An optical biosensing film for biochemical oxygen demand determination in seawater with an automatic flow sampling system

An on- line roboticized apparatus, including an optical biosensing film with an automatic flow sampling system, has been developed for biochemical oxygen demand ( BOD) determination of seawater. The sensing film employed in the apparatus consisted of an organically modified silicate ( ORMOSIL) film embedded with tri( 4,7- diphenyl- 1,10- phenanthroline) ruthenium( II) perchlorate. Three species of microorganism cultivated from seawater were immobilized in an ORMOSIL- polyvinyl alcohol matrix. Possible factors affecting BOD determination were studied, including sampling frequency, temperature, pH and sodium chloride concentration. Based on measurements of the linear fluctuant coefficients and the reproducibility of its response to seawater, the BOD apparatus showed the advantages of high veracity and short response time. Generally, the linear fluctuant coefficient ( R-2) in the BOD range 0.2 - 40 mg l(-1) was 0.9945 when using a glucose/ glutamate ( GGA) BOD standard solution. A reproducible response for the BOD sensing film of within +/- 2.8% could be obtained in the 2 mg l(-1) GGA solution. The BOD apparatus was applied to the BOD determination of seawater, and the values estimated by this biosensing apparatus correlated well with those determined by the conventional 5 day BOD ( BOD5) test.