Browsing by Author "Tanev D."

Now showing 1 - 6 of 6
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    Calibration of GC/MS method and validation of the modified sample preparation for determination of polycyclic aromatic hydrocarbons
    (2018-01-01) Givechev I.; Danalev D.; Yaneva S.; Tanev D.
    A modified procedure of EN 16619:2015 method for determination of four polycyclic aromatic hydrocarbons (PAH's) was proposed. A change in internal standard and in sample preparation procedure was made for two low fat food matrices (wheat flour and smoked pork leg). As a result a new calibration was obtained with very good linearity (correlation coefficient R2 = 0.999). Recovery rates for spiked samples from both matrices were also calculated and were found in a good fit with the European legislation specifications. The average values of the recovery rates amounted to 99.32 % (1.83 % relative standard deviation) for wheat flour and 97.25 % (2.50 % relative standard deviation) for smoked pork leg.
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    Development and validation of GC/MS method for simultaneous determination of 16 polycyclic aromatic hydrocarbons (PAHs) in pork meat matrix
    (2021-03-01) Givechev I.; Tanev D.; Danalev D.
    The major processes for introducing polycyclic aromatic hydrocarbons (PAHs) in food are smoking and grilling of different products. But in addition, PAHs can permeate in the food chain due to their high lipophilicity and ability to be accumulated in specific tissue, through contaminated animal feed. Further, when some parts of these animals are marketed as food, the accumulated PAHs can go to the human organism. Some of them are classified as highly toxic, carcinogenic and mutagenic for animal and human organisms so they are under consideration of International and European legislation. This work reports development and validation of simple and fast GC/MS method for 16 PAHs determination. Comparison of two methods for sample preparation in pork meat matrix standard extraction/saponification procedure and modified QuEChERS method is also done. In addition, this paper report the calibration step of instrument and a recovery study for 16 PAHs in model pork meat, using modified QuEChERS procedure for sample pretreatment. The calibration step with accessible and suitable for use in real laboratory conditions internal standard (chrysene D12) is done in the range 10–100 ppb using toluene as solvent. The obtained results show very good linearity (R2 5 0.99 to 1.00). For the recovery study six model samples were spiked with 16 PAHs and they all are subjected to QuEChERS procedure. The recovery is calculated and the obtained data (71–120%) is in a good correlation with requirements of international legislation. Finally, LOD values for all 16 investigated compounds of modified GC/MS method and for the instrument were determined.
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    Development and validation of HPLC-DAD methodology for simultaneous qualitative and quantitative determination of thirteen substances with a steroid structure
    (2023-01-01) Zaharieva Z.; Atanasova S.; Danalev D.; Jaber S.; Foteva T.; Nemska V.; Tanev D.; Georgieva N.
    Using supplements in different sports is a common practice for many athletes. Unfortunately, the growth of this market has entailed some speculations, such as the addition of excessive doses of potentially toxic ingredients. Sometimes the doses listed on the package do not correspond to the real content. Some nutritional supplements on sale may contain undeclared ingredients. Some of those supplements are prohibited substances according to different regulations. Herein, a simple HPLC/DAD procedure that is easy to apply in conventional laboratory practice was developed for the simultaneous determination of 13 substances with steroid structure in nutritional supplements for sport: testosterone, testosterone propionate, testosterone enanthate, methyltestosterone, nandrolone, nandrolone propionate, nandrolone decanoate, methandienone, androstenedione, trenbolone, trenbolone acetate, trenbolone enanthate and boldenone undecylenate. The methodology includes gradient elution with mobile phase A: MeOH:ddH2O (55:45) and mobile phase B: 100% MeOH in a standard HPLC system containing a Halo 90 Å, C18 (150 x 4.6 mm, 2.7 µm) column, flow rate 0.6 mL/min, UV wavelength of 254 nm, temperature of 40 °C and 20 μL injection volume. The developed methodology was validated according to the corresponding official documents. The key parameters used for the selection of the optimal HPLC conditions were the ability of the mobile phase and solvents to be used with both an HPLC/MS and a GC/MS chromatographic system. The obtained total run time, the reproducibility of the retention times, the separation of all peaks and peak characteristics meet all requirements.
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    Development and Validation of HPLC/DAD Method for Simultaneously Determination of Six Prohibited Substances in Model Matrices
    (2020-12-01) Zaharieva Z.; Tanev D.; Danalev D.
    The authorities have identified an emerging trend where over-the-counter products, represented as dietary supplements, contain hidden active ingredients that could be harmful. Consumers may unknowingly take products laced with varying quantities of approved prescription drug ingredients, controlled substances, and untested and unstudied pharmaceutically active ingredients. Hidden ingredients are increasingly becoming a problem in products promoted for sexual enhancement, weight loss, or bodybuilding. The tests have revealed the presence of some undesired substances like sildenafil, tadalafil, vardenafil, and their analogues in tainted sexual enhancement products. The content of these substances is usually around the daily curative dose. A simple high-performance liquid chromatography (HPLC) method for simultaneously determination of sildenafil, vardenafil, tadalafil, dapoxetine, yohimbine, and sibutramine was developed and validated. InfinityLab Poroshell 120 EC-C18 (150 '4.6 mm '4 μm particles) was used, as well as a diode-array detector (DAD) at 230 nm, and a gradient flow with 0.030 Eœ ammonium acetate buffer and acetonitrile. The method is linear in the following range: 2.5-37.5 μg/mL for yohimbine, 2.06-30.9 μg/mL for vardenafil, 2.0-30.0 μg/mL for sildenafil, 3.1-46.5 μg/mL for tadalafil, 1.98-29.7 μg/mL for dapoxetine, and 2.2-66.0 μg/mL for sibutramine. The linearity coefficient is R2 = 1 for all substances. Model matrices were spiked, and the analytical recoveries for all substances are in the range 97.5%-99.5%. The method exhibited an upper hand compared with previously reported methods in terms of speed and simplicity. Additionally, the mobile phase (also used as extracting, column washing, and diluting solvent) was composed of only buffer and acetonitrile, which rendered the method much cheaper than others.
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    First steps of development of a method for simultaneous determination of cholesterol and fatty acids in food matrices
    (2018-01-01) El Mazbouh H.; Givechev I.; Tanev D.; Yaneva S.; Danalev D.
    Cholesterol and fatty acids are compounds with a key role in the human organism. Their levels must be strictly controlled and maintained in the human body to ensure its proper biochemical functioning. Herein, we report first steps of development of a method for cholesterol determination in food using GC/FID. The calibration, the linearity and the choice of an appropriate internal standard are discussed. The obtained correlation coefficient is R2 = 0,9992. A very good analytical yield of cholesterol 100 % is achieved following a specific procedure of sample preparation. LOQ is 50 ppm, while LOD is 15 ppm.
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    Synthesis, antiproliferative and antimicrobial activities of (KLAKLAK)2-NH2 analogue containing nor-Leu and its conjugates with a second pharmacophore
    (2023-01-01) Jaber S.; Nemska V.; Iliev I.; Ivanova E.; Foteva T.; Georgieva N.; Givechev I.; Tanev D.; Naydenova E.; Danalev D.
    Peptides are a promising alternative of conventional medical drugs for the treatment of different diseases because they have no or have very few side effects owing to the natural mechanisms for their elimination. There are a lot of examples of drugs on the pharmaceutical market based on modified amino acids and peptides. Herein, we report the synthesis and studies on the antimicrobial peptide (KLAKLAK)2-NH2 where Leu is replaced by the unnatural amino acid nor-Leu. In addition, a second pharmacophore with well proven anticancer properties is introduced to the peptide moiety. All structures were synthesized by conventional solid phase peptide synthesis. The antiproliferative and antimicrobial activities were studied using MTT-dye reduction assay and disk-diffusion test, respectively. Biological activity assays showed that the introduction of nor-Leu in the primary structure of the parent compound does not lead to an increase in the antiproliferative activity. However, the combination with the second pharmacophore 1,8-naphtalimide in a hybrid structure 1,8-NphtG-(KNleAKNleAK)2-NH2 leads to a significant increase in the antiproliferative properties. The antimicrobial tests showed that all tested compounds exhibit antimicrobial activity. The peptide and the second pharmacophore had a synergistic effect. In combination with complete hydrolytic stability for 72 h in model systems, the compound 1,8-NphtG-(KNleAKNleAK)2-NH2 is the best candidate for a medical drug in the treatment of mammary gland type A adenocarcinoma (MCF-7) in combination with antimicrobial properties.