ABSTRACT
An evanescent wave infrared chemical sensor for the sensitive and selective detection of copper ions in aqueous solutions is described. Because copper ions have no vibrational features, a band-shifting technique was utilized to produce the analytical signal. To enhance the sensitivity of the detection process, a three-step procedure was employed to prepare acidified tris(2-aminoethyl)amine (ATAA) phase on an evanescent wave sensing element. This sensing phase has a chemical structure similar to that of ethylenediamine tetraacetic acid (EDTA), a common chelating agent for metal ions. After formation of complex with copper ions, the shifts in the absorption bands of the ATAA phase were used for quantitation. An additional four sensing phases having chemical structures related to that of EDTA were synthesized to compare their performances for detection of copper ions. The synthetic sensing phases are highly stable in water and insensitive to changes in solutions at pH greater than 4. ATAA was the most sensitive of the phases tested, probably because of the accessibility and flexibility of the functional groups in the ATAA phase. To explore these systems in greater detail and to optimize detection, the effects of parameters such as the buffer concentration, the pH of the sample solution, and the matrix effect on response time and linearity of detection were examined. The analytical signals for copper ions were similar - and highly selective - when the pH of the solution was between 5 and 6.5. For a detection time of 5min, these signals were linear for concentrations up to 200microM with a detection limit ca. 3microM.
ABSTRACT
An infrared (IR) chemical sensor based on immobilization of an acidified tris(2-aminoethyl)amine (ATAA) for the detection of tyrosine in urine is described. The sensing phase (i.e., coating) was saturated with nickel ions so that it would interact with tyrosine molecules in aqueous solution through the formation of stable ATAA-Ni2+-tyrosine complexes. Investigation of the signals of nine amino acids shows that only the three containing phenyl groups could be detected by this sensor system. A unique spectral feature located at 1515 cm(-1) allowed tyrosine to be discriminated from the other two amino acids. To examine the performance of the ATAA sensing phase in the quantitative analysis of tyrosine, the effects of several factors were examined. pH affected the ability of tyrosine to form complexes; the optimal signal occurred at ca. pH 8. The concentration of ammonia buffer also affected the analytical signals through a competition effect; lower concentrations of ammonia buffer provided higher intensity signals. It was found that nickel ions are the most useful for detection of tyrosine. Although the concentration of nickel ions had less influence on the analytical signal than did the concentration of the ammonia buffer, the signal intensity was optimal when the nickel ions and the target molecule had similar concentrations. The detected time profiles indicated that the ATAA sensor phase functioned via a surface adsorption mechanism. The linear range of signal intensities was up to 600 microM with a detection limit of 30 microM.
