Interactions of norfloxacin with DNA and determination of DNA at nanogram levels based on the measurement of enhanced resonance light scattering

A novel assay of DNA at nanogram levels is presented that is based on the measurement of resonance light scattering (RLS) signals in the presence of norfloxacin. The characteristics of RLS spectra, the effective factors and the optimum conditions of the reaction have been investigated. In Britton-Robinson buffer (pH 5.87), norfloxacin has a maximum peak at 405.5 nm and the RLS intensity is greatly enhanced by trace amounts of DNA due to the interaction between norfloxacin and DNA. Mechanistic studies show that the binding of norfloxacin to DNA forms large particles, which result in the significant enhancement of RLS intensity. The enhanced intensity of RLS is proportional to the concentration of DNA in the range from 0.01–2.0 μg mL⁻¹ for yeast DNA, and from 0.02 to 2.3 μg mL⁻¹ for calf thymus DNA. The determination limit (3σ) is 0.7 ng mL⁻¹ for yeast DNA and 1.2 ng mL⁻¹ for calf thymus DNA, respectively. Synthetic samples were determined satisfactorily.     

Fluorometric determination of DNA using nano-SiO2 particles as an effective dispersant and stabilizer for acridine orange

A sensitive fluorometric method for the determination of ctDNA (calf thymus DNA) is presented. It has good selectivity and sensitivity and uses nano-SiO₂ particles as an effective dispersant and stabilizer for acridine orange (AO). Compared to resonance light scattering (RLS) and the conventional method that uses organic dyes as fluorescence probe, the new method is more tolerant towards coexisting foreign substances and also more stable. With 20 mg nano-SiO₂ particles, 10 μmol L⁻¹ AO, at pH 8.01 and an ionic strength of 0.02 mol L⁻¹, the interaction of AO with nano-SiO₂ and ctDNA results in fluorescent signal enhancement. The extent of enhancement was in good proportion to the concentration of ctDNA at excitation/emission wavelengths of 490/523 nm, respectively. The calibration curve was linear over 0.66–55.60 μg mL⁻¹. The determination limit (3σ) was 15 μg mL⁻¹. The method was applied to the determination of ctDNA in synthetic samples with satisfactory results.     

Determination of proteins in human serum by combination of flow injection sampling with resonance light scattering technique

A flow injection method combined with Resonance light scattering detection was developed for the determination of protein concentration in human serum samples. This method is based on the enhanced RLS signals of protein binding with the dye acid chrome blue K. The enhanced RLS intensities at 264 nm, in an acidic aqueous solution, were proportional to the protein concentration over the range of 2.0–40.0 μg·mL⁻¹ for human serum albumin (HSA) and the limit of detection (3σ) is 85 ng·mL⁻¹. This method was successfully applied to the quantification of total proteins in human serum samples. The maximum relative standard deviation is less than 2% and the recovery is between 97 and 103% for the standard addition method. The sample throughput was 60 h⁻¹.     

A resonance light scattering method for determination of DNA using Ru(bpy)2PIP(V)2+

A novel method for DNA detection is proposed that is based on the enhancement of resonance light scattering (RLS) of Ru(bpy)₂PIP(V)²⁺ at pH 2.7. Under optimum conditions, good linear relationships were obtained in the wide concentration range of 16–5120 ng mL⁻¹. The linear equation is I _RLS = 13.15 + 171.4 c (μg mL⁻¹), the correlation coefficient (r) is 0.9999. The detection limit of calf thymus DNA is 5.02 ng mL⁻¹. Plasmid DNA extracted from bacillus subtilis was determined by the method with satisfactory results.     

Dimer of calcein used as fluorescence probe in the determination of proteins

In the presence of appropriate amounts of the cationic surfactant cetyl trimethyl ammonium bromide (CTMAB), the anionic dye calcein dimerizes. The weak fluorescence intensity of the dimer is enhanced by adding proteins at pH 6–8. The interaction between calcein-CTMAB and proteins was studied on the basis of this behavior and a new method was developed for determining proteins. Under optimal conditions, the enhanced fluorescence intensity is proportional to the concentration of proteins in the range 0.4–8 μg mL⁻¹ for human serum albumin (HSA) and 0.8–10 μg mL⁻¹ for bovine serum albumin (BSA), with detection limits of 0.034 μg mL⁻¹ and 0.032 μg mL⁻¹, respectively. Three samples were determined by using this method satisfactorily with relative standard deviations (RSD) of 1.1–3.1%.     

Highly sensitive determination of trace potassium ion in serum using the resonance light scattering technique with sodium tetraphenylboron

A resonance light scattering technique has been developed in order to determine potassium ion in serum. Potassium ion was found to bind the tetraphenylboronate anion [(C₆H₅)₄B]⁻ in acetate buffer (pH 8.0) in the presence of sodium dodecyl benzene sulfonate as a stabilizer, forming the B(C₆H₅)₄-K aggregate which produces intense resonance scattering light. Effects of factors such as acidity, ionic strength and interferents on the RLS of B(C₆H₅)₄-K were investigated. The solution pH close to neutral facilitates the production of RLS, and few biologically relevant species interfere in the determination of potassium ion. The resonance scattering light intensity at the maximum peak of 567 nm was linear to the concentration of potassium ion in the range of 0.2–2.0 μg mL⁻¹ with a detection limit of 20.0 ng mL⁻¹. The method was applied to determine trace amounts of potassium ion in serum and showed high sensitivity and accuracy compared with the clinically used ion-selective electrode method.     

Flow injection fluorimetric determination of L-dopa and dopamine based on a photochemical inhibition process

An automatic procedure has been developed for the determination of L-dopa and dopamine. It is based on the strong inhibition of the photochemical reaction between thionine blue and ethylenediamine-tetraacetic acid by these catecholamines. The proposed flow-injection method allows for the fluorimetric determination of L-dopa in the range of 1.9–98 μg mL⁻¹ and that of dopamine in the range of 1.9–75 μg mL⁻¹ with a sampling frequency of 35 samples h⁻¹. The method was applied successfully to the determination of dopamine in pharmaceutical preparations.     

Development of an acetylspiramycin sensor based on a single-walled carbon nanotubes film electrode

A simple and sensitive sensor is described for the determination of acetylspiramycin (ASPM) based on a single-wall carbon nanotubes (SWNTs)-dihexadecyl hydrogen phosphate (DHP) film coated glassy carbon electrode (GCE). Compared with a bare GCE, the SWNTs-DHP film modified GCE exhibits excellent enhancement effects on the electrochemical oxidation of ASPM. A well-defined oxidation peak of ASPM occurs at 0.89 V in 0.1 mol·L⁻¹ phosphate buffer (pH 5.5), which was used to determine ASPM. The electrochemical behavior of ASPM at the SWNTs-DHP modified GCE was examined by cyclic voltammetry and differential pulse voltammetry. The experimental parameters were optimized and a direct electrochemical method for the determination of ASPM is proposed. Under optimum conditions, the oxidation peak current is linear to the concentration of ASPM in the range of 5.0–100 μg·mL⁻¹, with a detection limit of 1 μg·mL⁻¹. The SWNTs-DHP film modified electrode also provides an efficient way of eliminating interferences from some inorganic species in the solution. This sensor was successfully utilized to determine ASPM in drugs.     

Comparison of the cold vapor generation using NaBH4 and SnCl2 as reducing agents and atomic emission spectrometry for the determination of Hg with a microstrip microwave induced argon plasma exiting from the wafer

A 2.45 GHz low power microwave microstrip plasma (MSP) exiting the wafer and operated with Ar at atmospheric pressure was used for the optical emission spectrometric determination of Hg with the aid of a miniaturized optical fiber spectrometer with a CCD detector and the cold vapor (CV) generation technique using NaBH₄ and SnCl₂ as reductants. The experimental conditions were optimized with respect to the relative intensity of the Hg I 253.6 nm line and its signal-to-background intensity ratio (SBR). So as to understand the results of the optimization experiments, the excitation temperatures as measured from Ar I lines (T _exc) and the electron number densities (n _e) for the Ar MSP loaded with Hg vapors were determined and found to be in the range from 5500 to 6300 K and from 1.4 to 2.0 × 10¹⁴ cm⁻³, respectively. Under the optimized conditions, the detection limit for Hg of the CV-MSP-OES using SnCl₂ as the reducing agent was found to be much lower (0.11 ng mL⁻¹) than in the case where NaBH₄ was used (9 ng mL⁻¹). The linearity range was found to be up to 1 μg mL⁻¹ while the precision was of the order of 0.7–5%. The procedure with SnCl₂ as reductant was used for the determination of Hg at a concentration of 0.2 μg mL⁻¹ in synthetic water samples containing 1 to 4% (m/v) of NaCl with an accuracy of 3% as well as in a solution of the domestic sludge standard reference material (NIST SRM 2781) with a certified concentration for Hg of 3.64 ± 0.25 μg g⁻¹ for which 3.55 ± 0.41 μg g⁻¹ was found. Correspondence: J. A. C. Broekaert, Institut für Anorganische und Angewandte Chemie, Universit?t Hamburg, 20146 Hamburg, Germany     

A novel kinetic determination of nitrite based on the perphenazine-bromate redox reaction

An extremely sensitive and selective kinetic method was developed for the determination of trace levels of nitrite based on its catalytic effect on the oxidation of perphenazine (PPZ) with bromate in a phosphoric acid medium. The reaction rate was monitored spectrophotometrically by tracing the formation of the red-colored oxidized product of PPZ at 525 nm within 30 sec of mixing. The optimum reaction conditions were 4.0 μmol L⁻¹ PPZ, 0.4 mol L⁻¹ H₃PO₄ and 30 mmol L⁻¹ bromate at 25 °C. Using the recommended procedure, nitrite could be determined with a linear calibration graph up to 4.50 ng mL⁻¹ and a detection limit of 0.07 ng mL⁻¹. The method was conveniently applied to the determination of nitrite in samples of rain, polluted well and formulated waste waters. Moreover, the published kinetic spectrophotometric methods for nitrite determination are reviewed.     

Study of Solid Phase Extraction Prior to Spectrophotometric Determination of Platinum with N-(3,5-Dimethylphenyl)-N′-(4-Aminobenzenesulfonate)-Thiourea

A highly sensitive, selective and rapid method for the determination of platinum based on the rapid reaction of platinum(IV) with N-(3,5-dimethylphenyl)-N′-(4-aminobenzenesulfonate)-thiourea (DMMPT) and the solid phase extraction of the Pt(IV)-DMMPT complex with C₁₈ membrane disks was developed. In the presence of pH = 3.8 buffer solution and cetyl trimethylammonium bromide (CTMAB) medium, DMMPT reacts with platinum to form a violet complex of a molar ratio of 1:3 (platinum to DMMPT). This complex was enriched by solid phase extraction with C₁₈ membrane disks, and an enrichment factor of 200 was obtained. The molar absorptivity of the complex is 9.51 × 10⁴ L · mol⁻¹ · cm⁻¹ at 755 nm, and Beer’s law is obeyed in the range of 0.01–3.0 μg mL⁻¹ in the measured solution. The relative standard deviation for eleven replicate samples of 0.01 μg mL⁻¹ level is 1.79%. The detection limit reaches 0.02 μg L⁻¹ in the original samples. This method was applied to the determination of platinum in water and soil samples. The relative standard deviations are 2.9–3.4%. The recoveries are 94–105%. The values of determination obtained agree with those of the ICP-MS method. The results are satisfactory.     

Selective square wave voltammetric determination of (+)-catechin in commercial tea samples using beta-cyclodextrin modified carbon paste electrode

Osteryoung square wave cathodic or anodic voltammetry has been used for the determination of (+)-catechin (CAT) at physiological pH in the presence of 0.05 mol · L⁻¹ phosphate/borate buffer using beta-cylcodextrin modified carbon paste electrode. A linear range up to 70.0 μg · mL⁻¹ CAT in cathodic voltammetry and up to 45.0 μg · mL⁻¹ CAT in anodic voltammetry was achieved. The method gave reproducible and reliable results with 1.35 μg · mL⁻¹ CAT as a detection limit with R.S.D. less than 2%. The proposed electrode was applied successfully for the determination of CAT in commercial tea samples with acceptable recovery range (98–102%). The extraction of CAT from commercial tea samples was rather simple, making it suitable for studies with a large number of commercial tea samples giving high accuracy of the proposed method. Correspondence: Deia El-Hady, Department of Chemistry, Faculty of Science, Assiut University, 71516 Assiut, Egypt     

Differential Pulse Voltammetric Determination of Traces of Hydrazine Using Magnetic Microspheres

 A new type of magnetic polymer microspheres containing aldehyde groups at the surface was synthesized. It can react with hydrazine to produce an electroactive adduct. Reduction of this derivative, which was adhering to the magnetic electrode is possible and shown to be effective in an indirect determination of hydrazine. The electrode structure and the experimental conditions were discussed. Under optimum conditions, it was found that the peak potential (Ep) of the derivative of hydrazine is −1.04 V (vs. Ag/AgCl). Hydrazine can be determined in the concentration range 1–800 μg l⁻¹. The detection limit for hydrazine is 0.5 μg l⁻¹. The relative standard deviation for determinations of 100 μg l⁻¹ of hydrazine is 2.51%. The method could be applied to the determination of hydrazine in water samples at the 10–500 μg l⁻¹ level with satisfactory recovery. Received April 3, 2001. Revision July 2, 2001.     

Determination of rhodium in water samples using cloud point extraction (CPE) coupled with flame atomic absorption spectrometry (FAAS)

Cloud point extraction was applied as a method for preconcentration of rhodium after formation of a complex with 2-propylpiperidine-1-carbodithioate (2-PPC), and later determined by flame atomic absorption spectrometry using TritonX-114 as surfactant. Rhodium was complexed with 2-PPC in an aqueous phase and kept for 15 min in a thermostatted bath at 40 °C. Separation of the two phases was accomplished by centrifugation for 15 min at 4000 rpm. The chemical variables affecting the cloud point extraction were optimized and successfully applied to rhodium determination in various water samples. Under optimized conditions, the preconcentration system (100 mL sample) permitted an enhancement factor of 50. The detection limits obtained under optimal conditions was 0.052 ng mL⁻¹. The extraction efficiency was investigated at different rhodium concentrations (7.0–42.0 μg mL⁻¹), and good recoveries (96.42–99.14%) were obtained using this method. It has been applied to the determination of rhodium in water and was compared with reported methods in terms of Student’s ‘t’-test and variance ratio ‘f’-test.     

A Stopped Flow Injection – Chemical Relaxation – Catalytic Spectrophotometric Procedure for the Determination of Cobalt

 A concentration-jump chemical relaxation catalytic procedure by using stopped flow injection is described with detection by spectrophotometry. The photoreduction of the Fe(III)-bipyridyl complex to Fe(II)-bipyridyl is pre-equilibrated at dark for at least 12 h. This solution is afterwards delivered by a peristaltic pump and mixed up with a stream of Co²⁺ solution as a catalyst. The mixture is confluenced down-stream with a flow of Fe(III) solution from a second pump, the concentration of which is about 30% of the pre-equilibrated Fe(III)-bipyridyl solution and acts as the perturbation (concentration-jump). The chemical relaxation process was monitored under thermodynamically non-equilibrium state, and the characteristic parameter of the relaxation process, relaxation time τ, is derived. The calibration graph between 1/τ and cobalt concentration is linear within 0.1–2.5 μg mL⁻¹. The detection limit (LOD) and precision (RSD) are 9 ng mL⁻¹ and 1.6%, respectively, both have been improved as compared to 12 ng mL⁻¹ and 3.6% with a former reported manually operated procedure. The present procedure has been applied to the determination of cobalt in a certified reference material and a soil sample. Received June 15, 2002; accepted October 28, 2002     

Preparation of a novel fluorescence nanosensor based on calcein-doped silica nanoparticles, and its application to the determination of calcium in blood serum

A fluorescent nanosensor based on the use of calcein-doped silica nanoparticles (CDSNPs) for the determination of calcium in blood serum is detailed. Calcein is entrapped within silica nanoparticles by the inverse microemulsion polymerisation process that produces spherical sensors in the size region of 48 ± 4 nm. Calcein encapsulation reduces calcein leaching from the silica matrix when immersed in water and photobleaching which will affect the emission intensity from the irradiation of light. The calcein-doped silica nanoparticles (CDSNPs) have excellent stability to leaching and photobleaching, as well as the selectivity towards calcium over other substances such as K⁺, Al³⁺ and Mg²⁺. The dynamic range of these CDSNPs was found to be 0.003–2 μg mL⁻¹ calcium with a linear range from 0.01 to 2 μg mL⁻¹. The application of CDSNPs for the determination of calcium in the blood serum is demonstrated. We also explored the application of fluorescence microscopy imaging of calcium in serum with the CDSNPs. The results demonstrate that CDSNPs are insensitive to interferences and capable of determining calcium in serum.     

Rapid determination of hydroflumethiazide in dosage forms by time-resolved chemiluminescence

Hydroflumethiazide was determined from the chemiluminescence produced in its reaction with Ce(IV) in acidic medium containing rhodamine 6G as a sensitizer using flow injection techniques (stopped flow mode). A straightforward automatic method based on measuring the peak height and peak area, which are directly proportional to the hydroflumethiazide concentration, was thus developed. The calibration graphs were linear over the concentration range of 1.0–30 μg mL⁻¹. The limit of detection as determined according to Clayton was 0.97 and 0.91 μg mL⁻¹ for peak height and peak area measurements, respectively. The relative standard deviation for ten samples was less than 3.0% with both types of measurements. The procedure was applied to the determination of hydroflumethiazide in pharmaceutical formulations, yielding excellent recoveries, since the determination is free of interference from common excipients and other drugs which are present in the formulation.     

Voltammetric study on the interaction of heparin with toluidine blue, and its analytical application

The interaction of heparin with toluidine blue (TB) was studied by voltammetry. In pH 5.8 Britton-Robinson (BR) buffer, heparin, which is negatively charged, easily binds to the positively charged TB to form a polyelectrolyte complex. Due to the formation of the complex, the well-defined redox peaks of TB at the glass carbon electrode decreased correspondingly without the movement of the peak potential after the addition of heparin. The reaction conditions were optimized carefully. Based on the decrease of the peak current of TB solution, a new electrochemical analytical method was established for heparin with a linear range from 1.0 to 20.0 μg mL⁻¹ and a detection limit of 0.44 μg mL⁻¹. The relative standard deviation (RSD) for five parallel determinations of 10.0 μg mL⁻¹ heparin was 1.07%. This new method was applied to the determination of heparin in heparin sodium injection samples with satisfactory results.     

Microdialysis sampling and chemiluminescence detection for in vivo and real-time study of the lead metabolism in rabbit blood

The chemiluminescence (CL) system K₂MnO₄-luminol is shown to be useful for the determination of lead(II). The method is based on the catalytic effect of Pb(II) on the CL reaction. The linear range was 3 × 10⁻³–9 × 10⁻¹ mg L⁻¹ (r = 0.9971) and the relative standard deviation (R.S.D.) for 5 × 10⁻² mg L⁻¹ Pb(II) measurement was 0.7% (n = 11). The detection limit was 3 × 10⁻⁴ mg L⁻¹ (3σ) Pb(II). Based on this, an in vivo, on-line, real-time analytical system for monitoring the metabolism of free lead(II) in rabbit blood was developed. A microdialysis probe, implanted in the vein of a rabbit, was perfused with perfusate at a flow rate of 5 μL min⁻¹. The concentration of free lead(II) in the dialysate was determined on-line with a flow-injection CL system. This system included microdialysis sampling, on-line separation and chemiluminescence detection. The concentration-time curve of lead(II) was in accordance with the one-compartmental open model, T_1/2 (elimination half-life), T_max (peak time) and C_max (peak concentration) were 37.77 min, 85.20 min and 0.137 mg L⁻¹, respectively.     

Indirect determination of free cyanide in water and industrial waste water by flow injection-atomic absorption spectrometry

A simple and rapid flow injection system is proposed for indirect determination of cyanide by flame atomic absorption spectrometry. It consists of a microcolumn of immobilized salen (N,N′-bis(salicylidene)ethylenediamine) on sodium dodecyl sulfate (SDS)-coated alumina saturated with silver ion and a carrier of dilute solution of sodium hydroxide (10⁻⁵ mol L⁻¹). The micro-column was located between the injection valve and nebulizer of atomic absorption spectrometry. Injection of 250 μL of aqueous cyanide standard or sample solution at pH range of 9–11 cause elution of silver as silver cyanide complexes, which was then measured by flame atomic absorption spectrometry. The absorbance was proportional to the concentration of cyanide in the sample. The graph of absorbance (as peak height) vs. cyanide concentration was linear over the concentration range of 0.1–10 mg L⁻¹ of cyanide, and the detection limit was 0.06 mg L⁻¹. The relative standard deviation at 1 and 3 mg L⁻¹ of cyanide concentration were 4.1 and 4.7%, respectively. The method was successfully applied to determination of cyanide in water and industrial waste waters, and the accuracy was examined through independent analysis by accepted method of pyridine-barbituric acid.