RU186501U1 - Spectrophotometric Flow Cell Device - Google Patents

Abstract

A spectrophotometric flow cell device for accurate and fast spectrophotometric studies in the flow field, consisting of two titanium pressure washers with viton gaskets and two working titanium washers with a viton gas spacing between them, and fluoroplastic cores pressed into each of the washers. cuvettes allow you to work in aggressive environments, control the optical path length and expand the range of measured concentrations of substances. 11 ill.

Description

The inventive utility model relates to the field of measurement technology, in particular, to devices for recording a spectrum of substances, and can be used for accurate and fast spectrophotometric studies in a flow field.

Flow cells are used to measure a continuous flow medium. There are a variety of designs of flow elements, which depend on the conditions and place of application of the cell. Flow cells were used in electrochemical and spectrophotometric studies in chemistry, medicine and other branches of science.

A device is known comprising a housing with a measuring flow channel in the form of a nickel capillary with a polished inner surface for multiple reflection of optical radiation (Russian patent RU 96974 U1).

There is also a device consisting of two transparent plates with two holes in one of them, additionally containing a gasket of sealing material, an annular capsule and a pressure cap (Russian patent RU 94037116 A).

The closest in technical solution is a flow cell having a Z-shaped channel for taking spectrophotometric data (Russian patent RU 80240 U1, prototype). The prototype consists of a body and plane-parallel optical plates, additionally equipped with a base made of fluoroplastic in the form of a parallelepiped, which is hermetically enclosed between plane-parallel optical plates. The base has two channels. One of the channels is intended for input and output of the analyzed liquid and is made according to the Z-shaped scheme, the input and output of which are located on opposite sides of the base. The second channel is intended for the passage of the light beam and is made direct, the input and output of which are located on the upper and lower sides of the base. Plane-parallel optical plates are made of quartz glass. This design of a flow spectrophotometric cell creates a turbulent flow of the analyzed fluid (eluate) in the working area, which prevents air bubbles from entering the cell, which impede the spectrophotometric analysis.

The disadvantages of the prototype are the inability to change the length of the optical path, which does not allow to measure a wide range of concentrations of the substance, and insecurity from aggressive environments.

The technical task of the proposed utility model is spectrophotometric measurements with an adjustable optical path length in a flowing chemically aggressive environment.

To solve this problem, a spectrophotometric flow cell (Fig. 1) is proposed, consisting of two titanium pressure washers (1) with viton gaskets (2) and two working titanium washers (3) located between them with viton gasket (4) (thickness which determines the optical path length and is regulated depending on the optical density of the medium being measured), and from fluoroplastic cores (5, 6), pressed into each of the washers.

The Avantes AvaSpec-2048 optical device is attached to the hole (8) pressed into the clamping titanium washers (1) (side view - Fig. 2, top view - Fig. 3) using the thread (7) in the hole (8). Working titanium washers (3) (side view - Fig. 6, top view - Fig. 7) also have fluoroplastic cores (6) with a through hole (9) filled with quartz glass. Through channels (10), the test liquid is supplied to the center of the device. To improve the sealing of the working part of the spectrophotometric flow cell between the clamping and working titanium washers, a viton gasket (2) with a central hole (11) is located (side view - Fig. 4, top view - Fig. 5). Between the two working washers there is a viton gasket (4) (side view - Fig. 8, top view - Fig. 9), the diameter of the hole (12) of which, like its thickness, is slightly larger than that of the viton gasket (2). All parts have five through holes (13) located around the circumference of the device. The device is fastened with five bolts from one of the clamping titanium washers, until the other clamping titanium washer is screwed on.

To demonstrate the operability of a spectrophotometric flow cell device, a spectroelectrochemical experiment was conducted in an aggressive environment to oxidize an aqueous solution of sodium bromide and to restore the resulting solution in a bromate flow redox battery.

The process of oxidation of the test solution proceeds on a membrane-electrode block, consisting of a Nation membrane 115 microns thick, on both sides of which there is a cathode - carbon paper Sigraset, and the anode - plated carbon paper Fieldberg. A 0.1 M NaBr solution in 0.2 M H ₂ SO ₄ with a volume of 21 ml is supplied to the cathode; a 20 ml H ₂ SO ₄ 0.5 M solution with a volume of 20 ml (at the stage of charging the flow redox battery) and molecular hydrogen (at the stage of discharge of the flowing one) are fed to the anode redox batteries). Solutions from the tanks are pumped by a LongerPump BT 100-IF peristaltic pump in a cyclic mode at a rate of 15 ml / min, hydrogen is supplied to the flow redox battery from a hydrogen generator at a speed of 25 l / h. At the outlet of the circuit for a sodium bromide solution, a flowing optical cuvette is connected. In this experiment, the optical path length of the cell is 420 μm. With an Elins P-50X potentiostat-galvanostat in galvanostatic mode, when charging a flowing redox battery, a current of 200 mA is applied for 8000 seconds, and then 200 mA for 6000 seconds in discharge mode. Avantes Avaspec-2048 high-sensitivity fiber-optic spectrophotometer is used to obtain the spectra of the test solution. Spectra are recorded in the range 200 - 1000 nm with an interval of 15 seconds. The spectra of the test solution at the stages of charge and discharge, corresponding to various values of the charge passed through the flow redox battery, are presented in FIG. 10 and 11. Spectra are plotted at wavelengths from 225 to 600 nm and optical absorption from 0 to 0.6, since this spectral region is of the greatest interest in studying the operation of the bromate flow redox battery.

При этом на спектре раствора наблюдается рост пиков при длинах волн λ=267 и 400 нм, которые соответствуют,

и Вr₂. Пик

растет быстрее, чем пик Вr₂, и через некоторое время достигает верхней границы чувствительности спектрофотометра, так как коэффициент экстинкции

на несколько порядков выше, чем у Вr₂. При пропущенном заряде 200 Кл в системе присутствует только Вr₂. Затем образующийся Вr₂ окисляется сначала до гипобромит-аниона ОВr^-, а потом до бромат-аниона

в результате при дальнейшем пропускании заряда на спектрах мы видим уменьшение пика Вr₂ и появление НОВr (об этом свидетельствует рост поглощения при λ=260 нм).

не поглощает излучение в исследуемой области, о его наличии мы можем судить только по характерному участку растущей кривой в средней УФ-области спектра (λ=230-260 нм). При прохождении заряда выше 1400 Кл бром в системе присутствует только в виде

At the initial stage of the charging stage of the flowing redox battery, the bromide anion (Br ^- ) is oxidized to bromine (Br ₂ ), and part of Br ₂ forms with the Br ^- tribromide anion

In this case, peak growth is observed in the spectrum of the solution at wavelengths λ = 267 and 400 nm, which correspond to

and Br ₂ . Peak

grows faster than the peak Br ₂ , and after some time reaches the upper limit of the sensitivity of the spectrophotometer, since the extinction coefficient

several orders of magnitude higher than that of Br ₂ . With a missed charge of 200 C, only Br _{2 is} present in the system. Then, the resulting Br ₂ is oxidized first to the hypobromite anion OBr ^- , and then to the bromate anion

as a result, upon further transmission of the charge in the spectra, we see a decrease in the Br ₂ peak and the appearance of HOBr (this is evidenced by an increase in absorption at λ = 260 nm).

It does not absorb radiation in the studied region; we can only judge its presence by the characteristic portion of the growing curve in the middle UV region of the spectrum (λ = 230-260 nm). When the charge passes above 1400 C, bromine in the system is present only in the form

With the passage of a charge of 100 C at the discharge stage, an increase in absorption at λ = 260 nm is observed, indicating the appearance of hypobromite in the system. With further transmission of the charge through the flowing redox battery, an increase in the Br ₂ concentration in the system is observed up to 800 C of the missed charge. Then, the accumulated Br _{2 is} reduced to Br ^- , and at the end of the discharge process, the absence of absorption characteristic of Br ^{- is} observed on the spectra.

Thus, this device provides the possibility of spectrophotometric measurements with an adjustable optical path length in a flowing medium with high chemical aggressiveness.

Claims (1)

A spectrophotometric flow cell device consisting of two clamping titanium washers with viton gaskets, and two working titanium washers with a viton gasket located between them, and fluoroplastic cores pressed into each of the washers.

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