Difference between revisions of "Nutrient analysers"

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==Introduction==
 
==Introduction==
Nutrient analysers are [[oceanographic instruments]] to measure the concentration of certain [[nutrient]]s [[in situ]]. While most measurements of nutrients are still made by taking water samples for later analysis in the lab a variety of [[in situ]] instruments has become available that automatically measure nutrient concentrations at pre-programmed intervals. These instruments allow a much higher temporal resolution of measurements than what can be achieved by taking samples.
+
Nutrient analyzers are [[oceanographic instruments]], which measure the concentration of certain [[nutrient]]s [[in situ]]. While most measurements of nutrients are still made by taking water samples for later analysis in the lab, a variety of [[in situ]] instruments have become available that automatically measure nutrient concentrations at pre-programmed intervals. These instruments allow a much higher temporal resolution of measurements than what can be achieved by taking samples.
  
Most of the nutrient analysers are based on proven wet-chemical laboratory analysis methods. In recent years nitrate analysers based on the absorbance of ultraviolet light by nitrate in water have been introduced.  
+
Most of the nutrient analyzers are based on proven wet-chemical laboratory analysis methods. In recent years, nitrate analyzers, based on the absorbance of ultraviolet light by nitrate in water, have been introduced.  
  
==Wet chemical analysers==
+
==Wet chemical analyzers==
A variety of wet chemical nutrient analysers exist on the market. These analysers draw in sample water and mix it with a reagent (or reagents). The resulting solution develops a characteristic property (e.g. colour complex or fluorescence) depending on the concentration of the target analyte, that is then measured in an absorption cell (colour complex) or by a light source and photodetector (fluorescence). In some cases heating of the solution is required to speed up development.
+
A variety of wet chemical nutrient analyzers exist on the market. These analyzers draw in sample water, which is then mixed with a reagent (or reagents). The resulting solution develops an attributive property (e.g. color complex or fluorescence) depending on the concentration of the target analyte, which is then measured either in an absorption cell (color complex) or by a light source and photodetector (fluorescence). In some cases, heating of the solution is required to speed up the development.
  
Depending on the chemical protocols followed (i.e. if heating and/or preconcentration steps are needed), the time response (time between independent measurements) is on the order of a few seconds to minutes.  
+
Depending on the chemical protocols followed (i.e. if heating and/or pre-concentration steps are needed), the time response (time between independent measurements) is on the order of a few seconds to minutes.  
  
Parameters limiting the deployment time of wet-chemical analysers are reagent consumption, reagent degradation time, available electrical energy (batteries) and [[biofouling]].
+
Parameters limiting the deployment time of wet-chemical analyzers are reagent consumption, reagent degradation time, available electrical energy (batteries) and [[biofouling]].
  
A distinct advantage of wet-chemical analysers is the capability of conducting [[in situ]] calibrations by piping a blank or standard solution of known concentration into the analyser instead of the sample. Any instrument drift can be detected and the measurements corrected for the drift.  
+
A distinct advantage of wet-chemical analyzers is their capability to conduct [[in situ]] calibrations by piping a blank or standard solution of known concentration into the analyzer instead of the sample. Any instrument drift can be detected and the measurements can be corrected for the drift.  
  
[[Nutrient]]s that can be measured [[in situ]] include dissolved nitrate, nitrite, ammonia, phosphate and silicate (see "external links" to companies below for details).
+
[[Nutrient]]s that can be measured [[in situ]] include dissolved nitrate, nitrite, ammonia, phosphate, and silicate (see "external links" to companies below for details).
  
==Optical nitrate analysers==
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==Optical nitrate analyzers==
Optical nitrate analysers use the property of dissolved nitrate that it absorbs ultraviolet light. The instrument consists of a light source (deuterium lamp of flash lamp), collimating optics, a light path through the sample water and a spectrometer with photodetector. The resulting absorption spectra have to be analysed (either by an on-board computer or after data recovery) as other constituents in the seawater also absorb ultraviolet light. (For details see Johnson & Colleti (2002<ref>Johnson, K.S., Coletti, L.J., 2002. In situ ultraviolet spectrophotometry for high resolution and long-term monitoring of nitrate, bromide and bisulfide in the ocean. Deep-Sea Research I 49, 1291-1305.</ref>))
+
Optical nitrate analyzers use the property of dissolved nitrate to absorb ultraviolet light. The instrument consists of a light source (deuterium lamp of flash lamp), collimating optics, a light path through the sample water, and a spectrometer with a photo detector. The resulting absorption spectra have to be analyzed (either by an on-board computer or after data recovery) as other constituents in the seawater also absorb ultraviolet light. (For details see Johnson & Colleti (2002<ref>Johnson, K.S., Coletti, L.J., 2002. In situ ultraviolet spectrophotometry for high resolution and long-term monitoring of nitrate, bromide and bisulfide in the ocean. Deep-Sea Research I 49, 1291-1305.</ref>))
  
Optical nitrate analysers do not require any chemical reagents and have a very fast response (on the order of 1 s) and therefore are also suitable for measurements during profiling work, on towed vehicles and AUV's. The detection limits depend on the length of the optical absorption path, generally these instruments are not well suited for low nitrate concentrations (< 1 umol).  
+
Optical nitrate analyzers do not require any chemical reagents and have a very fast response time (on the order of 1 s) making them very suitable for measurements conducted during profiling work, or those done on towed vehicles and AUV's. The detection limitations depend on the length of the optical absorption path Generally, these instruments are not well suited for low nitrate concentrations (< 1 umol).  
  
The deployment time of the optical instruments is limited by available electrical energy (batteries) and [[biofouling]] (though for some instruments anti-biofouling measures can be added).  
+
The deployment time of the optical instruments is limited by the availability of electrical energy (batteries) and [[biofouling]] (though for some instruments anti-biofouling measures can be added).  
  
 
==See also==
 
==See also==

Revision as of 11:26, 28 October 2009

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This article is recommended by the editorial team.

This article discusses two types of analysers to measure nutrients: a wet chemical analyser and an optical nitrate analyser. A nutrient analyser is an example of an oceanographic instrument to measure the concentration of certain nutrients (e.g. nitrate, nitrite, ammonia, phosphate and silicate) in situ.

Back to Instruments and sensors to measure environmental parameters

Introduction

Nutrient analyzers are oceanographic instruments, which measure the concentration of certain nutrients in situ. While most measurements of nutrients are still made by taking water samples for later analysis in the lab, a variety of in situ instruments have become available that automatically measure nutrient concentrations at pre-programmed intervals. These instruments allow a much higher temporal resolution of measurements than what can be achieved by taking samples.

Most of the nutrient analyzers are based on proven wet-chemical laboratory analysis methods. In recent years, nitrate analyzers, based on the absorbance of ultraviolet light by nitrate in water, have been introduced.

Wet chemical analyzers

A variety of wet chemical nutrient analyzers exist on the market. These analyzers draw in sample water, which is then mixed with a reagent (or reagents). The resulting solution develops an attributive property (e.g. color complex or fluorescence) depending on the concentration of the target analyte, which is then measured either in an absorption cell (color complex) or by a light source and photodetector (fluorescence). In some cases, heating of the solution is required to speed up the development.

Depending on the chemical protocols followed (i.e. if heating and/or pre-concentration steps are needed), the time response (time between independent measurements) is on the order of a few seconds to minutes.

Parameters limiting the deployment time of wet-chemical analyzers are reagent consumption, reagent degradation time, available electrical energy (batteries) and biofouling.

A distinct advantage of wet-chemical analyzers is their capability to conduct in situ calibrations by piping a blank or standard solution of known concentration into the analyzer instead of the sample. Any instrument drift can be detected and the measurements can be corrected for the drift.

Nutrients that can be measured in situ include dissolved nitrate, nitrite, ammonia, phosphate, and silicate (see "external links" to companies below for details).

Optical nitrate analyzers

Optical nitrate analyzers use the property of dissolved nitrate to absorb ultraviolet light. The instrument consists of a light source (deuterium lamp of flash lamp), collimating optics, a light path through the sample water, and a spectrometer with a photo detector. The resulting absorption spectra have to be analyzed (either by an on-board computer or after data recovery) as other constituents in the seawater also absorb ultraviolet light. (For details see Johnson & Colleti (2002[1]))

Optical nitrate analyzers do not require any chemical reagents and have a very fast response time (on the order of 1 s) making them very suitable for measurements conducted during profiling work, or those done on towed vehicles and AUV's. The detection limitations depend on the length of the optical absorption path Generally, these instruments are not well suited for low nitrate concentrations (< 1 umol).

The deployment time of the optical instruments is limited by the availability of electrical energy (batteries) and biofouling (though for some instruments anti-biofouling measures can be added).

See also

Internal links

External links

  • Satlantic Optical nitrate analysers, water quality monitor. Accessed 14.5.2007
  • TriOS Optical Sensors Optical nitrate analysers. Accessed 14.5.2007
  • Systea S.p.a., wet chemical nutrient analysers. Accessed 14.5.2007
  • SubChem Systems Inc., submersible chemical analysers for nutrients, trace metals. Accessed 14.5.2007
  • YSI Inc., nutrient analysers. Accessed 14.5.2007
  • EnviroTech LLC, nutrient analysers. Accessed 14.5.2007
  • Alliance for Coastal Technologies, database of instruments for studying and monitoring of the coastal environment, technology evaluations, needs & use assessments. Accessed 14.5.2007

Further reading

  • Grasshoff, K., Kremling, K., Erhardt, M. (eds.) (1999), Methods of Seawater Analysis, Wiley-VCH, 600 pp., ISBN: 978-3527295890
  • Hanson, A.K., Donaghay, P.L., 1998. Micro- to fine-scale chemical gradients and layers in stratified coastal waters. Oceanography, 11(1), 10-17.
  • Johnson, K.S., J.A. Needoba, S.C. Riser, W.J. Showers, 2007. Chemical Sensor Networks for the Aquatic Environment, Chem. Rev., 107, 623-640.

References

  1. Johnson, K.S., Coletti, L.J., 2002. In situ ultraviolet spectrophotometry for high resolution and long-term monitoring of nitrate, bromide and bisulfide in the ocean. Deep-Sea Research I 49, 1291-1305.
The main authors of this article are Schroeder, Friedhelm and Prien, Ralf
Please note that others may also have edited the contents of this article.