Violeta Milenkova Stefanova

Prof. Dr. Violeta Milenkova Stefanova


Research Focus & Metrics

Academic Career Length

47Years (1980-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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7 December 1998 in Talanta
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Journal Article
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DAD. Atanassova
D. Atanassova
VSVioleta Milenkova Stefanova
Violeta Milenkova Stefanova
ERE. Russeva
E. Russeva

29 February 2008 in Journal of Analytical Atomic Spectrometry
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KSKiril Simitchiev
Kiril Simitchiev
VSVioleta Milenkova Stefanova
Violeta Milenkova Stefanova
VKVeselin Kmetov
Veselin Kmetov
GAGeorge Andreev
George Andreev
NKNikolay Kovachev
Nikolay Kovachev
Antonio CanalsAntonio Canals
Antonio Canals
New approaches for acceleration of cloud point extraction of Rh, Pd and Pt by microwave and ultrasound irradiation have been investigated. 2-Mercaptobenzothiazole and Triton X-100 were used as ligand and non-ionic surfactant, respectively. Microwave irradiation substantially increased the procedure efficiency. In contrast no significant effect was observed when a micellar solution was treated with ultrasound energy. The acceleration of complex formation reactions by reducing agents (KI and SnCl2) has also been studied. The use of SnCl2 was a prerequisite for quantitative extraction of Rh. Since the extraction kinetics of platinum depends on its oxidation state and presence of Pd, the addition of SnCl2 equalized the platinum extraction behavior. For the first time the whole cloud point procedure was successively accomplished in a microwave system. 10 min of irradiation were sufficient for gravimetrical phase separation and quantitative extraction of platinum group metals. As a result the procedure time was shortened by a factor of 9 in comparison to conventional hot plate cloud point extraction. The surfactant-rich phase was analyzed after dilution with 1 M HCl by continuous nebulization to ICP-MS. Quantitative recoveries and good plasma tolerance were reported. Detection limits of 1 ng.l−1 (Rh), 5 ng.l−1 (Pd), and 6 ng.l−1 (Pt) were achieved regarding a preconcentration factor of 8. The microwave-assisted cloud point extraction has been successfully applied for simultaneous determination of trace amounts of platinum group metals in pharmaceutical products (Tritace, Vivace, Laprilen and Enalapril).

1 July 2004 in Analytica Chimica Acta
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DHDimitar Hristozov
Dimitar Hristozov
CDClaudia E Domini
Claudia E Domini
VKVeselin Kmetov
Veselin Kmetov
VSVioleta Milenkova Stefanova
Violeta Milenkova Stefanova
DGDeana Georgieva
Deana Georgieva
Antonio CanalsAntonio Canals
Antonio Canals

1 May 2012 in Spectrochimica Acta Part B: Atomic Spectroscopy
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KIKrasimir Ivanov
Krasimir Ivanov
PZPenka Zaprjanova
Penka Zaprjanova
MPMilena Petkova
Milena Petkova
VSVioleta Milenkova Stefanova
Violeta Milenkova Stefanova
VKVeselin Kmetov
Veselin Kmetov
VAViolina Angelova
Violina Angelova


24 June 2020 in Water
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Journal Article
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Gana GechevaGana Gecheva
Gana Gecheva
Vesela YanchevaVesela Yancheva
Vesela Yancheva
IVIliana Velcheva
Iliana Velcheva
EGElenka Georgieva
Elenka Georgieva
SSStela Stoyanova
Stela Stoyanova
Ivelin MollovIvelin Mollov
Ivelin Mollov
For the first time, transplants with moss-bags and mussels together were applied to study the water quality in standing water bodies. The tested species: Fontinalis antipyretica Hedw. and Sinanodonta woodiana (Lea, 1834) were collected from unpolluted sites and analyzed to obtain background levels. Then, the moss and mussels were left in cages for a period of 30 days in three reservoirs where both are not present naturally. Two of the reservoirs suffer from old industrial contamination and one is affected by untreated wastes. Twenty-four compounds were studied, among them trace elements Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Zn and organic priority substances: six polybrominated diphenyl ethers (PBDEs) congeners and short-chain chlorinated paraffins (SCCPs). The trace element accumulation was significant after the exposition period in all studied stations. PBDEs and SCCPs were also accumulated up to two times more in the moss tissues. PBDEs in the mussels exceeded the environmental quality standard (EQS). The applied combined transplants, and especially the moss-bags, revealed severe contamination with heavy metals not detected by the water samples. The moss and the mussel followed a different model of trace element and PBDEs accumulation. The SCCPs levels were alarmingly high in all plant samples. The study confirmed PBDEs and SCCPs as bioaccumulative compounds and suggested that an EQS for SCCPs in biota needs to be established.