GB2537881A - A method of operating a photoionisation detector to detect VOC's dissolved in water - Google Patents
A method of operating a photoionisation detector to detect VOC's dissolved in water Download PDFInfo
- Publication number
- GB2537881A GB2537881A GB1507343.0A GB201507343A GB2537881A GB 2537881 A GB2537881 A GB 2537881A GB 201507343 A GB201507343 A GB 201507343A GB 2537881 A GB2537881 A GB 2537881A
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- GB
- United Kingdom
- Prior art keywords
- water
- sensing chamber
- ionising radiation
- source
- ionisation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 49
- 238000000034 method Methods 0.000 title claims abstract description 13
- 230000005855 radiation Effects 0.000 claims abstract description 16
- 230000004044 response Effects 0.000 claims abstract description 16
- 239000012528 membrane Substances 0.000 claims abstract description 14
- 238000001514 detection method Methods 0.000 claims abstract description 9
- 150000001875 compounds Chemical class 0.000 claims abstract description 8
- 230000008859 change Effects 0.000 claims abstract description 5
- 230000001678 irradiating effect Effects 0.000 claims abstract description 5
- 238000013019 agitation Methods 0.000 claims abstract description 4
- 230000001052 transient effect Effects 0.000 claims abstract description 4
- 239000003039 volatile agent Substances 0.000 claims abstract description 4
- 230000003213 activating effect Effects 0.000 claims abstract description 3
- 230000007420 reactivation Effects 0.000 claims abstract description 3
- 239000012491 analyte Substances 0.000 claims description 12
- 239000000126 substance Substances 0.000 claims description 3
- 239000012855 volatile organic compound Substances 0.000 description 22
- 239000007789 gas Substances 0.000 description 18
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 6
- 239000000523 sample Substances 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 238000005286 illumination Methods 0.000 description 5
- 230000002209 hydrophobic effect Effects 0.000 description 4
- 239000012530 fluid Substances 0.000 description 3
- 230000006266 hibernation Effects 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 239000008346 aqueous phase Substances 0.000 description 2
- 238000005868 electrolysis reaction Methods 0.000 description 2
- 238000011067 equilibration Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000009736 wetting Methods 0.000 description 2
- 239000008096 xylene Substances 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 241001465754 Metazoa Species 0.000 description 1
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 235000012206 bottled water Nutrition 0.000 description 1
- 231100000357 carcinogen Toxicity 0.000 description 1
- 239000003183 carcinogenic agent Substances 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 230000009849 deactivation Effects 0.000 description 1
- 239000003651 drinking water Substances 0.000 description 1
- 239000000262 estrogen Substances 0.000 description 1
- 238000000855 fermentation Methods 0.000 description 1
- 230000004151 fermentation Effects 0.000 description 1
- 239000007792 gaseous phase Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000003116 impacting effect Effects 0.000 description 1
- 239000002085 irritant Substances 0.000 description 1
- 231100000021 irritant Toxicity 0.000 description 1
- 235000021056 liquid food Nutrition 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 238000005192 partition Methods 0.000 description 1
- 239000003348 petrochemical agent Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- -1 polytetrafluoroethylene Polymers 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- 125000006850 spacer group Chemical group 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 239000008399 tap water Substances 0.000 description 1
- 235000020679 tap water Nutrition 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
- 239000003643 water by type Substances 0.000 description 1
- 150000003738 xylenes Chemical class 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/62—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode
- G01N27/64—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber
- G01N27/66—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating the ionisation of gases, e.g. aerosols; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber and measuring current or voltage
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/0004—Gaseous mixtures, e.g. polluted air
- G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
- G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
- G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
- G01N33/0047—Organic compounds
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/18—Water
- G01N33/1826—Organic contamination in water
Landscapes
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Medicinal Chemistry (AREA)
- Food Science & Technology (AREA)
- Toxicology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Combustion & Propulsion (AREA)
- Sampling And Sample Adjustment (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
- Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
Abstract
A method of operating an apparatus comprising a submersible PID for the detection of volatile compounds in water 30, which detector includes a sensing chamber 20, gas permeable membrane 18 for allowing gas dissolved in the water into the sensing chamber, a source of ionising radiation 12 for irradiating the chamber and electrodes 24, 26 within the chamber for passing a current in response to ionisation of any gas therein by the ionising radiation; which method comprises activating the source intermittently and analysing the rate of change of resulting ionisation current in a transient period between each instant of reactivation of the source and a steady state current, to indicate solubility in water of any volatile compound in the chamber. A further method includes agitating the water contacting the membrane and correlating an ionisation current with a degree of agitation.
Description
A METHOD OF OPERATING A PHOTOIONISATION DETECTOR TO DETECT VOC'S DISSOLVED IN WATER
Field of the Invention
This invention relates to detection of gaseous and volatile analytes dissolved in water and other aqueous fluids using a detector within which such materials are sensed in the gaseous phase. Analytes of particular interest are volatile organic compounds (VOC's) as found in water and aqueous solutions in concentrations varying from less than a part per billion (ppb, 10-9) to parts per thousand (ppt, 10-3) by mass.
Background of the Invention
There is a need to detect and measure the presence of volatile compounds in natural and artificially contained sources of water, and in other aqueous fluids. Many such compounds are classed as volatile organic compounds, VOC's, and include irritants, oestrogens, carcinogens and other chemicals harmful to humans, animals and plant life. They are a matter of concern in marine environments, waterways, harbours, industrial process water, and waste water. They may also be of significance in other aqueous fluids such as in the detection of alcohols due to fermentation of liquid food stuffs and in brewing.
It is frequently of interest to search for the presence of gaseous species within large expanses of water, and to trace their source and extent in near real time, as for example may arise from spillage of petrochemicals into sea water. Such bodies of water are also subject to currents and drift. Therefore it is preferable for sensors which are -2 -able to detect target analytes in water to provide a fast and quantitative measurement of their concentration.
It should be noted that clean potable water contains very low or imperceptible concentrations of any VOC's, whilst polluted waters may contain any of a wide suite of VOC's. Therefore VOC in water detectors may be of most service in rapidly identifying the presence of a suite of different analytes in water, so as to confidently identify the source of VOC's before they disperse, and enable a select few samples of water to be retrieved for less time critical and more costly detailed analysis. A detector used in this way is commonly known as a screening tool.
One class of such sensors or detectors contain a membrane, typically hydrophobic, providing a barrier between the aqueous sensed environment and a detector enclosure, through which the analyte is able to diffuse. An example of such a detector can be found in GB Patent Applications 1421306.0 and 1506150.0 (incorporated herein by reference) which describe a gaseous enclosure located within a few millimetres of a preferably hydrophobic and a porous membrane separating the enclosure from water prospectively containing VOC's. The detector provides a response to VOC's in water at some gas equilibrated concentration.
The present invention concerns the operation of such a photoionisation detector for the detection of volatiles in water.
Summary of the Invention
According to a first aspect of the present invention, there is provided a method of operating an apparatus that comprises an submersible photoionisation detector for the detection of volatile compounds in water, which detector includes a sensing chamber, a gas permeable membrane for allowing gas dissolved in the surrounding water to pass into the sensing chamber, a source of ionising radiation for irradiating the sensing chamber and electrodes within the sensing chamber for passing a current in response to ionisation of any gas therein by the ionising radiation, which method comprises activating the source of ionising radiation intermittently and analysing the rate of change of the resulting ionisation current in a transient period between each instant of re-activation of the source of ionising radiation and the ionisation current subsequently reaching a steady state, the analysis providing an indication of the solubility in water of any volatile compound present in the sensing chamber.
One embodiment provides a submersible photoionisation detector for the detection of volatile compounds in water, which includes an illuminable source of ionising radiation, and is operable such that the source of illumination is turned off for a time, and then turned on for a time, the signal transient being obtained during the time of illumination being analysed, particularly in respect of its rate of decay to some steady state photoionisation current. The resulting output can be used to approximately determine the solubility of the analyte presented to the photoionisation detector.
Gas in water sensors are prone to a slow and variable response to scarcely soluble analytes. For a gas which is scarcely soluble in water, its concentration in air may be very high relative to the concentration in the aqueous phase, so that the time required for the analyte to equilibrate within the vapour space of a gas detecting sensor cavity in contact with water containing a scarcely soluble gas may be very long, even so long as to be indistinguishable from a natural changes in analyte concentration within the environment, or, indeed, to a natural change in temperature within the aqueous environment -4 -which causes a change to the equilibrium concentration of gas phase in contact with it.
In such circumstances it is known that agitation of the aqueous sample in the vicinity of the membrane separating it from a gaseous sensor cavity ensures a stable concentration at the membrane. This in turn ensures a more rapid, stable and repeatable response to a stable concentration of the analyte in the aqueous phase.
According to a second aspect of the present invention, there is further provided a method of operating an apparatus that comprises a submersible photoionisation detector for the detection of volatile compounds in water, which detector includes a sensing chamber, a gas permeable membrane for allowing gas dissolved in the surrounding water to pass into the sensing chamber, a source of ionising radiation for irradiating the sensing chamber, and electrodes within the sensing chamber for passing a current in response to ionisation of any gas therein by the ionising radiation, which method comprises providing an agitator for variably agitating the water in contact with the gas permeable membrane, and correlating the ionisation current flowing through the sensing electrode with the degree of agitation to provide an indication of the chemical identity (solubility, volatility or diffusability) of the analyte in water.
Brief Description of the Drawings
The invention will now be described in more detail by reference to the drawings provided.
Figure 1 shows a schematic representation of a volatile in water sensor as used in the present invention, and Figures 2 and 3 are graphs that illustrate the effect of pulsed illumination on the DID response. -5 -
Description of Embodiments
Hereinafter for convenience an electrode at which negative ions are attracted and neutralised, at which hydrogen may also be generated due to the electrolysis of water, will be referred to as a cathode, and an electrode to which positive ions are attracted, and at which oxygen may also be generated as a consequence of the electrolysis of water, shall be referred to as an anode.
Turning now to Figure 1, the schematic representation shows a section through a BID cell. The BID cell is similar to that of GB 2449664, which is incorporated herein by reference, in that it contains a UV light source 12 arranged adjacent a gas sensing chamber 20 and separated by means of a UV transparent window 22.
Inside the chamber 20 is a stack of at least three electrodes, consisting of a pair of sensing electrodes, 24 and 26, and a third electrode 28, referred to here, as the fence electrode. The fence electrode is sandwiched between the first and second sensing electrodes, the first sensing electrode (cathode) 24 being furthest from the UV light source and the second sensing electrode (anode) 26 being adjacent the window 22 separating the light source from the sensing chamber.
The illustrated apparatus, like that of GB1421306.0, differs from GB 2449664 in that the DID cell is adapted for use in submerged situations. The sensing chamber 20 is sealed from the sample liquid 30 by means of a, preferably hydrophobic, gas permeable membrane 18. . As described in GB1421306.0, the membrane allows an analyte in the sensing chamber 20 to reach near equilibrium with the concentration of the analyte in the adjoining liquid phase of the sample liquid 30. -6 -
The PID then measures the concentration of analyte inside the sensing chamber 20, which is indicative of the concentration of analyte in the sample liquid 30 by virtue of the equilibrium condition. The mechanism by which the PID measures the analyte concentration is essentially the same as when used in non-submerged conditions and need not therefore be described in further detail in the present context.
In addition, the electrodes (24,26,28) may be supported and separated by spacers made of a low dielectric hydrophobic material such as polytetrafluoroethylene. This forms a substantial portion of the walls of the sensing chamber 20 and serves to reduce the wetting effect of condensation. Wetting of the walls should be avoided since it permits conduction of currents between the sensing electrodes negatively impacting the accuracy of the sensor.
In a first embodiment of the present invention, the radiation source 12 is pulsed or intermittently switched on and off. Lamp pulse control is provided as a prospective means of discrimination of PID responses to VOC's which partition -chemically equilibrate -between water and air to differing extents, as expressed by Henry's Law constant, kn.
Figures 2 and 3 illustrate the effect of pulsed illumination on the PID response, in 1L bottles of water at 23 c"C containing 0.1 ppm mixed xylenes, and 40 ppm 1-butanol, for which the steady state responses were respectively 49 and 52 my vs fresh tap water. The lamp pulse control was set to lOs on variable hibernation times, and the '10s response' was taken as the last powered PID reading before cell deactivation. -7 -
The enhanced response to certain VOC's appears to relate to the Henry's Law constant for the gas: the fixed volume of the gas cavity within the PID in water probe demands, of water containing a VOC whose Henry Law constant is low, a very large volume of water for VOC equilibration.
This is the case for xylene for which 1:11 is 0.2 mol.ID.atm-. Correspondingly, the fixed volume of the gas cavity within the PID in water probe demands, of water containing a VOC whose Henry Law constant is high, the VOC from a relatively small volume of water for VOC equilibration. This is the case for 1-butanol, for which kH is 130 mol.L.atml. In the former case, VOC is destroyed by photoionisation at a rate comparable to the rate of supply of the VOC to the PID cavity. In the latter case, the rate of removal of the VOC by photoionisation is negligible compared to the rate at which VOC can be supplied by water containing it. Thus episodes of not powering the PID cause different relative enhancement in response.
In deploying stepped lamp illumination, lamp re-ignition is liable to vary over a few seconds. To suppress this effect, it is preferable to impose hibernation times of at least 60s, and to measure the effect of hibernation on response after at least 10s. -8 -
Claims (2)
- Claims 1. A method of operating an apparatus that comprises an submersible photoionisation detector for the detection of volatile compounds in water, which detector includes a sensing chamber, a gas permeable membrane for allowing gas dissolved in the surrounding water to pass into the sensing chamber, a source of ionising radiation for irradiating the sensing chamber and electrodes within the sensing chamber for passing a current in response to ionisation of any gas therein by the ionising radiation, which method comprises activating the source of ionising radiation intermittently and analysing the rate of change of the resulting ionisation current in a transient period between each instant of re-activation of the source of ionising radiation and the ionisation current subsequently reaching a steady state, the analysis providing an indication of the solubility in water of any volatile compound present in the sensing chamber.
- 2. A method of operating an apparatus that comprises a submersible photoionisation detector for the detection of volatile compounds in water, which detector includes a sensing chamber, a gas permeable membrane for allowing gas dissolved in the surrounding water to pass into the sensing chamber, a source of ionising radiation for irradiating the sensing chamber, and electrodes within the sensing chamber for passing a current in response to ionisation of any gas therein by the ionising radiation, which method comprises providing an agitator for variably agitating the water in contact with the gas permeable membrane, and correlating the ionisation current flowing through the sensing electrode with the degree of agitation to provide an indication of the chemical identity (solubility, volatility or diffusabilty) of the analyte in water.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1507343.0A GB2537881A (en) | 2015-04-29 | 2015-04-29 | A method of operating a photoionisation detector to detect VOC's dissolved in water |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1507343.0A GB2537881A (en) | 2015-04-29 | 2015-04-29 | A method of operating a photoionisation detector to detect VOC's dissolved in water |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB201507343D0 GB201507343D0 (en) | 2015-06-10 |
| GB2537881A true GB2537881A (en) | 2016-11-02 |
Family
ID=53488884
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1507343.0A Withdrawn GB2537881A (en) | 2015-04-29 | 2015-04-29 | A method of operating a photoionisation detector to detect VOC's dissolved in water |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2537881A (en) |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1059530A2 (en) * | 1999-06-11 | 2000-12-13 | Rae Systems, Inc. | Multiple channel photo-ionization detector for simultaneous and selective measurement of volatile organic compounds |
| EP2458375A1 (en) * | 2010-11-30 | 2012-05-30 | General Electric Company | Photo-ionization detectors and associated methods thereof |
| US8383046B1 (en) * | 2007-04-16 | 2013-02-26 | Murthy Tata | Analyzer apparatus for measuring dissolved volatile substances and method |
| GB2527867A (en) * | 2014-12-01 | 2016-01-06 | Ion Science Ltd | Detection of organics in water |
-
2015
- 2015-04-29 GB GB1507343.0A patent/GB2537881A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1059530A2 (en) * | 1999-06-11 | 2000-12-13 | Rae Systems, Inc. | Multiple channel photo-ionization detector for simultaneous and selective measurement of volatile organic compounds |
| US8383046B1 (en) * | 2007-04-16 | 2013-02-26 | Murthy Tata | Analyzer apparatus for measuring dissolved volatile substances and method |
| EP2458375A1 (en) * | 2010-11-30 | 2012-05-30 | General Electric Company | Photo-ionization detectors and associated methods thereof |
| GB2527867A (en) * | 2014-12-01 | 2016-01-06 | Ion Science Ltd | Detection of organics in water |
Also Published As
| Publication number | Publication date |
|---|---|
| GB201507343D0 (en) | 2015-06-10 |
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| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |