Chemiluminescence determination of citrate and pyruvate and their mixtures by the stopped-flow mixing technique

A novel kinetic chemiluminescent method using the stopped-flow mixing technique has been investigated for the rapid and sensitive determination of citrate and pyruvate. The method is based on a tris(2,2′-bipyridiyl)ruthenium(III) (Ru(bpy)₃³⁺) chemiluminescence (CL) reaction. Ru(bpy)₃³⁺ was generated in the mixing chamber by oxidising tris(2,2′-bipyridyl)ruthenium(II) with cerium(IV). After selecting the best operating parameters, calibration graphs were obtained over the concentration ranges 0.38-38 μg ml⁻¹ and 8.7-1300 ng ml⁻¹ for citrate and pyruvate, respectively. The limits of detection were 0.1 μg ml⁻¹ for citrate and 0.3 ng ml⁻¹ for pyruvate. Based on the differential rate of the chemiluminescent reaction corresponding to citrate and pyruvate, a very simple kinetic procedure was developed for the simultaneous determination of both compounds. Mixtures of citrate and pyruvate in ratios between 15:1 and 1.5:1 were satisfactorily resolved. The proposed method was successfully applied to the determination of citrate in pharmaceutical formulations, pyruvate in animal blood serum and both compounds in human urine.     

Application of generalized artificial neural networks coupled with an orthogonal design to optimization of a system for the kinetic spectrophotometric determination of Hg(II)

A simple and sensitive kinetic method for the determination of traces of mercury (70-760 ng ml⁻¹) based on its inhibitory effect on the addition reaction between methyl green and sulfite ion is proposed. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of methyl green at 596 nm between 2 and 4 min using a fixed time method. Artificial neural networks with back propagation algorithm coupled with an orthogonal array design were applied to the modeling of the proposed kinetic system and optimization of experimental conditions. An orthogonal design was utilized to design the experimental protocol, in which pH, concentration of sulfite, temperature, and concentration of methyl green were varied simultaneously. Optimum experimental conditions in term of sensitivity were generated by using ANNs. The rate of decrease in absorbance is inversely proportional to the concentration of Hg(II) over entire concentration range tested (100-550 ng ml⁻¹) with a detection limit of 45 ng ml⁻¹ and a relative standard deviation at 200-400 ng ml⁻¹ Hg(II) of 3.2% (n=5). A simple preconcentration step improved the limit of detection and linear dynamic range of the method to about 8 and 12-760 ng ml⁻¹, respectively, by about 10 times enrichment of mercury between 12 and 75 ng ml⁻¹. The method was based on enrichment of Hg(II) from dilute samples on an anionic ion exchanger fixed on a plastic strip and was applied to the determination of Hg(II) in environmental samples with satisfactory results.     

Kinetic spectrophotometric method for gold(III) determination

The kinetic spectrophotometric method for Au(III) determination was developed and validated. It was based on the catalytic effect of gold on the oxidation of methylene blue B (3,7di-(dimethyl amino)-10-dehydro-phenotiazin chloride) by ammonium peroxo-disulfate in citric buffer solution. There was the linearity of the calibration curve in the concentration range from 0.09 to 2.90 μg ml⁻¹ Au(III). The relative standard deviation was 2.50% and correlation coefficient of 0.9999. The limit of detection was determined as signal to noise ratio (3:1) and it was 5.5 ng ml⁻¹. The limit of quantification, based on signal to noise ratio 10:1 was 19.25 ng ml⁻¹. The selectivity was tested on the basis of influence of known amounts of different ions in the reaction mixture, upon the reaction rate. Kinetic and thermodynamic parameters were reported for both catalytic and non-catalytic reactions. The method was verified by Au(III) determination in anti-rheumatic drug “Tauredon” and in human urine samples, using ICP-AES as the comparative method. As the method is accurate, reliable, quick and simple it could be useful for clinical and toxicological practice.     

Highly sensitive spectrofluorimetric kinetic determination of ultratrace amounts of vanadium(V) based on the oxidation of 1,8-diaminonaphthalene by bromate

A highly sensitive catalytic quenching spectrofluorimetric method was described for the determination of V(V) based on its catalytic effect on the oxidation of 1,8-diaminonaphthalene by potassium bromate with Tiron as an activator in weakly acidic medium and the reaction mechanism was investigated. The reaction was followed spectrofluorimetrically by measuring the fluorescence intensity of 1,8-diaminonathphlene (DAN) (λ_ex=356 nm, λ_em=439 nm) at a fixed time of 5 min from initiation of the reaction. Under the optimum conditions, vanadium(V) can be determined in the range 0.05-50.0 ng ml⁻¹ with a S.D.=0.024 for 15 times measurements. The detection limit of the method was down to 0.0088 ng ml⁻¹ and the catalytic reaction activation energy was found to be 43.92 kJ mol⁻¹. The proposed method was tested for the determination of vanadium(V) in rice and natural water samples.     

Highly sensitive catalytic determination of molybdenum

A novel, highly sensitive, selective, and simple kinetic method was developed for the determination of Mo(VI) based on its catalytic effect on the oxidation of 1-amino-2-naphthol-4-sulfonic acid (ANSA) with H₂O₂. The reaction was followed spectrophotometrically by tracing the oxidized product at 465 nm after 30 min of mixing the reagents. The optimum reaction conditions were: 10 mmol l⁻¹ ANSA, 50 mmol l⁻¹ H₂O₂, 100 mmol l⁻¹ acetate buffer of pH 5.0 ± 0.05 and at 40 °C. Addition of 200 μg ml⁻¹ diethylenetriaminepentaacetic acid (DTPA) conferred high selectivity for the proposed method. Following the recommended procedure, Mo(VI) could be determined with a linear calibration graph up to 2.5 ng ml⁻¹ and a detection limit, based on the 3S_b-criterion, of 0.027 ng ml⁻¹. The unique sensitivity and selectivity of the implemented method allowed its direct application to the determination of Mo(VI) in natural and industrial waste water. The method was validated by comparison with the standard ETAAS method. Moreover, published catalytic-spectrophotometric methods for the determination of molybdenum were reviewed.     

On-line separation, preconcentration and determination of trace amounts of gold in mineral sample by flow injection catalytic kinetic spectrofluorimetry

2-Pyridine carboxaldehyde furfuralhydrazone (PCFH) was newly synthesized and its ionization, IR and elemental analysis were established. An on-line separation and preconcentration system was developed for the flow injection (FI) catalytic kinetic spectrofluorimetric determination of trace amounts of gold. The method was based on the fluorescence enhancing reaction of PCFH with potassium bromate, which was catalysed by Au³⁺ in aqueous medium at pH 4.20 and 35 °C. A micro polyamide resin column was used to separate and collect gold from sample solution. Under these experimental conditions, the oxidized product of PCFH had excitation and emission maxima at 296 and 404 nm, respectively. The linear range of this method was 0.53-144 ng ml⁻¹ with the RSD of 1.6%. The detection limit was 0.16 ng ml⁻¹. A high analysis rate of 15 samples h⁻¹ was obtained. The proposed method had been applied successfully to the determination of gold in synthetic mixture and mineral sample with satisfactory results.     

Direct spectrophotometric determination of calcium in clinical samples with carboxyazo-p-CH3

A highly sensitive and relatively interference-free spectrophotometric method for determination of calcium is described. The method is based on the reaction between calcium ions and carboxyazo-p-CH₃ in aqueous citrate medium of pH 7, to form a blue complex with maximum absorption at 716 nm. The calibration is linear up to 0.12 μg ml⁻¹ calcium with a repeatability (R.S.D.) of 1.0% at a concentration of 0.04 μg ml⁻¹ (n=5). The molar absorptivity of the complex and Sandell’s sensitivity are 3.5×10⁵ l mol⁻¹ cm⁻¹ and 0.11 ng cm⁻², its 10σ limit of quantification and the 3σ limit of detection were found to be 0.3 ng ml⁻¹ and 0.09 ng ml⁻¹ respectively. The influence of reaction variables and the effect of interfering ions are studied; no interference was observed in clinical samples. The proposed method has been applied directly to the determination of calcium in clinical samples without the need for pre-concentration, masking metal ions and digesting samples.     

Potassium permanganate-glyoxal chemiluminescence system for flow injection analysis of cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium in pharmaceutical preparations

A sensitive flow injection chemiluminescence (FL-CL) method for the determination of cephalosporin antibiotics, was developed. The method was based on that cephalosporin antibiotics could enhance the CL reaction of glyoxal and KMnO₄ in sulfuric acid. Method development included the optimization of reagent concentrations and flow-rate. Under the optimized conditions, three cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium, were determined. The detection limits of the method are 10 ng ml⁻¹ cefalexin, 2 ng ml⁻¹ cefadroxil, and 2 ng ml⁻¹ cefazolin sodium. The method was successfully applied to the determination of three cephalosporin antibiotics in pharmaceutical preparations.     

A novel kinetic determination of dissolved chromium species in natural and industrial waste water

A highly sensitive, selective and simple kinetic method was developed for the determination of dissolved chromium species based on the catalytic effect of Cr(III) and/or Cr(VI) on the oxidation of 2-amino-5-methylphenol (AMP) with H₂O₂. The fixed time and initial rate variants were used for kinetic spectrophotometric measurements by tracing the oxidized product at 400 nm for 10 min after starting the reaction. Boric acid and Tween-40 exerted pronounced activating and micellar sensitizing effects on the studied redox reaction, respectively. The optimum reaction conditions were: 3.0 mmol l⁻¹ AMP, 0.45 mol l⁻¹ H₂O₂, 0.50 mol l⁻¹ boric acid, 4 v/v% Tween-40, 10 mmol l⁻¹ phosphate buffer and pH 6.45 ± 0.02 at 35 °C. Both Cr(III) and Cr(VI) ions exerted the same catalytic effect on the studied reaction. Linear calibration graphs were obtained for the determination of up to 6.0 ng ml⁻¹ Cr with detection limits of 0.054 and 0.10 ng ml⁻¹ Cr; following the fixed time and initial rate methods, respectively. The proposed method was successfully applied to the speciation and determination of trace levels of dissolved Cr(III) and Cr(VI) in natural and effluents of industrial waste water. The total dissolved Cr(III) and Cr(VI) species was determined first. In a second run, Cr(VI) was determined alone after precipitation of Cr(III) ions in presence of Al(OH)₃ collector, where Cr(III) is then determined by difference. Moreover, published catalytic-spectrophotometric methods for chromium determination were reviewed.     

Flow injection kinetic spectrophotometric determination of trace amounts of Se(IV) in seawater

A simple, accurate, sensitive and selective flow injection catalytic kinetic spectrophotometric method for rapid determination of trace amounts of selenium is proposed in this paper. The proposed method is based on the accelerating effect of Se(IV) on the reaction of ethexlenediamine tetrecetic acid disodium salt (EDTA) and sodium nitrate with ammonium iron(II) sulfate hexahydrate in acidic media. The absorbance intensity was registered in this reaction solution at 440 nm. The calibration graph is linear in the range of 5 × 10⁻⁹-2 × 10⁻⁷ and 2 × 10⁻⁷-2 × 10⁻⁶ g ml⁻¹. The detection limit is 2 × 10⁻⁹ g ml⁻¹. The relative standard deviation was 3.4% for 5 × 10⁻⁸ g ml⁻¹ Se(IV) (n = 11), 2.7% for 5 × 10⁻⁷ g ml⁻¹ Se(IV) (n = 11). This method is very simple, rapid and suitable for automatic and continuous analysis. The presented system has been applied successfully to determination of Se(IV) of seawater samples.     

Kinetic method for determination of nanogram amounts of copper(II) by its catalytic effect on hexacynoferrate(III)-citric acid indicator reaction

This paper describes a highly sensitive, selective catalytic-kinetic-spectrophotometric method for the determination of copper(II) concentration as low as 6 ng ml⁻¹. The method is based on the catalytic effect of copper(II) on the oxidation of citric acid by alkaline hexacyanoferrate(III). The reaction was followed by measuring the decrease in absorbance of hexacyanoferrate(III) at 420 nm (λ_max of [Fe(CN)₆]³⁻, ∈ = 1020 dm³ mol⁻¹ cm⁻¹). The dependence of rate of the indicator reaction on the reaction variables has been studied and discussed to propose a suitable mechanism to get a relation between the reaction rate and [Cu²⁺]. A fixed time procedure has been used to obtain a linear calibration curve between the initial rate and lower [Cu²⁺] or log[Cu²⁺] in the range 1 × 10⁻⁷ to 4 × 10⁻⁴ mol l⁻¹ (6.35-25,400 ng ml⁻¹). The detection limit has been calculated to be 4 ng ml⁻¹. The maximum average error is 3.5%. The effect of the presence of various cations, commonly associated with copper(II) and some anions has also been investigated and discussed. The proposed method is sensitive, accurate, rapid and inexpensive compared to other techniques available for determination of copper(II) in such a large range of concentration. The new method has been successfully applied for the determination of copper(II) in various samples.     

Flow-injection catalytic spectrophotometic determination of molybdenum(VI) in plants using bromate oxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine

A novel flow-injection spectrophotometry has been developed for the determination of molybdenum(VI) at nanograms per milliliter levels. The method is based on the catalytic effect of molybdenum(VI) on the bromate oxidative coupling of p-hydrazinobenzenesulfonic acid with N-(1-naphthyl)ethylenediamine to form an azo dye (λ_max = 530 nm). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonic acid) acted as an effective activator for the molybdenum(VI)-catalyzed reaction and increased the sensitivity of the method. The reaction was monitored by measuring the change in absorbance of the dye produced. The proposed method allowed the determination of molybdenum(VI) in the range 1.0-20 ng mL⁻¹ with sample throughput of 15 h⁻¹. The limit of detection was 0.5 ng mL⁻¹ and a relative standard deviation for 10 ng mL⁻¹ molybdenum(VI) (n = 10) was 2.5%. The interfering ions were eliminated by using the combination of a masking agent and on-line minicolumn packed with cation exchanger. The present method was successfully applied to the determination of molybdenum(VI) in plant foodstuffs.     

Determination of proteins with Alizarin Red S by Rayleigh light scattering technique

A new protein determination method by enhanced Rayleigh light scattering (RLS) technique has been developed. In acid condition (pH=3.60), RLS of 1,2-dihydroxyanthraquinone-3-sulfonate (Alizarin Red S) can be greatly enhanced by addition of proteins, resulting in two characteristic peaks, 360 and 505 nm, respectively. The new protein assay is based on the RLS enhancement and spectrum change. The optimum condition for the reaction was investigated. The linear range is 0.20-24.9 μg ml⁻¹ for BSA and 0.20-15.5 μg ml⁻¹ for HSA. The detection limits (S/N=3) are 9.59 ng ml⁻¹ for BSA and 9.51 ng ml⁻¹ for HSA. The results of determination for human serum samples were comparable to those obtained by Bradford method. The binding stoichiometry was determined.     

Electrochemiluminescence assay for the detection of acridinium esters

An electrochemiluminescence (ECL)-based method for rapid and sensitive detection of acridinium ester in neutral solution was described. Strong ECL emission was observed when a positive voltage over 2.0 V (versus Ag/AgCl) was applied to the working electrode (Pt) immersed in the acridinium ester solution of 2.0 mol l⁻¹ KNO₃ (pH 7.0). The possible ECL mechanism was discussed. It was proposed that the ECL emission came out of N-methylacridone, the oxidization product of acridinium ester by the nascent oxygen generated on the surface of working electrode in the course of oxidization of water. Other influenced factors including the electrochemical parameters, the ECL reaction medium and pH value, were investigated in detail. Under the optimal conditions, ECL intensity has a linear relationship with the concentration of acridinium ester in the range of 0.24-96 ng ml⁻¹ (r=0.9999). The relative standard deviation for 24 ng ml⁻¹ acridinium ester was 4.6% (n=11). The limit of detection was 0.16 ng ml⁻¹.     

Determination of mercury species with a resin functionalized with a 1,2-bis(o-aminophenylthio)ethane moiety

A method for the simultaneous preconcentration and determination of Hg(II) and MeHg(I) at the ng ml⁻¹ level has been developed. This method is based on solid phase extraction using a newly synthesized chelating resin containing nitrogen and sulphur donor sites of the 1,2-bis(o-aminophenylthio)ethane moiety that is very selective for mercury. The characterization of the resin has been carried out by elemental analyses, infrared spectral data, thermogravimetric analysis and metal ion capacities. The resin is highly selective for Hg(II) and MeHg(I) with an exchange capacity of 0.38 and 0.30 mmol g⁻¹, respectively. Various parameters like pH, column flow rate, desorbing agents are optimized. Cold vapour atomic absorption spectrometry (CVAAS) was used to measure the concentration of both species of mercury. The calibration graph was linear upto 10 ng ml⁻¹ with a 3σ detection limit of 0.09 ng ml⁻¹. The recovery of Hg(II) and MeHg(I) was found to be 98.9±2.0 and 98.0±1.1%, respectively. The method has been used for routine determination of trace levels of mercury species in natural waters to comply with more stringent regulations.     

Quantification of sex pheromone from Anocentor nitens by gas chromatography-mass spectrometry-selected ion monitoring

Two highly sensitive and selective methods based on gas chromatography coupled to mass spectrometry (GC-MS) in the selected ion monitoring (SIM) mode have been developed for the quantification of 2,6-dichlorophenol (2,6-DCP), a sex pheromone of the tick females of Anocentor nitens. Standard addition method and calibration curve techniques using 5-bromine-4-hydroxy-3-methoxybenzaldehyde (5-BrV) as internal standard (IS) afforded detection limit of 0.1 ng ml⁻¹. The calibration curve was linear over the concentration range from 0.5 to 500 ng ml⁻¹ for 2,6-DCP. Results show that the concentration range of sex pheromone in the extracts samples was 1.08-10.35 ng ml⁻¹. The methods developed provided reliable procedures to determine amounts of 2,6-DCP present in ticks.     

Synthesis and characterization of a novel cross-linking complex of beta-cyclodextrin-o-vanillin furfuralhydrazone and highly selective spectrofluorimetric determination of trace gallium

A novel host inclusion complex of cross-linking-polymeric-β-cyclodextrin-o-vanillin furfuralhydrazone (β-CDP-OVFH) was synthesized and characterized with IR and ¹H NMR spectra to confirm its structure. A highly selective and sensitive fluorescent determination of trace amounts of gallium was proposed based on the reaction between Ga³⁺ with β-CDP-OVFH in acetic acid-ammonium acetate buffer medium of pH 4.10. The maximum excitation and emission wavelengths were 392 and 499 nm, respectively. The linear range of this method was 1.5-330 ng ml⁻¹ with a detection limit of 0.44 ng ml⁻¹. The effect of interferences in the determination of gallium was investigated and the results showed that the same race elements such as Al³⁺ and In³⁺ did not interfere the determination of Ga³⁺ even when their concentration is 100 times of Ga³⁺, the host reagent had quite high capacity of identifying Ga³⁺. This method was successfully applied to the determination of trace amounts of Ga³⁺ in artificial and semiconductor samples.     

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between heptamethylene cyanine and Alcian blue 8GX

A new method based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic heptamethylene cyanine (HMC) and a polycationic phthalocyanine dye, Alcian blue 8GX, is presented for the determination of nucleic acids. With a maximum excitation wavelength at 766 nm and a maximum emission wavelength at 796 nm, the fluorescence recovery is linear with the concentration of nucleic acids added. Factors including the acidity of the medium, the reaction time, the optimal ratio of the two reagents, as well as the influence of foreign substance were all investigated. Meanwhile, the mechanism of fluorescence recovery was also studied. Under the optimal conditions, the linear ranges of the calibration curves were 10-250 ng ml⁻¹ for calf thymus DNA (CT DNA) and 10-200 ng ml⁻¹ for yeast RNA. The detection limits were 6.8 ng ml⁻¹ for CT DNA and 6.3 ng ml⁻¹ for yeast RNA, respectively. The method has been applied to the analysis of practical samples and the recovery results were satisfactory.     

A rapid determination of propiverine and its N-oxide metabolite in human plasma by high performance liquid chromatography-electrospray ionization tandem mass spectrometry

A simple, fast and sensitive high-performance liquid chromatography (HPLC)-electrospray ionization (ESI) tandem mass spectrometric method (LC-MS/MS) has been developed for determination of propiverine and propiverine N-oxide metabolite in human plasma using oxybutynin as internal standard. Instead of extracting propiverine from plasma using organic solvents, which should be separated from the aqueous phase and evaporated before injecting the sample into the chromatograph, plasma sample containing propiverine and N-oxide was directly injected after precipitating proteins with acetonitrile. Numerous compounds in the plasma did not interfere with the highly specific multiple reaction monitoring in tandem mass spectrometric detection following C₈ reversed-phase chromatographic separation under conditions that eluted propiverine, N-oxide and oxybutynin within 2 min (0.1% formic acid in water/acetonitrile, 25:75, v/v). The LC-MS/MS method and an alternative LC-MS method, using methyl-t-butyl ether extraction and selected ion monitoring, were validated over 1-250 ng ml⁻¹ of propiverine and 2 to 500 ng ml⁻¹ of N-oxide, and successfully applied in a pharmacokinetic study. The lower limit of quantitation was 1 ng ml⁻¹ for propiverine and 2 ng ml⁻¹ for N-oxide in both methods.     

Studies on the supramolecular interaction between napropamide and β-cyclodextrin by spectrofluorimetry and its analytical application

The supramolecular interaction between N,N-diethyl-2-(1-naphthalenyloxy)propanamide (napropamide) and β-cyclodextrin (β-CD) has been studied by spectrofluorimetry. The results showed that β-CD reacted with napropamide to form an inclusion complex with an association constant of 3.18×10³ l mol⁻¹. The composition of the complex was 1:1 (β-CD:napropamide). Based on the significant enhancement of fluorescence intensity of napropamide in inclusion complex, a spetrofluorimetric method with high sensitivity and selectivity was developed for the determination of napropamide in aqueous solution. Under the optimum conditions, the complex had excitation and emission maxima at 285 and 339 nm, respectively. The linear range of the method was 3.7-1500 ng ml⁻¹ with a detection limit of 1.1 ng ml⁻¹. The proposed method was successfully used to determine napropamide in river water.