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Methods for the determination of ammonium ions

Contents

• Introduction
• 1. Main part
• 1.1 Control of the stability of the calibration characteristic (GC)
• 1.2 Algorithm of operational control of the error of determination of ammonium ions in drinking water
• 2. Practical part
• 2.1 Determination of ammonium ion content
• 2.2 Safety precautions when performing the analysis
• Conclusion
• List of used literature

Introduction

Ammonium ion (NH4+) accumulates in waters when ammonia gas (NH3) is dissolved in water, which is formed during the biochemical decomposition of nitrogen-containing organic compounds. The presence of ammonium ion in concentrations exceeding the background value indicates fresh contamination and the proximity of the source of contamination (municipal sewage treatment plants, industrial waste settling tanks, livestock farms, manure accumulations, nitrogen fertilizers, etc.)

Ammonia dissolves well in water, because when ammonia is dissolved in water, a reversible reaction of the formation of ammonium ions and hydroxide ion occurs, i.e. water is alkalinized and the pH (hydrogen index) becomes greater than 7.0 (alkaline reaction) this is an indicator of biological contamination. The increase in the content of ammonium ions increases with an increase in the pH value of water. The maximum permissible concentration (MPC) of ammonium ions for objects of household and drinking and cultural purposes, respectively, are 2.0 mg/dm3 and 1.0 mg/dm3.

To date, the main method of measuring the mass concentration of ammonia and ammonium ions in accordance with GOST is the method of photometric determination using the Nessler reagent. However, there are many factors that make it difficult to determine ammonium nitrogen using this MVI. Studies conducted by the Hydrochemical Institute have led to the conclusion that this MVI gives erroneous results in the following cases:

when analyzing waters with a mass concentration of ammonium nitrogen less than 0.3 mg/dm3;

in the analysis of waters with increased mineralization and hardness;

in the analysis of waters contaminated with compounds reacting with Nessler's reagent - amines, chloramines, acetone, aldehydes, sulfides, etc.

When monitoring technological parameters in the process of water treatment, it is possible to determine ammonium ions by photometric method with Nessler reagent, in this case, the disadvantages of this MVI do not matter much. However, when monitoring water quality from the point of view of sanitary standards, the use of MVI with Nessler reagent for the determination of ammonium ions is highly questionable. Therefore, in the State Unitary Enterprise "Center for Water Research and Control" (St. Petersburg), an MVI of the mass concentration of ammonium ions was developed by capillary electrophoresis, which is free from the listed disadvantages.

When using the capillary electrophoresis method, the determination of the ammonium ion is not hindered by the above compounds, since before detection, the ammonium ion is separated from other ions and compounds during migration through the capillary filled with electrolyte. The capillary electrophoresis method makes it possible to determine the content of ammonium ions in water without disturbing the equilibrium of chemical processes, except for the shift of the equilibrium of the dissociation process of aquated ammonia molecules towards the formation of ammonium ions, since in this technique the electrolyte used has a pH value of 4.0, which also makes it possible to determine the aquated ammonia molecules.

The purpose of my course work is to perform operational control of the measurement error of ammonium ions in drinking water by photometric method.

1. Main part

1.1 Control of the stability of the calibration characteristic (GC)

There is little literature on the control of GC stability. In 2003, the document "Algorithms for constructing calibration characteristics of measuring instruments for the composition of substances and materials and estimating their errors (uncertainties)" was published, in the sixth section of which the procedure for monitoring the stability of GC is described. According to this technique, the procedure for monitoring the stability of GC SI (measuring instruments) consists in comparing the measured value of the output signal at the calibration points with its estimate by GC SI (this result is not used in the construction of GC). For linear GC SI, the number of control points must be at least two. This methodology specifies two conditions for monitoring the stability of GC.

In the first case, if the errors of the calibration mixtures are not correlated, then the following conditions are checked in accordance with the formulas:

|y₁-y₁|? 2²(y)+b²O²(x₁)/3 при N?5,

|y₁-y₁|?2²(y)+b²O²(x₁)/3 при N?4

Where y1 is the measured value of the output signal at point x1;

Y1- estimation of the output signal by GC SI at point x1;

S(Y)2 is the variance of the average value of the output value;

b is the coefficient of the calibration equation;

O(x) is the error of the calibration mixtures.

Uncorrelated are those calibration solutions that are not related by chemical composition. With the photometric method of analysis, calibration solutions are most often related by chemical composition, i.e. correlated (for example, they are prepared from one standard solution). In this case, check the following conditions according to the formulas:

|y₁-y₁|?2S(y); при N?5

|y₁-y₁|?2,5S(y); при N?4

Where S(y) is the COE of the average value of the output value. The output signal in the photometric analysis method is the optical density.

S(y) is calculated as follows:

The variance of a single measurement calculated for the i-th calibration sample from n parallel measurements is calculated.

S_i²= (1)

The average variance is calculated for a series of calibration samples (for a single measurement)

N is the number of calibration samples.

The COE of the average value of the output signal is calculated

S()= (3)

Most often, modern regulatory documents (ND) contain a GC control algorithm. For example, in the HDPE F "Methodology for measuring the mass concentration of total iron in natural and wastewater by photometric method with sulfosalicylic acid". It states that GC stability control is carried out at least once a month or when changing batches of reagents. The means of control are prepared samples for calibration (at least 3 samples). The calibration characteristic is considered stable when the following condition is met for each sample for calibration:

?1,96*?_Rn;

Where X is the result of a control measurement of the mass concentration of iron in the sample for calibration;

C- certified value of the mass concentration of iron in the sample for calibration;

?R is the standard deviation of intra-laboratory precision, established during the implementation of the technique in the laboratory.

The permissible standard deviation of intra-laboratory precision when implementing the technique in the laboratory is established on the basis of the expression: ?RN = 0.84?R, with subsequent refinement as information accumulates in the process of monitoring the stability of the analysis results (the values of ?R are given in Table 1 in this technique). If the stability condition of the calibration characteristic is not met for only one calibration sample, it is necessary to re-measure this sample in order to exclude the result containing a gross error. If the calibration characteristic is not stable, the reasons are found out and the control is repeated using other calibration samples provided by the methodology. Upon repeated detection of instability of the calibration characteristic, a new calibration graph is constructed.

1.2 Algorithm of operational control of the error of determination of ammonium ions in drinking water

To perform operational control of measurement errors, I analyzed drinking water for the content of ammonium ions in it according to GOST 4192-82 "Methods for determining mineral nitrogen-containing substances". The methodology described in the GOST does not contain an algorithm for operational control of measurement stability. For such techniques, the necessary values of the error characteristic are calculated in accordance with GOST R 51232-98 "Drinking water. General requirements for the organization and methods of quality control".

In case of operational accuracy control, the control means is a specially selected working sample from among those analyzed earlier with the addition of a standard sample or a certified mixture. It is recommended that the interval of the component content in the working sample should be in the area of the most typical (average) values for working samples. The content of the introduced additive should be comparable in magnitude with the average content of the measured component in the working samples and correspond to the range of determined contents according to the method used. The additive is introduced into the sample before the sample is prepared for analysis in accordance with the methodology. The decision on the satisfactory accuracy of the results of the definitions and on their continuation is made under the condition:

? K,

Where Y is the content of the detectable component in the sample with the additive;

X is the content of the element to be determined in the sample without an additive;

C is the content of the detectable component in the administered additive.

K is the standard of operational accuracy control.

K=0.84 , (4)

Where is the - error characteristic corresponding to the content of the component in the sample with the additive;

- error characteristic corresponding to the content of the component in the sample without additives.

Calculation of the introduction of the additive

The content of the introduced additive should be comparable in magnitude with the average content of the measured component (ammonium ions) in working samples. I chose the additive value equal to 50%.

To calculate the additive, a sample of drinking water was analyzed using the photocolorimetric method according to GOST 4192-82 "Methods for determining mineral nitrogen-containing substances". The method for determining the concentration of ammonium ions is based on their ability to form a yellow-brown colored compound with a Nessler reagent. The color intensity of the solution, proportional to the mass concentration of ammonium ions, is measured on a photocolorimeter at a wavelength of 400-425nm. I conducted the analysis according to the following scheme:

To 50 cm3 of the test sample, I added 1 cm3 of potassium-sodium tartaric acid solution, mixed, then added 1 cm3 of Nessler reagent and mixed again. After 10 minutes, profotometrirovala on a photocolorimeter

KFK-2MP.

As a result of the experiment , the following data were obtained:

D Idle.(optical density of the blank sample)=0,268

D Samples=0.389

D(useful analytical signal)= D Samples- D Idle=0.121

GC equations (from the GC journal): D= 0.053=0.183*S, where C is in mg/dm3.

From the GC equation we find the content of ammonium ions in the sample

С ==0,372 мг/дм³.

The additive is prepared from GSO (state standard samples) with an ammonium ion concentration of 1 mg / cm3.

The concentration of ammonium ions in the additive is calculated by the formula:

Sdob = 0.372 mg/dm3 * 0.5= 0.185 mg/dm3 = 0.20 mg/dm3

Knowing the concentration of ammonium ions in the additive and in the GSO, we calculate the volume of GSO for the preparation of 100 cm3 of the additive according to the formula:

AGSO= ; (6)

V GSO=0.02 cm³;

Due to the fact that the volume of the aliquot is very small, it is necessary to prepare an intermediate solution from GSO, diluted 100 times. To prepare it, dilute 0.5 cm3 GSO in a measuring flask by 50 cm3 with distilled water. Next, we prepare a sample solution with an additive: dilute 2 cm3 of the intermediate solution in a measuring flask by 100 cm3 of the sample.

2. Practical part

2.1 Determination of ammonium ion content

Ammonium ions and ammonia appear in groundwater as a result of the vital activity of microorganisms. Their presence in drinking waters is also explained if these substances were not added to the mixture with chlorine during water treatment. In surface waters, ammonia appears in small quantities, usually during the vegitation period, as a result of the decomposition of protein substances. In an anaerobic environment, ammonia is formed during the reduction of organic substances. Due to the vital activity of nitrifying bacteria, the ammonia content in reservoirs decreases with the simultaneous formation of nitrates. The increased ammonia content in surface waters is explained by the discharge into them of domestic wastewater and some industrial waters containing significant amounts of ammonia or ammonium salts, which are waste products.

The essence of the method

The method is based on the ability of ammonia and ammonium ions to form a yellow-brown colored compound with the Nessler reagent in the presence of ferrotic salt. At low concentrations of ammonia in water, the solution turns yellow, and at high concentrations, a red-brown precipitate appears.

Ferrotic salt KNaC4H4O6 is added to prevent a side reaction between Mg2+ ions and hydroxide ions (magnesium ions are always present in water in some quantities, and OH ions are introduced into the solution with the Nessler reagent):

Mg2+ + OH- = Mg(OH)₂,

since magnesium hydroxide, precipitating in the form of white turbidity, interferes with colorimetric determination.

Interfering influences. The interfering effect of residual active chlorine is eliminated by adding sulfuric acid sodium, hardness - by adding a solution of ferrotic salt, a large amount of iron, color and turbidity - by preliminary clarification of the solution with aluminum hydroxide.

Canning of the sample. If the sample cannot be analyzed immediately, it is stored at a temperature of 3 ... 4 ° C for no more than a day or preserved by adding 1 ml of concentrated sulfuric acid or 2 ... 4 ml of chloroform per liter of water. The shelf life of canned samples is 2 days.

Reagents and equipment

· test water;

· ferrotic salt, 50% solution;

· Nessler reagent, 50% solution;

· pipettes of 2 and 10 ml;

· test tube - for accelerated determination;

· two Gener cylinders - for determination with colorimetric cylinders;

· measuring flasks with a capacity of 50 and 100 ml, photoelectrocolorimeter, standard solutions - for photometric determination.

Conducting an analysis

Accelerated method. 0.3 ml of 50% ferrotic salt and 0.5 ml of 50% Nessler reagent are added to 10 ml of the solution (in a test tube). After 10 minutes, the content of ammonia nitrogen and ammonium salts is determined according to Table 3.3 or by comparison with standards.

More precisely, the nitrogen content of ammonia is determined in colorimetry cylinders or on a photocolorimeter.

Colorimetric determination with Gener cylinders. 100 ml of test water is poured into cylinder 1. In cylinder 2 - a standard solution with a known concentration of ammonium salt. The standard solution is prepared by dissolving 1 or 2 ml of an ammonium chloride solution containing 0.01 mg of nitrogen in 1 ml to 100 ml of ammonia-free water. Then, 2 ml of 50% ferrotic salt and 50% Nessler reagent are poured into both cylinders. After 10 minutes, the content of ammonia nitrogen and ammonium salts is determined by pouring water from cylinder 1 until the color in the cylinders becomes the same (when viewed from above)

The concentration of ammonium ion is calculated by the formula:

х=

where Cst = 0.01ЧVЧ1000 / 100 is the concentration of the ammonia nitrogen ion in the standard solution, mg / l; V is the volume of the ammonium chloride solution containing 0.01 mg/ml of ammonia nitrogen, ml; hst and hiss are, respectively, the heights of the columns of the standard and test solutions.

The nitrogen content of ammonia depending on the color of the test solution

Photocolorimetric determination. In a flask with a capacity of 100 ml, 50 ml of the test water is poured, 1 ml of 50% ferrotic salt and 50% of Nessler reagent, the mixture is thoroughly mixed. After 10 minutes, the optical density of the solution is determined in a cuvette with an absorbing layer thickness of 30 mm with a blue light filter No. 4. Then, the optical densities of standard solutions Dst with a concentration of ammonia nitrogen Cst = 0.1 and 0.2 mg / l are determined, to which the same reagents are added. The nitrogen content of ammonia x is calculated by the formula using data for two standard solutions, and then determining the average value.

x = ,

2.2 Safety precautions when performing the analysis

Work in a chemical laboratory is inevitably associated with a number of dangerous and harmful production factors, therefore, the basis for normal work can only be the conscious observance of safety rules by each laboratory employee. When analyzing drinking water for the content of ammonium ions in it, the danger of the chemist's work may be related to the following factors:

Working with glassware. Do not use dishes that have cracks or chipped edges. When heating, use only heat-resistant dishes.

Work with electrical appliances (Photo colorimeter KFK-2MP). When using, it is impossible to neglect any malfunctions detected on the device. You need to make sure that the sockets are working properly.

Working with reagents. In my work, I used the following reagents: sodium-potassium tartaric acid, Nessler reagent. GOST 5845-79 "Reagents. Potassium-sodium tartaric acid 4-water" does not contain a section on safety requirements, there are no special instructions. Nessler's reagent contains mercury and is therefore poisonous. It should not get on food and skin.

Conclusion

My term paper consists of two parts: theoretical and practical. In the theoretical part, the issues of monitoring the stability of the calibration characteristic were considered. In the practical part of my course work, I analyzed a sample of drinking water for the content of ammonium ions in it according to GOST 4192-82 "Methods for determining mineral nitrogen-containing substances" According to the results obtained (shown in Table 1) I performed operational control of the measurement error of ammonium ions in drinking water according to GOST R 51232-98 "Drinking water. General requirements for the organization of quality control methods". After that, it is possible to make a conclusion about the satisfactory accuracy of the analysis results.

The method is applicable for determining the concentration of ammonium nitrogen in terms of ammonium NH4 ions in natural water, feed water and its components, steam condensates, boiler and heating waters. This method is applicable for waters containing and not containing hydrazine.

The essence of the method consists in the interaction of ammonium nitrogen in an alkaline medium with the Nessler reagent and measurement of the optical density of the yellow-orange suspension formed in this case. Nessler proposed using this compound to determine the concentration of ammonium ions as early as 1856. Nessler's reagent is an alkaline solution of a double salt of divalent mercury iodide and potassium iodide H §12 * 2K.1.

For analysis, such a sample volume is taken that the concentration

ammonium did not exceed 1 mg/dm3. The course of the analysis depends on the presence of substances in the water that interfere with the determination, such as hydrazine, colored organic compounds and some metal ions.

Ammonium ion (NH4+) accumulates in waters when ammonia gas (NH3) is dissolved in water, which is formed during the biochemical decomposition of nitrogen-containing organic compounds. The presence of ammonium ion in concentrations exceeding the background value indicates fresh contamination and the proximity of the source of contamination (municipal sewage treatment plants, industrial waste settling tanks, livestock farms, manure accumulations, nitrogen fertilizers, etc.)

Ammonia dissolves well in water, because when ammonia is dissolved in water, a reversible reaction of the formation of ammonium ions and hydroxide ion occurs, i.e. water is alkalinized and the pH (hydrogen index) becomes greater than 7.0 (alkaline reaction) this is an indicator of biological contamination. The increase in the content of ammonium ions increases with an increase in the pH value of water. The maximum permissible concentration (MPC) of ammonium ions for objects of household and drinking and cultural purposes, respectively, are 2.0 mg/dm3 and 1.0 mg/dm3.

Ammonium ions and ammonia appear in groundwater as a result of the vital activity of microorganisms. Their presence in drinking waters is also explained if these substances were not added to the mixture with chlorine during water treatment. In surface waters, ammonia appears in small quantities, usually during the growing season, as a result of the decomposition of protein substances. In an anaerobic environment, ammonia is formed during the reduction of organic substances. Due to the vital activity of nitrifying bacteria, the ammonia content in reservoirs decreases with the simultaneous formation of nitrates. The increased ammonia content in surface waters is explained by the discharge into them of domestic wastewater and some industrial waters containing significant amounts of ammonia or ammonium salts, which are waste products.

control ammonium ion photocolorimetric

List of used literature

1. Lurie Yu.Yu., Rybnikova A.I. Chemical analysis of industrial wastewater. Ed. 4th, perab. and an addendum, "chemistry", 1974

2. GOST 4192-82 "Methods for the determination of mineral nitrogen-containing substances"

3. GOST R 51232-98 "Drinking water. General requirements for the organization of quality control methods"

4. GOST 5845-79 "Reagents. Potassium-sodium tartaric acid 4-water"

5. Recommendations on metrology "Algorithms for constructing calibration characteristics of measuring instruments for the composition of substances and materials and evaluating their errors (uncertainties)"

6. HDPE F "Quantitative chemical analysis of waters. Methodology for measuring the mass concentration of total iron in natural and wastewater by photometric method with sulfosalicylic acid"

7. Zakharov L.N. Safety in chemical laboratories. - L.: Chemistry, 1985. - 184s., ill.

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