the proposed method, among which (i) reduced risk of stationary phase deterioration, (ii) avoiding the risk of carotenoids transformations and (iii) substantial labour and time savings. The TBC and CBC in diluted vegetable oils were reliably measured at ultratrace level (1–26 ng ml⁻¹) with the S/N ratio ranging from 4 to 140 and precisely determined (imprecision 0.4–8.3%). The concentrations of TBC+CBC estimated in the original oils were as follows: 90.5+51.2 ng ml⁻¹ in sesame oil, 146.0+164 ng ml⁻¹in safflower oil, 464.6+206.1 ng ml⁻¹in linseed oil, 453.7+143.3 ng ml⁻¹ in olive oil and 2.31+2.63 μg ml⁻¹ in wheat germ oil. The characteristic and variable portion of TBC within total β-carotene may serve as a reliable indicator of both, quality and authenticity of the vegetable oil. The HPLC–TLS assay proposed may therefore be successfully applied in nutritional, agricultural and epidemiological studies.     

Rapid determination of aluminum by UV-vis diffuse reflectance spectroscopy with application of suitable adsorbents

Diffuse reflectance spectroscopy (DRS) can be used as a rapid and sensitive method for the quantitative determination of low amounts of aluminum. In this analytical technique, the analyte in samples are extracted onto a solid sorbent matrix loaded with a colorimetric reagent and then quantified directly on the adsorbent surface. Alternatively, colored aluminum complexes formed in solution can also be immobilized onto adsorbent surface and be measured by DRS technique. Octadecyl silica disk, methyltrioctylammonium chloride–naphthalene and MCM-41 were examined as adsorbents. Eriochrome cyanine R and quinalizarin were used as coloring reagents. Optimal sorption conditions were found for each system of analyte–reagent–adsorbent. The concentration of analyte is determined using the appropriate form of the Kubelka–Munk function. We obtained for each of the aluminium–reagent–adsorbent system a calibration curve by plotting the absorbance versus the log 10²[Al³⁺] μg ml⁻¹. The linear dynamic range extends over two orders of magnitude within 0.01–15 μg ml⁻¹ with little differences in the range and in the correlation coefficients among the adsorbents. We consider that for a rapid determination of aluminum a spot-test-DRS combination with a detection limit of 1.0 × 10⁻² μg ml⁻¹ is the more facile and preferred technique.     

Reverse flow injection spectrophotometric determination of iron(III) using norfloxacin

A reversed flow injection colorimetric procedure for determining iron(III) at the μg level was proposed. It is based on the reaction between iron(III) with norfloxacin (NRF) in 0.07 mol l⁻¹ ammonium sulfate solution, resulting in an intense yellow complex with a suitable absorption at 435 nm. Optimum conditions for determining iron(III) were investigated by univariate method. The method involved injection of a 150 μl of 0.04% w/v colorimetric reagent solution into a merged streams of sample and/or standard solution containing iron(III) and 0.07 mol l⁻¹ ammonium sulfate in sulfuric acid (pH 3.5) solution which was then passed through a single bead string reactor. Subsequently the absorbance as peak height was monitored at 435 nm. Beer's law obeyed over the range of 0.2–1.4 μg ml⁻¹ iron(III). The method has been applied to the determination of total iron in water samples digested with HNO₃–H₂O₂ (1:9 v/v). Detection limit (3σ) was 0.01 μg ml⁻¹ the sample through of 86 h⁻¹ and the coefficient of variation of 1.77% (n=12) for 1 μg ml⁻¹ Fe(III) were achieved with the recovery of the spiked Fe(III) of 92.6–99.8%.     

Preparation of dendrimer-like polyamidoamine immobilized silica gel and its application to online preconcentration and separation palladium prior to FAAS determination

A amino-terminated G 4.0 dendrimer-like polyamidoamine (PAMAM) immobilized silica gel (PAMAMSG) was prepared with a divergent method by repeating two processes: (1) Michael addition of methyl acrylate (MA) to surface amino groups; and (2) amidation of the resulting esters with ethylenediamine (EDA) from γ-aiminopropyl silica gel (APSG) core. It was then used for the first time as microcolumn packing for the flame atomic absorption spectrometry (FAAS) determination of trace or ultra trace Pd(II), after flow injection (FI) online preconcentration and separation process. A limit of detection (LOD) of 3.9 ng ml⁻¹ was achieved when 0.200 μg ml⁻¹ Pd(II) was preconcentrated in 0.2 mol l⁻¹ HCl medium with a sampling flow rate of 6.0 ml min⁻¹ for 60 s and the relative standard deviation (R.S.D.) was 1.7%. The proposed method was successfully used for the determination of Pd in two metallurgical samples.     

Speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry

A simple procedure was developed for the speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry (EcHG–AAS), without pre-reduction of As(V). Glassy carbon was selected as cathode material in the flow cell. An optimum catholyte concentration for simultaneous generation of arsine from As(III) and As(V) was 0.06 mol l⁻¹ H₂SO₄. Under the optimized conditions, adequate sensitivity and difference in ratio of slopes of the calibration curves for As(III) and As(V) can be achieved at the electrolytic currents of 0.6 and 1 A. The speciation of inorganic arsenic can be performed by controlling the electrolytic currents, and the concentration of As(III) and As(V) in the sample can be calculated according to the equations of absorbance additivity obtained at two selected electrolytic currents. The calibration curves were linear up to 50 ng ml⁻¹ for both As(III) and As(V) at 0.6 and 1 A. The detection limits of the method were 0.2 and 0.5 ng ml⁻¹ for As(III) and As(V) at 0.6 A, respectively. The relative standard deviations were of 2.1% for 20 ng ml⁻¹ As(III) and 2.5% for 20 ng ml⁻¹ As(V). The method was validated by the analysis of human hair certified reference material and successfully applied to speciation of soluble inorganic arsenic in Chinese medicine.     

A simple and sensitive assay of nucleic acids based on the enhanced resonance light scattering of zwitterionics

A new assay of nucleic acids at nanogram level was established based on the enhanced resonance light scattering (RLS) signals of two zwitterionics cocamidopropyl hydroxysultaine (HSB) and lauryl betaine (BS-12). Under optimum conditions, the weak RLS signal of HSB is enhanced by nucleic acids, and the enhanced RLS intensity is proportional to the concentration of nucleic acids in the range of 0.02–7.3 mg l⁻¹ for calf thymus DNA and 0.01–8.6 mg l⁻¹ for fish sperm DNA. The detection limits were 1.5 ng ml⁻¹ for calf thymus DNA and 1.9 ng ml⁻¹ for fish sperm DNA. Plasmid DNA extracted from K-12-HB101 colt was determined with satisfactory results.     

Indirect determination of ascorbic acid by solid-phase spectrophotometry

Solid-phase spectrophotometry (SPS) technique, in the visible region, was used for the spectrophotometric determination of ascorbic acid based on the reducing effect on iron(III) ion, followed by formation of the iron(II)-ferrozine chelate. The chelate is easily sorbed on a dextran-type anion-exchange gel and the absorbance of the resin at 567 and 800 nm, packed in a 1 mm cell, is measured directly. The apparent molar absorptivity using 100 ml of sample was 2.1×10⁷ l mol⁻¹ cm⁻¹ and it allowed the determination of ascorbic acid in the range 5–90 ng ml⁻¹; the detection limit was 0.91 ng ml⁻¹ and the RSD 0.91% for a concentration of 50 ng ml⁻¹ of ascorbic acid (n=10). The proposed method permits a highly sensitive and selective determination of ascorbic acid without any preconcentration and it has been satisfactorily applied for its determination in fruit juices, pharmaceuticals, urine and conservative liquids.     

1-(2,3,4-Trihydroxybenzylideneamino)-8-hydroxynaphthalene-3,6-disulfonic acid as reagent for spectrophotometric determination of boron in plants

A highly sensitive and selective method has been developed for spectrophotometric determination of boron in plants, the method based on the color reaction of new reagent 1-(2,3,4-trihydroxybenzylideneamino)-8-hydroxynaphthalene-3,6-disulfonic acid (THBA) with boron (III). In an ammonium acetate solution of pH 8.0, boron(III) reacts with THBA to form a 1:2 yellow complex which has a maximum absorption peak at 430 nm. The reaction can complete within 90 min and the absorbance of the complex remains maximum and almost constant at least for 24 h under a temperature range from 0 to 35 °C. The apparent molar absorptivity and Sandell's sensitivity are 2.95 × 10⁴ l mol⁻¹ cm⁻¹ and 0.00036 ng cm⁻², respectively. The limit of quantification, limit of detection and relative standard deviations were found to be 5.1, 1.5 ng ml⁻¹ and 1.12%, respectively. Under the optimum conditions, the absorbency of the complex (λ_max = 430 nm) increases linearly with concentration up to 0.8 μg ml⁻¹ of boron(III). The influences of foreign ions on the determination of boron were investigated in detail. Most of foreign ions can be tolerated in considerable amounts. Experiments have indicated that THBA as chromogenic reagent for spectrophotometric determination of boron has excellent analytical characteristics. Its sensitivity is more than 4.2-fold that of azomethine-H, and stability is advantage over other derivatives of azomehine-H remarkably. Moreover, the synthesis of THBA and its physicochemical properties of THBA were also investigated in detail. Proposed method has been applied to the determination of boron in plants with satisfactory results.     

Development of a luminol-based chemiluminescence flow-injection method for the determination of dichlorvos pesticide

A simple, fast chemiluminescence (CL) flow-injection method based on the reaction of luminol with H₂O₂ in the presence of a cationic surfactant (cyltrimethylammonium bromide, CTMAB) has been described for the direct determination of dichlorvos pesticide (DDVP). Under the optimal conditions, the CL intensity was linear to the DDVP concentration in the range of 0.02–3.1 μg ml⁻¹ (r=0.9998, n=10). The relative standard deviation was 3.4% at 0.35 μg ml⁻¹ (n=10), with a detection limit (3σ) of 0.008 μg ml⁻¹ DDVP. The possible reaction mechanism was also discussed. This method has been successfully applied to the determination of trace DDVP residue in vegetable sample and results have been compared with that of the UV method.