Document Detail

Integrated optical NIR-evanescent wave absorbance sensorfor chemical analysis.
MedLine Citation:
PMID:  15048449     Owner:  NLM     Status:  Publisher    
A new, long-path integrated optical (IO) sensor for the detection of non-polar organic substances is described. The sensing layer deposited on a planar multimode IO structure is built by a suitable silicone polymer with lower refractive index (RI). It acts as a hydrophobic matrix for the reversible enrichment of non-polar organic contaminants from water or air. Light from the near-infrared (NIR) range is coupled into the planar structure and the evanescent wave part of the light field penetrating into the silicone layer interacts with the enriched organic species. As a result, light is absorbed at the characteristic frequencies of the corresponding C-H, N-H or O-H overtone and combination band vibrations of the analytes. To perform evanescent field absorbance (EFA) measurements, the arc-shaped strip waveguide structure of 172 mm interaction length was adapted to a tungsten-halogen lamp and an InGaAs diode array spectrograph over gradient index fibers. Dimethyl-co-methly(phenyl)polysiloxanes with varying degrees of phenylation were prepared and used as sensitive coating materials for the IO structure. Light attenuation in the arc-shaped waveguides is high and typical insertion losses in the range of 14-18 dB were obtained. When the coated sensors were brought in contact with aqueous samples, the light transmission decreases, which is due to the formation of H(2)O micro-emulsions in the silicone superstrates. Nevertheless, after reaching constant light transmissions, absorbance spectra of aqueous trichloroethene samples were successfully collected. For gas measurements, where water cross sensitivity problems are absent, the sensitivity of the IO device for trichloroethene was tested as a function of the RI of the silicone superstrate. The slope of the TCE calibration function increases by a factor of 10 by using a poly(methylphenylsiloxane) layer with a RI of 1.449 instead of poly(dimethylsiloxane) (RI: 1.41). A comparison of the IO-EFA and an earlier developed fiber-optic EFA sensor for trichloroethene measurements in the gas phase showed an increase in sensitivity per unit length of the waveguide by a factor of up to 120.
J Bürck; B Zimmermann; J Mayer; H J Ache
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Analytical and bioanalytical chemistry     Volume:  354     ISSN:  1618-2650     ISO Abbreviation:  Anal Bioanal Chem     Publication Date:  1996 Jan 
Date Detail:
Created Date:  2004-03-29     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101134327     Medline TA:  Anal Bioanal Chem     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  284-90     Citation Subset:  -    
Forschungszentrum Karlsruhe, Technik und Umwelt, Institut für Radiochemie, P.O. Box 3640, D-76021, Karlsruhe, Germany.
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