## 1 Introduction  
Accurate and reliable laboratory results are essential for scientific research. Results can be affected by many factors, including the test methods used, the accuracy and precision of the test performed, and the laboratory equipment used [1]. Measurements of concentrations of various chemical compounds/elements are carried out, among others, to study the composition of soils. Soil is a complex three-phase solid-liquid-gas system, in which continuous processes of decomposition and synthesis of mineral and organic compounds and their transfer between different soil horizons take place. The infiltration of compounds into the soil is made possible by infiltrating water. Rainwater percolates through the different soil layers, dissolving and/or transporting dissolved substances and suspended solids to deeper soil layers. From an agronomic point of view, the soil must be protected and used in such a way that it is possible to continuously produce sufficient quantities of high-quality plant raw materials [2]. Heavy metals play an important role here as excessive accumulation of these elements in soils may cause far-reaching, often irreversible chemical degradation of soils. In the short term, negative effects of heavy metal pollution may be hardly noticeable, however, their gradual accumulation may lead to exceeding the sorption capacity of soils and, as a consequence, release of those metals into the environment. This can be a source of significant contamination of the water-soil environment and consequently the food chain. Contaminants accumulating in soils may also affect soil organisms and/or plants, which may lead to a reduction in biodiversity or decrease in soil vegetation cover, and consequently to an increase in water and aeolian erosion processes [3; 4]. In times of rapid economic development, the content of heavy metals in soil can be significant. The biggest amount of heavy metals are emitted to the environment in the areas of mining and metallurgical processing of metal ores, cement production and industrial combustion of fossil fuels. The environment can also be a source of toxic substances. An example is Pb, which can be leached from the rock environment or derived from geothermal H\({}_{2}\)S sources [4; 5]. All over the world, the problem of heavy metal contamination of soils is common, which is a frequent subject of scientists' research, e.g., in Europe [6; 7] or in Asia, including, among others, China [8; 9], in Mongolia [10], in Tibet [11], India [12], and Pakistan [13]. Heavy metal ions are retained in the surface layer of soils mainly due to sorption, and their movement into the soil profile is relatively slow. Excessive accumulation of heavy metals in the surface layer of soils is one of the basic causes of chemical degradation of soils and pollution of soil-soil and surface waters. Heavy metals occurring in the soil lead to an imbalance in the recycling of soil nutrients and a decline in soil quality [13; 14]. Furthermore, heavy metals are characterised by the easy accumulation in soils of different types [15; 16]. The occurrence of elevated concentrations of heavy metals in agricultural soils and consequently also in food poses a threat to animal and human health. For example, too high concentrations of Cu can cause liver cirrhosis and chronic anaemia. Apart from affecting soft tissues, heavy metals can also accumulate in bone tissue, Pb being one example. Cr is also worth mentioning. Its deficiency in the body may be manifested by diabetic symptoms, while compounds of this element on high oxidation levels (+4, +6) are directly toxic and carcinogenic for humans. Based on a comprehensive analysis of heavy metal hazards, the United Environmental Protection Agency has listed eight heavy metals (Pb, Cd, Cr, Hg, As, Cu, Zn, Ni) as major contaminants of the groundwater environment [17]. Due to the high danger of heavy metals contained in soils, numerous studies have been undertaken on soil contamination with these elements e.g., [18; 19; 20].