Electrochemical analyzers for medical purposes. Portable electrochemical analyzers Electrochemical analyzers
RelevanceIn the modern world, the influence of scientific and technological progress on all spheres of our life is increasingly observed. Concerning
there is a need for more accurate and faster methods of analysis
various substances.
Accuracy
Rapidity
Price policy
The purpose of the work: to study the principles of operation of ECMI and to set up demonstration laboratory work on the topic "Electrochemical
medical analyzers.Tasks to be solved:
1. The study of electrochemical methods for the analysis of substances,
used in laboratory medicine.
2. Market research of medical equipment for laboratory
analysis and selection of various models of electrochemical
analyzers for demonstration in the educational laboratory.
Studying the principles of operation of the selected models.
3. Development of demonstration laboratory works based on
proposed models of electrochemical analyzers and
descriptions for them.
1. Classification of electrochemical methods of analysis
PotentiometryConductometry
Voltammetry (polarography)
Coulometry
electrochemical cell
1 - solution, 2,3 - electrodes.
1.1. Potentiometry
The principle of operation of potentiometric analyzers is based onmeasuring the potential of the electrode placed in the electrolyte, according to
which determines the concentration of the test component
analyzed liquid medium.
1.2. Conductometry
The principle of operation of conductometers is to measure
electrical conductivity (electrical conductivity) of solutions
electrolytes, which determines the concentration of dissolved
substances.
1.3. Voltammetry
The principle of operation of polarography is to determine the dependencecurrent flowing between two electrodes
voltage applied to the electrodes.
1.4. Coulometry
Coulometric analyzers use the phenomenon
electrolysis, described by Faraday's law, during which
information about the concentration of the analyte is obtained
by measuring the amount of electricity used for
electrode reaction.
pH meter pH-009 (potentiometer)
2. Choice of electrochemical modelsanalyzers for demonstration in
educational laboratory
pH meter pH-009 (potentiometer)
Appearance of the pH meter and
consumables
Electrode system
Conductometer Ap-2
1- measuring electrolyticcell; 2 - electrodes; 3-
thermistor in case
Appearance
Electrochemical cell
as part of an electric bridge
10. Glucometer one touch UltraEasy (voltammeter)
AppearanceStrip test
11.
The dependence of the current through the electrodefrom voltage
Electrode system
12. 3. Laboratory work
Demonstration of the operation of the PH meterThe purpose of the work: measurement of the hydrogen index (pH) of solutions at
using potentiometric and colorimetric methods;
determination of the buffer capacity of the buffer solution and
consolidation of theoretical material on the topic "Potentiometry".
The content of the work:
Make solutions of acidic (coffee) and alkaline (soap) environments. changing
water/dissolved ratio measure pH values
instrument and indicator paper.
Compare readings and plot them.
13.
Demonstration of the operation of the ConductometerThe purpose of the work: to get acquainted with the operation of the conductometer and to fix
theoretical knowledge of students in the section "conductometry".
The content of the work:
Prepare two solutions of different concentrations of the solute
Measure conductivity and temperature, heat up and re-take off
indications. Calculate the temperature coefficient and display
addiction:
14.
Demonstration of the operation of the glucometerThe purpose of the work: to get acquainted with the glucometer and consolidate theoretical knowledge
on the topic "Voltammetry".
The content of the work:
Calculate theoretically and measure the concentration of sugar in a 5% solution
glucose. Dilute the solution with water 50/50 and repeat Calculation and
measurements. Explain possible reasons for the discrepancies in the results.
15.
ConclusionIn this paper, we consider the main electrochemical methods
research (ECMI).
A brief analysis of the market for medical devices was carried out
based on ECMI.
Work was carried out with foreign literature and patents. Revealed
the most popular of the ECMI methods and are described with an example
specific devices.
The choice of devices was carried out on the basis of several criteria:
- The cost of the device and related consumables
- Ease of use
- Service life
Developed introductory laboratory work on the topic
“Electrochemical analyzers” based on the studied devices.
16. Thank you for your attention!
17.
18.
Ag│AgCl │HCl (0.1 M)│glass membrane│external solution, (pHext,ex) (5)Let us denote the potential difference between Ag and AgCl DU1, between AgCl and HCl (0.1 M) DU2, between HCl (0.1 M)
and external solution DU3.
The potential difference between Ag and AgCl is determined by the equilibrium associated with the exchange on this
border with Ag+ ions. The fact is that, although silver chloride belongs to n-type semiconductors, that is,
the main carriers of electricity in it are electrons, due to the characteristics of the crystalline
structures of silver salts and properties of the silver ion the vast majority of electrical conductivity
provided by mobile silver ions that are not in the correct places in the crystal
(Frenkel defects) (minor carriers).
On the other hand, metallic silver is a crystalline body, where there are
silver ions, and an electron gas is distributed between them. Thus. silver ions
are present in sufficient quantities in both phases, and it is their rapid interfacial exchange
leads to an equilibrium that ensures the stability of DU1 at a fixed temperature.
Thus DU1 is a constant.
The potential difference between AgCl and HCl (0.1 M) is determined by the equilibrium associated with the exchange for
this border with Cl- ions. A dynamic equilibrium is established in the solution, determined by
solubility product of silver chloride. How much chloride goes into solution, so much
precipitates from hydrochloric acid solution.
The potential-determining reaction can be written as follows:
Cl- in silver chloride ↔ Cl- in hydrochloric acid (6)
19.
The magnitude of the potential difference in this case can be expressed by the well-known Nernst equation:DU2 = DU20 + (RT/F) ln (in silver chloride/[Cl-] in hydrochloric acid) (7)
Here DU2 is the potential difference between silver chloride and hydrochloric acid at a chloride concentration of
acid 0.1 mol/l, DU20 is the potential difference between silver chloride and hydrochloric acid at
chloride concentration in acid 1 mol/l (standard), R, T and F - respectively universal gas
constant, absolute temperature and Faraday number. Since the effective concentration of chloride in
silver chloride is constant by nature, and in hydrochloric acid it is constant due to the fact that the tube is closed and not
exchanges matter with external space, which means that both their ratio and the logarithm of the ratio are constant:
DU2 = const.
Only one component of the chain of series-connected DU3 electrochemical cells remains.
This is the potential difference across the glass membrane. The membrane material is chosen in such a way that it
Glass is permeable to hydrogen ions and impervious to other ions.
Numerous experimental studies have shown that this potential difference is determined by
equation:
DU3 = (RT/F) ln (ext/[H+] in hydrochloric acid) (8)
To date, there is no rigorous theory to explain this fact, although there are several
explanations.
The logarithm of the ratio is equal to the difference of the logarithms:
DU3 = (RT/F) ln (ext) - (RT/F) ln [H+] in hydrochloric acid) (9)
The second term on the right side of equation (9) does not depend on the composition of the external solution, so we can
consider it a constant.
20.
In general, if a fluid is part of an electrical circuit, then it behavesunder certain conditions as electrical resistance, conductivity G
which is defined by the expression
Electrochemical methods of analysis are based on the measurement of potentials, current strength and other characteristics during the interaction of the analyte with an electric current.
Electrochemical methods are divided into three groups:
¨ methods based on electrode reactions occurring in the absence of current (potentiometry);
¨ methods based on electrode reactions occurring under the influence of current (voltammetry, coulometry, electrogravimetry);
¨ methods based on measurements without an electrode reaction (conductometry - low-frequency titration and oscillometry - high-frequency titration).
According to the methods of application, electrochemical methods are classified into straight, based on the direct dependence of the analytical signal on the concentration of the substance, and indirect(establishment of the equivalence point during titration).
To register an analytical signal, two electrodes are required - indicator and comparison. An electrode whose potential depends on the activity of the ions being determined is called indicator. It must quickly and reversibly respond to changes in the concentration of ions to be determined in the solution. An electrode whose potential does not depend on the activity of the ions being determined and remains constant is called reference electrode.
POTENTIOMETRY
Potentiometric method is based on the measurement of the electromotive forces of reversible galvanic cells and is used to determine the concentration of ions in a solution.
The method was developed at the end of the last century, after in 1889 Walter Nernst derived an equation relating the electrode potential to activity (concentration of substances):
where is the standard electrode potential, V; 0.059 is a constant including the universal gas constant (), absolute temperature and Faraday's constant (); is the number of electrons participating in the electrode reaction; and are the activities of the oxidized and reduced forms of the substance, respectively.
When a metal plate is immersed in a solution, an equilibrium is established at the metal-solution interface
Me 0 ↔ Me n+ + nē
and an electrode potential occurs. This potential cannot be measured, but the electromotive force of a galvanic cell can be measured.
The investigated galvanic cell consists of two electrodes, which can be immersed in the same solution (element without transfer) or in two solutions of different composition, having liquid contact with each other (transfer circuit).
An electrode whose potential depends on the activity of the ions being determined is called indicator: E \u003d f (c). An electrode whose potential does not depend on the concentration of the ions being determined and remains constant is called reference electrode. It is used to measure the potential of the indicator electrode.
Brief historical background. The beginning of the development of electroanalysis is associated with the emergence of the classical electrogravimetric method (circa 1864, W. Gibbs). The discovery by M. Faraday in 1834 of the laws of electrolysis formed the basis of the coulometry method, but the application of this method began in the 30s of the twentieth century. A real turning point in the development of electroanalysis occurred after the discovery in 1922 by J. Heyrovsky of the polarography method. Polarography can be defined as electrolysis with a dropping mercury electrode. This method remains one of the main methods of analytical chemistry. In the late 1950s and early 1960s, the problem of environmental protection stimulated the rapid development of analytical chemistry, and in particular electroanalytical chemistry, including polarography. As a result, improved polarographic methods were developed: alternating current (Barker, B. Breuer) and pulsed polarography (Barksr, A. Gardnsr), which significantly exceeded the classical version of polarography proposed by J. Geyrovsky in their characteristics. When using solid electrodes of various materials instead of mercury (used in polarography), the corresponding methods began to be called voltammetric. At the end of the 1950s, the work of V. Kemuli and Z. Kublik laid the foundation for the stripping voltammetry method. Along with the methods of coulometry and voltammetry, methods are being developed based on measuring the electrode potentials and electromotive forces of galvanic cells - the methods of potentiometry and ionometry (see).
Voltammetry. This is a group of methods based on studying the dependence of the current strength in an electrolytic cell on the magnitude of the potential applied to an indicator microelectrode immersed in the analyzed solution. These methods are based on the principles of electrolysis; the analytes present in the solution are oxidized or reduced at the indicator electrode. In addition to the indicator electrode, a reference electrode with a much larger surface is placed in the cell so that its potential practically does not change when the current passes. As indicator microelectrodes, stationary and rotating electrodes made of platinum or graphite are most often used, as well as a mercury dripping electrode, which is a long narrow capillary, at the end of which small mercury drops 1–2 mm in diameter are periodically formed and detached (Fig. 1). The qualitative and quantitative composition of the solution can be established from voltammograms.
Rice. 4. Electrochemical cell with dropping mercury electrode: 1 - analyzed solution, 2 - dropping mercury electrode, 3 - reservoir with mercury, 4 - reference electrode
Voltammetric methods, especially sensitive variants such as differential pulse polarography and stripping voltammetry, are in constant use in all areas of chemical analysis and are most useful in solving environmental problems. These methods are applicable to the determination of both organic and inorganic substances, for example, to the determination of most chemical elements. With the help of stripping voltammetry, the problem of determining traces of heavy metals in waters and biological materials is most often solved. So, for example, voltammetric methods for the simultaneous determination of Cu, Cd and Pb, as well as Zn and Pb or Ti in drinking water are included in the standard. Germany. An important advantage of voltammetry is the ability to identify the forms of presence of metal ions in waters. This makes it possible to assess the quality of water, since different chemical forms of the existence of metals have different degrees of toxicity. From organic substances, it is possible to determine compounds that have groups capable of reduction (aldehydes, ketones, nitro -, nitroso compounds, unsaturated compounds, halogen-containing compounds, azo compounds) or oxidation (aromatic hydrocarbons, amines, phenols, aliphatic acids, alcohols, sulfur-containing compounds). The possibilities of determining organic substances by stripping voltammetry are significantly expanded when chemically modified electrodes are used. By modifying the electrode surface with polymeric and inorganic films containing reagents with specific functional groups, including biomolecules, it is possible to create conditions for the component to be determined in which the analytical signal will be practically specific. The use of modified electrodes provides selective determination of compounds with similar redox properties (for example, pesticides and their metabolites) or electrochemically inactive on conventional electrodes. Voltammetry is used to analyze solutions, but it can also be used to analyze gases. Many simple voltammetric analyzers have been designed for use in the field.
Coulometry. An analysis method based on measuring the amount of electricity (Q) that has passed through the electrolyzer during the electrochemical oxidation or reduction of a substance at the working electrode. According to Faraday's law, the mass of an electrochemically converted substance (P) is related to Q by the relationship:
P = QM/Fn,
where M is the molecular or atomic mass of the substance, n is the number of electrons involved in the electrochemical transformation of one molecule (atom) of the substance, p is the Faraday constant.
A distinction is made between direct coulometry and coulometric titration. In the first case, an electrochemically active substance is determined, which is deposited (or transferred to a new oxidation state) on the electrode at a given electrolysis potential, while the amount of electricity consumed is proportional to the amount of the reacted substance. In the second case, an electrochemically active auxiliary reagent is introduced into the analyzed solution, from which a titrant (coulometric titrant) is electrolytically generated, and it quantitatively chemically interacts with the analyte. The content of the component to be determined is estimated by the amount of electricity that passed through the solution during the generation of the titrant until the end of the chemical reaction, which is determined, for example, using color indicators. It is important that, during coulometric analysis, there are no foreign substances in the test solution that can enter into electrochemical or chemical reactions under the same conditions, that is, no side electrochemical and chemical processes occur.
Coulometry is used to determine both trace (at the level of 109-10 R mol/l) and very large amounts of substances with high accuracy. Many inorganic (practically all metals, including heavy metals, halogens, S, NO 3, NO 2) and organic substances (aromatic amines, nitro- and nitroso compounds, phenols, azo dyes) can be determined coulometrically. Automatic coulometric analyzers for the determination of very low concentrations (up to 104%) of gaseous pollutants (SO2 "Oz, H 2 S, NO, N0 2) in the atmosphere have successfully proven themselves in the field.
Potentiometry. An analysis method based on the dependence of the equilibrium electrode potential E on the activity a of the components of the electrochemical reaction: aA + bB + ne = mM + pP.
In potentiometric measurements, a galvanic cell is made up of an indicator electrode, the potential of which depends on the activity of one of the components of the solution, and a reference electrode, and the electromotive force of this element is measured.
There are direct potentiometry and potentiometric titration. Direct potentiometry is used to directly determine the activity of ions by the value of the potential (E) of the corresponding indicator electrode. In the method of potentiometric titration, the change in E is recorded during the reaction of the analyte with a suitable titrant.
When solving problems of environmental protection, the most important method is direct potentiometry using membrane ion-selective electrodes (ISE) - ionometry. Unlike many other methods of analysis, which allow only the total concentration of substances to be estimated, ionometry allows one to estimate the activity of free ions and therefore plays an important role in studying the distribution of ions between their various chemical forms. To control environmental objects, automated monitoring methods are especially important, and the use of ISE is very convenient for this purpose.
One of the main indicators in characterizing the state of the environment is the pH value of the medium, the determination of which is usually carried out using glass electrodes. Glass electrodes coated with a semi-permeable membrane with a film of the appropriate electrolyte are used in the analysis of water and atmosphere to control pollution (NH s, SO 2 NO, NO 2 , CO 2 , H 2 S). ISEs are usually used to control the content of anions, for which there are traditionally much fewer methods of determination than for cations. To date, ISEs have been developed and are widely used for the determination of F, CI, Br, I, C1O 4, CN, S 2, NO] and NO 2, which make it possible to determine the listed ions in the concentration range from 10 -6 to 10 -1 mol / l .
One of the important areas of application of ionometry is hydrochemical research and determination of the concentration of anions and cations in different types of water (surface, sea, rain). Another area of application of ISE is food analysis. An example is the determination of NO - 3 and NO 2 - in vegetables, meat and dairy products, baby food. A miniature ISE in the form of a needle has been created for the determination of NO - 3 directly in the pulp of fruits and vegetables.
Ionometry is also widely used to determine various biologically active compounds and drugs. At present, it can already be said that there are carriers that are selective to almost any type of organic compounds, which means that it is possible to create an unlimited number of corresponding ISEs. A promising direction is the use of enzyme electrodes, the membrane of which includes immobilized enzymes. These electrodes have a high specificity inherent in enzymatic reactions. With their help, for example, it will be possible to determine cholinesterase-inhibiting insecticides (organophosphorus compounds, carbamates) at concentrations of -1 ng/ml. The future of the method is associated with the creation of compact specific sensors, which are modern electronic devices in combination with ion-selective membranes, which will make it possible to dispense with the separation of sample components and significantly speed up analyzes in the field.
Waste water analysis
Electroanalytical methods, which are usually used in the analysis of water to determine inorganic components, are often inferior in sensitivity to the methods of gas and liquid chromatography, atomic absorption spectrometry. However, cheaper equipment is used here, sometimes even in the field. The main electroanalytical methods used in water analysis are voltammetry, potentiometry and conductometry. The most effective voltammetric methods are differential pulsed polarography (DIP) and inversion electrochemical analysis (IEA). The combination of these two methods allows the determination to be carried out with a very high sensitivity - approximately 10 -9 mol/l, while the instrumentation is simple, which makes it possible to do analyzes in the field. Fully automated monitoring stations operate on the principle of using the IEA method or a combination of IEA with DIP. The methods of DIP and IEA in the direct version, as well as in combination with each other, are used to analyze water pollution with heavy metal ions and various organic substances. In this case, the methods of sample preparation are often much simpler than in spectrometry or gas chromatography. The advantage of the IEA method is (unlike other methods, for example, atomic absorption spectrometry) also the ability to “distinguish” free ions from their bound chemical forms, which is important both for assessing the physicochemical properties of the analyzed substances and from the point of view of biological control ( for example, when assessing the toxicity of waters). The analysis time is sometimes reduced to a few seconds by increasing the polarizing voltage sweep rate.
Potentiometry using various ion-selective electrodes is used in water analysis to determine a large number of inorganic cations and anions. The concentrations that can be determined in this way are 10 0 -10-7 mol/l. Control using ion-selective electrodes is characterized by simplicity, rapidity and the possibility of continuous measurements. At present, ion-selective electrodes have been created that are sensitive to certain organic substances (for example, alkaloids), surfactants and detergents. In water analysis, compact probe-type analyzers are used with the use of modern ion-selective electrodes. At the same time, a circuit processing the response and a display are mounted in the probe handle.
Conductometry used in the work of analyzers of detergents in wastewater, in determining the concentration of synthetic fertilizers in irrigation systems, in assessing the quality of drinking water. In addition to direct conductometry, indirect methods can be used to determine certain types of pollutants, in which the substances to be determined interact with specially selected reagents before measurement and the recorded change in electrical conductivity is caused only by the presence of the corresponding reaction products. In addition to the classical versions of conductometry, its high-frequency version (oscillometry) is also used, in which the indicator electrode system is implemented in continuous conductometric analyzers.
Electrochemical measurements
Foxboro's 45 years of experience in analytical instrumentation contains a galaxy of significant technical innovations. The durable DolpHin series sensors have revolutionized pH measurement. The latest sensor to be released is the unique FT10 sensor, an electrodeless in-line conductivity sensor designed for the most aggressive environments in the semiconductor, fine chemicals, and other industries.
The 875 Series Intelligent Electrochemical Analyzer is the ideal platform for all your electrochemical analysis needs. Choose it to make accurate measurements of a variety of variables, from electrical conductivity and resistivity to ph/OR P measurement with the contact method and electrical conductivity with the electrodeless method. This analyzer is the most user-friendly analyzer available on the market today.
All models in the 875 Series are equipped with useful features, from an event log (up to 100 events with time and date stamps) to full sensor and analyzer diagnostics. The 875H analyzer features automatic buffer recognition for flawless pH calibration and remote service for sensor cleaning and calibration.
The Model 875C offers application switching and storage for up to three application configuration kits that contain custom curve kits. Each Model 875 has all the benefits an analyzer needs. It is characterized by maximum speed and ease of installation, configuration, calibration and operation. Model 875 has a large backlit LCD display; on-screen prompts with an intuitive menu; panel or field mounting; easy access to electrical wiring, and a range of other advanced features and capabilities tailored to your industry or application. This analyzer is mains powered and certified for use in a Class I, Division 2 hazardous area.
Easy-to-use analyzer that has become the de facto industry standard The 870IT Foxboro Intelligent Two-Wire Analyzer also incorporates many of the features and capabilities used by the 875. It has become the industry standard, offering the same set of built-in features such as advanced sensor diagnostics, using a guided menu system, and PC-based configuration. The 870IT is loop powered, resulting in reduced wiring costs. This analyzer is also intrinsically safe and is certified for use in a Class I, Division 1 hazardous area.
We offer a wide variety of innovative sensor technologies, materials, sizes and shapes. From the finest pure water to the most aggressive acids, we can handle any of your working solutions. Our offerings include electrodeless conductivity sensors, pH/ORP/ISE sensors, in-line conductivity sensors, contact conductivity/resistivity sensors, and dissolved oxygen sensors from Foxboro.
The wide range of sensors available greatly simplifies your installation, calibration, accessibility, troubleshooting and maintenance requirements.
Foxboro sensors provide specific benefits for every required application:
For pure and ultrapure water measurements, our 871CR sensors, with cell ratios from 0.1 cm-1 to 10 cm-1, have the highest measurement accuracy possible.
For harsh chemicals or continuous process applications, our 871FT in-line sensors use an innovative, non-invasive method for measuring conductivity.
For conductivity and concentration measurements, our 871EC sensors come with the widest range of materials, sizes and mounting accessories available.
To measure the conductivity of the most aggressive and/or high purity chemicals with a completely non-invasive, non-metallic (all parts made of Teflon, PFA) flow-through design, choose our new FT10 sensor.
For dissolved oxygen measurements, our rugged, rebuildable 871DO sensors, with regular maintenance, can operate for years even in the harshest of applications.
Simplify the calibration of any Foxboro electrodeless conductivity sensor with our high precision EP485 resistive calibration plugs. Precision calibration with a tool that fits in your shirt pocket!
The DolpHin family of sensors has revolutionized field instrumentation. With outstanding durability in the harshest environments, as well as extreme ease of use for any application, DolpHin has become the industry standard for pH/ORP sensors. DolpHin technology is also used in the 871PH repairable sensors.
DolpHin sensors remain exceptionally accurate even with twice the lifetime of competitive sensors in high temperature and thermal cycling applications up to 121°C. They maintain high temperature response - they are twice as fast as standard sensors - under the same harsh conditions, and they operate at pressures up to 100 psi.
The latest development is a family of high performance, disposable pH sensors available in the very popular 12mm form factor design. The new PH12 series from Foxboro is the first in the manufacturing industry to feature a sensor in a PEEK package; making the 12mm pH sensor the most durable in the world. It is supplied with a flat membrane measuring electrode and no process-wetted metal parts. Its non-metallic base is a standard feature, allowing for very cost-effective sensor diagnostics.
