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Abstract

Content

Introduction

Around the person, as well as in the person, constantly occurs big number of various chemical processes. The elucidation of the mechanism of these processes and their orientation is one of the main problems not only in solving specific problems of chemistry and chemical technology, but is also an important element for a common understanding of the device and functioning of the world. Representations about the mechanism of chemical reactions can not be obtained without knowledge of the rates of chemical transformations.

Chemical kinetics has a huge practical solution, since it allows one to determine the possibility or impossibility of a process, as well as the conditions in which it occurs. This, in the final analysis, allows us to develop new methods for synthesizing a wide variety of substances, including pharmaceuticals, to solve environmental problems. Kinetic analysis methods are distinguished by high accuracy and are often used in the determination of small and ultra-small contents (up to 10-8 – 10-6 microgram) [1].

1. Relevance of the topic

The speed of various chemical reactions or one reaction can differ by many orders of magnitude. If some reactions can take hours, years or centuries, then others can flow in seconds, milliseconds or even, the fastest, in a billionth of a second. If the slow reactions can be monitored using only a clock, a stopwatch or some sensor with a large time constant, to research fast reactions we need special methods and equipment.

In scientific work [2] described jet, relaxation, electrochemical, photostationary, and pulsed methods of chemical analysis. Much attention is also paid to the methods of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). The time range of these methods lies in the interval from microseconds to several seconds. The application of relaxation, photostationary and impulse methods is limited to systems in which chemical equilibrium is established. Electrochemical methods are limited by the presence of electrochemically active substances in the system. NMR and EPR can be used in systems with substances with half-integral nuclear or electron spin.

Sufficiently universal are the jet methods proposed by B. Chance [2, pp 15–79]. Despite the fact that the dead time of jet methods is 0.1–2 milliseconds, by decreasing the concentration of reactants it is possible to increase the time of the reaction  [3].

For realization of flow methods use flow devices. It is a complex of hardware and software that allows you to automate the necessary research. The basis of the installation is a spectrophotometer – a device designed to measure the intensity of radiation transmitted through a sample. This intensity depends on the concentration of the substance absorbing light. The device makes it possible to make measurements for different wavelengths of optical radiation .[4]

At present, jet plants are produced only by foreign companies. At the same time, the cost of even the simplest equipment ranges from 10,000 dollars and more

The theme of the master's work is the creation of hardware and software that allows to analyze the data from the jet installation automated and to facilitate the user's work. The cost of the developed computer model will be incommensurable lower than the cost of the ready systems presented on the market.

2. The purpose and objectives of the investigation, the planned results

The aim of the work is to create a registration device and a software for processing the obtained data from a spectrophotometer. The main tasks include:

  1. Analysis of the characteristics of the signal at the output of the spectrophotometer.
  2. Selection and justification of hardware for the implementation of the task.
  3. Selection and justification of the software environment for data processing.
  4. Development of hardware based on selected equipment.
  5. Creation of algorithms for reading, digitizing and analyzing the signal.
  6. Perform a useful signal filter to eliminate interference and interference.
  7. Development of the user interface of the visualization program.
  8. Analysis of chemical reactions of the first and second order by the jet method.

3. Theoretical basis

Depending on the flow rate, the concentration of matter can be constant, increasing or instantaneously falling to zero, distinguish between continuous, accelerated or stopped jet methods [5].

The continuous flow method is used in those cases where each observation takes several seconds when the detector reacts too slowly or there is no possibility of automatic recording [6].

In the accelerated flow method, the reagent concentrations are determined at a fixed point of flow at a continuously changing reaction rate. Reagents are placed in two syringes, the pistons of which are manually driven by the researcher. However, the disadvantage of the accelerated flow method is the accumulation of a systematic error in the turbulence of the flow. In connection with this, the stopped-flow method the most widely used in the analysis of fast kinetics  [7]. The installation scheme is shown in Figure 1. This method was developed in 1934 by Rowton [8] and was significantly improved by six years later by Chance [9].

Figure 1 - Diagram of the installation using the stopped flow method.

Figure 1 – Diagram of the installation using the stopped flow method. (1 – transient tap, 2 – mixer, 3 – surveillance camera, 4 – lamp, 5 – monochromator, 6 – detector, 7 – stop-syringe, 8 – output device).

A significant limitation of the method of the stopped-flow - is the need for fast data recording. Due to the presence detector with sufficiently low time constant, stopped-flow method can be used to study reactions with half-times of a few milliseconds. Also, this method requires significantly less liquid (0.1–0.2 ml) with a small tube diameter [10]. This is relevant in cases where reagents are available in limited quantities.

4. Analysis of laboratory equipment for measuring the concentration of substances

Currently, foreign companies that produce scientific equipment, produce devices that consume small amounts of substances and are highly accurate. Instruments based on the stopped flow method are produced by at least five companies: KinTek Corporation (USA), Bio-Logic (France), Applied Photophysics Limited (UK), TgK Scientific Limited (UK), Olis, Inc (USA ) [11].

One of the most productive and functional is the SX20 Applied Photophysics Limited (UK) (Figure 2) designed for high-quality research. The SX20 is one of the most advanced of its kind and allows research into the kinetics of chemical reactions in a stopped flow.

Figure 2 - General view of the SX20 Applied Photophysics Limited stopped spectrometer (UK).

Figure 2 – General view of the SX20 Applied Photophysics Limited stopped spectrometer (UK).

The cost of this installation exceeds 53 thousand dollars [12]!

Among the developments of Kintek we will single out the system SF–300X. SF–300X Stopped-Flow has a powerful, computer-controlled servomotor, which provides accurate and reproducible mixing. Dual mixing experiments can easily be performed by consuming minimal volumes of precious samples and providing a minimum response time of just 5 ms. The engine is digitally controlled. There is a high-performance digital power supply that provides almost instantaneous starts and stops of driving syringes [13]. However, in the secondary market the cost of the installation is almost 4 thousand dollars. When ordering from a supplier, the cost of equipment will be even greater.

Among the more approachable systems can be identified the development of the company BioLogic. Model SFM–100 (Fig. 3) is the simplest in the line of Bio–Logic. Used for basic research and training. The installation includes a pair of syringes of 5 milliliters, supplied as basic. The system is easy to configure, but does not have the hardware and software to visualize the signal.

Figure 3 – Stopped flow installation SFM-100

Figure 3 – Stopped flow installation SFM–100

The system in Donetsk National Technical University was designed on the basis of the SF-26 spectrophotometer. The installation in the presented version was used to study the oxygen reactions with synthetic hemoglobin analogs [14–16]. A significant disadvantage of the installation is the lack of an automatic data collection and processing system.

It is advisable to use in the registration system inexpensive and approachable microcontrollers that have a sufficiently high speed and can be connected to a personal computer via a COM/USB interface. At present for measuring systems is widely used the Arduino card line based on Atmega328 microcontrollers.

The Nano platform, built on the microcontroller ATmega328 (ArduinoNano 3.0) or ATmega168 (ArduinoNano 2.x), has small dimensions (1.85 cm x 4.2 cm) and can be used in laboratory work or for building automated systems of various complexity [17]. The board is powered by a personal computer. The maximum input voltage is 5 volts. There are 14 digital and 6 analog inputs/outputs. ArduinoNano 3.0 has 32 KB of flash memory, which allows you to store a large amount of data. The presented microcontroller uses an 8-channel 10-bit ADC. The analog-to-digital conversion time of the standard function takes on average up to 100 ?s, which is permissible within the creation of the method of the stopped jet.

The issues of measuring analog signals in various applications were solved by DonNTU masters. Pitcha Tatyana performed a digital monitor for a 24-hour ECG recording, which involved the use of an analog-to-digital conversion based on the AD7714 sigma-delta ADC [18]. ]. The device for registration of signals based on the Arduino hardware platform was studied by the Master of DonNTU Pavlyn Alexander [19]. The issues of analog-digital conversion were solved in bachelor's work on the basis of the ADUC 841 microcontroller [20,21].

5. The software environment

As a software environment, it was decided to use the Matlab package. It is used to solve a wide class of problems and has its own programming language. The package is used by more than one million engineering and scientific workers. It works on most modern operating systems, including Linux, Mac OS, and Windows[22]. Standard tools allow you to work with the COM port, and also perform signal processing in accordance with the tasks.

The built-in GUI development environment allows you to create graphical user interfaces with various control elements, such as buttons, input fields and others[23].

Сonclusions

Methods of analysis of chemical kinetics has an important practical solution and are used for research in various fields of science. The ability to operate these methods directly depends on the effectiveness of the equipment and software used. Given the exorbitant cost of equipment for chemical analysis, the task of developing more approachable means is always topical.

The master's work is devoted to the actual scientific problem of creating a computer model for studying fast chemical reactions by the stopped flow method and determining the characteristics and type of reactions.

Bibliography

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