Flow injection chemiluminescence determination of polyhydroxy phenols using luminol-ferricyanide/ferrocyanide system

It was found that the weak chemiluminescence produced from the reaction of polyhydroxy phenols with luminol in alkaline solution could be strongly enhanced by ferricyanide and ferrocyanide. Based on this found, a new flow injection chemiluminescence method is proposed for the determination of four polyhydroxy phenols: pyrogallol, phlorglucinol, quinol and resorcinol. The detection limits of the method are 0.03 μg ml⁻¹ pyrogallol, 0.03 μg ml⁻¹ phlorglucinol, 0.04 μg ml⁻¹ quinol, and 0.02 μg ml⁻¹ resorcinol. The possible mechanism of CL reactions is also discussed briefly.     

Spectrophotometric method for determination of vanadium and its application to industrial, environmental, biological and soil samples

The very sensitive, fairly selective direct spectrophotometric method for the determination of trace amount of vanadium (V) with 1,5-diphenylcarbohydrazide (1,5-diphenylcarbazide) has been developed. 1,5-diphenylcarbohydrazide (DPCH) reacts in slightly acidic (0.0001–0.001 M H₂SO₄ or pH 4.0–5.5) 50% acetonic media with vanadium (V) to give a red–violet chelate which has an absorption maximum at 531 nm. The average molar absorption coefficient and Sandell’s sensitivity were found to be 4.23×10⁴ l mol⁻¹ cm⁻¹ and 10 ng cm⁻² of V^v, respectively. Linear calibration graph were obtained for 0.1–30 μg ml⁻¹ of V^v: the stoichiometric composition of the chelate is 1:3 (V: DPCH). The reaction is instantaneous and absorbance remain stable for 48 h. The interference from over 50 cations, anions and complexing agents has been studied at 1 μg ml⁻¹ of V^v. The method was successfully used in the determination of vanadium in several standard reference materials (alloys and steels), environmental waters (potable and polluted), biological samples (human blood and urine), soil samples, solution containing both vanadium (V) and vanadium (IV) and complex synthetic mixtures. The method has high precision and accuracy (s=±0.01 for 0.5 μg ml⁻¹).     

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%.     

Spectrofluorimetric determination of levofloxacin in tablets, human urine and serum

A spectrofluorimetric method to determine levofloxacin is proposed and applied to determine the substance in tablets and spiked human urine and serum. The fluorimetric method allow the determination of 20–3000 ng ml⁻¹ of levofloxacin in aqueous solution containing acetic acid–sodium acetate buffer (pH 4) with λ_exc=292 and λ_em=494 nm, respectively. Micelle enhanced fluorescence improves the sensibility and allows levofloxacin direct measurement in spiked Human serum (5 μg ml⁻¹) and urine (420 μg ml⁻¹), in 8 mM sodium dodecyl sulphate solutions at pH 5.     

A sensitive flow-injection method for determination of trace amounts of nitrite

A new sensitive colour reaction for nitrite determination is presented. In acidic medium, nitrite was reacted with safranine to form a diazonium salt which caused the reddish-orange dye colour of the solution to change to blue. The carrier stream, into which the sample solution was injected, was doubly distilled water. The reagent solution stream, which contained safranine dye, hydrochloric acid and potassium chloride, was mixed with the carrier in a 3-m length of silicon tubing (bore 0.5 mm) maintained at 30°C in a thermostatic bath. The absorbance intensity was measured at 520 nm. The detection limit was 20 ng ml⁻¹ and the RSD% of 20 injections of 1 μg ml⁻¹ of nitrite was 0.65%. Analysis can be done at a rate of up to 30 h⁻¹. Under the optimum conditions in the concentration range of 30–4000 ng ml⁻¹ of nitrite ion, a linear calibration graph was obtained (r=0.9999). The method was applied successfully to the determination of nitrite in sausages.     

Determination of glyphosate by ion chromatography

An ion chromatography system for the determination of glyphosate was described. Ion chromatograph was carried out by suppressed conductivity detection (DX-100). The eluent contained 9 mmol l⁻¹ Na₂CO₃ and 4 mmol l⁻¹ NaOH. The detection limit was 0.042 μg ml⁻¹ (S/N=3). The relative standard deviation was 1.99% and the correlation coefficient of the calibration curve for area was 0.9995. The linear range was 0.042100 μg ml⁻¹. Common inorganic ion and organic acids did not interfere. The recovery was 96.4103.2%. The method was simple, rapid, reliable and inexpensive.     

Flow-injection chemiluminescence determination of chlortetracycline using on-line electrogenerated [Cu(HIO(6))(2)](5-) as the oxidant

A novel chemiluminescence (CL) flow system for the determination of chlortetracycline is described. It is based on the direct CL reaction of chlortetracycline and [Cu(HIO₆)₂]⁵⁻ in KOH medium. The unstable [Cu(HIO₆)₂]⁵⁻ was on-line electrogenerated by constant-current electrolysis. The CL intensity was linear with chlortetracycline concentration in the range of 0.1–100 μg ml⁻¹. The determination limit was 5.3×10⁻⁸ g ml⁻¹. The whole process could be completed in 1 min. The proposed method is suitable for automatic and continuous analysis, and has been applied satisfactorily to analysis of chlortetracycline in biological fluid.     

Two different strategies for the fluorimetric determination of piroxicam in serum

Two different spectrofluorimetric methods for the determination of piroxicam (PX) in serum are presented and discussed. One of them is based on the use of three-way fluorescence data and multivariate calibration performed with parallel factor analysis (PARAFAC) and self-weighted alternating trilinear decomposition (SWATLD). This methodology exploits the so-called second-order advantage of the three-way data, allowing to obtain the concentration of the studied analyte in the presence of any number of uncalibrated (serum) components. The method was developed following two different procedures: internal standard addition and external calibration with standard solutions, which were compared and discussed. The second approach investigated is based on the combination of solid-phase extraction (SPE) and room temperature fluorimetry. Both methods here presented yield satisfactory results. The concentration range in which PX could be determined in serum was 1–10 μg ml⁻¹. The limits of quantification for the experimental solutions using the chemometric approach were 0.09 μg ml⁻¹ for the standard addition mode and 0.12 μg ml⁻¹ using external calibration (both for PARAFAC and SWATLD algorithms). In the solid-surface fluorimetric method, the calibration graph was linear up to 0.22 μg ml⁻¹ and the limit of quantification was 0.02 μg ml⁻¹.     

Fast and highly selective determination of cyanide with 2,2-dihydroxy-1,3-indanedione

A very simple, accurate, fast, selective and sensitive assay of cyanide based on its reaction with 2,2-dihydroxy-l,3-indanedione at basic pH is proposed. As little as 0.01 μg ml⁻¹ of cyanide can be determined. The molar absorptivity may reach 5.1–8.0×10⁴ l mol⁻¹ cm⁻¹ depending on the reaction conditions. Thus, 1 ml of sample solution is mixed with 500 μl of 5 mg ml⁻¹ solution of 2,2-dihydroxy-1,3-indanedione monohydrate in 2% sodium carbonate. The absorbance of the purple color is measured at 510 nm in 1-cm glass cuvettes, 10–15 min after mixing the reagents. The procedure could also be used to identify free CN⁻ in natural waters and hydrocyanic acid in the environment.     

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.     

Simple spectrophotometric determination of tinidazole in formulation and serum

A simple and rapid spectrophotometric method for the determination of tinidazole is presented. This method is based on the measurement of the absorbance of the signal at 368 nm yielded by bathochromic shift during alkaline hydrolysis of tinidazole in 0.1 N NaOH. The method is linear within the range of 1–30 μg ml⁻¹, and the detection and quantification limits are 0.07 and 0.25 μg ml⁻¹, respectively. The precision of the method, expressed as the relative standard deviation, is 0.19% for a tinidazole concentration of 15 (μg ml⁻¹. The method was applied to the analysis of tinidazole in pharmaceutical formulations and serum.     

Turbidimetric determination of sulphate in waters employing flow injection and lead sulphate formation

An analytical flow-injection procedure based on PbSO₄ colloidal formation is proposed as a turbidimetric determination of sulphate in natural waters. Ethanol-water was used as a medium in order to improve the sensibility of the method. Both chemical and flow variables as well as interfering species were studied. A detection limit of 0.3 μg SO²⁻₄ ml⁻¹ was found, and the analytical range (according to Beer's law) was 2–20 μg SO²⁻₄ ml⁻¹. The precision was better than 3% R.S.D. and the sample throughput was ca. 35 h⁻¹. The method, when compared with a standard methodology, gave good results when applied to water analysis.     

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.     

Simple and rapid flow-injection spectrophotometric determination of carbaryl after liquid-liquid extraction

A simple procedure was developed for the spectrophotometric determination of carbaryl and its hydrolysis product 1-naphthol in water. These compounds are extracted into xylene and back-extracted, as the 1-naphtholate, with 0.2 M NaOH. A 600-μl volume of the alkaline extract is injected into a flow analysis manifold which provides the reaction between naphtholate and 50 μg ml⁻¹ p-aminophenol solution in the presence of 0.004 M KIO₄ and spectrophotometric measurement is carried out at 596 nm. The method provides a limit of detection of 26.5 ng ml⁻¹ carbaryl and a sample frequency of 110 injections per hour. Recoveries in different types of matrices vary from 95 to 102%.     

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%.     

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.     

Use of silica gel chemically modified with zirconium phosphate for preconcentration and determination of lead and copper by flame atomic absorption spectrometry

An analytical method using silica gel chemically modified with zirconium (IV) phosphate for preconcentration of lead and copper, in a column system, and their sequential determination by flame atomic absorption spectrometry (FAAS), was developed. Sample solutions are passed through a glass column packed with 100 mg of the sorbent material, at pH 4.5, and lead and copper are eluted with 1.0 mol l⁻¹ HNO₃ at a flow rate of 2.0 ml min⁻¹. The extraction of copper is affected by Fe(II), Mn(II), Zn(II), Ni(II) and Co(II) while only Fe(II) interferes in the lead determination. These interferences may be overcome with an appropriate addition of a KI or NaF solution. An enrichment factor of 30 was obtained for both metals. While the limits of detection (3σ) were 6.1 and 1.1 μg l⁻¹, for Pb and Cu, respectively, the limits of determination were 16.7 and 3.3 μg l⁻¹. The precision expressed as relative standard deviation (R.S.D.) obtained for 3.3 μg l⁻¹ of Cu and 16.7 μg l⁻¹ of Pb were 4.3 and 4.7%, respectively, calculated from ten measurements. The proposed method was evaluated with reference material and was applied for the determination of lead and copper in industrial and river waters.     

Simultaneous derivative spectrophotometric determination of thorium and uranium in a micellar medium

Derivative photometric methods for trace analysis of Th(IV) and UO₂(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO₂(II) complexes at their λ_max, 614.5 nm and 637.0 nm are, 1.19 × 10⁴ 1/mol/cm and 1.12 × 10⁴ 1/mol/cm and 1.95 × 10⁻² μg/cm² and 2.13 × 10⁻² μg/cm² μg/cm², respectively. Calibration graph is linear over the range 9.28 × 10⁻²−18.56 μg/ml of Th(IV) and 9.52 × 10⁻²−19.04 μg/ml of UO₂(II). Though presence of Th(IV) and UO₂(II) causes interference in each others determination, 9.28 × 10⁻¹−9.28 μg/ml Th(IV) and 9.52 × 10⁻¹−9.52 μg/ml UO₂(II) when present together, can be simultaneously determined using derivative spectra.     

Extraction and spectrophotometric determination of cobalt(II) with isonitroso-5-methyl-2-hexanone

A simple and selective method is proposed for the extraction of cobalt(II) for its spectrophotometric determination using (HIMH) as an extractant. Cobalt(II) forms a yellow coloured complex with HIMH which can be extracted into chloroform. The calibration curve is rectilinear in the concentration range 0.1–5.0 μg ml⁻¹ of cobalt(II). The extracted species shows an absorption maximum at 400 nm with molar absorptivity of 1.135×10⁴ l mol⁻¹ cm⁻¹. The method has been applied for the determination of cobalt in synthetic mixtures, pharmaceutical, biological and high speed steel samples.     

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.