Laboratory research of soil, waste and marine fauna moisture

The weight humidity for the same soil sample will be lower than the volume humidity, while the value of the weight humidity may be higher than 100%, as, for example, in peats, where the weight moisture content can reach 200 or even 300%.

By connectivity, the soil moisture content is divided into bound, which includes chemically bound moisture, the so-called crystallization water, which is part of the crystal lattice of minerals (for example, CaSO4 · 2H2O), and unbound, which includes hygroscopic and natural humidity.

By connectivity, the soil moisture content is divided into bound, which includes chemically bound moisture, the so-called crystallization water, which is part of the crystal lattice of minerals (for example, CaSO4 · 2H2O), and unbound, which includes hygroscopic and natural humidity.

Hygroscopic soil humidity HH (%) is the humidity that characterizes the content of water adsorbed by the soil from air and released from it during drying at 105 °C. HH is in equilibrium with vaporous atmospheric moisture and characterizes the humidity of air-dry soil.

HH value is used to convert the results of the analysis of air-dry soil to absolutely dry, i.e. to soil dried at 105 °C. The need for such a recalculation is caused by the fact that the amount of HH in different types of soil is not the same, and therefore the results calculated for air-dry suspension are not comparable.

In addition, the HH value is of independent interest.

By the amount of HH, it is possible to evaluate the differences in the granulometric composition and the content of organic matter in the soil.

Natural soil moisture W ( % ), or absorbed moisture, is the moisture retained by the soil under natural conditions (pressure, temperature, volume, etc.).

The value of natural humidity is used to calculate soil classification indicators such as the fluidity index (consistency index), dry soil density, and water saturation coefficient.

Value of natural humidity is also used to recalculate the results of analysis of wet soil to absolutely dry soil and to calculate the weight of the suspension of wet soil during analysis.

Methods for determining humidity in the area of laboratory accreditation

In addition to soils, moisture determination in our laboratory is carried out in various other objects of research (solid and liquid waste of production and consumption, medicinal vegetation raw materials, seafood) according to the methods corresponding to each of them.

Standard analysis procedure includes the following steps:

• Preparation of a representative sample, including careful homogenization of the sample, selection and elimination of foreign inclusions (where required), and taking an average weight (for example, by quartering);
• Preparation of laboratory glassware-gravimetric methods of analysis have special requirements for the cleanliness of the used laboratory glassware and determining its weight using technical and analytical scales. When determining humidity, porcelain (evaporating cups) and glass (weighing cups, buckets) laboratory utensils with a set constant weight are used;
• Weighing a wet sample on a laboratory scale. Accuracy of weighing varies depending on the measurement method used.
• Drying the sample in a certified laboratory drying oven at a set temperature, which is usually (105±2) °C, and bringing the samples to a constant mass.
• Weighing the dried sample and establishing a constant mass.
• Calculation of humidity.

Initial moisture content, together with the characteristics of the chemical and mineralogical composition of the samples, greatly affect the time spent on bringing the samples to a constant mass, which is on average from 5 to 6 hours. However, the advantage of gravimetric methods for determining humidity is the ability to perform mass analysis, and their performance is limited only by the number of laboratory dishes and the capacity of the drying oven.

Our laboratory is equipped with high-performance MX-50 humidity analyzers (A&D, Japan), which allow to accurately determine the individual humidity of samples in the shortest possible time.

Humidity detection by the analyzer is based on the heating method. The heating method assumes that the moisture content level is calculated by the weight of water evaporated from a solid or liquid sample after it has been heated for some time, at a temperature equal to or greater than the evaporation temperature of the sample. Weight loss increases as the sample heats up and eventually tends to a constant value. Sample is heated on an electronic scale, with a discreteness of weighing up to 0.001 g, which weighs the sample before and after heating to determine the loss of moisture. Efficient drying and accurate weighing of the sample before and after heating is provided by a halogen lamp and a SHS weight sensor developed for analytical scales. The sample is heated to a temperature of 105 °C for less than a minute. The minimum possible weight for analysis is only 0.1 g, the maximum – 50 g. Humidity measurement range on the analyzer is (0.1-100)%, which allows accurate measurements even in liquid samples. Accuracy of the humidity determination results is controlled by testing the analyzer with the use of sodium dihydrate tartrate with a known level of moisture content, as well as by calibration of the weight sensor and the heating temperature.

High speed of humidity detection on the analyzers allows you to significantly reduce the time to conduct quantitative chemical analysis of your samples for a wide range of indicators.