RU2176077C2 - Method of determining solid residue in a liquid - Google Patents

Abstract

FIELD: chemical-ecology analyses. SUBSTANCE: liquid is preliminarily filtered and sample of it in amount of 1-3 mcl is applied on piezoelectric AT-cut resonator with frequency at least 5 MHz. Resonator frequency changes Δf₁ and Δf₂, are determined before and after vaporization of liquid, respectively. Weight of sample and solid residue therein are calculated in terms of formula presented in description. EFFECT: accelerated analysis and increased determination accuracy.

Description

 The invention relates to the field of chemical ecology and can be used for express analysis of the degree of contamination of water and chemically pure liquids.

Known photometric method for determining the concentration of dissolved substances in liquid solutions, based on the law of Bouguer-Lambert-Bera:
D = E • L • C,
where D is the optical density of the solution;
E is the molar absorption coefficient;
L is the thickness of the solution layer;
C is the concentration of solute.

 The photometric method involves the preparation of 5-6 standard colored solutions, the concentrations of which cover the range of possible changes in the concentrations of the test solution, measuring their optical densities, plotting the optical density of the solutions on their corresponding concentration values, measuring the optical density of the test solution and graphically determining its concentration.

 However, this method does not allow to determine the content of dissolved substances in multicomponent colorless solutions that do not absorb light in the visible spectrum [1].

The closest method to the claimed one is the weight method for determining the dry residue containing mineral and organic impurities in liquids [2], which consists in the fact that the liquid in the amount of 50 - 250 ml is filtered, placed in a weighed cup of heat-resistant material, dried to a constant weight, and evaporated to dryness. Then the cup with the residue is dried in an oven for two hours, cooled in a desiccator and weighed on an analytical balance. After that, the cup with the residue is again placed in the oven for 30 minutes, cooled in a desiccator and weighed. The drying process is carried out until the difference between two successive weighings is not more than 0.0004 grams. The solids content is determined by the formula
X = (A-B) • 1000 / V,
where X is the solids content, mg / l;
A is the mass of the cup with a dry residue, mg;
B is the mass of an empty cup, mg;
V is the volume of fluid taken for analysis, ml.

This method does not allow quick and accurate analysis, since it involves a long (of the order of several hours), thorough preparation of chemical glassware and liquid samples, and the accuracy of weighing is determined by the sensitivity of the analytical balance (~ 10 ^-7 kg).

 The objective of the invention is to reduce the duration of the analysis and increase the accuracy of determining the dry residue in a liquid.

The problem is solved due to the fact that in the method in which the liquid is pre-filtered, it is sampled, heated until complete evaporation, the dry residue is weighed, a sample is taken in an amount of 1-3 μl, and an AT-cut piezoelectric resonator with a frequency of at least 5 MHz, determine the frequency change of the piezoelectric quartz resonator Δf ₁ and Δf ₂ , respectively, before and after the evaporation of the liquid, and the weight of the sample and the dry residue in it is determined by the formulas:
m _samples = ρ • N • S • Δf ₁ / f $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ (1),
m _{dry residue} = ρ • N • S • Δf ₂ / f $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ (2)
where ρ is the density of quartz (2650 kg / m ³ );
N is the frequency coefficient of the AT-cut quartz plate (1680 kHz • mm);
S is the area of the electrodes;
f ₀ is the natural frequency of the piezoelectric crystal;
Δf ₁ - change in the frequency of the piezoelectric crystal after applying a liquid sample to it;
Δf ₂ - change in the frequency of the piezoelectric quartz resonator after complete evaporation of the liquid.

The mass of solids in 100 g of liquid is determined by the formula
M _{dry. residue / 100 g} = 100 • m _{dry. residue} / m _sample (3)
Example. The specified method was carried out to determine the solids and suspended solids in drinking water. To determine the dry residue, water was filtered through a paper filter, using a microsyringe, a sample was taken in an amount of 1 μl, applied to a piezoelectric quartz AT-cut resonator with a natural frequency f ₀ equal to 5 MHz, and the mass of the sample was determined from the frequency shift Δf ₁ (m _samples ) by the formula (1). Then the piezoelectric crystal was heated at 50-60 ^° C until the water completely evaporated. Evaporation was considered complete if there was no change in the frequency of the piezoelectric crystal. The dry residue on the surface of the piezoelectric crystal changes its resonant frequency by Δf ₂ . The mass of solids (M _{sol. Residue} ) was determined by the formula (2) and was calculated per 100 grams of water by the formula (3). She was 0.37531776 g.

 To determine the mass of suspended particles in 100 grams of water in this way was determined the mass of solids in 100 grams of unfiltered water. It was 0.91893700 g. Then, the mass of dry residue in 100 grams of filtered water was subtracted from the dry mass in 100 grams of unfiltered water. Hence, the mass of suspended particles was 0.54362000 g in 100 g of water.

The analysis duration was 1-2 minutes, and the weighing accuracy of 10 ^-11 kg.

Sources of information
1. M.I. Bulatov, I.P. Kalinkin. A practical guide to photocalorimetric and spectrophotometric methods of analysis. L .: Chemistry, 1968, p. 92.

 2. Unified methods of water analysis. / Ed. Yu.Yu. Lurie. M .: Chemistry, 1971, p. 44.

Claims (1)

The method of determining the mass of dry residue in a liquid, by which the liquid is pre-filtered, take its sample and heat until complete evaporation, characterized in that the liquid sample is taken in an amount of 1-3 μl, applied to an AT-cut piezoelectric crystal resonator with a natural frequency f ₀ not less than 5 MHz, determine the frequency change of the piezoelectric quartz resonator Δf ₁ and Δf _2, respectively, before and after evaporation of the liquid, and the weight of the sample and the dry residue in it is determined by the formulas:
m _samples = ρ • N • S • Δf ₁ / f $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ , m _max . _residual = ρ • N • S • Δf ₂ / f $\genfrac{}{}{0ex}{}{\text{2}}{\text{0}}$ ,
where ρ is the density of quartz (2650 kg / m ³ );
N is the frequency coefficient of the AT-cut quartz plate (1680 kHz • mm);
S is the area of the electrodes;
f ₀ is the natural frequency of the piezoelectric crystal;
Δf ₁ - change in the frequency of the piezoelectric crystal resonator after applying a liquid sample to it;
Δf ₂ - change in the frequency of the piezoelectric quartz resonator after complete evaporation of the liquid.