Browsing by Author "Surleva A."
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Item A new generation of cyanide ion-selective membranes for flow injection application. Part III. A simple approach to the determination of toxic metal-cyanide complexes without preliminary separation(2008-08-15) Surleva A.; Neshkova M.A new flow injection approach to total weak acid-dissociable (WAD) metal-cyanide complexes is proposed, which eliminates the need of a separation step (such as gas diffusion or pervaporation) prior to the detection. The cornerstone of the new methodology is based on the highly selective flow-injection potentiometric detection (FIPD) system that makes use of thin-layer electroplated silver chalcogenide ion-selective membranes of non-trivial composition and surface morphology: Ag2 + δSe1 - xTex and Ag2 + δSe. An inherent feature of the FIP-detectors is their specific response to the sum of simple CN- + Zn(CN)4 2- + Cd(CN)4 2-. For total WAD cyanide determination, ligand exchange (LE) and a newly developed electrochemical pre-treatment procedure for release of the bound cyanide were used. The LE pre-treatment ensures complete recovery only when the sample does not contain Hg(CN)4 2-. This limitation is overcome by implementing electrochemical pre-treatment which liberates completely the bound WAD cyanide through cathodic reduction of the complexed metal ions. A complete recovery of toxic WAD cyanide is achieved in the concentration range from 156 μg L-1 up to 13 mg L-1. A three-step protocol for individual and group WAD cyanide speciation is proposed for the first time. The speciation protocol comprises three successive measurements: (i) of non-treated, (ii) LE-exchange pre-treated; (iii) electrochemically pre-treated sample. In the presence of all WAD complexes this procedure provides complete recovery of the total bound cyanide along with its quantitative differentiation into the following groups: (1) Hg(CN)4 2-; (2) CN- + Cd(CN)4 2- + Zn(CN)4 2-; (3) Cu(CN)4 3- + Ni(CN)4 2- + Ag(CN)2 -. The presence of a 100-fold excess in total of the following ions: CO3 2-, SCN-, NH4 +, SO4 2- and Cl- does not interferes. Thus the proposed approach offers a step ahead to meeting the ever increasing demand for cyanide-species-specific methods. The equipment simplicity makes the procedure a good candidate for implementing in portable devices for in-field cyanide monitoring. © 2008 Elsevier B.V. All rights reserved.Item Assessment of Persistence of Gunshot Residues Produced by Firearms from Criminal Cases in the Republic of Kosovo(2022-10-01) Tahirukaj M.; Surleva A.; Vizureanu P.; Olluri B.; Sandu A.V.Gunshot residue (GSR) is a material formed during firearm discharge with a specific spheroidal/noncrystalline morphology and chemical composition. The examination of gunshot residue by SEM/EDS is an important tool in forensic studies and presents supporting evidence in criminal investigations. This study is aimed at exploring the number of particles characteristic of GSR identified by SEM/EDS as a function of time, gun caliber, the number of shots, and weather conditions. Firearms typically used in criminal cases in Kosovo were studied, and the experiments were conducted outdoors in the summer and winter seasons. Nine people made different numbers of shots from one to nine and followed a common office routine. An optimized and validated SEM/EDS protocol was applied with a sensitivity of 95%, a bias of −5%, a repeatability of 2% (RSD), a within-lab reproducibility of 2% (RSD), and an expanded uncertainty of the number of GSR particles of 6% at coverage factor k = 2. The results showed that GSR particles could be identified by SEM/EDS five to seven hours after shooting, depending on the weapon used and number of produced shots. The results will benefit forensic scientists by providing a supportive tool for hypothesizing the time interval between firearm discharge and GSR sampling.Item Biosynthesis of Copper Nanoparticles Using Hylocereus Costaricensis Peel Extract and its Photocatalytic Properties(2023-01-01) Putri S.E.; Herawati N.; Fudhail A.; Pratiwi D.E.; Side S.; Rahman A.; Desa S.S.; Ahmad N.; Junaedi S.; Surleva A.A green chemistry method was used for the first time to synthesize copper nanoparticles (Cu-NPs) using CuSO4 as a precursor and red dragon fruit (Hylocereus costaricensis) peel wasted extract as a bio-reductor. Cu-NPs produced were then used as a photocatalysts for acid orange 7 (AO7) dyes degradation. The results showed that the smallest average crystallite size of the products ranged from 8.84 to 8.86 nm with the FCC crystal structure and surface area of 244.38e278.85 m2g-1. Furthermore, the optimum degradation of AO7 dye occurred at a ratio of 1:3 with a percentage of 81.07% for four cycles. These findings indicated that Cu-NPs can be used for the treatment of textile wastewater under sunlight in the future.Item Characterization of Bulgarian Copper Mine Tailing as a Precursor for Obtaining Geopolymers(2024-02-01) Ilieva D.; Angelova L.; Radoykova T.; Surleva A.; Chernev G.; Vizureanu P.; Burduhos-Nergis D.D.; Sandu A.V.Valorization of high-volume mine tailings could be achieved by the development of new geopolymers with a low CO2 footprint. Materials rich in aluminum and silicon with appropriate solubility in an alkaline medium can be used to obtain a geopolymer. This paper presents a study of copper mine tailings from Bulgaria as precursors for geopolymers. Particle size distribution, chemical and mineralogical composition, as well as alkaline reactivity, acidity and electroconductivity of aqueous slurry are studied. The heavy metal content and their mobility are studied by leaching tests. Sequential extraction was applied to determine the geochemical phase distribution of heavy metals. The studied samples were characterized by high alkalinity, which could favor the geopolymerization process. The water-soluble sulphates were less than 4%. The Si/Al ratio in mine tailing was found to be 3. The alkaline reactivity depended more so on the time of extraction than on the concentration of NaOH solution. The main part of the heavy metals was found in the residual fraction; hence, in high alkaline medium during the geopolymerization process, they will stay fixed. Thus, the obtained geopolymers could be expected to exert low environmental impact. The presented results revealed that studied copper mine tailing is a suitable precursor for geopolymerization.Item COMPARATIVE EVALUATION OF METHODS FOR QUANTIFICATION OF MERCURY AT TRACE LEVEL IN AQUATIC BIOTA SAMPLES AS A BIO-INDICATOR(2022-01-01) Ivanova V.; Oster C.; Surleva A.; Fisicaro P.This study presented detailed evaluation of analytical characteristics of four advanced methods for total mercury quantification in aquatic biota samples. The method comparison as a validation strategy to ensure reliable and comparable results according to the ISO 17025 was presented. An analytical performance of the advanced mercury analyzer was compared with isotope dilution mass spectrometric measurements. Certified reference materials for mussel, oyster and scallop tissue were used during methods evaluation. The methods were then applied to unknown samples, such as Gammarus and Sea Bass samples. The highest values obtained for total mercury content in these samples was below maximum permissible limits: (0.222 ± 0.030) and (0.724 ± 0.022) mg kg-1. This comparative study could be of interest to laboratories for environmental monitoring or quality control of fishery products, as well as to other industriesItem Comparative study of soil test methods for determination of plant available potassium in Bulgarian arable soils(2021-01-01) Angelova L.; Genova N.; Stoyanova S.; Surleva O.; Nekov I.H.; Ilieva D.; Surleva A.This comparative study was aimed at estimating analytical behavior of methods for determination of plant available potassium applied to Bulgarian arable soils and to reveal the relationship between the amount of extractable K. Twenty-four samples from two traditional agricultural regions in Bulgaria were studied. Soil potassium was extracted by NH4OAc/HOAc pH 4.5 (AA), diluted double acid (Mehlich 1), CaCl2, BaCl2 and a modified acetate/lactate method (ALM) and determined by Flame AES. The factors influencing the methods accuracy were identified and uncertainty was estimated. The expanded uncertainty was (in mg K2O (100 g dry soil)-1): 0.10 (ALM), 0.64 (Mehlich 1), 0.17 (CaCl2) and 1.1 (AA). The study revealed that the factor which mainly influence the uncertainty of the applied analytical methods for plant available potassium in soil was the calibration of Flame AES determination. The obtained results showed that extractable potassium lowered in the following order KALM ≥ KAA > KMechlich1 > KBaCl2 > KCaCl2. Soil potassium extracted by ALM procedure correlated with AA, BaCl2-K, CaCl2 –K and Mehlich 1 - K at 0.05 level of significance. ALM extracted between 1.2 to 5.8 times more soil K than other methods did. The obtained results provided a base for further study on correlation between extractable K and soil fertility indices for particular soil types and climatic regions in Bulgaria.Item Contribution to the Molybdenum Blue Reaction and its Application in Soil Analysis(2022-01-01) Angelova L.; Genova N.; Pencheva G.; Statkova Y.; Yotova V.; Surleva A.This paper presents a study on the molybdenum blue reaction (MB) as a finishing detection step in soil analysis for quantification of plant available phosphorus. An ammonium acetate/calcium lactate reagent (pH= 4.2) was used for soil phosphorus extraction. The molybdenum blue color reaction using premixed Murphy-Riley reagent and ascorbic acid as a reductant was reinvestigated. UV-Vis characteristics of MB, optimal wavelength, reaction time and concentration of reductant were studied. The effect of ascorbic acid concentration and the reaction time on linearity, bias and uncertainty was discussed. The molybdenum blue reaction was found to obey Beer’s law in the targeted concentration range of 0.04 – 1.0 mg L-1 PO4 3--P. The linearity was proved by “lack-of-fit” test. The uncertainty budget was made and the uncertainty was estimated by modelling approach, as well as single laboratory and quality control approach. The recovery and the expanded uncertainty were found to be, respectively, (95.7 ± 8.7) % (P= 95%, n = 3) and 9.2 mg PO4 3--P /kg dry soil (k = 2). The results showed that the soil sample inhomogeneity and the repeatability of extraction process were the main factors which contribute to the uncertainty of measurement in soil analysis.Item Ensuring the Quality of the Analytical Process in a Research Laboratory(2024-04-01) Surleva A.; Angelova L.; Ilieva D.; Ivanova V.; Surleva O.; Chavdarova K.Featured Application: The approaches for estimation of the analytical behavior of measuring methods could be applied in a research laboratory aiming at the characterization of new materials or a new method for analysis. The limitations of well-known approaches are described, and the alternatives are discussed. This paper discusses approaches for verification of methods of measurements of chemical and physical characteristics of specific samples. The limitations of well-known approaches are discussed. Some examples of alternatives are given to demonstrate specific issues encountered in the research laboratory analyzing new materials or characterizing new properties of materials. Application of sequential procedure using lower quantities of samples and reagents is presented. A standard addition to solid samples is discussed. The approach of control charts for estimation of method uncertainty for determination of plant available phosphorus is presented. The method comparison is applied as an approach to verification of alkaline reactivity by inductively coupled plasma–optical emission spectroscopy (ICP-OES) measurement, as well as density of newly synthesized chalcogenide glass materials. The presented examples demonstrated that alternative approaches are needed in order to verify the methods applied due to the great variety of activities and corresponding tasks in a research laboratory.Item Estimation of soil and tailing dump toxicity: Development and validation of a protocol based on bioindicators and ICP-OES(2019-08-02) Ilieva D.; Angelova L.; Drochioiu G.; Murariu M.; Surleva A.A protocol for estimation of soil toxicity based on germination test, open acid sample digestion and ICP-OES determination of heavy metals and metalloids was proposed. Triticum aestivum was used as a bioindicator and germinated on contaminated soils. After estimation of the state of the plantlets, the accumulated heavy metals and metalloids content were determined. The sample digestion procedure and ICP-OES measurement were validated by analysing plant certified reference material. Additionally, standard addition before sample pretreatment was applied for estimation of method recovery at the levels of heavy metals found in plants from contaminated region. The recovery obtained was between 97 and 105 %. The precisions of the complete protocol (RSD), which included germination tests, sample digestion and ICP-OES measurements, ranged between 4.7% for Mn and 11 % for As. The expanded uncertainty was estimated. The proposed protocol was applied for estimation of soil toxicity and heavy metals bioavailability of tailing dump material and surrounding soils from an abandoned barite mine in Tarnita, Suceava, Romania. The coltsfoot used for remediation of the soil in the studied region was analysed. Cu, Ni, Zn, Mn, Pb, Fe and Al were found in the sample harvested nearby the tailing dump.Item Improvement of the turbine blade surface phase structure recovered by plasma spraying(2020-01-01) Savinkin V.V.; Vizureanu P.; Sandu A.V.; Ratushnaya T.Y.; Ivanischev A.A.; Surleva A.This paper presents the results of research on the construction, technological parameters and criteria that control the process of formation of optimal phase structure of austenitic-and martensitic-class material for steam turbine blades. The hypothesis that the established correlation could increase the quality of blade recovery and its resistance against dynamic and vibrational loads was proved. The efficiency of the developed implantation method for the recovery of steam turbine blades was demonstrated. The optimal technological parameters of the process of laser plasma recovery were established empirically, allowing the development of the system for the fine tuning of the phase composition of austenitic-and martensitic-class steel.Item OBTAINING OF BALSAMIC POPLAR EXTRACT AS BIOSTIMULANT FOR AGRICULTURAL PLANTS(2024-01-01) Mechshanova A.; Polyakov V.; Surleva A.; Radoykova T.Modern varieties of agricultural plants have reached the limits of natural genetic variability in a few key parameters, and a further significant increase in their productivity and stress resistance using traditional approaches is extremely difficult. The use of biostimulants of various nature is considered as a promising way of sustainable development, allowing to increase yields without harmful effects on the environment. Plants are a source of a wide variety of biologically active substances (BAS), such as vitamins, alkaloids, glycosides, saponins, tannins, polysaccharides (gums, mucus, pectins, inulin, fibre, starch), flavonoids, resins, essential and fatty oils, organic acids, phytoncides, pigments and others. An important argument in favour of obtaining biologically active substances from poplar is the environmental friendliness of such a solution, since a lot of unused waste (bark, branches, wood) is generated during the logging process. The purpose of this study is to find the optimal extraction conditions and to investigate the influence of balsamic poplar extract on the change in physiological and biological parameters, as well as the productivity of soybean, cucumber, and sugar beet seeds. The qualitative composition of extracts from buds, twigs, catkins, and poplar wood processing waste has been determined. Among these extracts, the one from poplar wood processing waste is the most promising for further study due to its high content of flavonoids, tannins, saponins, amino acids, and polysaccharides. The optimal technological parameters for extracting these compounds have been identified, including the degree of grinding of the raw materials, the ratio of raw materials to extractant, the duration of extraction, and the concentration of the extractant. It has been found that the best extraction of flavonoids occurs when the raw materials are ground to a size of up to 15 mm and mixed with a ratio of 1:15 of raw materials to extractant for 36 hours using 96 % ethanol. The aftereffect of the application of the extract was traced in the ontogenesis of plants on the change in important physiological processes that influenced the productivity of products and their quality.Item Spectrophotometric study of competitive complexation equilibria involving overlapped spectral responding species: Determination of the stability constant of bismuth-pyrophosphate complex(2012-12-01) Nedeltcheva T.; Surleva A.; Nikolova L.; Borissova R.; Georgieva S.Spectrophotometric study of competitive complex formation equilibria involving overlapped spectral responding species applying a simple and versatile algorithm was carried out. The algorithm involves multivariable regression for calculation of equilibrium concentrations from multiwavelength data and mass action law for the stability constant calculation. The used regression functions are part of common statistical software. Stability constants and complex stoichiometry of competing equilibria were simultaneously determined. The species concentration profiles at several spectral overlapping and α-coefficient of competing reaction were obtained. Non-absorbing bismuth - pyrophosphate (PPh) system was studied as a competitive reaction of bismuth - 4-(2-Pyridylazo) resorcinol (PAR) complex. The formation of Bi-PPh complex with 1:1 stoichiometry was proved in the studied concentration region (C Bi = 1×10 -5 mol L -1; C PPh = 5×10 -6 - 1×10 -4 mol L -1). The stability constant of the complex at pH 1 and μ= 1.0 have been determined: logβ = 4.2±0.2. © Versita Sp. z o.o.Item Study of the complex equilibrium between titanium (IV) and tannic acid(2014-01-01) Surleva A.; Atanasova P.; Kolusheva T.; Costadinnova L.Titanium-tannin (Ti-TA) complex is used in the modern leather technology as an alternative of chromium tannage and as an effective modification of vegetable tanning. The ratio between metal and tanning reagent is a key factor for minimizing the unused quantities of tannic acid that could reach the environment by waste waters and cause damages on aqueous ecosystems. However, a lack of reliable data about Ti-TA complexation limits the possibility for fine tuning of the composition of tanning solutions. This study is aimed at characterization of titanyl-tannin complex: its structure, stoichiometry and stability constant. The data of alpha-coefficient of titanyl-hydroxocomplexation at different pH values were also presented.The results obtained showed that in the concentration interval 5×10-6 - 2×10-5 M and pH 4, the main titanium IV species in titanyl/tannin/formate solutions is titanyl-hydroxo-tannin complex TiO(OH)TA. It was proved by UV-Vis and IR spectrometry that the aromatic carboxylic oxygen (Ar-C=O) and probably phenolic oxygen of tannin are involved in the coordination of titanyl ion. The stability constant of TiO(OH)TA was estimated: lgβ = 16.53. The obtained molar ratio curves and the calculated values of the equilibrium constants could be used in leather technology for selecting an appropriate composition of tanning solutions.Item Validation of Ion Chromatographic Method for Determination of Standard Inorganic Anions in Treated and Untreated Drinking Water(2018-06-12) Ivanova V.; Surleva A.; Koleva B.An ion chromatographic method for determination of fluoride, chloride, nitrate and sulphate in untreated and treated drinking waters was described. An automated 850 IC Professional, Metrohm system equipped with conductivity detector and Metrosep A Supp 7-250 (250 x 4 mm) column was used. The validation of the method was performed for simultaneous determination of all studied analytes and the results have showed that the validated method fits the requirements of the current water legislation. The main analytical characteristics were estimated for each of studied analytes: limits of detection, limits of quantification, working and linear ranges, repeatability and intermediate precision, recovery. The trueness of the method was estimated by analysis of certified reference material for soft drinking water. Recovery test was performed on spiked drinking water samples. An uncertainty was estimated. The method was applied for analysis of drinking waters before and after chlorination.