Browsing by Author "Chavdarova K."

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    Contribution to the turbidimetric method for sulphur determination in arable soils
    (2025-01-01) Surleva O.; Chavdarova K.; Kazanlaklieva V.; Angelova L.; Surleva A.
    Sulphur (S) plays an important role in agriculture, being the fourth major contributor to improved quality of crops and increased yields. The applied methods for the estimation of different forms of S in soil aimed at assessing the sulphur availability to plants in various conditions. Nowadays, the wider spreading of regions with sulphur deficiency imposes optimisation of the soil testing procedures in order to increase their availability for laboratories. This study contributes to improving the analytical performance of the turbidimetric method in determining water-soluble sulphate in soil after leaching with the CaCl2 reagent. The modified testing protocol showed: method limit of quantification of 5.0 mg/kg; precision as relative standard deviation less than 3%; recovery of fortified soil samples 103 ± 18%. The expanded uncertainty was 2.3 mg/kg SO42–-S (K = 2, norm.). The proposed testing protocol was inexpensive, fast, used simple equipment and procedures, easily adoptable in regular laboratories, and showed characteristics suitable for the estimation of water-soluble sulfate in arable soils. A set of 546 soil samples was tested, and 74% were found to be sulphur deficient with SO42–-S < 10 mg/kg and sulfur availability index < 6.0. Thus, the availability of laboratory analysis to a broader group of farmers could contribute to effective fertilisation programs, as the newly proposed fertiliser blending technologies are based on adequate estimation of sulfur availability in arable soils.
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    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.