Papers by Mirko Gorazd Prosek
Annals of Nutrition and Metabolism, 2008
Analytical Chemistry, 1989
ABSTRACT
Antimutagenesis and Anticarcinogenesis Mechanisms III, 1993
According to some contemporary theories, the aging process in humans may be the result of the acc... more According to some contemporary theories, the aging process in humans may be the result of the accumulation of unsuccessfully repaired genetic damage. The critical changes determining cell senescence are most probably the changes that take place in macromolecules such as DNA and RNA, enzymes, and structural parts of biomembranes--lipids and proteins.
Journal of High Resolution Chromatography, 1993
The quantitative CE analysis of fluorine and monofluorophosphate in toothpastes is described. Sep... more The quantitative CE analysis of fluorine and monofluorophosphate in toothpastes is described. Separation is performed using a Waters CIA-Pak chemistry kit with Waters Electro Osmotic Flow Modifiers on a CE instrument from Spectra Physics (Spectra-phoresis 500) at elevated temperatures up to 40 °C and at a low temperature of 10 °C. The quantitative results and the simplicity are compared for the CE method, the existing standard GC procedure described in the Official Journal of the European Communities, and the procedure employing a fluoride-ion-specific electrode.
Chromatographia, 1995
Separation of dansyl and di-dansyl derivatives of amino acids present in natural products (corn s... more Separation of dansyl and di-dansyl derivatives of amino acids present in natural products (corn seed flour, wheat flour fraction gliadine) is described. Problems with coelution of derivatization by-products and reagent with some dansyl amino acids (DNS-AA) were solved. A preconcentration step after derivatization of real sample is described. DNS-AA peak areas for different varieties of corn seed flour were compared. Di-dansyl histidine is not separated from di-dansyl lysine and didansyl tyrosine. Additional separation mechanisms have to be introduced to achieve separation of these three species.
Journal of Chromatography A, Nov 1, 1999
A high-performance thin layer chromatographic (HPTLC) method for the rapid and simple quantificat... more A high-performance thin layer chromatographic (HPTLC) method for the rapid and simple quantification of the four major anthraquinone derivatives i.e. physcion, chrysophanol, emodin and chrysophanol glycoside in Rheum emodi is described. HPTLC of anthraquinone derivatives was performed on pre-coated RP-18 F 254S HPTLC plates. For achieving good separation, the mobile phase of methanol-water-formic acid (80:19:1, v/v/v) was used. The densitometric determination of anthraquinone derivatives was carried out at 445 nm in reflection/absorption mode. The calibration curves were linear in the range of 20-100 ng for physcion, 80-400 ng for chrysophanol and emodin, and 200-1000 ng for chrysophanol glycoside. The method was found to be reproducible and convenient for quantitative analysis of anthraquinone derivatives in the methanolic extract of rhizomes of R. emodi collected from three different locations of Western Himalaya, India.
TLC is a very suitable microanalytical method because it is quick, simple, and inexpensive.
Applied Microbiology and Biotechnology, Nov 1, 1989
A semicontinuous fermentation with immobilized mycelium of Claviceps paspali, producing mainly me... more A semicontinuous fermentation with immobilized mycelium of Claviceps paspali, producing mainly methylcarbinolamide of lysergic acid, ergometrine and the amide of lysergic acid, was carried out. It was found that immobilization itself improved ergometrine production. The type and concentration of alginate used dit not influence the alkaloid spectrum. The age and quantity of inoculum as well as the length of a particular cycle affected total alkaloid production but did not seem to affect the changes in relative amounts of particular alkaloids. The best results were obtained with 1000 mg dry mycelium weight of 6-day-old fungus from the vegetative phase in 100 ml production medium immobilized in 4% alginate of medium or low viscosity and by recycling every 10 days. When no fungus was found outside the gel beads it was possible to improve the yield of ergometrine from 52% in the first cycle to 85% in the fourth cycle of the semicontinuous procedure.
Journal of Chromatography B: Biomedical Sciences and Applications, Sep 1, 1998
Ranitidine hydrochloride and its two related compounds, used in the USP TLC purity testing of the... more Ranitidine hydrochloride and its two related compounds, used in the USP TLC purity testing of the drug, were separated on a high-performance thin-layer chromatography (HPTLC) RP-18 WF254S precoated plate using methanol-3% NH4OH (4:1, v/v) as the mobile phase. The main advantage of the proposed HPTLC system over the USP TLC system for testing the purity of ranitidine is a better and more efficient separation of these three compounds in a shorter time and with less consumption of solvents. The system is promising from the point of view of the development of a new method for the TLC purity testing of ranitidine hydrochloride. A video system was used for imaging thin-layer chromatograms. Direct UV densitometric quantitation of the three compounds and a model for the calculation of analytical performance parameters is presented in the second part of the paper.
Hrvatska vodoprivreda, 2001
Svaki analiticki laboratorij trebao bi korisniku svojih analitickih usluga jasno pokazati svoju t... more Svaki analiticki laboratorij trebao bi korisniku svojih analitickih usluga jasno pokazati svoju tehnicku osposobljenost i dokazati tocnost i pouzdanost prezentiranih analitickih rezultata. To se postiže uvedbom kljucnih elemenata sustava za osiguranje kvalitete u svoj svakodnevni rad, sto može rezultirati i uvrstenjem laboratorija u cjelokupni međunarodno priznati sustav, te izdavanjem odgovarajucih ovlastenja i akreditacija. U tom slucaju laboratorij mora izraditi poslovnik kvalitete rada laboratorija, te razraditi sustav unutarnje kontrole rada. U poslovniku kvalitete rada, laboratorij je dužan navesti sve postupke rada, kao i dodatne mogucnosti instaliranih mjernih sustava, te svoje mogucnosti za zadovoljavanjem kvalitete dobivenih rezultata. Akreditacijska osoba je tada u mogucnosti pregledati laboratorij po predloženom poslovniku kvalitete rada, te u slucaju pozitivne ocjene, laboratorij dobiva ovlastenje ili akreditaciju za rad. U akreditiranom laboratoriju sve se analize izrađuju po validiranim metodama, a analiticke postupke izvodi strucan i osposobljen kadar, koji je dužan obnavljati i usavrsavati svoja strucna znanja, u skladu s planom i programom poslovanja laboratorija. Sudjelovanje laboratorija u kružnim testovima omogucuje laboratorijima da provjere svoju osposobljenost za izvođenje specificnih analitickih postupaka, te da svoju kvalitetu rada kontinuirano kontroliraju, održavaju na određenom nivou ili je unapređuju. Sudjelovanje u kružnim testovima omogucuje laboratorijima pregled svoje kvalitete rada, uvid u možebitne probleme i neispravnosti rezultata, a posebno treba naglasiti važnost kružnih testova za laboratorije koji uvode ili razvijaju novu analiticku metodu, sto dovodi do znatne ustede u vremenu. Laboratoriji koji su ukljuceni u kružne testove, samim time dobivaju jos jednu referencu u službi prikazivanja svoje kakvoce rada, te se lakse i bolje mogu prezentirati na tržistu. Međulaboratorijski kružni testovi su osnova buducih harmonizacijskih standarda. Dobivanje akreditacije nije jedini i najvažniji uvjet za zadovoljavanje kvalitete rada laboratorija. Potrebno je primijeniti sustav ISO, koji je nastao kao posljedica standardizacije u americkoj vojnoj industriji u toku drugog svjetskog rata. Danas postaju popularni TQM (Total Quality Managment), VAM (Validated Analytical Measurements), GLP (Good Laboratory Practice), Peer reviev, benchmarking itd. U ovom radu su prikazani rezultati dvaju međulaboratorijskih kružnih testova određivanja anorganskih aniona u vodama u vremenskom razmaku od sest mjeseci. Sva ispitivanja su nacinjena metodom ionske kromatografije, a postupci validacije i vrednovanja rezultata analiza su nacinjeni u skladu s najnovijim svjetskim preporukama i normama. U prvom kružnom testu sudjelovalo je dvadeset dok u drugom osamnaest laboratorija iz Slovenije i Hrvatske sa ionskim kromatografima razlicitih proizvođaca.
Materials Research Bulletin, Feb 1, 1974
The first order phase transition in GexV1_xO2 (0~< x < 0,4) has ben studied by means of different... more The first order phase transition in GexV1_xO2 (0~< x < 0,4) has ben studied by means of differential thermal analysis, resistivity, magnetic susceptibility, and X-ray measurements. In agreement with the theory an intermediate,orthorhombic phase has been found between the tetragonal and monocllnic ones. The dependence of the transition temperature on Ge 4+ concentration has been examined and explained on the basis of the Goodenough's theory.
Hrc-journal of High Resolution Chromatography, Nov 1, 1979
The main limitation of image processing based on charge-coupled device (CCD) imaging in quantitat... more The main limitation of image processing based on charge-coupled device (CCD) imaging in quantitative evaluation of thin-layer chromatography (TLC) is its nonuniform illumination. This paper presents a novel method to solve the problem. First, the background is estimated by employing the cubic spline surface construction. Then the estimated background is subtracted from the original image to make the image segmentation; Finally, the gray level integration for each object is calculated, which is proportional to the value of samples. Experiment shows that the linear correlation coefficient between gray integration and concentration of samples is 0.9978.
Elsevier eBooks, 2000
Among many techniques used for quantiRcation of thin-layer chromatograms, slit-scanning densitome... more Among many techniques used for quantiRcation of thin-layer chromatograms, slit-scanning densitometry is the most common. It gives the opportunity to choose between either reSectance or transmission mode according to the nature of the supporting material. For instance, glass-backed plates can only be used for transmission measurements above 320 nm due to absorption of the UV radiation, while aluminium-backed plates are opaque at all wavelengths. The matrix of sample and stationary phase, which consists of small particles, is optically opaque and strongly light-scattering. Therefore, densitometric measurements of separated substances are much more difRcult than equivalent photometric measurements in solution. A further problem with densitometry is the fact that it is unable to detect the vertical and radial concentration proRles of the separated substance within the spot as a result of diffusion and the chromatographic process. ReSectance and transmission are particularly sensitive to changes in sorbent quality, thickness, spot shape and size, eluent and development conditions. To reduce the errors due to plate-to-plate variation, standards should always be applied to the same plate as the unknown samples. The errors due to migration differences as a result of edge effects, deviations in layer thickness and nonlinear solvent fronts can be further minimized using the data-pair technique introduced by Bethke and co-workers in 1974. This technique is based on an internal compensation, by pairing up the measurements of two spots on the same plate. Most thin-layer chromatography (TLC) analysis is performed in the UV and visible spectral region by applying reSectance scanning densitometry. However, the results of reSectance measurements are restricted to the surface of the sorbent on the TLC plate and are therefore strongly dependent upon the indepth distribution of the analysed compound inside the sorbent. Nonuniformity of the in-depth distribution of a compound inside the sorbent as a result of secondary chromatography can occur during the evaporation}drying stage. Differences in the indepth concentration proRles of the samples and standards can cause signiRcant errors and cannot be completely eliminated by the data-pair technique.
Journal of Biomedical Science and Engineering, 2013
In this paper we described the effect of administrated CoQ 10 , and alfa-lipoic acid on the conce... more In this paper we described the effect of administrated CoQ 10 , and alfa-lipoic acid on the concentration of total CoQ 10 in plasma end body tissues of eggs laying hens. Organisms raise a complex network of enzymes, metabolites and molecules with antioxidant activities in order to prevent oxidative damage of theirs bodies. Adequate blood concentrations of small weight molecules ingested with food and food additives are important for the proper functioning of the antioxidant defense. To test this hypothesis we prepared following experiment. Forty weeks old hens were selected from two genotypes; Ross 308 broiler mothers and Lohmann breed hens. Animals were fed for a period of 84 days. Concentrations of supplemented CoQ 10 and ALA were calculated from feed instruction tables so each hen received an average of approximately 5 mg of CoQ 10 and 50 mg of ALA per kg of animal weight per day. During the experiment blood samples were taken and at the end of the experiment different body tissues (heart, liver, breast, legs) were collected and analyzed with originally developed HPLC-MS/MS method based selective ionization with LiCl on MRM scanning. We found a number of interesting and unexpected results. Supplemented CoQ 10 increased concentrations of coenzyme CoQ 10 in plasma and different hen's tissues. Increased concentration of CoQ 10 is the result of its transfer with chylomicrons from the digestive tract to various organs of the body and to the liver where exogenous and endogenous CoQ 10 has been re-redistributed through lipoproteins. Supplemented ALA caused much greater concentration of CoQ 10 in different tissues and plasma then CoQ 10. Plausible explanation of our results is such that ALA may regenerates the antioxidants and accelerate the formation of endogenous CoQ 10 which is distributed with lipoprotein carriers and increases overall concentration of CoQ 10. Our experiments definitely show that Lipoic acid beside glutathione promotes also a synthesis of CoQ 10 and increases the total concentration especially in liver and heart tissues.
Journal of Chromatography B: Biomedical Sciences and Applications, 1983
A quantitative high-performance thin-layer chromatographic (HPTLC) method was developed for the a... more A quantitative high-performance thin-layer chromatographic (HPTLC) method was developed for the analysis of ampicillin in urine. A dioxane-water-n-butanol-formic acid mobile phase system and HPTLC Silica gel 60 F254 as stationary phase were used. Quantitation was realized on a Zeiss PMQ 2 densitometer connected to a Varian A-25 recorder and an Apple II microcomputer or alternatively with an HP 9830A computer and HP 9862A plotter. A good linear range of detection (0.05-1.00 pg) at 480 nm was obtained. Standard statistical methods demonstrated good reproducibility (coefficient of variation is not greater than 3%). The method is appropriate for ampicillin quality control and pharmacokinetic studies.
Journal of Chromatography A, Aug 1, 1991
Abstract Two-dimensional thin-layer chromatography (TLC) is seldom used as a quantitative method ... more Abstract Two-dimensional thin-layer chromatography (TLC) is seldom used as a quantitative method in spite of its enormous potential, the main reasons being a single sample, a complicated solvent system optimizing procedure, and lack of adequative evaluation procedures. A special set of computer programs which enable scanning and evaluation TLC scanner is described. A whole TLC plate is scanned in linear mode with normal slit shape, for instance 0.2 x 8 mm, with as small as 0.5 to 1.0 mm steps between scans. Each run is processed as for a normal densitogram, the baseline is constructed, substracted, and the eventual peaks are located and integrated. In the next step a special program selects the correct positions of peaks, according to the biggest peak height, of all the scans. The selected scans are reintegrated and peak heights and areas are reported. Manual mode results were prepared in addition to the automatic mode. The operator selects the most convenient scan and integrates it using the cursors and chromatograms on the screen. The practical application of the scanning and evaluation programs is presented with quantitative determination of some phenolic components in propolis. Plates are developed with the solvent system: toluene—ethyl acetate—formic acid (75:15:3) and in the perpendicular direction with the solvent system: chloroform—methanol—formic acid (75:5:4). Identification and quantification of some characteristic flavonoids is performed with the 2-aminoethyldiphenylborinate/polyethylene glycol 4000 derivation reagent and external standards.
Intensive Care Medicine, Feb 17, 1999
高等学校化学学报, Dec 31, 1999
用溶液电化学方法及固态电极方法研究了Na 5 YSi 4 O 12 (NYS)与K + 和Ag + 的离子交换性质,对离子交换后得到的KNYS和AgNYS样品的结构、密度及离子导电性质进行了表征... more 用溶液电化学方法及固态电极方法研究了Na 5 YSi 4 O 12 (NYS)与K + 和Ag + 的离子交换性质,对离子交换后得到的KNYS和AgNYS样品的结构、密度及离子导电性质进行了表征。与其它离子交换方法相比,上述方法可获得较高的离子交换度,而且元素分析结果与密度测试结果符合良好。
Chromatographia, Mar 1, 1997
SummaryA method has been developed for qualitative determination, in some natural products, of th... more SummaryA method has been developed for qualitative determination, in some natural products, of those amino acids which form di-dansyl derivatives. The capillary electrophoresis methods so far developed have not completely solved the problem of separation of di-dansyl amino acids. These amino acids are highly non-polar, because they contain two dansyl groups linked to the amino acid part of the molecule, and are poorly separated from each other, or not separated at all, by micellar electrokinetic chromatography. A new separation mechanism has been tested using a different co-surfactant. Preliminary data have led to 2-methyl-1-propanol being chosen for further investigation of the capabilities of the method of separation.
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Papers by Mirko Gorazd Prosek