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PubMed1997

Spectrofluorimetric determination of vitamin K3 by a solid-phase zinc reactor immobilized in a flow injection assembly.

The spectrofluorimetric determination of vitamin K3 (menadione) using a flow injection (FI) assembly provided with a solid-phase reactor with immobilized zinc is described. The naphthohydroquinone was produced by means of two coupled steps in the FI system: hydrolysis of the sodium sulfite derivative of the menadione in a basic medium and reduction of the generated menadione in the zinc reactor in an acidic medium. The fluorescent product was monitored spectrofluorimetrically (lambda ex 325 nm; lambda em 425 nm). The calibration graph was linear over the range 0.1-18 micrograms ml-1 with a reproducibility of 1.6%; the limit of detection was 0.005 microgram ml-1 and the sample throughput was 70 h-1. The influence of foreign compounds was studied and the procedure was applied to the determination of vitamin K3 in three different pharmaceutical formulations.

Flow Injection Analysis↗
PubMed1997

Miniaturized graphite sensors doped with metal-bathophenanthroline complexes for the selective potentiometric determination of uric acid in biological fluids.

Miniaturized poly(vinyl chloride) matrix membrane sensors in an all-solid-state graphite support, responsive to urate anion, were developed. The membranes incorporate lipophilic ion-pair complexes of urate anion with ruthenium(III), iron(II), nickel(II) and copper(I) bathophenanthroline (4,7-diphenyl-1,10-phenanthroline) counter cations. The sensors demonstrate a near-Nernstian response to urate over the concentration range 1 x 10(-2)-1 x 10(-5) mol l-1 and have micromolar detection limits and good selectivity properties. The response is virtually unaffected by pH changes in the range 7-10 and the response times are 5-10 s in aqueous solutions and in human serum and urine samples. A flow injection detector incorporating an iron(II) bathophenanthroline-urate graphite sensor was used for continuous monitoring of uric acid. The minimum detectable concentration was approximately 8 micrograms ml-1 and the sample throughput was approximately 120 h-1. Direct potentiometric determination of uric acid in the static and hydrodynamic modes of operation over the range 15 micrograms ml-1-1.5 mg ml-1 showed average recoveries of 98.7 and 97.8% with RSDs of 0.6 and 0.7%, respectively. Application of the method to the determination of uric acid in human serum and urine gave results that compared favourably with those obtained by the standard spectrophotometric method.

Flow Injection Analysis↗
PubMed1997

Flow-injection detector incorporating a screen-printed disposable amperometric biosensor for monitoring organophosphate pesticides.

The construction of a wall-jet flow cell, which houses a screen-printed amperometric pesticide biosensor, together with a complete flow-injection system, is described. This system was initially employed in studies to stabilise the enzyme acetylcholinesterase (AChE), which was immobilised on a cobalt phthalocyanine screen-printed carbon electrode to form a biosensor. A combination of dextran sulfate and lactitol, and carbodiimide for enzyme immobilisation, resulted in biosensor lifetimes of at least 76 d (at 37 degrees C). Flow-injection and biosensor conditions were optimised, then the system was evaluated by monitoring the model organophosphate pesticides (OP) dichlorvos and paraoxon. The detection limits were 7 x 10(-11) mol dm-3 (for 1 U of AChE) and 4 x 10(-11) mol dm-3 (for 0.05 U of AChE), respectively, which are better than for other electrochemical methods. Initial evaluations on two river water samples have been carried out to test the validity of the system for OP determination in field samples.

Biosensing Techniques↗
PubMed1998

Flow injection on-line photochemical reaction coupled to spectrofluorimetry for the determination of thiamine in pharmaceuticals and serum.

The photochemical reaction of thiamine was studied with a photochemical reactor made by coiling a knotted PTFE reactor around a low-pressure mercury lamp. Acetone, which was previously reported to be a sensitizer for the photochemical reaction that took place in situ in a flow-through cell, severely depressed the fluorescence signal of the photochemical reaction that took place on-line in the knotted PTFE reactor when sodium sulfite was involved in the photochemical reaction. Experiments revealed that the effect of acetone on the photochemical reaction was dependent on the intensity of the irradiation that was used to induce the photochemical reaction, and that acetone might impair the photochemically induced fluorescence if strong UV irradiation was applied to induce the photochemical reaction and sodium sulfite was used to enhance the fluorescence signal. Based on these observations, a flow injection on-line photochemical-spectrofluorimetric method for the determination of thiamine was developed without using acetone. With the proposed method, a detection limit of 0.11 micrograms l-1 thiamine, a relative standard deviation of 0.36% for 11 determinations of 1 mg l-1 thiamine and a sampling frequency of 100 h-1 were achieved. The developed method was successfully applied to the determination of the thiamine content in various pharmaceutical preparations and serum.

Flow Injection Analysis↗
PubMed1998

Flow injection determination of free and total cholesterol in animal greases using enzymes in non-aqueous media.

A non-covalently coimmobilized bienzymic reactor of horseradish peroxidase (HRP) and cholesterol oxidase (COD), operating in a continuous organic flowing stream of 1X10-3 M p-anisidine in buffer-saturated (pH 7.0) toluene, has been employed for cholesterol determination in animal greases, such as pig, beef, and chicken fat, and codfish liver oil. The method provides a good linear relationship up to 1.8 X 10-3 M cholesterol and average recoveries of 99.5%, a high sensitivity, with a detection limit of 1 X 10-6 M of cholesterol and a good precision (an interday RSD of 1.8% for the determination of total cholesterol in a codfish oil sample). The method permits the direct spectrophotometric determination of free cholesterol present in animal grease samples without any pre-treatment, and the total cholesterol determination after a microwave-assisted saponification. The bienzymic reactor exhibits a good stability in the water-restricted environment, being possible to perform more than 180 analyses during a period of 10d with 1mg of HRP, and 1 mg of COD, equivalent to 220 purpurogallin units and 23 U, respectively.

Animals↗
PubMed1998

Spectrofluorimetric determination of paraquat by manual and flow injection methods.

The reaction involving the formation of a fluorescent charge-transfer complex between paraquat and benzaldehyde was studied in ethanol-water medium. In the presence of a large excess of benzaldehyde, the fluorescence intensity is linearly related to paraquat concentration from 0.13 to 7.4 micrograms ml-1. The method can be easily adapted to a flow system using a two-channel manifold, the peak height being proportional to the paraquat concentration over the range 1.6-22.3 micrograms ml-1. Manual and flow-injection procedures were satisfactorily applied to the determination of paraquat in commercial herbicides, waters, soils and potatoes.

Benzaldehydes↗
PubMed1998

Non-aqueous enzymology approach for improvement of reagentless mediator-based glucose biosensor.

The formation of Nafion membranes containing glucose oxidase and dimethylferrocene as a mediator was optimized using a previously reported non-aqueous enzymology approach for biosensor development. Enzyme immobilization in Nafion membranes was carried out from water-organic mixtures with a high content of organic solvent. The mediator based reagentless glucose electrode was tested in a flow injection system. The response towards glucose addition was stable: the reproducibility during 50 assays exceeded 95%. The response was linear over the glucose concentration range 0.5-50 mM.

Biosensing Techniques↗
PubMed1999

Flow injection determination of vitamin K3 by a photoinduced chemiluminescent reaction.

The determination of vitamin K3 using the coupling between a photochemical reaction and a chemiluminescent reaction in a flow system is described. The method is based on the photooxidation of ethanol sensitized by vitamin K3 to yield hydrogen peroxide, which is monitored through the chemiluminescent reaction with luminol catalysed by hematin. The new approach allows the determination of vitamin K3 in a wide concentration range (1 x 10(-7)-5 x 10(-4) mol l-1) with a throughput of 30 samples h-1. The applicability of the method was demonstrated by the determination of vitamin K3 in pharmaceutical preparations.

Flow Injection Analysis↗
PubMed1999

The use of emulsions for the determination of methylmercury and inorganic mercury in fish-eggs oil by cold vapor generation in a flow injection system with atomic absorption spectrometric detection.

An on-line time based injection system used in conjunction with cold vapor generation atomic absorption spectrometry and microwave-aided oxidation with potassium persulfate has been developed for the determination of the different mercury species in fish-eggs oil samples. A three-phase surfactant-oil-water emulsion produced an advantageous flow when a peristaltic pump was used to introduce the highly viscous sample into the system. The optimum proportion of the oil-water mixture ratio was 2:3 v/v with a Tween 20 surfactant concentration in the emulsion of 0.008% v/v. Inorganic mercury was determined after reduction with sodium borohydride while total mercury was determined after an oxidation step with persulfate prior to the reduction step to elemental mercury with the same reducing agent. The difference between total and inorganic mercury determined the organomercury content in samples. A linear calibration graph was obtained in the range 0.1-20 micrograms l-1 of Hg2+ by injecting 0.7 ml of samples. The detection limits based on 3 sigma of the blank signals were 0.11 and 0.12 microgram l-1 for total and inorganic mercury, respectively. The relative standard deviation of ten independent measurements were 2.8 and 2.2% for 10 micrograms l-1 and 8.8 and 9.0% for 0.1 microgram l-1 amounts of total and inorganic mercury, respectively. The recoveries of 0.3, 0.6 and 8 micrograms l-1 of inorganic and organic mercury added to fish-eggs oil samples ranged from 93.0 to 94.8% and from 100 to 106%, respectively. Good agreement with those values obtained for total mercury content in real samples by electrothermal atomic absorption spectrometry was also obtained, differences between mean values were < 7%. With the proposed procedure, 22 proteropterous catfish-eggs oil samples from the northwestern coast of Venezuela were measured; while the organic mercury lay in the range 2.0 and 3.3 micrograms l-1, inorganic mercury was not detected.

Animals↗
PubMed1999

Flow injection Fourier transform infrared determination of nicotine in tobacco.

A fully automated procedure is proposed for the Fourier transform infrared (FTIR) determination of nicotine in tobacco. The method is based on the on-line extraction of nicotine with CHCl3. Samples, weighed inside empty extraction cartridges, were humidified with NH3 and the cartridges were installed in a flow manifold in which they were extracted with 2 ml CHCl3 for 2 min, then 400 microliters of the extract were introduced into a micro-flow cell using a carrier of CHCl3 and the IR spectrum was registered continuously. The absorbance, in the wavenumber range 1334-1300 cm-1, was measured, obtaining a peak as a function of time. The area of this peak was interpolated on a calibration line established from standard solutions of nicotine in chloroform treated in the same way as samples. The method provided a limit of detection of 0.1 mg ml-1 nicotine, an RSD lower than 2% and a sampling frequency of the whole procedure of 6 h-1. Results obtained for natural samples of cut tobacco and cigar compared well with those obtained by a batch FTIR procedure, involving an off-line extraction with a total time of 16 min. However, for yellow tobacco cigarette, an on-line extraction time of 10 min was required to obtain a good recovery of nicotine.

Flow Injection Analysis↗
PubMed1999

Determination of formaldehyde in liquid, solid and semisolid pharmaceuticals and cosmetics by flow injection-pervaporation.

A spectrophotometric method is proposed for the determination of formaldehyde in liquid, solid and semisolid cosmetic and pharmaceutical samples, employing, for the first time in this field, the coupling of a continuous flow configuration to a pervaporation unit. The method is based on the reaction of the analyte with pararosaniline in acidic medium and subsequent formation of a coloured product (alkylsulfonic acid chromophore) with sodium sulfite, which was monitored spectrophotometrically. The method was applied to samples in which the formaldehyde content is regulated by law.

Cosmetics↗
PubMed1999

Flow injection determination of lactate based on a photochemical reaction using photometric and chemiluminescence detection.

A photochemical method for the determination of lactate using a flow-injection system is proposed. The method is based on the decomposition of lactate in the presence of UO2(2+) and Fe3+ upon irradiation with UV or visible light. The Fe2+ produced in the photochemical process was monitored by measuring the absorbance after complexation with ferrozine (lambda max = 562 nm) or the chemiluminescence (CL) intensity in a luminol system without added oxidant. The range of measurements depended on the length of the irradiation time and the detection system used. The detection limits using CL and photometric detection were 2 ng ml-1 and 50 ng ml-1, respectively. The sample throughput was 45 samples h-1. The usefulness of the method was demonstrated by determining lactate levels in blood serum, milk, yoghurt, beer and pharmaceutical preparations.

Animals↗
PubMed1999

Automated stand-alone flow injection immunoanalysis system for the determination of cephalexin in milk.

A fully automated stand-alone flow injection immunoanalysis (FIIA) device for the determination of cephalexin in milk is developed with a main focus on the investigation of the influence of the sample matrix. The system is based on principles of flow-through immunoassays and on sequential addition of the assay components to an immunoreactor. Protein G is immobilised on the surface of the immunoreactor serving as affinity matrix for the polyclonal anti-cephalexin antibodies. A cephalexin-alkaline phosphatase conjugate is mixed with the analyte-containing sample and binds in a competitve manner to the corresponding antibodies in the immunoreactor. After substrate addition enzymatically generated p-aminophenol is detected at a carbon electrode at +150 mV vs. Ag/AgCl. One assay cycle takes 16 min including regeneration of the immunoreactor. The large excess of protein G allows for more than 150 regenerations without significant loss of signal height. Due to the high specificity of the anti-cephalexin antibodies, other beta-lactam antibiotics like penicillin, amoxicillin and cloxacillin do not interfere in the measurements, even when added at 10 mg l-1. To deactivate alkaline phosphatase present in milk, samples are heat-treated for 3 min prior to measurements. Cephalexin recoveries from two milk samples are 90 and 110%. The detection limit in milk is 1 microgram l-1 (mean relative standard deviation of 3%), less than the maximum residue level of 4 micrograms per kg milk fixed for some beta-lactam antibiotics in the European Union. The device is suitable for fast quantitative data generation from consecutively measured samples and thus adds to analytical screening methods.

Animals↗
PubMed2000

Enzymatic determination of choline in milk using a FIA system with potentiometric detection.

The development of a FIA system for the determination of total choline content in several types of milk is described. The samples were submitted to hydrochloric acid digestion before injection into the system and passed through an enzymatic reactor containing choline oxidase immobilised on glass beads. This enzymatic reaction releases hydrogen peroxide which then reacts with a solution of iodide. The decrease in the concentration of iodide ion is quantified using an iodide ion selective tubular electrode based on a homogeneous crystalline membrane. Validation of the results obtained with this system was performed by comparison with results from a method described in the literature and applied to the determination of total choline in milks. The relative deviation was always < 5%. The repeatability of the method developed was assessed by calculation of the relative standard deviation (RSD) for 12 consecutive injections of one sample. The RSD obtained was < 0.6%.

Animals↗
PubMed1992

Flow injection spectrophotometric determination of calcium, phosphate and chloride ions in milk.

Flow injection procedures for the determination of calcium, phosphate and chloride ions in milk samples are described. The reactions are based on the formation of coloured complexes and their spectrophotometric monitoring. A sample pre-treatment with acetate buffer was carried out owing to the complexity of the sample matrix. For chloride, a rapid and reliable automated procedure for direct measurement of its content in milk (using a dialyser to eliminate interferences) is also described. After optimizing the sample pre-treatment and flow injection variables, the procedures were applied to commercial milk; the results obtained agreed satisfactorily with those of the reference methods. With 50 mm3 samples, a working range of 0-15 ppm for calcium, 50-150 ppm for phosphate and 5-100 ppm for chloride is covered with a precision of better than 1.1%. The sample throughput was higher than 50 samples h-1. These preliminary experiments are the basis for the automation of the determination of calcium, phosphate and chloride ions using a computer-controlled, self-designed and laboratory-built autoanalyser.

Animals↗
PubMed1992

Flow injection spectrophotometric determination of the antibiotic ciprofloxacin in drug formulations.

A flow injection spectrophotometric method for the assay of ciprofloxacin was developed. The method was based on the chelation of iron(III) with the drug in 0.023 mol dm-3 sulfuric acid solution in a 72 cm long coil and the brown-red complex produced was monitored at 447 nm. The super modified simplex computer program was employed for the optimization of the system and chemical parameters with respect to throughput and sensitivity as a measure of system performance. A working range for ciprofloxacin determination of 50-500 ppm for a 110 mm3 sample size with an optimum of 250 samples per hour was achieved with a relative standard deviation of less than 0.92%. The method was successfully applied to the determination of ciprofloxacin in drug formulations.

Chemistry, Pharmaceutical↗
PubMed1993

Organic-phase biosensors for monitoring phenol and hydrogen peroxide in pharmaceutical antibacterial products.

Organic-phase biosensors open new opportunities for assays of challenging pharmaceutical products. Such opportunities are illustrated for the rapid determination of phenol and peroxide antiseptics in different anti-infective formulations. The tyrosinase and peroxidase enzyme electrodes offer reliable quantification of these antibacterial agents following sample dissolution in the organic solvent. The dynamic properties of these enzyme electrodes are exploited for rapid and reproducible flow-injection assays of the pharmaceutical products (relative standard deviation = 1.6-1.9%). Such developments should facilitate rapid quality control testing in the pharmaceutical industry and should be applicable to other therapeutic agents and products. Applicability to cosmetic products containing hydrogen peroxide is also demonstrated.

Anti-Infective Agents, Local↗
PubMed1993

Extraction-spectrofluorimetric method for the determination of erythromycin and its esters in pharmaceutical formulations using manual and flow-injection procedures.

A sensitive and rapid extraction-spectrofluorimetric method for the determination of erythromycin, based on the formation of an ion pair with Erythrosine B, is described. The calibration graph resulting from the measurement of the fluorescence of the chloroform extract (10 cm3) at 560 nm with excitation at 544 nm is linear over the range 10-600 micrograms of erythromycin per 20 cm3 of total volume of aqueous phase, with a relative standard deviation (RSD) of 1.5% for 3.7 micrograms cm-3 erythromycin. The method can be successfully adapted to an unsegmented flow system, the peak height being proportional to erythromycin concentration over the range 0.65-5.88 micrograms of erythromycin per 400 mm3 of sample solution injected. Up to 45 samples h-1 can be processed with an RSD of 2.9-3.8%. Manual and flow-injection methods were satisfactorily applied to the determination of erythromycin in pharmaceutical preparations.

Erythromycin↗