2ND-ORDER FIBER OPTIC HEAVY-METAL SENSOR EMPLOYING 2ND-ORDER TENSORIAL CALIBRATION

A fully selective and versatile fiber optic heavy metal sensor based on the concept of second-order instrumentation has been fabricated and evaluated. This sensor uses chemically facilitated Donnan dialysis as the means of temporal species discrimination and reagent-assisted spectroscopy for spectral species discrimination. The signals in both orders (time and wavelength) are combined and analyzed with second-order tensorial analysis algorithms-generalized rank annihilation method (GRAM) and trilinear decomposition (TLD)-in order to extract the information of analytes form the sensor responses that are interfered by unknown interferents. Principal component analysis (PCA) is used to evaluate sensor characteristics. With second-order calibration, the sensor can measure Pb(II) or Cd(II) in the presence of other interfering transition metal ions. The prediction accuracy is affected by the response linearity of the sensor and the competition effect of co-existing cations with the analyte ions in the ion-exchange process. The specificity of the sensor can be easily switched from Pb(II) measurement into Cd(II) measurement by just changing the calibration standard. The sensor was also tested with ''real-world'' samples. With the stopped-flow preconcentration measuring mode, the sensor gains in sensitivity so that low concentration Pb(II) in tap water and lake water samples can be measured. For tap water samples, the sensor agrees with the graphite furnace atomic absorption (GFAA) verification very well. Due to complexation of Pb(II) in the lake water samples, some complexed Pb(II) ions are rejected by the cation-exchanging membrane, causing the sensor results to be lower than the GFAA data.