Biomedical subjects

V Stefuca

Publications and source records attributed to V Stefuca.

8 recordsLinked to original sources

PubMed2005

Fast gas chromatography with solid phase extraction clean-up for ultratrace analysis of pesticide residues in baby food.

A sample preparation method based on single solvent phase extraction and solid-phase extraction (SPE-NH2) clean-up is studied in combination with fast capillary gas chromatography (GC) to determine 18 selected pesticides belonging to various chemical classes in apples, the common raw material for baby food production and baby food, at the concentration level < or = 10 microg/kg maximum residual limit (MRL). Possibilities of mass spectrometry (MS) detector and electron capture detector (ECD) in fast gas chromatography (GC) of samples with complex matrice at ultra trace levels of pesticide residues were studied and compared. MS detection in single ion monitoring (SIM) mode provided higher selectivity compared to ECD. Optimisation of extraction as well as the simplifying of the whole process of sample preparation was carried out. Recoveries obtained at concentration level of 5 microg/kg (the required value for limit of quantification (LOQ) in baby food) were >90%, except of dimethoate (77.7%) and captan (46.4%) with MS detection. The obtained LOQs were at least 1 order lower than 5 microg/kg for the majority of compounds. The repeatability of gas chromatography-mass spectrometry (GC-MS) measurements of the matrix matched standards expressed as relative standard deviation was <11% except of captan and cypermethrin.

Chromatography, Gas↗

PubMed1999

Investigation of catalytic properties of immobilized enzymes and cells by flow microcalorimetry.

The investigation of catalytic properties of immobilized biocatalysts (IMB) is a time-consuming and not-always-simple procedure, requiring a simple and accurate method of enzyme-activity measurement. In comparison with generally-used techniques, flow microcalorimetry (FMC) has proven to be a very practical and versatile technique for direct monitoring of the course of enzyme reactions. The principal advantage of FMC is integration of the enzyme reaction and its monitoring in one step. This review summarizes the information needed for the complete kinetic or catalytic characterization of the IMB by FMC, without the requirement of any independent analytical method. The optimal experimental procedure is proposed. Examples of experimental studies on immobilized biocatalysts using the FMC are provided. The method is applicable to purified enzymes as well as to enzymes fixed in cells.

Calorimetry↗

PubMed1998

Cellulose as a (bio)affinity carrier: properties, design and applications.

This contribution presents a framework for the rational design of affinity sorbents based on cellulose materials as a support. A three-level evaluation procedure, utilizing the knowledge of physical, chemical and engineering theories, is discussed, which integrates the design of support, affinity sorbent and chromatographic contactor. The principal support properties, such as morphological, diffusional, hydrodynamic, mechanical or ligand-binding properties, are presented and literature data on them are surveyed.

Affinity Labels↗

PubMed1998

Amplification of flow-microcalorimetry signal by means of multiple bioaffinity layering of lectin and glycoenzyme.

This paper demonstrates a positive influence of a special, stepwise technique of enzyme immobilization based on the biospecific adsorption of the glycoenzyme invertase on immobilized concanavalin A (Con A), subsequent adsorption of the free Con A on the immobilized invertase:Con A support and repeated adsorption of invertase on the support. A 3-fold repetition of the same procedure designed preliminarily as bioaffinity layering afforded up to a 10-fold increase in catalytic activity of the immobilized invertase. Reactive hydrogels based on bead cellulose and bead poly(glycidyl methacrylate) were used as immobilization supports for the preparation of these highly active preparations. The enhancement in catalytic activity of immobilized invertase preparations was demonstrated thermometrically, by flow microcalorimetry. Further attractive aspects for utilizing the signal amplification of biosensors with immobilized enzymes are discussed.

Adsorption↗

PubMed1993

Biochemical engineering of biocatalysts immobilized on cellulosic materials.

Complete design of the optimum immobilized biocatalyst seems to still be a matter of the future. To be successful, it would require numerical determination of all significant parameters at each enzyme engineering phase, that is at the design of the carriers, immobilized biocatalysts and immobilized reactors. Future research trends should follow this strategy. For processing, cellulosic materials have been considered carriers that fulfill requests to an example model: they represent a unique family of carriers that cover a broad variety of physical and chemical properties, immobilizing techniques, and immobilized reactors as well. The reason for writing this review article was to test the reliability of such a processing and subsequently, to confront theoretical considerations with practical applications of biocatalysts immobilized on cellulose materials.

Biotechnology↗

PubMed1993

Direct determination of the cephalosporin transforming activity of immobilized cells with use of an enzyme thermistor. 1. Verification of the mathematical model.

A simple method for the direct measurement of the catalytic properties of immobilized cells in the flow minicalorimeter, the enzyme thermistor (ET), is presented. A Trigonopsis variabilis strain with cephalosporin C-transforming activity was used as the model system. The yeast cells were immobilized either by crosslinking with a homobifunctional reagent or by entrapment in gels. The actual activity of the immobilized cells used in the ET was estimated by means of a stirred-batch reactor measurement in conjunction with HPLC analysis of substrate and products. Similar results were also obtained using D-amino acid oxidase (EC 1.4.3.3) isolated from T. variabilis cells and immobilized by gel entrapment. This calibration procedure was found to be appropriate for all biocatalyst systems used. The thermometric signal was proportional to the amount of biocatalyst immobilized in the ET minicolumn. It was shown that the rate of reaction catalyzed by T. variabilis entrapped in calcium pectate gel was limited by internal diffusion to an extent depending on the cell concentration in the biocatalyst particle. This approach offers a direct method for studying the kinetic properties of immobilized cells.

Acremonium↗

PubMed1993

Formate dehydrogenase activity in methanol-utilizing yeasts.

The growth and activity of formate dehydrogenase (FDH) in five methanol-utilizing yeasts at various methanol concentrations were investigated. The parameters observed were inhibited at 4% methanol concentration in the medium. For Candida boidinii and Pichia trehalophila FDH activity was not found. The highest value was detected for Pichia lindneri (0.14 U/mg protein).

Candida↗

PubMed1990

Application of the enzyme thermistor to the direct estimation of intrinsic kinetics using the saccharose-immobilized invertase system.

The possibility of using the enzyme thermistor (ET) for the direct determination of kinetic parameters (Km, Ki, Vm) of immobilized enzyme (IME) was evaluated using different preparations of invertase conjugated to bead celluloses. Two different ET columns packed with IME were operated in the mode of a differential enzyme reactor (short length, low substrate conversion). Kinetic parameters of the above IME reactor were computed by a nonlinear curve-fitting procedure. The obtained kinetic parameters were superverified by means of an independent differential reactor (DR) system. This system utilized an indirect postcolumn analytical method based on determination of glucose concentration in the stirred reservoir. Best agreement between the data acquired by direct (ET) and indirect (DR) methods was obtained if the ET column was operated at flow rates within the range of 1.0-1.5 ml min-1 using invertase-cellulose chlorotriazine conjugate. Influence of heat loss and flow nonideality is discussed. The proposed ET method offers a rapid, convenient, and general approach to determination of kinetic constants of IME preparations by omitting postcolumn analytical methods.

Biosensing Techniques↗