Kinetic Determinations and Some Kinetic Aspects of Analytical Chemistry

A New Kinetic Spectrophotometric Method for the Quantitation of Amorolfine

Amorolfine (AOF) is a compound with fungicide activity based on the dual inhibition of growth of the fungal cell membrane, the biosynthesis and accumulation of sterols, and the reduction of ergosterol. In this work a sensitive kinetic and spectrophotometric method for the AOF quantitation based on the AOF oxidation by means of KMnO4 at 30 min (fixed time), pH alkaline, and ionic strength controlled was developed. Measurements of changes in absorbance at 610 nm were used as criterion of the oxidation progress. In order to maximize the sensitivity, different experimental reaction parameters were carefully studied via factorial screening and optimized by multivariate method. The linearity, intraday, and interday assay precision and accuracy were determined. The absorbance-concentration plot corresponding to tap water spiked samples was rectilinear, over the range of 7.56 × 10-6-3.22 × 10-5 mol L-1, with detection and quantitation limits of 2.49 × 10-6 mol L-1 and 7.56 × 10-6 mol L-1, respectively. The proposed method was successfully validated for the application of the determination of the drug in the spiked tap water samples and the percentage recoveries were 94.0-105.0%. The method is simple and does not require expensive instruments or complicated extraction steps of the reaction product.

Determination of sulpiride in pharmaceutical preparations and biological fluids using a Cr (III) enhanced chemiluminescence method

A highly sensitive and simple method for identifying sulpiride in pharmaceutical formulations and biological fluids is presented. The method is based on increased chemiluminescence (CL) intensity of a luminol-H2O2 system in response to the addition of Cr (III) under alkaline conditions. The CL intensity of the luminol-H2O2-Cr (III) system was greatly enhanced by the addition of sulpiride and the CL intensity was proportional to the concentration of sulpiride in a sample solution. Various parameters affecting the CL intensity were systematically investigated and optimized for determination of the sulpiride in a sample. Under the optimum conditions, the CL intensity was proportional to the concentration of sulpiride in the range of 0.068-4.0 µg/mL, with a good correlation coefficient of 0.997. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 8.50 × 10(-6) µg/mL and 2.83 × 10(-5) µg/mL, respectively. The method presented here produced good reproducibility with a relative standard deviation (RSD) of 2.70% (n = 7). The effects of common excipients and metal ions were studied for their interference effect. The method was validated statistically through recovery studies and successfully applied for the determination of sulpiride in pure form, pharmaceutical preparations and spiked human plasma samples. The percentage recoveries were found to range from 99.10 to 100.05% for pure form, 98.12 to 100.18% for pharmaceutical preparations and 97.9 to 101.4% for spiked human plasma.

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (lambda(max) of [Fe(CN)(5)PhNHNH(2)](3-), complex) under the optimum reaction conditions at: 2.5x10(-3)M [Fe(CN)(6)](4-), 1.0x10(-3)M [PhNHNH(2)], 8.0x10(-7)M [Ag(+)], pH 2.8+/-0.02, ionic strength (mu) 0.02 M (KNO(3)) and temperature 30+/-0.1 degrees C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8-8.0x10(-8)M with a detection limit of 2x10(-9)M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst-inhibitor (K(CI)), catalyst-substrate (K(s)) and Michaelis-Menten constant (K(m)) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.

Spectrophotometric determination of nitrite based on its catalytic effect on the reaction of nuclear fast red and potassium bromate

A highly selective and sensitive catalytic spectrophotometric method was developed for the determination of nitrite in water samples. The method is based on its catalytic effect on the nuclear fast red-potassium bromate redox reaction in acidic medium. The reaction was followed spectrophotometrically by measuring the change in the absorbance at 518 nm of nuclear fast red 5 min after initiation of the reaction. In this study, the experimental parameters were optimized and the effects of other cations and anions on the determination of nitrite were examined. The calibration graph was linear in the range 2.0-45 ?g mL-1 of nitrite. The relative standard deviations for the determination of 15 and 30 ?g mL-1 of nitrite were 3.1 and 1.75 %, respectively (n = 8). The detection limit calculated from three times the standard deviation of the blank 3Sb was 0.7 ?g mL-1. The method was successfully applied to the determination of nitrite in spiked tap, natural and wastewater samples.

Serum cobalt in children with essential hypertension

The effect of cobalt on the cardiovascular system is one of many aspects of cobalt metabolism in humans. Elastin and collagen are the main proteins of the vascular wall. The aims of this study were: 1) to determine serum cobalt concentrations in children with hypertension; and 2) to study the correlation between serum cobalt and some biological markers of the extracellular matrix of the vascular wall, i.e., anti-elastin and anti-collagen type IV antibodies. Patients showed statistically significant higher levels of systolic and diastolic blood pressure, and significantly lower serum cobalt concentrations, than controls. Children with hypertension showed significantly higher levels of total cholesterol (P = 0.0003) and collagen type IV IgM (P = 0.04). Collagen type IV IgG levels (P = 0.027) were lower than in controls. Serum cobalt in patients showed a correlation with systolic blood pressure (r = -0.44, P = 0.05), elastin IgM (r = 0.60, P = 0.007), and collagen type IV IgG (r = -0.46, P = 0.04). Our data suggest the existence of a correlation between changes in levels of serum cobalt, total cholesterol, anti-collagen type IV antibodies, and essential hypertension in children. This is the first study of serum cobalt in children with essential hypertension.

Enhancing effect of DNA on chemiluminescence from the decomposition of hydrogen peroxide catalyzed by copper(II)

In the absence of any special luminescence reagent, emission of weak chemiluminescence has been observed during the decomposition of hydrogen peroxide catalyzed by copper(II) in basic aqueous solution. The intensity of the chemiluminescence was greatly enhanced by addition of DNA and was strongly dependent on DNA concentration. Based on these phenomena, a flow-injection chemiluminescence method was established for determination of DNA. The chemiluminescence intensity was linear with DNA concentration in the range 2 x 10(-7)-1 x 10(-5) g L(-1) and the detection limit was 4.1 x 10(-8) g L(-1) (S/N=3). The relative standard deviation was less than 3.0% for 4 x 10(-7) g L(-1) DNA (n=11). The proposed method was satisfactorily applied for determination of DNA in synthetic samples. The possible mechanism of the CL reaction is discussed.

Simultaneous determination of copper(II) and cobalt(II) by ion chromatography coupled with chemiluminescent detection

In the absence of any special luminescent reagents, a weakly chemiluminescent emission was observed during the decomposition of hydrogen peroxide, catalyzed by transition-metal ions, such as Cu(II) and Co(II), in basic aqueous solution. The chemiluminescent intensity was significantly enhanced by the addition of ethyldimethylcetylammonium bromide and uranine. The signal-to-noise ratio (S/N) was proportional to the concentrations of Cu(II) and Co(II). Based on these phenomena, a flow-injection chemiluminescent method for the simultaneous separation and determination of Cu(II) and Co(II) was developed. The detection limits of the present chemiluminescent method for Cu(II) and Co(II) were 7.5 and 0.01 ng/ml, respectively. After ion chromatographic separation of Cu(II) and Co(II) by an IonPac CS5A column with oxalic acid and lithium hydroxide monohydrate as the eluent, the present chemiluminescent system was used as a post-column detector for these two transition metal ions in natural water samples.

Luminol chemiluminescence in unbuffered solutions with a cobalt(II)-ethanolamine complex immobilized on resin as catalyst and its application to analysis

Using a heterogeneous catalyst, Co(II)-ethanolamine complex sorbed on Dowex-50W resin, the chemiluminescence (CL) of luminol in unbuffered or weakly acidic solution was studied in the presence of H2O2. The maximum luminol CL wavelength at pH 5.7 was 448 nm, 23 nm longer than that in a basic solution (pH 10.5). Three different ligands, mono-, di-, and triethanolamine, and six transition metal ions, Co(II), Cu(II), Ni(II), Mn-(II), Fe(II), and Fe(III) were compared by CL measurements. The CL intensity decreased in the order mono- > di- > triethanolamine and Co(II) > Cu(II) > Ni(II) > Fe-(III) > Mn(II) > Fe(II). This heterogeneous CL system was developed as H2O2 and glucose flow-through sensors. Detection limits (S/N = 3) of H2O2 and glucose using Dowex-50W-X4-Co(II)-monoethanolamine as catalyst are 1 x 10(-7) M and 1 x 10(-6) M, respectively. On the basis of the studies of the CL, fluorescence, UV-vis and ESCA spectra and the effect of dissolved oxygen in luminol solution, a mechanism for CL emission in unbuffered solution was considered as the formation of a superoxide radical ion during the decomposition of H2O2 catalyzed by the Co(II)-ethanolamine immobilized resin. Then the superoxide radical ion acted on luminol and the CL was emitted. The applications of the proposed method to determine H2O2 in rainwater without any special pretreatment and glucose in human urine and orange juice samples give satisfactory results.

Matrix-assisted laser desorption/ionization mass spectrometry for locating abasic sites and determining the rates of enzymatic hydrolysis of model oligodeoxynucleotides

A method using a combination of exonuclease enzymatic digestion and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was developed to locate model abasic sites in a series of model 21-base oligodeoxynucleotides in which a nucleobase was replaced by a hydrogen atom. The exonuclease digestion rate, with either snake venom phosphodiesterase (SVP) or bovine spleen phosphodiesterase (BSP), clearly slows as the digestion approaches the abasic sites and stops as it reaches it. An oligodeoxynucleotide containing an abasic site in which OH replaces the nucleobase shows similar results. MALDI mass spectra taken at appropriate times during the course of hydrolysis are the basis for rate measurements, and the kinetics also reveal the location of the abasic site. A mathematical treatment of the time-dependent MALDI data was implemented to obtain rate curves and rate constants for the enzymatic digestion of both modified and unmodified oligodeoxynucleotides.