Interest in the additive method in ionometry is due to the fact that it plays a more significant role than the additive method in other analytical methods. The ionometric addition method offers two great advantages. Firstly, if the fluctuation in ionic strength in the analyzed samples is unpredictable, then the use of the common calibration curve method gives large determination errors. The use of the additive method radically changes the situation and helps to minimize the determination error. Secondly, there is a category of electrodes whose use is problematic due to potential drift. With moderate potential drift, the addition method significantly reduces the determination error.

The following modifications of the additive method are known to the general public: standard additive method, double standard additive method, Gran method. All these methods can be sorted into two categories according to an explicit mathematical criterion that determines the accuracy of the results obtained. It lies in the fact that some additive methods necessarily use a previously measured value of the slope of the electrode function in the calculations, while others do not. According to this division, the standard addition method and the Gran method fall into one category, and the double standard addition method into another.

1. Standard addition method and Gran method.

Before outlining the individual characteristics of one or another type of additive method, we will describe the analysis procedure in a few words. The procedure consists of adding a solution containing the same analyzed ion to the analyzed sample. For example, to determine the content of sodium ions, additions of a standard sodium solution are made. After each addition, electrode readings are recorded. Depending on how the measurement results are further processed, the method will be called the standard addition method or the Gran method.

The calculation for the standard addition method is as follows:

Cx = D C (10DE/S - 1)-1,

where Cx is the desired concentration;

DC is the amount of additive;

DE is the potential response to the introduction of the DC additive;

S is the slope of the electrode function.

The calculation by Gran's method looks somewhat more complicated. It consists of plotting a graph in coordinates (W+V) 10 E/S from V,

where V is the volume of added additives;

E - potential values ​​corresponding to the introduced additives V;

W is the initial sample volume.

The graph is a straight line intersecting the x-axis. The intersection point corresponds to the volume of added additive (DV), which is equivalent to the desired ion concentration (see Fig. 1). From the law of equivalents it follows that Cx = Cst DV / W, where Cst is the concentration of ions in the solution that is used to introduce additives. There can be several additives, which naturally improves the accuracy of determination compared to the standard additive method.

It is easy to notice that in both cases the slope of the electrode function S appears. From this it follows that the first stage of the additive method is the calibration of the electrodes for the subsequent determination of the slope value. The absolute value of the potential is not involved in the calculations, since to obtain reliable results, only the constancy of the slope of the calibration function from sample to sample is important.

As an addition, you can use not only a solution containing a potential-determining ion, but also a solution of a substance that binds the detected sample ion into a non-dissociating compound. The analysis procedure does not fundamentally change. However, there are some specific features that should be taken into account in this case. The features are that the experimental results graph consists of three parts, as shown in Fig. 2. The first part (A) is obtained under conditions where the concentration of the binding substance is less than the concentration of the potential-determining substance. The next part of graph (B) is obtained with approximately equivalent ratios of the above substances. And finally, the third part of the graph (C) corresponds to conditions under which the amount of binding substance is greater than the potential-determining one. Linear extrapolation of part A of the graph to the x-axis gives the value DV. Region B is not usually used for analytical determinations.

If the titration curve is centrally symmetric, then region C can be used to obtain analytical results. However, in this case, the ordinate should be calculated as follows: (W+V)10 -E/S.

Since the Gran method has greater advantages than the standard additive method, further discussions will primarily concern the Gran method.

The advantages of using the method can be expressed in the following points.

1. Reducing the determination error by 2-3 times due to an increase in the number of measurements in one sample.

2. The additive method does not require careful stabilization of the ionic strength in the analyzed sample, since its fluctuations are reflected in the absolute value of the potential to a greater extent than in the slope of the electrode function. In this regard, the determination error is reduced compared to the calibration curve method.

3. The use of a number of electrodes is problematic, since the presence of an insufficiently stable potential requires frequent calibration procedures. Since in most cases the potential drift has little effect on the slope of the calibration function, obtaining results using the standard addition method and the Gran method significantly increases the accuracy and simplifies the analysis procedure.

4. The standard addition method allows you to control the correctness of each analytical determination. Control is carried out during processing of experimental data. Since several experimental points take part in the mathematical processing, drawing a straight line through them each time confirms that the mathematical form and slope of the calibration function have not changed. Otherwise, the linear appearance of the graph is not guaranteed. Thus, the ability to control the correctness of the analysis in each determination increases the reliability of the results.

As already noted, the standard addition method allows determinations to be 2-3 times more accurate than the calibration curve method. But to obtain such accuracy of definition, one rule should be used. Excessively large or small additions will reduce the accuracy of the determination. The optimal amount of additive should be such that it causes a potential response of 10-20 mV for a singly charged ion. This rule optimizes the random error of the analysis, however, in those conditions in which the additive method is often used, the systematic error associated with changes in the characteristics of ion-selective electrodes becomes significant. The systematic error in this case is completely determined by the error from changing the slope of the electrode function. If the slope changes during the experiment, then under certain conditions the relative error of determination will be approximately equal to the relative error from the change in slope.

It is necessary to determine the amount of dry matter and the required amount of working solution of the ShchSPK additive to prepare 1 ton of cement-sand mixture.

For the calculation, the following mixture composition (% mass) was adopted:

sand - 90, cement - 10, water - 10 (over 100%), ShchSPK (% of the mass of cement based on dry matter). Sand moisture content is 3%.

For the adopted composition, the preparation of 1 t (1000 kg) of the mixture requires 1000·0.1 = 100 kg (l) of water. The filler (sand) contains 1000·0.9·0.03 = 27 liters of water.

The required amount of water (taking into account its content in the filler) is: 100 - 27 = 73 l.

The amount of anhydrous additive ShchSPK for preparing 1 ton of the mixture with a content of 10% (100 kg) of cement in 1 ton of the mixture will be: 100·0.020 = 2 kg.

Due to the fact that the ShchSPK additive is supplied in the form of a solution of 20 - 45% concentration, it is necessary to determine the dry matter content in it. We take it equal to 30%. Therefore, 1 kg of a solution of 30% concentration contains 0.3 kg of anhydrous additive and 0.7 l of water.

We determine the required amount of ShchSPK solution of 30% concentration to prepare 1 ton of the mixture:

The amount of water contained in 6.6 kg of concentrated additive solution is: 6.6 - 2 = 4.6 liters.

Thus, to prepare 1 ton of the mixture, 6.6 kg of additive solution of 30% concentration and 68.4 liters of water for dilution are required.

Depending on the need and capacity of the mixer, a working solution of the required volume is prepared, which is defined as the product of the consumption of the additive solution and water (per 1 ton of mixture), the productivity of this mixer and the operating time (in hours). For example, with a mixing plant capacity of 100 t/h for one shift (8 hours), it is necessary to prepare the following working solution: 0.0066 100 8 = 5.28 (t) of a 30% solution of ShchSPK and 0.684 100 8 = 54.72 (t) water for dilution.

A solution of 30% concentration of ShchSPK is poured into water and mixed well. The prepared working solution can be fed into the mixer using a water dispenser.

Appendix 27

FIELD METHODS FOR QUALITY CONTROL OF SOILS AND SOILS TREATED WITH CEMENT

Determination of the degree of soil crushing

The degree of crushing of clay soils is determined according to GOST 12536-79 on average samples weighing 2 - 3 kg selected and sifted through a sieve with holes of 10 and 5 mm. Soil moisture should not exceed 0.4 soil moisture at the yield limit W t. At higher humidity, the average soil sample is first crushed and dried in air.

The remaining soil on the sieves is weighed and the content of the sample in the mass is determined (%). The content of lumps of the appropriate size P is calculated using the formula

where q 1 - sample mass, g;

q is the mass of the residue in the sieve, g.

Determination of moisture content of soils and mixtures of soils with binders

The moisture content of soils and mixtures of soils with binders is determined by drying an average sample (to constant weight):

in a thermostat at a temperature of 105 - 110 °C;

using alcohol;

radioisotope devices VPGR-1, UR-70, RVPP-1 in accordance with the requirements of GOST 24181-80;

carbide moisture meter VP-2;

moisture meter of the N.P. system Kovalev (the density of wet soils and the density of the soil skeleton are also determined).

Determination of humidity by drying an average sample with alcohol

A weighed amount of 30 - 50 g of sandy fine-grained soils or 100 - 200 g of coarse-grained soils is poured into a porcelain cup (for the latter, the determination is made on particles finer than 10 mm); the sample together with the cup is weighed, moistened with alcohol and set on fire; then the sample cup is cooled and weighed. This operation is repeated (approximately 2 - 3 times) until the difference between subsequent weighings does not exceed 0.1 g. The amount of alcohol added the first time is 50%, the second - 40%, the third - 30% of the sample weight soil.

Soil moisture W is determined by the formula

where q 1, q 2 are the mass of wet and dried soils, respectively, g.

The total moisture content for all particles of coarse soils is determined by the formula

W = W 1 (1 - a) + W 2 , (2)

where W 1 is the moisture content of the soil containing particles smaller than 10 mm, %;

W 2 - approximate moisture content of soil containing particles larger than 10 mm, % (see table of this appendix).

	Approximate humidity W 2,%, when coarse soil contains particles larger than 10 mm, fractions of one
Erupted
Sedimentary
Mixed

Determination of humidity with a carbide moisture meter VP-2

A sample of soil or a mixture of sandy and clayey soils weighing 30 g or coarse soils weighing 70 g is placed inside the device (the moisture content of coarse soil is determined on particles smaller than 10 mm); Ground calcium carbide is poured into the device. After tightly wrapping the lid of the device, shake it vigorously to mix the reagent with the material. After this, you need to check the tightness of the device, for which you bring a burning match to all its connections and make sure that there are no flashes. The mixture is mixed with calcium carbide by shaking the device for 2 minutes. The pressure reading on the pressure gauge is carried out 5 minutes after the start of mixing if its readings are less than 0.3 MPa and after 10 minutes if the pressure gauge readings are more than 0.3 MPa. The measurement is considered complete if the pressure gauge readings are stable. The moisture content of fine-grained soils and the total moisture content for all fractions of coarse-grained soils are determined using formulas (1) and (2).

Determination of natural humidity, density of wet soil and density of the soil skeleton using the N.P. device. Kovaleva

The device (see figure in this appendix) consists of two main parts: a float 7 with a tube 6 and a vessel 9. Four scales are printed on the tube, indicating the density of soils. One scale (Vl) is used to determine the density of wet soils (from 1.20 to 2.20 g/cm 3), the rest - the density of the skeleton of chernozem (Ch), sandy (P) and clayey (G) soils (from 1.00 up to 2.20 g/cm 3).

Device N.P. Kovaleva:

1 - device cover; 2 - device locks; 3 - bucket-case; 4 - device for sampling with a cutting ring; 5 - knife; 6 - tube with scales; 7 - float; 8 - vessel locks; 9 - vessel; 10 - calibration weight (plates);

11 - rubber hose; 12 - bottom cover; 13 - float locks; 14 - cutting ring (cylinder) with bottom cover

The auxiliary accessories of the device include: a cutting steel cylinder (cutting ring) with a volume of 200 cm 3, a nozzle for pressing the cutting ring, a knife for cutting the sample taken by the ring, a bucket-case with a lid and locks.

Checking the device. An empty cutting ring 4 is installed in the lower part of the float 7. A vessel 9 is attached to the float using three locks and immersed in water poured into a bucket-case 3.

A correctly balanced device is immersed in water until the beginning of the “Vl” scale, i.e. readings P (Yo) = 1.20 u/cm3. If the water level deviates in one direction or another, the device must be adjusted with a calibration weight (metal plates) located in the bottom cover 12 of the float.

Sample preparation. A soil sample is taken with a soil carrier - a cutting ring. To do this, level the platform at the test site and, using a nozzle, immerse the cutting ring until the ring with a volume of 200 cm 3 is completely filled. As the cutting cylinder (ring) is immersed, the soil is removed with a knife. After filling the ring with soil with an excess of 3 - 4 mm, it is removed, the lower and upper surfaces are cleaned and cleared of adhering soil.

Work progress. The work is carried out in three steps: determine the density of wet soil on the “Vl” scale; establish the density of the soil skeleton according to one of three scales “H”, “P”, “G” depending on the type of soil; calculate natural humidity.

Determination of the density of wet soil on the "Vl" scale

The cutting ring with soil is installed on the lower cover of the float, securing it with the float with locks. The float is immersed in a bucket-case filled with water. On the scale at the water level in the case, a reading is taken corresponding to the density of wet soil P (Yck). The data is entered into a table.

Determination of the density of the soil skeleton using the “H”, “P” or “G” scales

The soil sample from the soil carrier (cutting ring) is transferred completely into the vessel and filled with water to 3/4 of the vessel’s capacity. The soil is thoroughly ground in water with a wooden knife handle until a homogeneous suspension is obtained. The vessel is connected to a float (without a soil carrier) and immersed in a bucket-case with water. Water through the gap between the float and the vessel will fill the rest of the space of the vessel, and the entire float with the vessel will be immersed in water to a certain level. A reading taken from one of the scales (depending on the type of soil) is taken as the density of the soil skeleton Pck (Yck) and entered into the table.

Calculation of natural humidity

Natural (natural) humidity is calculated from test results using the formulas:

where P (Yo) is the density of wet soil on the “Vl” scale, g/cm 3 ;

Pck (Yck) - density of the soil skeleton according to one of the scales ("H", "P" or "G"), g/cm 3 .

Determination of strength in an accelerated way

To quickly determine the compressive strength of samples from mixtures containing particles smaller than 5 mm, samples weighing about 2 kg are taken from every 250 m 3 of the mixture. Samples are placed in a vessel with a tight-fitting lid to maintain moisture and delivered to the laboratory no later than 1.5 hours later.

Three samples measuring 5 x 5 cm are prepared from the mixture using a standard compaction device or by pressing and inserted into hermetically sealed metal molds. Forms with samples are placed in a thermostat and kept for 5 hours at a temperature of 105 - 110 ° C, after which they are removed from the thermostat and kept for 1 hour at room temperature. The aged samples are removed from the molds and the compressive strength is determined (without water saturation) according to the method of App. 14.

The result of the determination is multiplied by a factor of 0.8, and a strength is obtained corresponding to the strength of the samples after 7 days of hardening in wet conditions and tested in a water-saturated state.

The quality of the mixture is determined by comparing the compressive strength values ​​of samples determined by the accelerated method and 7-day-old laboratory samples from the reference mixture. In this case, the strength of the reference samples must be at least 60% of the standard. Deviations in the strength indicators of production and laboratory samples should not exceed when preparing mixtures:

in quarry mixing plants +/- 8%;

single-pass soil mixing machine +/- 15%;

road mill +/- 25%.

For mixtures of soils containing particles larger than 5 mm, the compressive strength is determined on water-saturated samples after 7 days of hardening in wet conditions and compared with the compressive strength of reference samples. The quality of the mixture is assessed similarly to mixtures made from soils containing particles smaller than 5 mm.

Appendix 28

SAFETY INSTRUCTION CHECKLIST

1. Site (working place)

2. Last name, initials

3. What kind of work is it aimed at?

4. Last name, initials of the foreman (mechanic)

Introductory briefing

Introductory safety training in relation to the profession

Conducted ___________

Signature of the person conducting the safety briefing

____________ " " _________ 19__

On-the-job training

Safety briefing at the workplace ___________________

(Name of workplace)

workers comrade ___________________ received and assimilated.

Worker's signature

Signature of the master (mechanic)

Permission

Comrade _____________________ allowed to work independently

___________________________________________________________________________

(Name of workplace)

as ________________________________________________________________

" " ___________ 19__

Head of the section (foreman) _________________________________

IN one standard solution method measure the value of the analytical signal (y st) for a solution with a known concentration of the substance (C st). Then the magnitude of the analytical signal (y x) is measured for a solution with an unknown concentration of the substance (C x).

This calculation method can be used if the dependence of the analytical signal on concentration is described by a linear equation without a free term. The concentration of the substance in the standard solution must be such that the values ​​of the analytical signals obtained when using the standard solution and a solution with an unknown concentration of the substance are as close as possible to each other.

IN method of two standard solutions measure the values ​​of analytical signals for standard solutions with two different concentrations of a substance, one of which (C 1) is less than the expected unknown concentration (C x), and the second (C 2) is greater.

or

The method of two standard solutions is used if the dependence of the analytical signal on concentration is described by a linear equation that does not pass through the origin.

Example 10.2.To determine the unknown concentration of a substance, two standard solutions were used: the concentration of the substance in the first of them is 0.50 mg/l, and in the second - 1.50 mg/l. The optical densities of these solutions were 0.200 and 0.400, respectively. What is the concentration of a substance in a solution whose optical density is 0.280?

Additive Method

The additive method is usually used in the analysis of complex matrices, when the matrix components influence the magnitude of the analytical signal and it is impossible to accurately copy the matrix composition of the sample. This method can only be used if the calibration graph is linear and passes through the origin.

When using calculation method of additives First, the magnitude of the analytical signal is measured for a sample with an unknown concentration of the substance (y x). Then a certain exact amount of the analyte is added to this sample and the value of the analytical signal (y ext) is measured again.

If it is necessary to take into account dilution of the solution

Example 10.3. The initial solution with an unknown concentration of the substance had an optical density of 0.200. After 5.0 ml of a solution with a concentration of the same substance of 2.0 mg/l was added to 10.0 ml of this solution, the optical density of the solution became equal to 0.400. Determine the concentration of the substance in the original solution.

= 0.50 mg/l

Rice. 10.2. Graphical method of additives

IN graphical method of additives take several portions (aliquots) of the analyzed sample, add no additive to one of them, and add various exact amounts of the component being determined to the rest. For each aliquot, the magnitude of the analytical signal is measured. Then a linear dependence of the magnitude of the received signal on the concentration of the additive is obtained and extrapolated until it intersects with the x-axis (Fig. 10.2). The segment cut off by this straight line on the abscissa axis will be equal to the unknown concentration of the substance being determined.

The standard additive method is based on the fact that an exact weighed portion of the analyte present in the control mixture is added to a sample of the control mixture, and chromatograms are taken of the original control mixture and the control mixture with the standard additive added to it.

Method of analysis. About 2 cm 3 of the control mixture (800 mg) is pipetted into a pre-weighed flask with a ground stopper and weighed, and then one of the substances (100 mg) present in the control mixture is added (as directed by the teacher) and weighed again.

Next, chromatograms of the initial control mixture and the control mixture with a standard additive of the component being determined are taken. The area under the peak of the analyzed component is measured on chromatograms and the analysis result is calculated using the formula

, (1.6)

Where S X– area under the peak of the analyzed component in the sample;

S x+st– area under the peak of the analyzed component in the sample after introducing its standard additive into the sample WITH st ;

WITH(X) – concentration of the analyzed component in the sample;

WITH st– concentration of standard additive of the analyzed component, %:

Where m ext– mass of additive, g;

m samples – mass of the chromatographed sample, g.

Absolute calibration method (external standardization)

The absolute calibration method consists of constructing a calibration graph of the dependence of the chromatographic peak area ( S) on the substance content in the chromatographic sample ( m). A necessary condition is the accuracy and reproducibility of sample dosing, and strict adherence to the operating mode of the chromatograph. The method is used when it is necessary to determine the content of only individual components of the analyzed mixture and therefore it is necessary to ensure complete separation of only the peaks of the substances being determined from neighboring peaks in the chromatogram.

Several standard solutions of the component being determined are prepared, equal quantities are introduced into the chromatograph, and the peak areas are determined ( S 1 , S 2 , S 3). The results are presented graphically (Figure 1.3).

Figure 1.3 – Calibration graph

Concentration i th component in the sample (%) is calculated using the formula

Where m samples– mass of the chromatographed sample, g;

m i- content i th component, found from the calibration graph (see Figure 1.3), g.

1.2.3 Block diagram of a gas chromatograph

The block diagram of a gas chromatograph is shown in Figure 1.4.

Figure 1.4 – Block diagram of a gas chromatograph:

1 – cylinder with carrier gas; 2 – drying, cleaning system and unit for regulating and measuring the rate of supply of carrier gas; 3 – sample injection device (dispenser); 4 – evaporator; 5 – chromatographic column; 6 – detector; 7 – thermostatic zones ( T And– evaporator temperature, T To – column temperature, T d – detector temperature); 8 – chromatogram

A chromatographic column, usually steel, is filled with a solid carrier (silica gel, activated carbon, red brick, etc.) with an applied stationary phase (polyethylene glycol 4000 or another modification, vaseline, silicone oil).

The temperature of the evaporator thermostat is 150 °C, the column temperature is 120 °C, and the detector thermostat is 120 °C.

Carrier gas – inert gas (nitrogen, helium, etc.).