ES2388976A1 - Autonomous equipment for the measurement of ph in sea water. (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Autonomous equipment for ph measurement in seawater. The present invention relates to an autonomous equipment for ph measurement of the type of ph measurement sensor in marine environment characterized in that it comprises elements that allow the injection of the sample and indicator (4) independent of external environmental conditions, elements to facilitate the elimination of bubbles (6), elements to eliminate the effects of pressure change (16) due to the movement of the equipment in aquatic environment and electronic elements (17) that allow to reduce the electrical consumption. The present invention provides an autonomous equipment for the measurement of ph in surface and deep water capable of taking measurements at different depths and supplying the data in real time. (Machine-translation by Google Translate, not legally binding)

Description

Autonomous equipment for pH measurement in seawater

The present invention relates to a stand-alone device for the measurement of pH of the pH type sensor in marine environment.

The pH of surface waters has decreased 0.1 units since the beginning of the industrial revolution, in the 19th century, and will continue to decrease as a result of the increase in carbon dioxide emissions, reaching values at the end of this century of 0.2-0.3 units lower than the current ones (Orr et al., 2005). This decrease may have a great impact on marine ecosystems and could also result in a decrease in the ability to capture CO2 from the oceans (Sabine et al., 2004), affecting the global organic and inorganic carbon cycle (Feely et al., 2004). The measurements made in large-scale ocean time series stations confirm a decrease of 0.02 pH units per decade (IPCC, 2007; Santana-Casiano et al., 2007). To understand and predict the exchange of atmosphere-ocean carbon and from surface waters to the deepest waters, new and improved autonomous equipment is needed that is capable of determining the characteristic parameters of the carbon system with great precision and high temporal resolution. that is, pH, total alkalinity of seawater, total dissolved inorganic carbon content and partial pressure of carbon dioxide (pC02).

Currently, the specific pH measurements of surface and deep water are carried out using spectrophotometric measurement systems installed in oceanographic vessels. The maintenance of observations through oceanographic campaigns is a highly expensive activity and depends largely on the availability of ships capable of working in the Atlantic waters. To reduce costs and maintain a large-scale data record capable of predicting future trends, in the face of a changing world, a possible solution could be the establishment of a network of fixed ocean stations using anchored buoys, at strategic oceanic points (p (eg oceanic platforms), capable of performing high frequency measurements and daily pH and pC02 resolution, for this, new autonomous measuring equipment is required that can take measurements at different depths and that, through telemetry, provide real-time data .

The present invention provides autonomous equipment for pH measurement in water

Superficial and deep capable of taking measurements at different depths and providing data in real time.

Background of the invention

Nakano et al. (2006) developed a spectrophotometric system capable of obtaining vertical pH and pC02 profiles in the first 1000 m depth from an oceanographic ship. In this same sense, the SEAS instrument designed by the group led by R. Byme (Liu et al., 2006) allows the measurement of pH and other parameters of the carbonate system in seawater and freshwater with an accuracy of ± 0.0014 in The column of sea water. Both systems have a high energy consumption which makes them valid for use in oceanographic ships and limits their use in oceanographic buoys.

The SAMI-pH sensor (Submersible Autonomous Moored Instrument, autonomous submersible anchoring instrument) improved over a first version (DeGrandpre et al., 1995; Martz et al., 2003) uses a new flow cell system, mixing and of detection (Seidel et al., 2008). The Sunburst Sensor, LC company manufactures this sensor using m-Creso! Purple as an indicator, a commercial static mixer instead of a rolled tube for mixing the indicator and sample, and a commercial type Z flow cuvette. The spectrophotometric detection system is replaced by three silica detector photodiodes with interference filters connected to the flow cell by optical fiber. In the new design a 50! -! 1 low power pulse solenoid pump is used that drives the sample and the indicator towards the measuring cuvette.

US5283767A describes an oceanographic profiler that moves to different

depths measuring temperature, salinity (conductivity), etc., with inclusion

current of an oxygen sensor, which emits data via satellite. Does not measure pH or others

carbon parameters.

US6356205B 1 discloses a system for monitoring the quality of water from wells, but which does not have associated the development of a pH sensor.

Patent ES2209641Al describes a system for the remote acquisition of oceanographic data consisting of an autonomous buoy for the registration of variables in

Study under the control of a remote operator or a data processing center. Without

However, a sensor is not developed, and in particular a measurement sensor of the

pH

On the other hand, US20050207939 describes a system for quality measurement.

of the water comprising a plurality of sensors including one of pH level but

which corresponds to a commercial electrochemical that uses an electrode combined with

5

epoxy membrane not applicable to the marine environment.

The main characteristics of the autonomous equipment for pH measurement in seawater,

which is intended to protect, which are not included in the state of the art are that allows

act intelligently to detect pressure changes due to movements

randomized oceanographic buoys and counteract them, detect and eliminate bubbles from

1 o

air that interfere with the measurement and produces independent measurements of both the effects of

indicator on the actual value of the sample as of the age of the indicator.

Summary of the invention

The present invention relates to autonomous equipment for the measurement of pH of the type

pH measurement sensor in marine environment characterized by comprising elements that

fifteen

allow the injection of the sample and indicator (4) independent of conditions

external environmental elements to facilitate the elimination of bubbles (6), elements

to eliminate the effects of pressure change (16) due to the movement of the equipment in

aquatic environment and electronic elements (17) that allow reducing electricity consumption.

According to the invention, the mixing of the indicator and sample is carried out by means of a tube

twenty

rolled (4) 2 meters long and 0.3 mm internal diameter to improve the

mixing and distribution of the indicator, being located inside a block

metallic in direct contact with the walls of the equipment to conserve the temperature

Initial sample.

It is also characteristic of the invention that a tube (6) 8 mm long and

25

1 O cm long between the measuring cuvette (7) and the peristaltic pump (1) to dampen the

Pulsating effects of the peristaltic pump (1) and facilitate the elimination of bubbles under the

vacuum action on the equipment.

It is also characteristic of the invention that the peristaltic pump (1) has a

second channel (16) that isolates the water to be analyzed, to eliminate effects of changes in

30

   pressure due to the movement of the equipment in marine environment.

According to the invention, the autonomous equipment has a pressure sensor (10)

located between the peristaltic pump (1) and the tube (6) located after the measuring cuvette (7), which regulates the pressure to a lower value than the external pressure.

It is also characteristic of the invention that the autonomous team has a system

electronic (17) that controls all the functions of the equipment and that allows the realization of

more than 40 pH measurements at different amounts of indicator for the same sample and

eliminates the effect of the indicator on the final pH reading.

It is also characteristic of the invention that the autonomous equipment uses as a source

light a spectrophotometric lamp (12), as it increases the intensity of light

emitted in the low visible range (380-450 nm) and facilitates the realization of total spectra.

Description of the figures

Figure 1 is a schematic representation of the elements that make up the autonomous equipment for pH measurement in seawater.

Detailed description of a preferred embodiment of the invention

Although the invention is described in terms of a specific preferred embodiment, it will be

easily apparent to those skilled in this art that can be made diverse

modifications, redispositions and replacements. The scope of the invention is defined by

the claims attached thereto.

The equipment uses a two-channel peristaltic pump (1), one channel in the system inlet (2) and the other at the end of the path (3) that aspirates the seawater sample. Two speeds of action are used, one high for the processes of cleaning and elimination of possible bubbles and another slow in the measurement phase, indicator injection, mixing and displacement of the sample through the spectrophotometric measurement system. The indicator injection is performed with the peristaltic pump (1) stopped and having created a controlled depression and changing the position of the three-way membrane valve (11) for a period that can be adjusted. Once injected, the position of the valve is switched and pushed into the rolled tube (4) by the action of the peristaltic pump (1), where the mixing takes place.

The mixture of indicator and sample is carried out using a rolled tube (4) of two meters long and 0.3 mm internal diameter since this system allows to improve both the quasi-Guasian mixture and distribution of the indicator as well as the ease of cleaning and

Preparation for the next measure. The tube is located inside a

metal block in direct contact with the walls of the equipment to conserve in all

moment the initial temperature of the sample and that is not affected by changes due

to gradients inside the device. A silicone tube (6) of 8 mm diameter and

5

1 cm long it is placed after the measuring cup type Z (7) and just before pump

peristaltic (1) to dampen the pulsating effects of the peristaltic pump (1) and facilitate

the elimination of bubbles under the action of vacuum on the equipment. To perform the vacuum, the

two-way solenoid valve (8) closes, and at this time the solenoid valve opens

two-way (9) recirculating water through the second channel of the peristaltic pump (1),

1 o

isolating the system from the outside and producing a vacuum that increases the size of any

bubble and facilitates its removal once the two-way solenoid valve is opened again

(8) (the two-way solenoid valve (9) returns to its initial position of always closed) and

circulate water through the circuit at low revolutions.

To eliminate effects of pressure changes due to sensor movement in the middle

fifteen

marine, the second channel (16) of the peristaltic pump (1) that isolates the water has been included

be analyzed as well as a pressure sensor (10) that regulates the pressure to a value lower than

external pressure To do this, the two-way solenoid valve (8) closes and the valve

Two-way solenoid (9) opens, and at low speed the peristaltic pump (1) occurs

a slight vacuum that is controlled to a value lower than the external one in 50 mbars accompanied

twenty

of a slight compression of the silicone tube (6). Once that internal pressure has been reached in

the equipment, the return to the original position of the solenoid valves keeps that depression

generated during the measurement process and not affected by external changes. That depression

allows the opening of the three-way membrane valve (11) to inject the

indicator (purple m-cresol, 5.6 mM in 0.7 M NaCl) from a 500 ml kevlar bag (5)

25

in times that can be varied according to the initial concentration of indicator.

The equipment uses a spectrophotometric lamp (12) as a light source, since

increases the intensity of light emitted in the low visible range (380-450 nm) and facilitates the

realization of total spectra, unlike other existing designs that perform

measures at fixed lengths. The spectrophotometric detector (13) is compact, without units

30

mobile, to avoid possible effects of the marine environment if it is installed in a

oceanographic buoy. The light source is connected to the measuring cup type Z (7) and

   This is with the spectrophotometric detector (13) by means of optical fiber (14) of 600 ... mt (25 cm).

The measuring cup type Z (7) is placed on a metal block (15) to maintain the

temperature at the initial measurement.

The measurement process begins with a period of system heating

spectrophotometric about one minute. Subsequently we proceed to a

5

equipment washing by passing the seawater to be analyzed at high speed, making use

of the peristaltic pump (1) for approximately 20 seconds. With high speed, it

closes the bypass valve (8) and the bypass valve (9) is opened, producing an action of

vacuum that eliminates possible bubbles that may exist in the passage of light and tubes

connectors At low speed of the peristaltic pump (1) seawater is recirculated a

1 o

once the valves are returned to their initial position favoring the passage of seawater and the

Drag the possible bubbles for approximately 20 seconds. At this time

a zero is made by closing the lamp shutter. Then

and alternating slow displacements of seawater and stops it is verified that the reading

of seawater bills without indicator (white) is constant regardless of whether

fifteen

There is or not displacement. Finally, a rapid passage of the peristaltic pump is performed (1)

to verify that there are no bubbles that affect the number of detector accounts

spectrophotometric (13). If not, a new cleaning process would take place

including the realization of vacuum. A normal cycle of cleaning and bubble detection

It lasts about 2 minutes. At that time the two valve closes again

twenty

tracks (9) and the two-way valve (8) is opened for, at slow speed of the peristaltic pump

(1), generate a depression in the system. Next, and with the peristaltic pump (1)

stopped, the injection into the water flow of a quantity of indicator is produced by

the opening of the three-way valve (11) for a period that can be adjusted. One time

injected, the three-way valve (11) is closed and pushed into the rolled tube (4) by

25

action of the peristaltic pump (1) where the mixture is produced reaching a

distribution that at its back allows measuring absorbance ratios and pH

of seawater in more than 40 points of the mixture. For this, the electronic system (17)

it follows the evolution of the absorbance of the basic form detecting its maximum value and

starting to measure pH values in the range of absorbances at the isosbestic point

30

between 0.6 and 0.15. The corresponding pH measurements of each of the registers

made are used to calculate the corresponding line obtained when represented against

to the absorbance of the isosbestic point. The ordinate at the origin of said line provides the

   pH of the analyzed seawater sample without the disturbing effect of the added indicator

for each sample analyzed. The standard deviation of the residuals between the line obtained and the experimental values is always less than ± 0.0004. In the measurement phase, as the sea-indicator water mixture moves at a low speed due to the peristaltic pump (1), the spectrophotometric system takes approximately

5 40 measurements throughout its passage following the evolution of the mixture. The equipment eliminates absorbance readings greater than 0.6 (adjustable) for the 578 nanometer peak and takes measurements until the absorbance of the isosbestic peak is 0.15 (adjustable). Subsequently, it calculates the pH for each reading and calculates the ordinate at the origin of the values.

10 The electronic system (17) of the equipment controls all the sequencing, opening and closing the valves, activating the peristaltic pump (1) and activating the spectrophotometric detector (13). The ignition of the spectrophotometric lamp (12) is carried out at the beginning of each measurement to favor its stability and is maintained for 6 minutes on average. Only when the peristaltic pump (1) is operated at a higher speed does the

15 consumption rises to 1.1 Amp. While in the rest of the processes its consumption is less than 1 Amp. Outside the measurement process the equipment is at rest with a consumption of less than 0.05 Amp. In this state, only the micro-controller unit remains active.

(17) and communication. Considering a pH measurement every hour as the most usual determination value in an oceanographic buoy, this implies a consumption of less than 0.2 Amp / h.

twenty

Claims (8)

1.-Autonomous equipment for pH measurement of the pH sensor type sensor in marine environment characterized in that it includes elements that allow the injection of the sample and indicator (4) independent of external environmental conditions, elements to facilitate the elimination of bubbles ( 6), elements to eliminate the effects of pressure change (16) due to the movement of the equipment in an aquatic environment and electronic elements (17) that allow reducing the electrical consumption. 2. -Autonomous equipment for pH measurement according to claim 1, characterized in that the mixing of the indicator and sample is carried out by means of a rolled tube (4) of 2 meters long and 0.3 mm internal diameter for the improvement of the mixture and distribution of the indicator. 3. Autonomous equipment for pH measurement according to claim 2, characterized in that the mixing tube (4) is located inside a metal block in direct contact with the walls of the equipment to maintain the initial temperature of the sample. 4.-Autonomous equipment for pH measurement according to claim 1, characterized in that a tube (6) 8 mm long and 1 O cm long is placed between the measuring cuvette (7) and the peristaltic pump (1) for cushion the pulsating effects of the peristaltic pump (1) and facilitate the elimination of bubbles under the action of vacuum on the equipment. 5. Autonomous equipment for pH measurement according to claim 1, characterized in that the peristaltic pump (1) has a second channel (16) that isolates the water to be analyzed, to eliminate effects of pressure changes due to the movement of the equipment In half man. 6. -Autonomous equipment for pH measurement according to claim 1, characterized in that it has a pressure sensor (10) located between the peristaltic pump (1) and the tube (6) located after the measuring cuvette (7), which regulates the pressure to a value lower than the external pressure. 7. Autonomous equipment for pH measurement according to claim 1, characterized in that it has an electronic system (17) that allows more than 40 pH measurements to be made at different amounts of indicator for the same sample and eliminates the effect of the indicator in the final pH reading.
8. Autonomous equipment for pH measurement according to claim 1, characterized in that it uses a spectrophotometric lamp (12) as a light source, since it increases the intensity of light emitted in the visible low range (380-450 nm) and facilitates the realization of total spectra.