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Review of Scientific Instruments / Volume 79 / Issue 10 / OPTICS; ATOMS AND MOLECULES; SPECTROSCOPY; PHOTON DETECTORS

Rev. Sci. Instrum. 79, 103105 (2008); http://dx.doi.org/10.1063/1.3000682 (8 pages)

Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the field

A. J. Palma1, J. M. Ortigosa1, A. Lapresta-Fernández2, M. D. Fernández-Ramos2, M. A. Carvajal1, and L. F. Capitán-Vallvey2

1Departamento de Electrónica y Tecnología de Computadores, E.T.S.I.I.T, Universidad de Granada, Granada 18071, Spain
2Departamento de Química Analítica, Facultad de Ciencias, Universidad de Granada, Granada 18071, Spain

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(Received 16 June 2008; accepted 25 September 2008; published online 21 October 2008)

This report describes the electronics of a portable, low-cost, light-emitting diode (LED)-based photometer dedicated to one-shot optochemical sensors. Optical detection is made through a monolithic photodiode with an on-chip single-supply transimpedance amplifier that reduces some drawbacks such as leakage currents, interferences, and parasitic capacitances. The main instrument characteristics are its high light source stability and thermal correction. The former is obtained by means of the optical feedback from the LED polarization circuit, implementing a pseudo-two light beam scheme from a unique light source with a built-in beam splitter. The feedback loop has also been used to adjust the LED power in several ranges. Moreover, the low-thermal coefficient achieved (−90 ppm/°C) is compensated by thermal monitoring and calibration function compensation in the digital processing. The hand-held instrument directly gives the absorbance ratio used as the analytical parameter and the analyte concentration after programming the calibration function in the microcontroller. The application of this photometer for the determination of potassium and nitrate, using one-shot sensors with ionophore-based chemistries is also demonstrated, with a simple analytical methodology that shortens the analysis time, eliminating some calibrating solutions (HCl, NaOH, and buffer). Therefore, this compact instrument is suitable for real-time analyte determination and operation in the field.

© 2008 American Institute of Physics

Article Outline

  1. INTRODUCTION
  2. INSTRUMENTATION
    1. Instrument outline
    2. LED bias settling and light intensity stabilization
    3. Analog conditioning electronics
    4. Absorbance measurement procedure
  3. APPLICATIONS
    1. Chemical sensors
    2. Calibrations and technical specifications
      1. Nitrate
      2. Potassium

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KEYWORDS and PACS

Keywords

chemical sensors, light emitting diodes, optical sensors, photodiodes, photometers, photometry

PACS

  • 07.60.Dq

    Photometers, radiometers, and colorimeters

  • 85.60.Jb

    Light-emitting devices

  • 07.07.Df

    Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

  • 82.80.-d

    Chemical analysis and related physical methods of analysis

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.3000682

PUBLICATION DATA

ISSN

0034-6748 (print)  
1089-7623 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

For access to fully linked references, you need to log in.
    A. S. Farmer, D. P. Fries, W. Flannery, and J. Massini, Rev. Sci. Instrum., 76, 115102 (2005)RSINAK000076000011115102000001.


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