Determination of cadmium in polished rice by low-temperature ashing and atomic absorption spectrometry

A method is described for the enthalpimetric determination of serum cholinesterase activity. Physiological amounts of cholinesterase (2–5 IU cm^-3) in aqueous solutions and reconstituted sera are determined with a precision of 2.5% and 1.4% (r.s.d.), respectively. Typical errors of 1.0% are observed when the enthalpimetric results are compared with a standard colorimetric procedure.     

The potentiometric determination of insecticides: Part I. Organophosphorus insecticides inhibiting cholinesterase

A potentiometric method for the determination of organophosphorus insecticides based on the inhibition of cholinesterase is presented. The acetic acid formed by hydrolysis of acetylcholine is sensed by a glass electrode in a weakly buffered system. The insecticide is incubated with cholinesterase for 1 h at 25°C or 37°C before addition to the substrate. The effects of incubation time and temperature are discussed. The method is applied to the insecticides bromophos and dichlorvos. The detection limits are 2 × 10^-5 M (7 ppb) for bromophos and 1 × 10^-7 M (22 ppb) for dichlorvos. The initial rates of hydrolysis decrease linearly up to 2 × 10^-7 M and 1 × 10^-6 M, respectively.     

The determination of some selected penicillins by enzymatic enthalpimetry

An enzymatic, enthalpimetric procedure is described for the determination of penicillin G, ampicillin sodium or phenoxymethylpenicillin in pure and dosage forms. The technique employed allows up to 20 assays with the same reagent solution. Enthalpy assignments are presented along with error (range) and precision data. The lower limit of determination is about 10^-3 mol dm^-3.     

Flow enthalpimetric determination of glucose, based on oxidation by 1,4-benzoquinone and use of an immobilized glucose oxidase column

A flow enthalpimetric method for the determination of glucose is presented. The method is based on the reaction of glucose with 1,4-benzoquinone in the presence of immobilized glucose oxidase. d-Glucose concentrations ranging from 0.02 to 75mM can be determined. The method is applicable to the determination of glucose in soft drinks, wines, beers, jams and serum.     

Hydrogenation enthalpimetry--I: microcomputer-assisted calibration and data-acquisition

A calorimetric device is described which permits enthalpimetric determination of unsaturated hydrocarbons through the enthalpy change for their catalytic hydrogenation. Samples with weights from < 1 to about 20 mg can be analysed with a mean error of about 2%. The method makes extensive use of digital electronics and is well suited to routine automated determination of unsaturation. The principal drawback is lack of specificity.     

Enthalpimetry with catalytic reactions-II Determination of thioureas by the iodine-azide reaction after thin-layer chromatographic separation

A enthalpimetric method for the determination of thiourea and its N-alkyl derivatives (1,3-dimethyl, 1,3-diethyl and 1,3-di-n-butyl), based on thei.     

Use of a manganese dioxide column in the flow enthalpimetric determination of hydrogen peroxide

A method for flow enthalpimetric determination of H₂O₂ is described. The method uses manganese dioxide to catalyse the decomposition of H₂O₂. The catalyst is stable enough to be used for at least 500 analyses. H₂O₂ in the concentration range 0.01–10mM is determined with coefficients of variation < 2%. The method has been used for determination of glucose in a non-alcoholic beverage and wines, with glucose oxidase as the peroxide-producing enzyme.     

Enthalpimetric determination of sulphide and thiosulphate by the catalysis of the iodine-azide reaction

The enthalpimetric determination of sulphide and thiosulphate, in the presence and absence of Zn²⁺ and Cd²⁺, making use of the catalysis of the iodine-azide reaction is studied. An excess of the cations avoids losses of sulphide as H₂S and, when cadmium is used, a 30% enhancement of the sensitivity is observed in the determination of sulphide. On the other hand, both cations depress the analytical response produced by thiosulphate, but iodide can be used as an enhancement agent. Limits of detection of 0.1 and 0.3 ppm are obtained for sulphide and thiosulphate, respectively, and linear dynamic ranges comprise about two orders of magnitude.     

Application of the iodine-azide reaction to the catalytic determination of divalent sulphur compounds in alcoholic medium: Determination of ethylenethiourea in some biological materials

A new catalytic method for the determination of divalent sulphur compounds, which are soluble or insoluble in water, based on the iodine–azide reaction in various alcoholic solutions is described. As model divalent sulphur catalysts the sodium sulphide and thiourea were chosen. Determination of ethylenethiourea in alcoholic extracts from apples and bananas was an example of practical application of the proposed method. To that purpose five previous elaborated techniques were adopted: titration, volumetric, gas chromatographic, enthalpimetric and potentiometric. The effect of other organic solvents, salts, acids and pH on the determination of divalent sulphur catalysts was also evaluated.     

Isoquinoline Alkaloid Contents in Macleaya cordata Extracts and Their Acetylcholinesterase and Butyrylcholinesterase Inhibition

An important strategy for treating neurodegenerative disorders is to maintain the levels of acetylcholine in the synaptic cleft by blocking the cholinesterases. Searching for new effective compounds with inhibited acetylcholinesterase and butyrylcholinesterase activity is one of the most significant challenges of the modern scientific research. The aim of this study was the optimization of the condition for cholinesterase activity determination by high-performance liquid chromatography coupled with diode array detector (HPLC-DAD) in terms of concentrations of enzymatic reaction mixture components, temperature of incubation, and incubation time. In vitro investigation of acetylcholinesterase and butyrylcholinesterase activity inhibition by some isoquinoline alkaloids and extracts obtained from the aerial part and roots of Macleaya cordata collected in May, July, and September. Acetylcholinesterase and butyrylcholinesterase activity inhibition of the extracts obtained from the plant had not been tested previously. The application of the HPLC method allowed eliminating absorption of interfering components, for example, alkaloids such as sanguinarine and berberine. The HPLC method was successfully applied for the evaluation of the acetylcholinesterase inhibitory activity in samples such as plant extracts, especially those containing colored components adsorbing at the same wavelength as the adsorption wavelength of 5-thio-2-nitro-benzoic acid, which is the product of the reaction between thiocholine (product of the hydrolysis of acetyl/butyrylthiocholine reaction) with Ellman’s reagent. Moreover, liquid chromatography coupled with a triple quadrupole mass spectrometer (LC–QqQ–ESI–MS/MS) analysis allowed evaluating the identification of relevant bioactive compounds in the obtained plant extracts. The investigated alkaloids, especially sanguinarine and chelerythrine, and all the Macleaya cordata extracts, especially the extract obtained from the aerial part collected in May, exhibited very high cholinesterase activity inhibition. HPLC-DAD was also applied for the kinetics study of the most active alkaloids sanguinarine and chelerythrine. Our investigations demonstrated that these plant extracts can be recommended for further in vivo experiments to confirm their cholinesterase inhibition activity.     

Laminar Flow-Through Cell for Enthalpimetric Determination of Biological Substrates

Abstract

This paper describes a very versatile laminar flowthrough cell designed to perform enthalpimetric determinations of biochemical substrates in the field of clinical and biochemical analysis. The performance of the apparatus is demonstrated for the glacose/glucose-oxidase system instrument. Sensitivity allows determination of glucose concentrations in the range of 10^?3 Moles/litre. Other enzyme-substrate exothermic reactions can be used without any modification of the instrument.     

Enzymatic inhibition enthalpimetry: The analytical potential of the inhibitory action of a series of physiologically active alkaloids on the activity of serum cholinesterase

A kinetic method is described for the enthalpimetric determination of a series of physiologically active alkaloids based on their inhibitory effect on the cholinesterase-catalysed hydrolysis of butyrylcholine iodide. All analyses are done at pH 8.0 and at 25.0°C (short term stability ± 0.002°C). Precision (< 3.0%) data are reported for the determination of physostigmine sulphate (1.0–4.0 × 10^-8), quinine sulphate (1.0 × 10^-6–4.0 × 10^-5), procaine hydrochloride (1.0 × 10^-5–× 2.5 × 10^-4), atropine sulphate (5.0 × 10^-5–3.0 × 10^-4), morphine sulphate (1.0–8.0 × 10^-4), codeine phosphate (3.0 × 10^-4–2.4 × 10^-3), pilocarpine nitrate (5.0 × 10^-4––6.0 × 10^-3) and thiamine hydrochloride (1.0–5.0 × 10^-3); the linear response ranges in mol dm^-3 are given in parentheses. Complete inhibition curves are presented and relative “potency” is inferred. The effects of several interfering inhibitors are discussed.     

Novel Enzymatic Potentiometric Approaches for Surfactant Analysis

The present study described a novel application of simple potentiometric enzymatic method for analysis of surfactants based on their inhibitory effect on acetylcholinesterase enzyme (AChE). The enzymatic activity was measured through monitoring hydrolysis of acetylcholine (ACh) with a disposable acetylcholine potentiometric sensor. Comprehensive investigations were carried out including the effect of incubation time, cholinesterase enzyme and the working calibration ranges. Based on inhibition of AChE, different cationic, anionic and nonionic surfactants were determined in the concentration range from 0 to 40 μg mL⁻¹ with detection limits reaching 0.07 μg mL⁻¹ depending on the nature of surfactants. The degree of AChE inhibition caused by different tested surfactants were as follows: cetylpyridinium chloride (CPC) > benzyldimethylhexadecyl ammonium chloride (BDHAC) > Hyamine (Hy)>cetyltrimethylammonium bromide (CTAB) > Triton X‐100 (TX‐100) > sodium dodecyl sulphate (SDS). The proposed method was applied for determination of surfactants in pharmaceutical formulation, detergents products and environmental samples with acceptable sensitivity and reproducibility.     

Determination of carbohydrates by direct injection enthalpimetry

An analytical method for the determination of carbohydrates is described, which is based on the enthalpimetric signal obtained at the beginning of the reaction with periodate. The apparatus is described and relevant aspects of the procedure are discussed. Single carbohydrates can be determined in a few minutes with a precision of 1%. Analysis of mixtures of glucose and fructose is reported.     

A sequential injection cold-vapor atomic absorption method for the determination of total mercury

A sequential injection (SI) method for the determination of mercury via cold vapor atomic absorption spectrophotometry is presented. The method differs from flow injection (FI) cold vapor methods for the determination of mercury because of the simplicity of the system required for the method: one pump, one valve, a gas-liquid separator, and an atomic absorption spectrophotometer equipped with a quartz cell. Under optimal conditions, the method has the following figures of merit: a linear ¶calibration range of 1.0 to 20 μg L^–1; a detection limit of 0.46 μg L^–1; and a precision of 0.90% RSD (8 μg L^–1). The procedure allows for a sampling rate of one injection per 80 s (excluding sample pretreatment). Results from the determination of mercury in water and fish specimens are also presented. The figures of merit of the method are compared to two other SI methods for the determination of mercury.     

Optimization of analytical methods based on non-linear asymptotic calibration graphs: Effect of the Time of Hydrolysis on the Enzymatic Determination of Pyridostigmine

A method for enzymatic determination of pyridostigmine is considered. The nonlinear calibration graphs obtained are functions of nine independent variables. The optimization of the curves is discussed, with the relative error as the criterion of optimization. A graphical method is suggested, which allows easy determination of the relative error, of the best concentration for sampling, and of the limit of response. A shortcut method of optimization for asymptotic calibration curves is suggested, and illustrated by optimizing the time of hydrolysis of acetylcholine by cholinesterase. Some determinations of pyridostigmine in water, urine and bovine serum are presented, employing the suggested method.     

Surface-enhanced Raman scattering detection of cholinesterase inhibitors

A new sensitive surface-enhanced Raman scattering (SERS) assay for detection of cholinesterase inhibitors such as organophosphorous pesticides using silver colloidal nanoparticles was developed and optimized. Acetylcholinesterase (AChE) mediated the hydrolysis of acetylthiocholine to produce thiocholine, which interacted with the silver nanoparticles to give a specific SERS spectrum. Variation in enzyme activity due to inhibition was measured from changes in intensity of a characteristic peak (772 cm⁻¹) of the SERS spectrum that was directly correlated with the concentration of produced thiocholine. The method was demonstrated for the detection of paraoxon as reference AChE inhibitor. Limit of detection of paraoxon for 5 min incubation at 25 °C was 1.8 × 10⁻⁸ M. This assay can be utilized for the detection of trace amounts of any AChE inhibitor.     

Amperometrisches Verfahren zur Bestimmung der Aktivit?t von Cholinesterasen und Nachweis der Inhibitoren dieser Enzyme

Summary An electrochemical procedure based on the anodic oxidation of thiocholine iodide for the determination of the activity of cholinesterase both in serum and in the red blood cells is described. Using electronic differentiation of the current time curve the enzyme activity is directly available. The values obtained agree very well with the established method. Furthermore, both reversible and irreversible inhibitors of the cholinesterase have been quantified by using standardized serum samples.     

Determination of Gentamicin with an Amperometric Enzyme Immunosensor

A new version of enzyme immunoassay with the use of an amperometric immunosensor was proposed for the determination of an aminoglycoside antibiotic gentamicin. The biosensing part of the enzyme immunosensor simultaneously incorporates immobilized enzyme cholinesterase and antibodies against gentamicin. The detection limit for gentamicin in this method is 1 × 10^–9 mg/mL. The time of determination is no longer than 20 min. The stability constants of the immunocomplex and the kinetic parameters of the enzymatic reaction in its presence were determined. Gentamicin was determined in samples of pharmaceutical preparations and foodstuffs (milk).     

A comparison of three methods for cholinesterase analysis

Three methods of cholinesterase analysis in blood are compared: the ΔpH (modified Michel method), pH Stat, and radiometric methods. The ΔpH method was determined to be the best choice for routine laboratory screeening for organophosphate exposure. The methods all agree within experimental variation. The radiometric method uses a thin-layer chromatography (TLC) separation of acetate (¹⁴C) activity from acetylcholine (¹⁴C) activity with direct β counting or scintillation counting to determine the concentration of acetate activity. The methods were compared on freeze-dried human blood and on experimentally carbamate-inhibited mouse blood. The radiometric analysis may be performed using as little as 5 μl of blood. The radiometric method may enhance the ability to detect sublethal exposure to cholinesterase inhibitors. It should be of particular use where sampling size is of greatest importance.