The Magdalena Ridge Observatory Interferometer (MROI) has completed its design phase and is currently in the
construction phase. The first telescope will be deployed at the MROI site in 2011. Five different vendors are involved
in the design and fabrication of a unit telescope, and a much larger number for the full observatory.
This paper addresses the steps that the MRO Interferometry project will undertake to integrate subsystems developed by
different parties, through commissioning into an operational optical interferometer.
Finally we present the commissioning plan to bring the interferometer to an operational mode. We have developed
"performance verification milestones" that successively increase the "science readiness" of the interferometer and
transitions to an operational phase.
The Magdalena Ridge Observatory Interferometer is a 10 x 1.4 meter aperture long baseline optical and near-infrared
interferometer being built at 3,200 meters altitude on Magdalena Ridge, west of Socorro, NM. The interferometer layout
is an equilateral "Y" configuration to complement our key science mission, which is centered on imaging faint and
complex astrophysical targets. This paper serves as an overview and update on the status of the observatory and our
progress towards first light and first fringes in 2012.
KEYWORDS: Mirrors, Telescopes, Mechanical engineering, Fourier transforms, Optical benches, Interferometers, Spectrographs, Aluminum, Beam splitters, Simulation of CCA and DLA aggregates
We report on the mechanical design currently performed at the Magdalena Ridge Observatory
Interferometer (MROI) and how the construction, assembly, integration and verification are planned
towards commissioning. Novel features were added to the mechanical design, and high level of automation
and reliability are being devised, which allows the number of reflections to be kept down to a minimum
possible. This includes unit telescope and associated enclosure and transporter, fast tip-tilt system, beam
relay system, delay line system, beam compressor, automated alignment system, beam turning mirror,
switchyard, fringe tracker and vacuum system.
We present the verification procedure for the 1.4 meter primary mirrors of the Magdalena Ridge Observatory
Interferometer (MROI). Six mirrors are in mass production at Optical Surface Technologies (OST) in Albuquerque.
The six identical parabolic mirrors will have a radius of curvature of 6300 mm and a final surface wavefront quality of
29 nm rms.
The mirrors will be tested in a tower using a computer generated hologram, and the Intellium™ H2000 interferometer
from Engineering Synthesis Design, Inc. (ESDI). The mirror fabrication activities are currently in the early stage of
polishing and have already delivered some promising results with the interferometer. A complex passive whiffle tree
has been designed and fabricated by Advanced Mechanical and Optical Systems (AMOS, Belgium) that takes into
account the gravity loading for an alt-alt mount. The final testing of the primary mirrors will be completed with the
mirror cells that will be used in the telescopes.
In addition we report on shear tests performed on the mirror cell pads on the back of the primary mirrors. These pads are
glued to the mirror. The shear test has demonstrated that the glue can withstand at least 4.9 kilo Newton. This is within
the requirements.
We report on the design, application, and testing of custom protected silver and aluminum coatings for use on the Magdalena Ridge Observatory Interferometers (MROI) unit telescopes. The coatings were designed by Optical Surface Technologies (OST), and tested under normal observational conditions on Magdalena Ridge. Mirror coating samples fabricated by OST were given to MRO, and then placed in an insulated automated enclosure at the observatory site. Within the enclosure, environmental conditions such as temperature and humidity were continuously monitored. The automated enclosure was instructed to open during the night dependent upon weather conditions matching those that would occur under normal operations of the interferometer. This paper tracks the affect of the Magdalena Ridge environment on the performance of the coatings, specifically with regards to reflectivity.
The Magdalena Ridge Observatory Interferometer is a 10-element 1.4 meter aperture optical and near-infrared
interferometer being built at 3,200 meters altitude on Magdalena Ridge, west of Socorro, NM. The
interferometer layout is an equilateral "Y" configuration to complement our key science mission, which is
centered around imaging faint and complex astrophysical targets. This paper serves as an overview and
update on the status of the observatory and our progress towards first light and first fringes in the next few
years.
We present a parametric cost estimate for the Kilometric Optical Interferometer (KOI) in a classical array configuration:
24 telescopes, 4-meter primary mirror, up to 1 km baseline. The parametric cost estimate is based on available cost
information from the Magdalena Ridge Observatory (MRO) Interferometer at New Mexico Tech. A Kilometric Optical
Interferometer based on a classical array concept has an estimated construction cost between $1B and $3B if it would be
built today (2008 dollars and technology).
The implication of the estimated construction cost is that cost reductions are critical in the planning phase to bring the
cost within a reasonable envelope. Hence we propose to set a budget ceiling that seems feasible given the support to be
expected from the scientific community and funding agencies. Given a budget ceiling, a design-to-cost process should
be followed. We propose to set a construction phase budget cap of $800M (2008 dollars) for KOI as an initial goal.
Narrowing down of the science goals in combination with technology development to reduce cost and technological
complexity are the main areas of activities for the next decade. We propose to establish a virtual project office to
coordinate these activities.
This paper discusses the challenges faced in designing and building a new astronomical observatory. Which factors
drive an organization (e.g. university) to invest considerable funding and human resources, and experience considerable
risk to establish a new research facility?
We identify four main drivers for establishing a new observatory: support for education, research, economic
development, and technology development. For public observatories, research is generally the main driver. For nonpublic
observatories, the situation is more complex and is for each situation different.
A detailed description is presented on the drivers and opportunities that resulted in establishing the Magdalena Ridge
Observatory. Three main opportunities are identified: a developed site, surplus equipment, and economic development
of the Socorro area.
The Magdalena Ridge Observatory Interferometer (MROI) is a US federally funded project to construct the world's most ambitious optical/IR (0.6-2.4micron) imaging interferometer at a 10,500ft-altitude site in New Mexico. In its initial phase it will consist of 6 telescopes, each 1.4m in diameter, separated by distances ranging from 7.5m to 340m. A second phase will upgrade the interferometer to a 10-telescope configuration, allowing a "snapshot" imaging capability. The MROI will deliver images with sub-milliarcsecond angular resolutions while simultaneously providing images over 5-70 spectral sub-bands. A key feature is that the array will have sufficient sensitivity to image a wide range of targets, including extragalactic targets and, potentially, geosynchronous satellites. We report on the design and current status of the array.
Magdalena Ridge Observatory (MRO) Interferometer is a ten telescope optical
interferometer array being built on the Magdalena Mountains 20 miles west of Socorro,
New Mexico. The interferometer is being designed by collaboration between New
Mexico Institute of Mining and Technology and the University of Cambridge. The
science mission and requirements have been finalized which has helped to begin
engineering design and development culminating in detailed conceptual designs. Some of
the proposed hardware and software implementations are currently being tested in the
lab. We present an engineering overview of the conceptual design and the proposed
hardware and software implementations.
We present an outline of the automated alignment system for the 350m baseline Magdalena Ridge Observatory
Interferometer (MROI) which will manage the simultaneous alignment of its six principal optical subsystems
(telescopes, beam relay trains, delay lines, beam reducing telescopes, switchyards, and beam combiners). Many of these
components will be held under vacuum, will be subject to varying thermal loads and will use different coatings
(optimized for either optical or near-IR wavelengths). We review the proposed architecture of our scheme and discuss
the procedures, tools, and optical analyses we have used to design it.
The Magdalena Ridge Observatory Interferometer (MROI) is a ten element optical and near-infrared imaging interferometer being built in the Magdalena mountains west of Socorro, NM at an altitude of 3230 m. The interferometer is being designed and built by a collaboration which includes the New Mexico Institute of Mining and Technology (NMT) as the prime contractor and center for the technical team, and the University of Cambridge, Physics Department at the Cavendish Laboratory, which participates in the design and executes work packages under contract with NMT. This manuscript serves as a status update on MROI, and will present progress and milestones toward the observatory's first fringes in 2008.
The Magdalena Ridge Observatory Interferometer (MROI) is part of a new observatory dedicated to astronomical research. It is a 6 element optical interferometer currently in its construction phase, with a planned phase B of 10 elements. The observatory is located within 32 km from the centre of the Very Large Array (VLA) at an altitude of approximately 3230 meters. The design is optimized for faint source imaging. This makes it one of the most advanced high spatial resolution optical instruments available to the scientific community. With a staffing of up to 20 scientists and engineers, and a large fraction of the telescopes, buildings, and delay lines outsourced to industry and consortium partners, it aims for an aggressive schedule to have first fringe with 6 telescopes in late 2009. A project this size in budget, tight milestones and deadlines, requires professional management. In this paper we address the basic principles that are followed in the project management approach. We describe a generic approach and at some instances the implementation chosen at MROI.
Knowledge of the dispersion due to (humid) air in the light path of the Very Large Telescope Interferometer (VLTI) is crucial to obtaining good science data from MIDI, PRIMA and GENIE. To calculate the refraction due to air at infra red wavelengths in the ducts and delay line tunnel, the temperature and humidity has to be monitored during observations. To accomplish these measurements an easy to use and reliable system was assembled, based on commercially available components. In-house calibration of four humidity and temperature sensors of the system was done in Leiden. A test and calibration program was carried out to make sure that they work reliably and accurately and to determine the sensor characteristics. For this purpose a calibration box was designed which isolates the sensors from the environment so that there is no exchange of air with the outside environment. Using constant humidity salt solutions, the humidity in the box can be controlled. This allows the calibrations to be carried out for typical values of relative humidity and temperature at Cerro Paranal. Calibration of the sensors includes: 1. Reducing the systematic relative humidity differences between the sensors to less than 0.1 % and 2. Reducing the systematic temperature differences between the sensors to less than 0.01 K. In this paper we will present the outcome of the calibrations and the future of the sensors at Paranal.
The PRIMA facility will implement dual-star astrometry at the VLTI. We have formed a consortium that will build the PRIMA differential delay lines, develop an astrometric operation and calibration plan, and deliver astrometric data reduction software. This will enable astrometric planet surveys with a target precision of 10μas. Our scientific goals include determining orbital inclinations and masses for planets already known from radial-velocity surveys, searches for planets around stars that are not amenable to high-precision radial-velocity observations, and a search for large rocky planets around
nearby low-mass stars.
We present an experiment to measure the thermal background level and its fluctuations with the European Southern Observatory (ESO) Very Large Telescope Interferometer (VLTI). The Mid Infrared
Instrument (MIDI) operating between 8 and 12 micron was used in both dispersed and non-dispersed modes. By using an interferometric instrument, in non-interferometric mode, we probe the same optical path as can be expected for other infrared interferometric instruments, e.g. GENIE and MIDI itself. Most of the infrared thermal background detected with MIDI originates from the VLTI infrastructure. This can be attributed to the absence of a pupil re-imaging mirror. Only for a small region around the optical axis of the system the signal from the VLTI infrastructure can be considered small and the atmospheric background fluctuations can be characterized.
The fluctuations of the thermal emission are described in terms of their power spectral densities (PSD). We have identified two regions in the PSD. For the low frequency range (0-10 Hz) the
fluctuations are dominated by the Earth atmosphere. The slope of the log-log PSD is close to -1. For the high frequency (larger than 10 Hz) range the fluctuations are due to photon noise and the PSD flattens off. Many narrow peaks are present in the PSD. Peaks at 1 and 50 Hz occur in almost all data sets and are identified as the effects of the MIDI closed cycle cooler and the power lines respectively. Other peaks at 10 and 30 Hz, as well as peaks above 50 Hz, are assumed to be VLTI or MIDI-specific frequencies.
A search for extrasolar planets using the ESO VLTI PRIMA facility
will become feasible in 2007. An astrometric accuracy of 10 micro-arcseconds will allow us to detect sub-Uranus mass planets around the
most nearby stars, as well as to conduct a planet search around stars of different ages. Most of the PRIMA hardware subsystems are currently being developed by industry. At the same time a scientific Consortium has formed that will deliver the differential delay lines and astrometric software for PRIMA to ESO.
In this paper we describe the planned efforts by the Consortium
related to the "PRIMA astrometry operations and software". These
activities include an overall "PRIMA astrometry error budget", a
"PRIMA astrometry calibration and observation strategy", the "PRIMA astrometry observation preparation tools" and the "PRIMA astrometry data reduction tools". We describe how all these components fit together in an overall approach to the flow of knowledge within the project. First by quantifying the fundamental limits of the VLTI infrastructure and the astronomical sources under study. Followed by elimination or suppression of the errors through either a hardware change to the system, software control of the system, or a proper calibration and observation strategy.
The ultimate goal is being able to calibrate all PRIMA astrometric data acquired over the full lifetime of PRIMA (5 to 10 years) to a uniform accuracy of 10 micro-arcseconds. This will allow identification of long-term trends in the astrometric parameters due to planetary companions around nearby stars and to determine the distances and proper motions for the selected sources.
This investigation focuses on observational measurements of the differential interferometric phase between spectral channels in the VLTI/MIDI instrument. Measurements of target stars are compared with theoretical predictions in order to investigate the effects of dispersion in humid air on differential phase measurements at N band (~10 micron wavelength). An accuracy of 1 degree RMS phase error is achieved after calibration during stable environmental conditions, but this accuracy is degraded if there are fluctuations in humidity between observations. Stabilisation and/or monitoring of the environmental conditions in the VLTI ducts and tunnels will be required in order to achieve the best differential phase performance with MIDI. The measured differential phases are found to be consistent with a model for the refractive index of air based on the HITRAN database.
One of the goals of the VLTI PRIMA (Phase Referenced Imaging and Micro-arcsecond Astrometry) facility will be to obtain high accuracy astrometry (of the order of 10 micro-arcsec) for the measurement of the reflex motion due to planets. In order to achieve this an offline astrometric Data Analysis Facility (DAF) is planned to perform a homogeneous and iterative analysis over several years of observations. This system will be part of the PRIMA Data Reduction Library (DRL), which also contains the online pipeline. The most important module of the DAF will be the Trend Analysis to identify and fit the systematic errors and feed them back into the data reduction. This requires an infrastructure which allows for comprehensive access to all raw and derived data and enough flexibility to easily introduce new algorithms in the system. We plan to realize this with a database, sophisticated middleware and Application Programmers' Interfaces (APIs) for the algorithms and user interface plug-ins. We present in this paper the requirements and preliminary design of the DAF, as well as the implementation issues concerning the integration with other modules of the DRL and ESO compliance.
We present direct detections of the spatial extent of the circumbinary disk around HR 4049 and its companion. Observations were obtained with the ESO Very Large Telescope Interferometer using the VLT Interferometric Commissioning Instrument (VINCI) at 2 micron and the Mid Infrared Instrument (MIDI) between 8 and 12 micron. A single uniform disk model fit to the VINCI data gives an angular diameter of 27 milli-arcseconds. After taking into account the contribution from an unresolved central star we find that the observed visibilities indicate a second component with a spatial extent of 37 milli-arcseconds (which is identified as the circumbinary disk). The MIDI interferometric spectra show features which are due to PAH emission lines (8.6 and 11.3 micron). The visibilities of the emission lines indicate that the spatial extent in the lines (50 to 60 milli-arcseconds) is larger than in the continuum (35 to 45 milli-arcseconds). This leads us to propose a three emission components model to explain the interferometric observations: a central unresolved star, a 37 milli-arcseconds circumbinary disk and polar lobes emitting in the PAH bands with a size of 50 to 60 milli-arcseconds.
Darwin is one of the most challenging space projects ever considered by the European Space Agency (ESA). Its principal objectives are to detect Earth-like planets around nearby stars and to characterise their atmospheres. Darwin is conceived as a space "nulling interferometer" which makes use of on-axis destructive interferences to extinguish the stellar light while keeping the off-axis signal of the orbiting planet. Within the frame of the Darwin program, the European Space Agency (ESA) and the European Southern
Observatory (ESO) intend to build a ground-based technology demonstrator called GENIE (Ground based European Nulling Interferometry Experiment). Such a ground-based demonstrator built
around the Very Large Telescope Interferometer (VLTI) in Paranal will
test some of the key technologies required for the Darwin Infrared Space Interferometer. It will demonstrate that nulling interferometry can be achieved in a broad mid-IR band as a precursor to the next phase of the Darwin program. The instrument will operate in the L' band around 3.8 μm, where the thermal emission from the telescopes and the atmosphere is reduced. GENIE will be able to operate in two different configurations, i.e. either as a single Bracewell nulling interferometer or as a double-Bracewell nulling interferometer with an internal modulation scheme.
Wide Field Imaging is a natural extension to single boresight interferometry with an optical/infrared telescope array. It is an important tool to obtain interferometric data of extended objects and for astrometric measurements. Visibilities from many points on the sky can be obtained in one shot saving observation time. In this paper we introduce a new technique, the "staircase mirror" concept which offers potential advantages with respect to existing techniques to perform wide field of view operation on an optical stellar interferometer. This new concept is based on a pupil plane recombination scheme with an automatic field-dependent path length compensation in the intermediate image field of each array single telescope. The pathlength compensation is obtained via a staircase mirror whose position and step depth are a function of the pointing direction and the baseline vector of each telescope. The mirror must be actuated to follow the changes of the baseline projected on the entrance pupil of the telescope. We have calculated the differential delay as a function of the field angle, studied and designed an experimental setup to show the applicability of the method and performed simulations for the Very Large Telescope Interferometer.
The field of view for the first generation VLTI instruments
(VINCI, MIDI, AMBER etc.) is limited to the diffraction limited
beam of a single telescope (for a 8.2-meter telescope at 2-micron
this is 0.6 arcseconds). However, the VLTI infrastructure with its
main delay lines, transfers a 2 arcseconds beam from the
telescopes to the interferometric laboratory. When we discuss wide
field imaging in the context of this paper, we refer to these 2
arcseconds. Although most current optical interferometers use
Michelson pupil plane beam-combination there is a convincing
scientific justification for wider field imaging capabilities to
allow astrometry, photometry and ultimately spectroscopy of
crowded fields (e.g. galactic center, globular clusters),
binaries, stellar disks and dust shells. In this paper we present
a newly developed tool to model a fringe tracker for a Fizeau
interferometer by retrieving the piston of each individual
telescope from the combined point spread function. This study
shows that the pistons can be retrieved. Detecting the signal in
at least two wavelength channels with an energy sensitive detector
(e.g. Superconducting Tunneling Junction) allows compensation for
the atmospheric piston and successively coherent integration of a
science channel. The examples provided in this paper are compliant
with the VLTI infrastructure and are part of a larger project to
study the feasibility of a wide field imager for the VLTI as a
third generation instrument. Finally we present a conceptional
design for a wide field imaging for the VLTI, referred to as
VLTI-WIDY.
The start of NEVEC was initiated by the opportunity in the Netherlands to reinstate instrumental efforts in astronomy through a funding program for 'Top Research Schools,’ which brought about the creation of NOVA. The fact that considerable experience exists in Radio Astronomical imaging through interferometry (the Westerbork Synthesis Radio Telescope started in 1970), and the relatively small size at the time of ESO's VLTI Team made it opportune to aim for a win-win situation through collaboration. So presently an MOU between ESO and NOVA is in force, which stipulates that 10 out of the 18 man-years funded by NOVA for NEVEC until 2005 [new personnel, in university setting (Leiden) but on project money] shall be used on tasks that are mutually agreed between NOVA and ESO.
The tasks presently are found in the domain of observing modes, calibration and modeling, as well as contributing to the commissioning of new instruments and thinking about future instruments. Another task, outside these 10 FTE, has been the data handling and analysis software for MIDI, and again contributing to its commissioning. Delivery of the first operational version in Heidelberg has just taken place (summer 2002) contributing to the successful Preliminary Acceptance in Europe for MIDI on September 10, 2002. The actual state of 'products and deliveries' and the future outlook are reviewed.
The mid-infrared interferometric instrument MIDI is currently undergoing testing in preparation for commissioning on the Very Large Telescope Interferometer VLTI at the end of this year 2002. It will perform interferometric observations over the 8 μm - 13 μm wavelength range, with a spatial resolution of 20 milliarcsec, a spectral resolution of up to 250, and an anticipated point source sensitivity of N = 4 mag or 1 Jy for self-fringe tracking, which will be the only observing mode during the first months of operation. We describe the layout of the instrument and the performance during laboratory tests, both for broadband and spectrally resolved observing modes. We also briefly outline the planned guaranteed time observations.
The first science instrument for the Very Large Telescope Interferometer (VLTI), the Mid-infrared instrument MIDI, will be commissioned in November 2002 with anticipated first fringe during that commissioning run on the 40-cm Siderostats and the 8.2-meter Unit Telescopes. In this paper we describe scientific and technical observing modes (also referred to as observation procedures) developed for MIDI and discuss in detail how an observing run with the instrument is planned.
MIDI is built by a consortium lead by the Max Planck Institute for Astronomy (MPIA Heidelberg), with contributions from among others ASTRON (Dwingeloo, The Netherlands), Leiden Observatory, University of Amsterdam, Paris Observatory, University of Groningen, the Kiepenheuer-Institut fur Sonnenpysik at Freiburg, Thuringer Landessternwarte Tautenburg, and the Observatoire de la Cote d'Azur.
Hyper spectral imaging is a technique that obtains a two-dimensional image of a scene, while for each pixel a spectrum is recorded. Hyper spectral imaging systems can be very powerful at extracting information by using the spectral information in addition to the more conventional information extraction algorithms based on the spatial information within an image. However it is very unlikely that a hyper spectral imager will be used as a sensor for day to day operations. Hyper spectral imagers have the disadvantage of being rather complex and generating huge amounts of data. In this paper we discuss the approach that hyper spectral imagers are most powerful as research instruments and that they can be used to develop dedicated sensors for a particular application. Such a dedicated sensor could be optimized by selecting the most appropriate wavelength bands and making these bands as broad, or as narrow, as needed in order to detect, classify, or identify targets. The number of bands needed for such a dedicated sensor may depend on the accepted false alarm rate of such a system. In this paper we present some example spectra of materials and atmospheric transmission and discuss how a dedicated sensor can be designed for a specific application.
A combination of algorithms has been developed for the detection, tracking, and classification of targets at sea. In a flexible software setup, different methods of preprocessing and detection can be chosen for the processing of infrared and visible-light images. Two projects, in which the software is used, are discussed. In the SURFER project, the algorithms are used for the detection and classification of small targets, e.g., swimmers, dinghies, speedboats, and floating mines. Different detection methods are applied to recorded data. We will present a method to describe the background by fitting continuous functions to the data, and show that this provides a better separation between objects and clutter. The detection of targets using electro- optical systems is one part of this project, in which also algorithms for fusion of electro-optical data with radar data are being developed. In the second project, a simple infrared image-seeker has been built that is used to test the effectiveness of infrared decoys launched from a ship. In a more complicated image seeker algorithm, features such as contrast and size and characterization of trajectory are used to differentiate between ship, infrared decoys and false alarms resulting from clutter. In this paper, results for the detection of small targets in a sea background are shown for a number of detection methods. Further, a description is given of the simulator imaging seeker, and some results of the imaging seeker software applied to simulated and recorded data will be shown.
Spectral imagery data (2.0 to 5.4 micrometer) was collected of plumes of ships by the NATO Special Working Group 4. It provides the means to study the signature of a target spectrally, spatially, and temporally. This experimental data has been used to validate the infrared signature of the plume of a ship as computed by NATO's flow-field program NPLUME v1.6 and the NATO Infra-Red Air Target Model NIRATAM v3.1. Two spatial positions in the spectral imagery data cube were selected. One which represents the background spectrum, and one which represents the spectrum of the plume of the ship. Theoretical spectra were computed by means of NPLUME v1.6 and NIRATAM v3.1. A computed background spectrum was fitted to the experimental background spectrum using a user-defined atmosphere in accordance with the meteorological conditions during the trial. A computed plume spectrum was fitted to the observed plume spectrum in order to determine the chemical composition of the exhaust gas. Since NIRATAM only takes into account plume radiation from CO, CO2, H2O, and soot, the analysis is necessarily limited to these species. Using the derived fitting parameters from the experimental data we make predictions about the infrared signature of the plume in two wavelength bands (mid-wave infrared and the long-wave infrared). The average transmission through the plume in the mid-wave infrared (3.0 to 5.0 micrometer) ranges from 65% close to the exit plane, to 100% where the plume dissolves in the ambient atmosphere. For the long-wave infrared (8.0 to 10.0 micrometer) the range in transmission is 90% to 100%. The active species in the mid-wave infrared and the long-wave infrared are the same for the plume as for the intervening atmosphere. The main difference is that the absorption features are deeper and wider for the plume. Based on this work we arrive at the conclusion that spectral imagery data of the plume of a ship can be adequately modeled using NIRATAM v3.1 in conjunction with NPLUME v1.6. Alternatively, the experimental data validates NIRATAM v3.1 and NPLUME v1.6. Some modifications to the NIRATAM source code have been proposed as a result of this study. A new release of NIRATAM and NPLUME which incorporates some of these changes is expected shortly (NIRATAM v3.2).
The principle of optodes has been shown to be efficient. Optodes are based on conventional ion-selective liquid membranes coupled with an indicator as an optical transducing agent. Calcium, sodium, potassium, and ammonium were assayed in real samples as well as the biological relevant trace elements zinc and lead in aqueous solutions. However, some kind of drawbacks were observed which can be eliminated by an improved optical measuring technique. A considerable gain in sensitivity of the optical measurements is achieved for clinical analysis of total potassium concentrations in plasma by the evanescent wave technique (ATR). For the sodium optode the analytical error is shifted towards the allowable range. Furthermore, the adsorption of biological sample components at the surface of the PVC- membrane does not influence the optical signal.
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