WO2020148571A1

WO2020148571A1 - Method and device for acid- or base concentration measurement

Info

Publication number: WO2020148571A1
Application number: PCT/IB2019/050336
Authority: WO
Inventors: Ivan Tomka; Daniel Jenny
Original assignee: Ivan Tomka
Priority date: 2019-01-16
Filing date: 2019-01-16
Publication date: 2020-07-23

Abstract

The subject of the invention is a method for acid- or base concentration measurement in a chemical compound, comprising the steps of mixing the compound with a hydrogen ion sensitive indicator solution to form a subject mixture for analysis, measuring the hydrogen ion concentration of the compound, and transmitting the measurement results to an observer. It is characterized in that it includes the steps of filling the indicator solution into a perforated device (14), placing the perforated device (14) into the compound, and mixing of the compound; where the indicator solution is applied into a semi-permeable container (7), and the hydrogen ions of the compound are diffused into the semi-permeable container (7). The subject of the invention also includes a device for the application of the method.

Description

Method and device for acid- or base concentration measurement

The subject of the invention is a method for detecting hydrogen ions in an environment by its reaction with an indicator solution, determining the concentration of the hydrogen ions in said environment, and transmitting the determined concentration value wirelessly to an observer outside of said environment. The subject of the invention also includes the device for the application of the method.

A common practice for determining the hydrogen ion concentration of an environment is the measurement of electromagnetic radiation absorbance quantitatively at two or more wavelengths. The principle can be illustrated by taking an indicator to be a simple acid, HA, which dissociates into H+ and A-.

HA H+ + A-

The value of the acid dissociation constant, pKa, must be known. The molar absorbances, eHA and eA- of the two species HA and A- at wavelengths lc and y must be also determined by previous experiments. Assuming Beer's law to be obeyed, the measured absorbances Ax and Ay at the two wavelengths are simply the sum of the absorbances due to each species. There are two equations in the two concentrations [HA] and [A-]. Once solved, the pH is obtained as pH = pKa + log (A-) / (AH)

If measurements are made at more than two wavelengths, the concentrations [HA] and [A-] can be calculated by e.g. linear least squares. In fact, a whole spectrum may be used for this purpose. The process is well illustrated by the indicator bromocresol green. The observed spectrum (green) is the sum of the spectra of HA (gold) and of A- (blue), weighted for the concentration of the two species. When a single indicator is used, this method is limited to measurements in the pH range pKa ± 1, but this range can be extended by using mixtures of two or more indicators. Because indicators have intense absorption spectra, the indicator concentration is relatively low, and the indicator itself is assumed to have a negligible effect on pH.

The state of the art includes the following solutions.

Rerolle el. al (Development of a colorimetric microfluidic pH sensor forautonomous seawater measurements, Analytica Chimica Acta 786 (2013) 124- 131) published a proposition for an in situ pH-sensing arrangement for buoys or any floating objects to access quality pH data with good resolution both in space and time. Their focus was on the investigation of ocean acidification, and aimed at a small and more sustainable sensor, and claimed successfully one such device for oceanographic purposes, consisting of thymol blue indicator solution (sodium salt dissolved in deionized water) which is discolored to an extent relatable to pH-level of the seawater. The seawater sample and the indicator solution are driven by two separate syringe pumps and forced into a static mixer to react.

Jokic et. al (Anal. Chem. 2012, 84, 6723-6730) also published a pH-value sensor for in situ seawater sampling. The applied pH-sensitive indicator solution is fluorescent in the near- infrared region, based on the indicator solution concentration change (measured by the apparent fluorescence change), the pH-value can be guessed. Upon injection with the indicator solution, corals were investigated.

The documentation of the Chinese utility model CN207280960 U discloses another sensor for seawater application, to measure ocean acidification. The sampling is solved by peristaltic pumps, then the sample is filtered for optical homogenization, and phenol red indicator is applied. The subject mixture is lit with a xenon-lamp or LED, and the transmission spectrum is observed through a CCD camera.

Patent application CN108254348 A describes a sensor using a fluorescent indicator to monitor the growth of bacteria samples and farms at a long term without human intervention. The indicator is solidified through multiple steps to form nano micelles and is embedded in a gel or paste. This encapsulated indicator functions are contacting a fluid phase of the subject matter. The indicator is based on the solution of phospholipid polyethylene glycol and 5-(N- hexadeconayol)-amino in ethanol. The indicator emits secondary radiation in green upon excitation with blue light. The stabilized nanoparticles provide long term duty. In contrast to this solution to prevent the chemical degradation of the pH sensing indicator, the present invention uses a polymer bound indicator solution free of nanoparticles, which is periodically and automatically exchanged and refreshed for continuous sampling. Also, instead of using an emitted light of the indicator requiring a shorter wavelength hence higher energy lightwave (blue light or UV irradiation) in the present invention we observe the transmission spectrum of the indicator solution, registering the light absorption changes with pH-concentration.

The patent document US2018306777 Al from the United States of America comprises an indicator solution which is aimed to measure both halide-ion and hydrogen-ion concentration at the same time, based on fluorescent polypeptides. The indicator has at least one amino acid sequence allowing it to enter living cells. The purpose of the simultaneous measurement is to provide a pH-corrected halide-ion concentration value. The Chinese patent application CN108285449 A contains yet another fluorescent indicator, capable to indicate hypochlorite ions if dissolved in ethanol or water (3-ethyl-2-(2-(4- phenylpyrido[ 1 ,2-alpha]benzimidazole)vinyl)benzothi azole-3 -iodide).

The problem to be solved is to provide a user with pH-values of a chemical compound without regular human intervention such as the exchange of the indicator solution, or maintenance and service necessary during the application of the method or device, while having a long and stable life-cycle.

The purpose of the invention is to eliminate the faults of known solutions and to provide a more robust, cost-efficient and compact solution, which allows users to monitor pH-values of various chemical compounds daily over several years.

The inventive step for the present method is based on the recognition that it is advantageous to use diffusion for mixing the subject compound and the indicator solution to save energy and hence make the method feasible for enclosed environments. The inventive step for the present device is based on the recognition, that the method is best implemented with a miniaturized fluid (hydraulic or pneumatic) system to lessen frictional losses, optimize power usage and save on moving parts. The novelty of the described invention is further comprised in the spatial arrangement of the indicator and the chemical bounding of the indicator to hydrophilic polymers. Any compound as indicator is useful in the present invention which maintains an indicator function, is water soluble and has molecular mass not less than 10000 dalton, preferably not less than 40000 dalton. The unwanted small molecules may be eliminated by dialysis or ultrafiltration. The indicator has phenolic hydroxyl and nitro groups which are essential for the indicator function and are not to be involved in the chemical bounding to the hydrophilic polymer. Instead, the indicator contains an oxo-group whereby the oxo-groups may be chemically bound to vinyl alcohol by forming acetal bonds.

The presented method and device have numerous advantages. The device is conceived to work continuously for several years but can function for minutes if desired. Due to the utilization of a transmitter, and the passive sampling, the method operates with little energy input, making it possible to monitor an enclosed aqueous solution or slurry or potentially the intestine of a live animal. The present method also makes it possible to use it downscaled, in very limited spaces. According to the above purpose, the most general application method of the solution according to the invention is described in claim 1. The device implementing the method is described in claim 7. The individual application forms are described in the dependent claims.

The invention is presented in more detail by examples of implementation, using drawings and an example.

On the following drawings,

Figure 1 shows a schematic 2D section view of one embodiment of a device implementing the invention,

Figure 2 shows a detailed view of Figure 1, showing one part of the measurement unit of the example device.

Figure 3 is an isometric 3D view of the inner structure of the example device on Figure 1 in wireframe representation.

Figure 1 is a schematic drawing showing one basic embodiment of the device implementing the invention. The device is in section view, the different hatchings representing the different parts of the device. The perforated device 14 has means for interaction between a subject compound surrounding the perforated device 14 itself, and the indicator solution contained inside the perforated device 14. The indicator solution is filled into its chamber 4a by removing the chamber sealing 8a, which is in the preferred embodiment, screwed into the perforated device 14. The degassed indicator solution should be stored and filled in under pure helium gas atmosphere to avoid the formation of gas bubbles in the measurement unit. The indicator solution is moved into- and out of the semi-permeable container 7, by means of the actuating piston 3a in the cylindrical-shaped chamber 4a. The piston 3a having the piston sealing 5a is driven by the spindle 2a which is connected to the motor 11a. The inflow and outflow of the indicator solution is regulated by the control pistons 10a, 10b in each measurement unit part 6a, 6b. Both parts are sealed by the measurement unit sealings 12a, 12b, and are connected to the other cylindrical chamber 4b. The chamber 4b houses the actuating piston 3b having the piston sealing 5b. The chamber 4b has a removable chamber sealing 8b. The actuating piston 3b is driven by the spindle 2b which is connected to the motor l ib. The piston sealings 5a, 5b can be any of the common sealings in fluid systems for example rubber O-rings. The hydrogen ions of the compound diffuse into the semi-permeable container 7 while the particles of the indicator solution are designed so that they are contained inside. The control piston 10a has the light source 17 covered with light transmitting, neutral glass window, facing the semi-permeable container. The other control piston 10b has the light sensor with a glass window of the same type. The windows are either glass, quartz or a polymer, and can be treated by anti reflex layer. The control pistons 10a, 10b may take up two extreme positions: in one of these positions (closed position) the control pistons 10a, 10b enable the gates on the two ends of the semi- permeable container 7, in the other extreme position (open position) the content of the semi- permeable container 7 can be exchanged by fresh indicator solution. The containment for electronics 1 comprises the transmitter to broadcast the signal of the light source 17 or to broadcast the computed pH values from microcontroller unit processing the signal of the light source 17. The containment for electronics 1 further comprises the battery 15 as electrical power source for the light source 17, and in the preferred embodiment, to the motors 11a, l ib being electric motors. All of the parts and units of the perforated device 14, excluding the measurement unit parts 6a, 6b and the semi-permeable container 7 in between, are separated from the compound by the sealed container 13.

Figure 2 is a close-up of the measurement unit part 6a having the light source 17 on the control piston 10a.

Figure 3 is an overview of the structure of the perforated device 14, omitting the housing to better demonstrate the connection of the various parts and units. It further shows the tubing 16 making the fluid connections for the measurement unit, and the closure plug 9 which closes the tubing 16 as an alternative to the unscrewing of the chamber sealing 8b for the exchange of the (either hydraulic or pneumatic) fluid actuating the control pistons 10a, 10b.

Example:

Polyvinylalcohol acetal of 5-hydroxy-2-nitro-benzaldehyde was synthetised by using partially hydrolysed polyvinylacetat PVA Airvol 425 with 95.5-96.5 % hydrolysed with a mass average molecular mass 100,000-146,000 dalton and 5-hydroxy-2-nitro-benzaldehyde. A 10 g of 10 % by weight in dimethyl sulfoxyd solution of PVA Airvol 425 and 10 g 10 % by weight in dimethyl sulfoxyd solution of 5-hydroxy -2 -nitro-benzaldehyde and 20 g of 10% by weight aqueous solution of phosphoric acid were mixed in a vessel. The reaction was conducted at 95 °C. The reaction product polyvinylalcohol acetal of 5-hydroxy-2 -nitro-benzaldehyde with a grade of substitution of 5% by weight was separated by dialysis against water from the reaction mixture and was used as indicator polymer in the optical part of the bolus for the detection of the pH. The most general form of the present invention is a method for acid- or base concentration measurement in a chemical compound, comprising the steps of mixing the compound with a hydrogen ion sensitive indicator solution to form a subject mixture for analysis, measuring the hydrogen ion concentration of the compound, and transmitting the measurement results to an observer. The specialty of the method is, that first we fill the indicator solution into a semi- permeable container 7 of a perforated device 14, and then we place it into a compound of interest having an unknown hydrogen ion concentration for a quick measurement or constant monitoring. We wait for the hydrogen ions to diffuse into the semi-permeable container 7 through its pores, mix, and react with the much larger particles of the indicator solution.

In a preferred form of the present invention we apply visible light or other electromagnetic radiation (EMR or EM radiation) to the subject mixture consisting of the diffusing hydrogen ions and the indicator solution. Then we observe the hydrogen ion concentration change through the absorption change of the transmission spectrum with optoelectronical devices such as photodiodes, phototransistors, photon- or quantum detectors, based on the signal and noise level. Most preferably the emission maxima of the applied EMR is at the wavelengths of the absorption maxima of the associated and dissociated forms of the indicator solution, and we observe the transmission spectrum with highest sensitivity at these wavelengths too. During experimentation, the absorbance of the indicator solution was measured at the above mentioned two wavelengths and determined by the voltage of the photo voltaic light sensor 18 at two conditions of the semi-permeable container 7. In the first case the semi-permeable container was filled with water in the second case it was filled with the indicator solution, in both cases the content of the semi-permeable container 7 was in equilibrium with the pH of the surrounding medium, and the pH of the buffer solution and the measured pH were in agreement by 0.02 pH unit.

A further possible feature of the method is to utilize one wave length of light, register the current on the light sensitive device as a response to the known pH of an aqueous buffer solution. This procedure is repeated for several pH values in the range of 4 to 6. Consecutively we determine the regression of the pairs of values of pH and current. The regression is then used to determine the unknown pH values of samples from subsequent measurements of current on the light sensor.

In another preferred form of the present invention we mix two or more indicator functions with different EMR absorption spectra to form the indicator solution having a spectrum of our choice, fitting the absorption spectrum of the compound we investigate. Another preferred form of the present invention is when we make the compound diffuse through the membrane of a hollow fiber dialyzer, which has a porous polymer membrane. The membrane can be made of polypropylene or polyethersulphon, and we must form it into a hollow tube to act as the semi-permeable container 7.

One preferred form of the present invention is when the perforated device 14 is placed inside of a living organism with aqueous bodily fluids. In the case of an animal subject the preferred method is to feed the perforated device 14 to it mixed into its food, or to surgically embed it into its place of interest.

Another preferred form of the present invention is when we specifically investigate the rumen of a cattle, by sampling from the digestive system of at least one specimen. From the calculated pH-values we can monitor subacute or acute ruminal acidosis. We may identify subacute acidosis if three or more out of twelve animals have a pH of 5.5 or less, per feeding group. We collect samples for measurement at 4-8 hours after a feeding instance. The calculation and measurement may take place before or after broadcasting the data through a transmitter, to an outside observer. The calculations can be performed by a microprocessor unit, or microcomputer unit, and we can broadcast through either Wi-Fi-, radio-, Bluetooth- or any other standard communicational procedure. We can transmit raw optical results encoded in electric voltage, either analogue or digitized, or digitized numerical values.

The most general form of the device implementing the present invention comprises a sealed container 13 and a measurement unit. The sealed container 13 is filled with a hydrogen ion sensitive indicator solution inside of a chamber 4a. The chamber 4a houses an actuating piston 3a, 3b. The sealed container 13 further comprises a containment for electronics 1, including a transmitter and a battery 15 as power supply. The device is distinguished by the semi -permeable container 7 between the two measurement unit parts 6a, 6b. One measurement unit part 6a yields a light source 17 while the other measurement unit part 6b yields a light sensor 18 facing said light source 17. The semi-permeable container 7 connects to the chamber 4a, having filled with the indicator solution. With the movement of actuating piston 3a the indicator solution is pumped into and out of the semi-permeable container 7. The semi-permeable container 7 is most preferably a capillary tube of length from 0.1 to 10 cm and diameter from 0.3 to 3 cm. The dimensions of the capillary tube and the chamber 4a for the reserve of the indicator solution can be appropriately selected. As an example: the distance between the closed glass windows of the measurement unit parts 6a, 6b is 1 cm and the internal diameter of the capillary tubing is 0.12 cm, then the internal volume of the capillary tubing is 10 micro L. If the volume of the chamber 4a for the containment of the indicator solution is 1000 micro L, 100 exchanges of the indicator solution in the capillary tube may be facilitated. One may operate the exchange of the indicator solution in the capillary tube every 12th day and the device is working altogether for three years.

Another preferred embodiment of the present device is when the source of energy apart from the electric current supply to the light source and to the microprocessor is a recoverable elastic deformation of an entity or pressurised gas in a tight container.

One preferred embodiment of the present device is if another chamber 4b is included, where an actuating piston 3b moves at least one control piston 10a, 10b by pumping a fluid through common tubing made of pure plastic or composite tubes. The control piston 10a, 10b opens, closes, or periodically opens-and-closes the path of the indicator solution into the semi- permeable container 7. The actuating pistons 3a, 3b are mounted on spindles 2a, 2b, or are connected to one or two spindles 2a, 2b by means of mechanical coupling such as gears or belts. The spindle 2a, 2b is turned by a motor 11a, 1 lb, moving the actuating pistons 3a, 3b along the axis of the spindle 2a, 2b. In the most preferred embodiment, the motor 11a, 1 lb is an electric and powered by the battery 15.

Another preferred embodiment of the present device is when the indicator solution is a mixture of such indicators or a polymer of such indicator/s containing a phenol and a nitro group, chemically bound by methylene- or di-methylene-ether-groups to, for example 4-hydroxy- b enzal dhy de-acetal .

Yet another preferred embodiment of the present device is when an indicator as a mixture of indicators is utilized, or a polymer of indicator or indicators, containing a 4-nitro-phenol group chemically bound by methylene- or di-methylene-ether-groups to a vinyl-polymer of 4- hydroxy-styrene. The 4-hydroxy styrene can be replaced by 3-hydroxy styrene, 5-hydroxy styrene, 4-hydroxy-2 nitro-styrene, 5-hydroxy-2 nitro-styrene.

In a preferred embodiment of the present device the indicator solution comprises 4-hydroxy- benzaldhyde-acetal of a polyalcohol as a chemically bound phenol and nitro group.

Still another preferred embodiment of the present device is when instead of 4-hydroxy- benzaldehyde a phenol-aldehyde is utilized, like salicylaldehyde, 3-hydroxybenzaldehyde, 5- hydroxy-benzaldehyde, 4-hydroxy-2 nitro-benzaldehyde, 5-hydroxy-2 nitro-benzaldehyde, vanillin, isovanillin, protochathecu aldehyde.

A preferred embodiment of the present device utilizes 5-hydroxy-2 -nitro-benzaldehyde bound to polyvinyl alcohol with acid catalyzed acetal formation as part of the indicator solution. In one preferred embodiment of the present device the indicator solution contains a copolymer or a block copolymer of 5-hydroxy-2-nitro-benzaldehyde-polyvinylalcohol-acetal or polyvinylalcohol.

In another preferred embodiment of the present invention porous polymer membrane is used as the semi-permeable container 7, and the membrane is shaped as a hollow tube.

One preferred embodiment of the present invention has silver nano particle coating as an antibacterial measure. This peculiar embodiment is especially advantageous if a compound of organic origin is tested and monitored. Particularly the free surfaces of the perforated device 14, the measurement unit parts 6a, 6b, the semi-permeable container 7 are to be coated, as the others are encapsulated water-tight in the sealed container 13.

The invention is not restricted to the above-described embodiment. In addition to the above examples, the invention may be implemented within the scope of protection in other forms.

Claims

1. A method for acid- or base concentration measurement in a chemical compound, comprising the steps of mixing the compound with a hydrogen ion sensitive indicator solution to form a subject mixture for analysis, measuring the hydrogen ion concentration of the compound, and transmitting the measurement results to an observer, characterized in that the method includes the steps of filling the indicator solution into a perforated device (14), placing the perforated device (14) into the compound, and mixing of the compound; where the indicator solution is applied into a semi-permeable container (7), and the hydrogen ions of the compound are diffused into the semi-permeable container (7).

2. The method according to claim 1, characterized in that measuring the hydrogen ion concentration of the compound further includes the steps of passing EM radiation consisting of two or more distinct wavelengths through the subject mixture, recording the intensity of the transmitted EM radiation at the two or more distinct wavelengths, calculating the hydrogen ion concentration assuming Beer’s law, and calculating the pH value of the compound.

3. The method according to any of claims 1 to 2, characterized in that the step of filling the indicator solution into a perforated device (14) comprises the step of mixing two or more indicator functions with different EMR absorption spectra to form the indicator solution having a tuned spectrum.

4. The method according to any of claims 1 to 3, characterized in that the compound diffuses into the semi-permeable container (7) through the membrane of a hollow fiber dialyzer.

5. The method according to any of claims 1 to 4, characterized in that we place the perforated device (14) inside a living organism, and placing the perforated device (14) includes the steps of feeding the perforated device (14) to the living organism, or surgically embedding the perforated device (14) inside the living organism.

6. The method according to any of claims 1 to 5, characterized in that we place the perforated device (14) in the digestive system of a cattle specimen, and the step of transmitting the measurement results comprises the step of evaluating a probability of bovine ruminal subacute or acute acidosis, and broadcasting the results wirelessly.

7. A device for the application of the method according to claim 1 for acid- or base concentration measurement in a chemical compound, comprising a sealed container (13), a measurement unit, the sealed container (13) includes a hydrogen ion sensitive indicator solution inside of a chamber (4a), an actuating piston (3a, 3b), and a containment for electronics (1), the containment for electronics (1) comprises a battery (15), a transmitter connected to the battery (15), characterized in that the measurement unit has a semi-permeable container (7) between two measurement unit parts (6a, 6b), one measurement unit part (6a) has a light source (17), the other measurement unit part (6b) has a light sensor (18), the semi-permeable container (7) is connected to the chamber (4a), the chamber (4a) comprises an actuating piston (3a) moving the indicator solution into and out of the semi-permeable container (7), the device is a perforated device (14) embedded into a compound.

8. The device according to claim 7, characterized in that the device further includes at least one motor (11a, l ib), a spindle (2a, 2b) connected to the motor (11a, l ib), another chamber (4b) having another actuating piston (3b), and the chamber (4b) is connected through tubing (16) to a control piston (10a, 10b).

9. The device according to any of claims 7 to 8, characterized in that the indicator solution comprises a phenol and a nitro group, the phenol and the nitro group are chemically bound by methylene- or di-methylene-ether-groups.

10. The device according to any of claims 7 to 9, characterized in that the nitro group is a 4-nitro- phenol group chemically bound to a vinyl-polymer, and the vinyl-polymer is 4-hydroxy-styrene or 3 -hydroxy styrene or 5 -hydroxy styrene or 4-hydroxy -2 nitro-styrene, or 5 -hydroxy -2 nitro- styrene.

11. The device according to any of claims 7 to 9, characterized in that the chemically bound phenol and nitro group is 4-hydroxy-benzaldhyde-acetal, and the acetal is of a polyalcohol.

12. The device according to any of claims 7 to 9, characterized in that the chemically bound phenol and nitro group is a phenol-aldehyde, and the phenol-aldehyde is salicylaldehyde, or 3- hydroxybenzaldehyde, or 5-hydroxy-benzaldehyde, or 4-hydrox-2 nitro-benzaldehyde, or 5- hydroxy-2 nitro-benzaldehyde, or vanillin, or isovanillin, or protochathecu aldehyde.

13. The device according to claim 12, characterized in that the 5-hydroxy-2-nitro-benzaldehyde is bound to polyvinyl alcohol with acid catalyzed acetal formation.

14. The device according to any of claims 7 tol3, characterized in that the indicator solution comprises a copolymer or a block copolymer of 5-hydroxy-2-nitro-benzaldehyde- polyvinylalcohol-acetal, and polyvinylalcohol.

15. The device according to any of claims 7 to 14, characterized in that the semi-permeable container (7) has a porous polymer membrane, the porous polymer membrane is polypropylene or polyethersulphon, and the porous polymer membrane is a hollow tube.

16. The device according to any of claims 7 to 15, characterized in that it further comprises silver nano particle coating.

17. The device according to any of claims 7 to 16, characterized in that the indicator solution is water soluble and has molecular mass not less than 10000 dalton, preferably not less than 40000 dal ton.