RU2408908C1 - Apparatus for measuring concentration of light-absorbing substances - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: waveguide element is in form of a channel cavity in diffusely scattering hydrophobic materials having cavities without direct contact with the channel cavity. Inside the cavities there are light sources and receivers spaced apart by a distance which provides the required assay sensitivity. Direct-flow of the analysed sample is created inside the channel cavity. The channel cavity can also be coated with porous material which enables extraction of the analysed substance with subsequent measurement of its optical absorption. The apparatus can also be fitted with washing apparatus. ^ EFFECT: high sensitivity of the apparatus and possibility of self-cleaning of the measurement channel. ^ 3 cl, 2 dwg

Description

The invention relates to the field of spectroscopic measurement of the concentration of substances (including environmentally harmful) in various states of aggregation by automatic analytical methods, especially in relation to natural conditions.

A feature of automatic instruments for measuring the concentrations of various substances in natural samples is the need to work with the constant supply of new portions of the sample in a wide, previously unknown, range of concentrations and the need for quick cleaning of the measuring cell from an unexpectedly high concentration of the substance in the sample. Under these conditions, the creation of devices that possess, along with high sensitivity, the ability not to be contaminated, comes to the fore.

Known devices for spectroscopic measurement of the concentration of substances, based on the use of the Bouguer-Lambert-Behr law that relates the optical density of a sample, measured in a certain spectral range, with the concentration of the substance and the length of the cuvette [M.I. Bulatov, I.P. Kalinkin. A practical guide to photometric analysis methods. L .: Chemistry, 1986]. The need to measure (especially in natural samples) low concentrations of substances and, therefore, a low level of light absorption has led to the use of either devices that collect the maximum of light that has passed many times through the sample, or the use of long cuvettes.

Patents are known, for example U.S. Patent No. 5570447, which describes a long (up to 5 m) capillary cell, the inner walls of which are coated with an inert fluoropolymer TEFLON AF (which is used, for example, in US Patent No. 5165773, US Patent No. 5608517), having a refractive index of n = 1,315-1 , 29, smaller than the refractive index of water (n = 1.33), which provides a waveguide effect for the light introduced into it. However, placing the light source and receiver directly in the sample stream under investigation, especially at its low speed, does not contribute to the quick washing of the cuvette from the previous sample.

The devices described in U.S. have a similar disadvantage. Patent No. 6246828 B1, U.S. Patent No. 6878943 B2, U.S. Patent No. 6016372, U.S. Patent No. 5444807, U.S. Patent No. 7343074 B1.

Another area of the technique for determining small concentrations of chemical compounds present in natural water is the use of the integral sphere in its various modifications. One of the options for implementing such a device is considered in the dissertation R.M. Pope [R.M. Pope. Optical absorption of pure water and sea water using the integrating cavity absorption meter. Ph.D. Thesis. 1993]. The integrating cavity is made of diffusely reflecting ceramics, a measuring cell is placed inside the cavity, filling almost its entire volume. The light is fed into the cuvette through several optical fibers; similarly, light scattered in the integrating cavity is recorded. In another embodiment of the device, PSICAM (point-source integrating-cavity absorption meter) uses a light source located in the center of an integrating sphere completely filled with the studied liquid. The light scattered by the integrating sphere is collected on its outer surface through a corresponding window. HOBI Labs produces a similar type of instrument for oceanographic research [D.R.Dana, R.A. Maffione. A new hyperspectral spherical-cavity absorption meter. HOBI Labs, Inc. http://www.hobilabs.com]. Both of these devices are not designed for flowing devices and have either stagnant zones or contaminated internal surfaces.

The flow-through version is implemented in US Patent No. 7057730 B2. The test sample flows through a central pipe made of a transparent material, which is surrounded by two concentric diffusely scattering cylinders with a gap between them. Light is introduced into this gap from a large number of evenly spaced sources illuminating the sample through an internal scattering cylinder. The measured signal is taken through the optical fibers from the receivers, which are also uniformly distributed over the integrating cavity. Thus, in this device there are no stagnant zones and protection against pollution of light sources and receivers due to the lack of their direct contact with the sample, but cleaning of the inner transparent cylinder made of a hydrophilic material is required. This device does not implement the waveguide process of light propagation along the sample, because the sample is lit evenly. The waveguide light propagation process along the sample is carried out in US Patent No. 6385380, which is adopted as a prototype of the invention. The test sample flows in a transparent capillary, illuminated through its wall by a light source using optical fiber. At a certain distance along the sample stream (directly in the stream), a recording optical fiber connected to the radiation receiver is located. The input and output of the sample is perpendicular to the axis of the capillary. The disadvantages of this device are the presence of stagnant zones due to the above geometry of the injection of the sample and the possibility of contamination of both the walls of the transparent capillary and the recording optical fiber.

The objective of the invention is to provide a device that, along with high sensitivity due to the long optical path in the analyzed sample, the ability to self-clean the measuring path.

In the claimed invention, this is ensured by the implementation of the waveguide process of the distribution of the analyzing light along the integrating cavity and the absence of its pollution due to the creation of a direct-flow nature of the flow of the sample, which does not directly contact the sources and receivers of the analyzing light.

This object is achieved in that the waveguide element is made in the form of a cavity channel in a diffusely scattering hydrophobic material with recesses in which light sources and receivers are placed spaced apart from each other to provide the required analysis sensitivity, the recesses being made with the possibility of light passing into cavity without contact with its inner surface. The cross section of the cavity in shape and area coincides with the line supplying the sample, and the absence of any elements inside the cavity allows you to create a direct-flow nature of the flow of the sample, the absence of stagnant zones and, as a result, self-cleaning of the measuring path.

The claimed invention is illustrated by drawings, where

figure 1 presents the design of the device.

Figure 2 shows the dependence of the optical density of a solution of vanadium salt in water on its concentration.

The cavity channel 1 (hereinafter channel 1) of FIG. 1 is made in element 3 of a hydrophobic material with a high coefficient of diffuse reflection of light, such as Teflon. Light sources 5 are placed around channel 1 in cavities 4 that do not have direct contact with channel 1. Such light sources can be either monochromatic sources such as light-emitting diodes or lasers, or non-monochromatic sources with optical filters corresponding to the absorption spectrum of the sample under study. The channel wall at the location of the light sources is thin enough to provide diffusely scattered light to the channel. In accordance with the scattering indicatrix, light propagates along channel 1 in a waveguide manner and the breakdown is absorbed. At a distance from the light sources 5, determined by the required sensitivity of the analysis, radiation receivers 7 are located in the cavities 6. The walls of the channel 1 at the location of the receivers are also made thin enough to provide illumination of the receivers 7 with light transmitted along the channel. The sealing of channel 1 is carried out by standard methods using ring gaskets. For pre-flushing the channel 1, an additional nozzle 8 can be provided through which the flushing fluid is wetted to wet the surface of the channel. If it is necessary to pre-extract the analyte from the sample, the walls of channel 1 are covered with a porous membrane, on which, as the sample passes, the analyte accumulates, the light absorption kinetics of which determine its concentration (during preliminary calibration using standard samples). Preliminary wetting of the membrane is carried out by the extracting liquid also through the nozzle 8.

The operation of the device is as follows. The analyzed sample 2 is passed through the cavity channel 1. The signals from 5 receivers 7 illuminated by the light passing through the analyzed sample are compared with the signals obtained by passing the reference samples with known concentrations of the analyte, and the concentration of the substance in the sample is calculated based on preliminary calibration.

Figure 2 shows an example of the use of the device when measuring the concentration of vanadium ions dissolved in water, analyzed using the complexation reaction with 4- (2-pyridylazo) resorcinol. An LED with a radiation wavelength of 520 nm was used as a radiation source, and an ORT-301 type photodiode as a receiver.

Claims (3)

1. A device for measuring the concentration of light-absorbing substances, containing a waveguide element, light sources and receivers, characterized in that the waveguide element is made in the form of a cavity channel in a diffusely scattering hydrophobic material with cavities that do not have direct contact with the cavity channel, in which light sources and receivers are placed, spaced apart from each other to provide the required sensitivity of the analysis, and a direct-flow nature of the flow of the analysis is created inside the channel-channel iruemoy sample. 2. The device according to claim 1, characterized in that the cavity channel is additionally coated with a porous material, which provides extraction of the test substance with subsequent measurement of its optical absorption. 3. The device according to claim 1, characterized in that it is additionally equipped with a washing means.

Images