RU2053507C1 - Method of determination of total content of organic substances in water and device for its implementation - Google Patents

Abstract

FIELD: analysis of materials. SUBSTANCE: content of organic substances is determined without advance calibration and sample preparation by burring of sample selected beforehand. Time of change of concentration of oxygen and value of maximum change of it are determined. This concentration is established in gas mixture. Analyzed sample is injected into low-temperature zone of combustion chamber to extract solved oxygen followed by sample burring in its high-temperature zone. Quantity of oxygen used for burring is found and by its quantity content of organic substances in water is judged. Device for implementation of method and determination of total content of organic substances in water includes means to supply inert gas, means to control gas stream, means to meter oxygen into gas stream in the form of solid electrolyte cell, chamber to inject liquid sample, combustion chamber, dish, measurement oxygen solid electrolyte cell and unit registering results of determination. EFFECT: enhanced efficiency of method in control of environment. 2 cl, 2 dwg, 1 tbl

Description

 The invention relates to analytical chemistry and instrumentation and can be used to control organic pollution in environmental objects, in particular in natural and waste waters and technological solutions.

A known method for determining the content of organic substances (in particular, organochlorine), including sample preparation by extraction of organochlorine, saturating the extract with water vapor and mixing it with an inert gas, burning the obtained sample in an oxygen stream, followed by cooling the gas component of the sample and determining organics in the electrochemical cell [1]
The disadvantage of this method is time-consuming and lengthy sample preparation. In addition, the method allows you to determine only organochlorine, and not all organics.

A device for determining organic substances (in particular, organochlorines) in liquids is known, including a means of sampling from the current medium, a sample preparation unit, a gas-vapor mixture burning chamber, a refrigerator and a detector for determining organochlorine (by the amount of chlorine), made in the form of an electrochemical cell with silver electrodes [1] Moreover, the sample preparation unit consists of vessels with an analyzed liquid and an organochlorine-extracting liquid, pumps, a mixing capillary, a vessel for saturating water vapor of an analyzed chlorine by pottery, a vessel for heating a mixture connected to its lower part, an inert gas cylinder (for example, N ₂ ). The combustion chamber is equipped with a gas mixer (for mixing a vapor-gas mixture with oxygen) installed in the lower part, a ceramic gas flow distributor, a high-voltage ignition unit with steel electrodes and a photo detector electrically connected to the ignition unit and designed to control the complete combustion of organochlorine in the chamber.

 The disadvantages of the device are the complexity of the sample preparation unit and the combustion chamber. In addition, the device is designed to determine organochlorine in the analyzed liquids and does not allow to determine the total organic content in them.

Closest to the invention, the technical solution is a method for determining the total content of organic substances in water by burning a sample in a stream of a mixture of inert gas and oxygen and then determining the content of analytes by changing the oxygen content using a solid electrolyte cell with oxygen-ion conductivity [2]
Oxygen from the cylinder is introduced into the inert gas stream or a mixture of inert gas with oxygen is prepared in advance. One part of the flow through a valve system is passed through the chamber in which the sample is burned, and then enters the detector. Another part of the flow, bypassing the combustion chamber, goes directly to the detector. A sample is injected into the combustion chamber. Detection is carried out by a solid-state electrolyte cell with oxygen-ionic conductivity, which in accordance with the Nerst equation generates an electrical signal corresponding to the difference in oxygen concentration in the two above flows, which occurs after oxygen depletion of the stream passing through the combustion chamber.

 The disadvantage of this method is the inability to directly determine the concentration of oxygen in the stream and the ability to determine the amount of oxygen dissolved in the sample. It is possible that oxygen is added to the gas stream during the combustion of the sample due to the partial decomposition of water on the catalytic substrate.

 Closest to the invention, the technical solution is a device for determining the total organic matter content in water, including inert gas supply means, means for regulating the gas flow, means for dispensing oxygen into the gas stream, a combustion chamber equipped with a furnace installed coaxially with its outer side, and means for holding the sample in the chamber, a measuring solid electrolyte cell with oxygen-ion conductivity and a unit for recording the results of [2] The gas flow control means is made in the form of a valve system allowing to divide the gas flow into two flows (1 flow through the combustion chamber to the measuring cell, 2 flow bypassing the combustion chamber directly to the measuring cell) or provide different gas flow rates at the inlet and the exit of the combustion chamber. The valve system involves receiving an electrical signal on the measuring cell corresponding to the difference in the oxygen concentration in the two gas streams. The sample is injected into the combustion chamber by an injection means or a syringe.

 The means for holding the sample in the chamber is made in the form of a catalytic ceramic substrate. The means for dosing oxygen into the gas stream is made in the form of a container with a previously prepared mixture or means for preparing a mixture of two gases for a given concentration of oxygen in the gas stream.

 The disadvantage of this device is the inability to quickly and with great accuracy to change, if necessary, the oxygen concentration in the stream to ensure complete combustion of the sample.

 In addition, the recording system requires graduation, and the sample injection system does not protect the reactor from the ingress of external air.

 The objective of the invention is to develop and create a new method and a new generation of analyzers for controlling organic matter in natural and waste waters and technological solutions. A fundamental feature of the invention is the ability to determine the total organic matter content without first calibrating the device. This makes the use of this invention in ecological expeditions in environmental monitoring, i.e. in those cases when the composition of organic matter is not known a priori.

(1) где I_max максимальное изменение ионного тока кислорода;
F число Фарадея;
Q расход газа в системе, устанавливают концентрацию кислорода в газовой смеси равной C_max, вводят анализируемую пробу в низкотемпературную зону камеры сжигания при t₂=85-115^oC, выдерживают последнюю в течение времени, необходимого до достижения установленного значения концентрации кислорода с последующим сжиганием пробы в высокотемпературной зоне камеры сжигания при t₁= 800-850^оС, определяют количество потребленного на сжигание кислорода по формуле
G= V

(C_max-C_i) (2) где V_o объем реакционной зоны; C_i текущая концентрация кислорода, при этом о содержании органических веществ в воде судят по величине определенного количества кислорода.To do this, in the method for determining the total content of organic substances in water by burning a sample in a stream of an inert gas and oxygen mixture and then determining the content of the determined organic substances by changing the oxygen content using a solid electrolyte cell with oxygen-ion conductivity, a coulometric solid electrolyte cell is used to determine the change in oxygen content , conduct combustion preselected analysis sample at t ₁ = 800-850 ^o C in a stream of a gas mixture with conc ntratsiey oxygen in the range of 1-10 ^-2 mg / l, determined time change of the oxygen concentration _of τ and the value of maximum change in oxygen concentration according to the formula
C _max

(1) where I _{max is the} maximum change in the ion current of oxygen;
F is the Faraday number;
Q is the gas flow rate in the system, the oxygen concentration in the gas mixture is set equal to C _max , the analyzed sample is introduced into the low-temperature zone of the combustion chamber at t ₂ = 85-115 ^o C, the latter is maintained for the time required to reach the set oxygen concentration value, followed by combustion samples in the high-temperature zone of the combustion chamber at t ₁ = 800-850 ^о С, determine the amount of oxygen consumed for combustion by the formula
G = v

(C _max -C _i ) (2) where V _{o is the} volume of the reaction zone; C _i current oxygen concentration, while the content of organic substances in the water is judged by the value of a certain amount of oxygen.

 To solve the problem, a device for determining the total content of organic substances, including inert gas supply means connected in series, means for regulating the gas flow, means for dosing oxygen to the gas stream, a combustion chamber equipped with a furnace installed coaxially from its outside and means for holding the sample in the chamber, measuring solid electrolyte cell with oxygen-ion conductivity and a unit for recording the results of determination, equipped with a reciprocating mechanism the effective movement of the sample retention means, a liquid sample injection chamber, a differential pressure stabilizer, a flow inducer and an electronic control unit, the oxygen metering device is made in the form of an oxygen solid electrolyte cell with a stabilized power source, the reciprocating movement mechanism is made in the form of a stepper motor, gear system and placed in the housing of the worm gear, on the carriage of which a rod is fixed with a means for holding the sample in the form of ditches mounted on its end s, the chamber for introducing a liquid sample is hermetically connected on one side to the worm gear housing coaxially to the rod with the cell and, on the other hand, with a coaxial combustion chamber and is made with an opening for introducing a liquid sample into the cell, the pipe inlet connecting the oxygen metering device and the combustion chamber is located between the opening of the chamber for introducing a liquid sample and the wall on the side of the combustion chamber, the differential pressure stabilizer and flow inducer are connected in series and are installed after the measuring cell and a electronic control unit electrically connected to the power source of oxygen dispensing means, the stepper motor mechanism of reciprocating movement, the furnace combustion chamber and measuring cell.

 The invention provides a method for determining the level of water pollution directly from the amount of oxygen required to oxidize the organic matter contained in the sample. This indicator, which can be called "oxygen oxidation" (by analogy with bichromate oxidation or chemical oxygen demand (COD)) of a substance in water.

 Oxygen oxidation is determined when a sample is burned in a stream of an inert gas, oxygen by the amount of oxygen spent on oxidation.

Q(C-C_τ)dτ (3) где τ_o продолжительность окисления; Q расход газа в потоке; С концентрация кислорода в окислительной атмосфере; C

конечная концентрация кислорода; τ время.The amount of oxygen spent on the oxidation of organic matter is determined by the following formula:
G =

Q (CC _τ ) dτ (3) where τ _{o is the} duration of oxidation; Q gas flow rate; C is the concentration of oxygen in an oxidizing atmosphere; C

final oxygen concentration; τ time.

 To determine the oxygen in an inert gas stream, a coulometric solid electrolyte cell (CTEC) with oxygen conductivity is used.

If, using CTEJ, the oxygen stream j is extracted from the gas stream flowing through the cell with the flow rate Q, then, in accordance with the Faraday law, the current flows through the CTEJ
i = F (n / A) j, (4) where F is the Faraday number; A / n electrochemical equivalent.

A/n

(7) где I_τ значение ионного тока кислорода в момент времени τ.The concentration of oxygen in the gas phase
C = j / Q, (5) therefore, the current
I = F (n / A) CQ (6)
An analytical signal (peak) is the dependence of the current (i.e., the function of the oxygen content in the gas phase) on time. The peak area is proportional to the amount of oxygen spent on oxidation (in accordance with Faraday’s law)
G =

A / n

(7) where I _τ is the ion current of oxygen at time τ.

 Recording of the analytical signal and its further mathematical processing is carried out on the IBM PC / XT.

 If dissolved oxygen is present in the analyzed sample, the oxygen concentration in the gas phase rises from the moment it begins to be released, and when organics are burned, the oxygen concentration in the stream decreases, i.e. the change in ion current during the course of these processes is opposite in sign. It has been experimentally proved that the stepwise injection of a sample into the reactor (with the sample held in the low-temperature region of the reactor) allows the analytical peaks that appear during the evolution of dissolved oxygen and during the oxidation of organic substances to be separated on a time scale, since the temperature of the output of dissolved oxygen is an order of magnitude lower than the temperature required for burning organics in the sample.

 In FIG. 1 presents a diagram of the proposed device; in FIG. Figure 2 shows the kinetic curve obtained on the display screen when analyzing a sample of a 0.01% solution of phenol in water in the coordinates of the oxygen ion current I time τ.

 The device consists of inert gas supply means (for example, inert gas cylinder 1) connected in series by pipelines, gas flow control means made in the form of a reducer 2 and a throttle 3, means for dispensing oxygen to the gas stream, including a coulometric solid electrolyte metering cell 4, a stabilized source 5 power and furnace 6, the combustion chamber 7, equipped with a furnace 8 installed coaxially from its outer side, means for holding the sample in the chamber 7, made in the form of a cell 9, measured solid electrolyte cell 10 with oxygen conductivity and the furnace 11. The device also contains connected in series with pipelines to the measuring cell 10, a choke 12, a differential pressure stabilizer 13, a flow inducer 14 and a flow meter 15. In addition, the device includes an electronic control unit and a unit for recording determination results, made in the form of a pairing unit 16 and a computer 17. The sample holding means of the cuvette 9 is equipped with a reciprocating movement mechanism made in the form of a stepping motor tor 18, gear system 19 and disposed in the housing 20 of the worm gear 21, which is fixed on a carriage rod 22, at whose end cell 9 is set.

 The device is equipped with a liquid sample inlet chamber 23, which is hermetically connected to the worm gear housing 20 coaxially to the stem 22 with the cell 9 and, on the other hand, with the combustion chamber 7 mounted coaxially. A liquid sample inlet chamber 23 is made in the upper part with an opening 24 for introducing a liquid sample into the cell 9. A pipe inlet connecting the metering cell 4 to the liquid sample inlet chamber 23 is located between the liquid sample inlet 24 and the wall of the chamber 23.

 The electronic control unit is electrically connected to the power supply 5 of the dosing oxygen cell 4, the stepper motor 18 of the reciprocating mechanism, the furnace 8 of the combustion chamber 7, the measuring cell 10 (electrical connections to the power supply 5 of the dosing oxygen cell 4 and the furnace 8 of the combustion chamber 7 Fig. 1 is not shown).

 The device operates as follows.

Inert gas from the cylinder 1 through the reducer 2 and the inductor 3 enters the coulometric solid electrolyte metering cell 4, which serves as an oxygen pump, providing the necessary concentration of oxygen in the gas stream. The total gas flow in the system is set by the throttle 3. The resulting gas mixture is divided into two parts. One part of the flow enters the combustion chamber 7, where the evaporation and combustion of the sample water at a temperature of about 860 ^{° C,} and the other input to the chamber 23 of the liquid sample. This part of the flow prevents atmospheric air from entering the cell 9 when a liquid sample is introduced into it through the opening 24 of the liquid sample inlet chamber 23. The introduction of the cell 9 with the sample in the combustion chamber 7 is automated. The cuvette 9 is introduced stepwise, first into the low-temperature zone of the chamber 7, and then into the high-temperature zone by means of a reciprocating movement mechanism. In this case, a stepper motor 18 is turned on, which transfers the translational movement to the rod 22 with the cuvette 9 through the gear system 19 and the worm gear 21. The parameters of the sample input (speed, speed, etc.) are set using the computer 17. The gas mixture, the flow rate of which is set throttle 12, and measured by a flow meter 15, from the chamber 7 enters the measuring solid electrolyte cell 10, which controls the partial pressure of oxygen in the stream. Cell 10, as well as cell 4, which has oxygen conductivity, is used to measure the amount of oxygen used to burn the sample. Furnaces 6 and 11 ensure the operation of TEYA 4 and 10. A constant gas flow in the system is provided by the stabilizer 13, and the separation of the flow into two parts is stimulated by the inducer 14.

 The analytical signal, which is a change in time of the ion current of oxygen from the moment the liquid sample is introduced into the combustion chamber 7, is recorded using the interface unit 16 by the computer 17, which performs mathematical processing of the signal.

 The method for determining the total content of organic substances in water is as follows.

Set the pressure of the carrier gas equal to 2-2.5 atm. Set the total gas flow in the system equal to 2-3 cm ³ / s by blocking the hole 24. In this case, the inductor 12 is open. The activator 14 is turned on with the open hole 24 for introducing the sample and the throttle 12. Set the flow rate at the system outlet 0.6-1.6 cm ³ / s, measuring it with a flow meter 15. Using metering CTEY 4, oxygen is introduced from the atmosphere into an inert gas stream, at the same time, oxygen is removed from the inert gas using a measuring CTEY 10 operating in the coulometric mode, and the background ion oxygen current is determined. Passing a stabilized current through the metering CTEY 4, ensure that the current I _o passing through the measuring cell 10 is in the range of 1-3 mA, which corresponds to the optimal levels of registration of thermal oxygen consumption (TPK) of the order of 100 mg O ₂ / l (by analogy with the chemical consumption of oxygen (COD)).

Pre-selected water sample volume 1-10 .mu.l using a precision pipette through the opening 24, is injected into the cuvette cuvette 9. 9 with the sample is introduced into the combustion chamber 7 is heated in the central zone to 800-850 ^{° C,} and measuring cell 10 fixed change in ion current oxygen over time. The maximum value of the ion current I _max value is recorded on the change curve, the difference between I _o and I _max equal to ΔI and the time τ _о elapsed from the moment the ion current changes start until its value returns to its original value I _{o are} determined.

By changing the magnitude of the current passing through the metering cell 4, it is ensured that the magnitude of the current passing through the measuring CTEY 10 is I ′ _o = K ΔI, where K = 1-1.9. The analyzed water sample is injected into the cell 9, the cell 9 is introduced stepwise into the combustion chamber 7, pre-heating the sample in the low-temperature zone of the chamber 7 (100 ^° C) and final heating in the central zone of the chamber 7. The analytical signal, which is a change in time of the ion oxygen flow from the moment the liquid sample is introduced into the combustion chamber 7 (into its high-temperature zone). The area under the curve of the change in the ionic current of oxygen over time (according to the Faraday law) is proportional to the amount of oxygen spent on oxidation. The kinetics of the oxidation process can be observed on the display screen.

 The result of the analysis is the amount of oxygen (mg) required for the oxidation of the organic matter per unit volume of the sample (l), and is determined by the formula (2).

 By the value of a certain amount of oxygen, the content of organic substances in water is judged.

 PRI me R 1. An experiment was carried out to determine phenol in water. The inert gas pressure at the outlet of the cylinder 1 is set to 2.5 atm.

 For analysis, a sample of a 0.01% solution of phenol in water with a volume of 5 μm was used.

When the composition of the sample and its quantity are known, the preliminary analysis of the sample is not carried out, but the oxygen oxidation (i.e., the amount of oxygen necessary for the oxidation of the analyzed sample) is determined by calculation according to the equation of the chemical reaction of oxidation and based on the calculated value of oxidation according to equation (2), the necessary concentration in the stream and according to equation (6) the ion current I _o .

The theoretical value of the amount of oxygen required for the complete oxidation of phenol contained in this sample is 238 mg O ₂ per 1 liter of sample. Using chokes 3 and 12 set the gas flow rate in the system equal to 1.4 cm ³ / s. The metering cell 4 sets the ion current of oxygen in the stream I _o = I _o equal to 1.6 · 10 ^-3 mA, which corresponds to the oxygen concentration in the stream of the order of 0.2 mg / L. A 5 μl sample was taken with a precision mirro pipette and a sample was introduced into hole 9 through hole 24.

 A cuvette 9 is introduced stepwise with a sample into the combustion chamber 7 at a speed of the order of 5 mm / s with a 60-second stop in the low temperature zone of the dissolved oxygen chamber 7.

 A kinetic curve of the oxidation process is obtained in coordinates of the ion current I (in microamperes) time τ (in seconds) (Fig. 2) when analyzing a sample with a phenol content of 0.01%. The appearance of two peaks in the curve is due to the presence of different phenol fractions in the sample having different kinetics and oxidation temperature (the bottom line in Fig. 2 menu of control commands).

 The area under the curve of changes in the ionic current of oxygen is determined and the amount of oxygen used to burn this sample is calculated by the formula (2).

The thermal oxygen consumption (TPK) is determined per unit volume of the sample (per 1 liter). The TPK value obtained from the graph (Fig. 2) is 214 mg O ₂ / L (calculated COD value is 238 mg O ₂ / L).

 The results of similar examples of the determination of TPK for phenol solutions of various concentrations in water are given in the table.

As can be seen from the table, the results of the analyzes given by the proposed method in a fairly wide range of concentrations (2 · 10 ^-2 3 · 10 ^-3 ) are in good agreement with the calculated ones, which indicates complete combustion of the organic matter. Judging by the value of the relative standard deviation Sr, the method is especially accurate in the analysis of contaminated water (natural or waste), for which the COD value is usually 100 mg O ₂ / L.

 At high concentrations of organic substances in the sample, an underestimation of the results of the analysis can be observed compared to the calculated one due to incomplete combustion.

The proposed method and device allows to determine the total content of organic matter in water, the oxidizability of which is in the range of 10-1000 mg O ₂ / L with a relative standard deviation of 0.15 for measuring chemical oxygen demand (COD). Unlike conventional methods, the proposed method is absolute, express (1-2 min), does not require graduation and preliminary sample preparation.

 The specified range of oxidizability guarantees the completeness of combustion of samples and the correctness of the obtained analysis results. The proposed device is automated and easy to use.

Claims (2)

1. The method of determining the total organic matter content in water by burning a sample in a stream of an inert gas and oxygen mixture in the combustion chamber and then determining the content of the determined organic substances by changing the oxygen content using a solid electrolyte cell with oxygen conductivity, characterized in that to determine the change in the content oxygen using a coulometric solid electrolyte cell, carry out the burning of a pre-selected analyzed sample at t ₁ = 800 - 850 ^o C in a gas mixture stream with an oxygen concentration in the range of 1 - 10 ^{- 2} mg / l, determine the time τ _o changes in oxygen concentration and the magnitude of the maximum change in oxygen concentration according to the formula

where I _{m a x} is the maximum change in the ion current of oxygen;
F is the Faraday number;
Q is the gas flow rate in the system,
set the oxygen concentration in the gas mixture equal to C _{m a x} , introduce the analyzed sample into the low temperature zone of the combustion chamber at t ₂ = 85 - 115 ^o C, maintain the latter for the time necessary to reach the set oxygen concentration, followed by burning the sample in high temperature zone of the combustion chamber at t ₁ = 800 - 850 ^o C and determine the amount of oxygen consumed for combustion by the formula

where V _about - the volume of the reaction zone;
C _i - current oxygen concentration.  2. A device for determining the total organic matter content in water, including inert gas supply means, gas flow control means, oxygen metering means, a combustion chamber equipped with a furnace installed coaxially from its outer side and sample holding means in the chamber , measuring solid electrolyte cell with oxygen conductivity and a unit for recording results of determination, characterized in that the device is equipped with a mechanism the reciprocating movement of the sample retention means, the liquid sample injection chamber, the differential pressure stabilizer, the flow inducer and the electronic control unit, the oxygen metering device is made in the form of an oxygen solid electrolyte cell with a stabilized power source, the reciprocating mechanism is made in the form of a stepper motor, system of gears and a worm gear housed in the housing, on the carriage of which a rod is mounted with a holding means installed at its end the sample in the form of a cuvette, the chamber for introducing a liquid sample is hermetically connected on one side to the worm gear housing coaxially to the stem with the cuvette and on the other hand with a coaxial combustion chamber mounted and made with an opening for introducing a liquid sample into the cuvette, and the inlet of the pipe connecting the dispensing means oxygen and the combustion chamber, located between the opening of the injection chamber of the liquid sample and its wall on the side of the combustion chamber, the pressure stabilizer and flow inducer are connected in series and installed after measurement the measuring cell, and the electronic control unit is electrically connected to the power source of the oxygen metering device, the stepper motor of the reciprocating movement mechanism, the combustion chamber furnace and the measuring cell.

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