08-08-2012, 03:46 PM
Application of Ammonium Sensor for Environment Analysis
[attachment=30625]
INTRODUCTION
In the context of a strict framework of the environmental
legislation, there is a great interest for continuous
monitoring of the environment quality [1]. The high demand
for complete and real time data regarding a variety of
parameters is actually more important than ever in the
complex and complete ecosystems. In such conditions, the
need for new sensors able of quick and reliable answer is
growing steadily. The most efficient fertilizers used are the
complex ones, known as “NPK” fertilizers. These contain
the major plant nutrients, “NPK” being the notation used for
total nitrogen, i.e. ammonium and nitrate concentration
together, P2O5 and K2O. In simple terms, nitrogen
compounds are used for leaf production, phosphates for root
production and potassium compounds for flowering [2].
EXPERIMENTAL
There were used PVC based selective membranes in
order to use them as reference for our determinations.
Ammonium – responsive PVC devices were obtained by
casting ammonium – doped films from tetrahydrofuran
(THF) solution over a PTFE support.
The following chemicals were used for preparing the
PVC selective solutions: PVC high molecular weight -
Breon, nonactin - Fluka, o-nitro phenyl octyl ether (o-
NOPE) – Fluka, potassium tetra phenyl borate – Fluka,
tetrahydrofuran (THF) – Fluka.
RESULTS AND DISCUSSIONS
After 24 h it occurred the separation of the ionophore
from the polyether imide membrane (PEI).
Our attempts to obtain a workable ammonium selective
membrane using PEI were unsuccessful due to poor
solubility of the ionophore within polymeric matrix as could
be observed in Figure 3.
ammonium chloride solutions. A solution of 10-1 mol.dm-3
ammonium chloride was diluted using the constant dilution
method. A Nernst response of 59.51 mV.dec-1 was
calibrated for this ISE. It was noticed that the performance
of electrodes deteriorated in time. Eventually, neither the
PVC based ISE nor the polyimide based ISE responded to
ammonium ions. Several attempts were made to reinstate the
ISE’s response by soaking the membranes in progressively
more concentrated (up to 1.0 mol.L-1) solutions of
ammonium chloride, for extended periods of time (12 h to
several days).
CONCLUSION
Rapid and reproducible analysis of fertilizers using
ISEs based on other polymer than PVC is possible. The
obtained device is shown to offer alternative solution,
capable of satisfying the increasing demand for precise
analytical information at lower cost through relatively
simple instrumentation.
Pre-calibration was found to be necessary before
analysis. Analysis using CVD method gave ammonium ion
concentrations about 10 times higher than those determined
experimentally using dip method and the manufacturer’s
values. This reinforced our previous claims that the CVD
method must be used with care.
The composition of the calibration solution should
match as close as possible that of the sample solution,
otherwise large liquid junction potentials errors may occur.
These variations in liquid junction arise due to large
differences in ionic strength between calibrant and sample
solutions, and it was believed to be true for the 2nd batch of
fertilizers and calibration standards.
[attachment=30625]
INTRODUCTION
In the context of a strict framework of the environmental
legislation, there is a great interest for continuous
monitoring of the environment quality [1]. The high demand
for complete and real time data regarding a variety of
parameters is actually more important than ever in the
complex and complete ecosystems. In such conditions, the
need for new sensors able of quick and reliable answer is
growing steadily. The most efficient fertilizers used are the
complex ones, known as “NPK” fertilizers. These contain
the major plant nutrients, “NPK” being the notation used for
total nitrogen, i.e. ammonium and nitrate concentration
together, P2O5 and K2O. In simple terms, nitrogen
compounds are used for leaf production, phosphates for root
production and potassium compounds for flowering [2].
EXPERIMENTAL
There were used PVC based selective membranes in
order to use them as reference for our determinations.
Ammonium – responsive PVC devices were obtained by
casting ammonium – doped films from tetrahydrofuran
(THF) solution over a PTFE support.
The following chemicals were used for preparing the
PVC selective solutions: PVC high molecular weight -
Breon, nonactin - Fluka, o-nitro phenyl octyl ether (o-
NOPE) – Fluka, potassium tetra phenyl borate – Fluka,
tetrahydrofuran (THF) – Fluka.
RESULTS AND DISCUSSIONS
After 24 h it occurred the separation of the ionophore
from the polyether imide membrane (PEI).
Our attempts to obtain a workable ammonium selective
membrane using PEI were unsuccessful due to poor
solubility of the ionophore within polymeric matrix as could
be observed in Figure 3.
ammonium chloride solutions. A solution of 10-1 mol.dm-3
ammonium chloride was diluted using the constant dilution
method. A Nernst response of 59.51 mV.dec-1 was
calibrated for this ISE. It was noticed that the performance
of electrodes deteriorated in time. Eventually, neither the
PVC based ISE nor the polyimide based ISE responded to
ammonium ions. Several attempts were made to reinstate the
ISE’s response by soaking the membranes in progressively
more concentrated (up to 1.0 mol.L-1) solutions of
ammonium chloride, for extended periods of time (12 h to
several days).
CONCLUSION
Rapid and reproducible analysis of fertilizers using
ISEs based on other polymer than PVC is possible. The
obtained device is shown to offer alternative solution,
capable of satisfying the increasing demand for precise
analytical information at lower cost through relatively
simple instrumentation.
Pre-calibration was found to be necessary before
analysis. Analysis using CVD method gave ammonium ion
concentrations about 10 times higher than those determined
experimentally using dip method and the manufacturer’s
values. This reinforced our previous claims that the CVD
method must be used with care.
The composition of the calibration solution should
match as close as possible that of the sample solution,
otherwise large liquid junction potentials errors may occur.
These variations in liquid junction arise due to large
differences in ionic strength between calibrant and sample
solutions, and it was believed to be true for the 2nd batch of
fertilizers and calibration standards.