The analytical application of surface-enhanced Raman spectroscopy (SERS) to the determination of nicotine is demonstrated. A simple spectroelectrochemical method using a copper or silver electrode as the SERS substrate has been developed, consisting of three steps: polishing a working electrode to a mirror finish; roughening the electrode in an electrolyte solution; and, finally, depositing the nicotine analyte onto the roughened electrode after immersion in a sample solution. During the reduction cycle, a large enhancement in nicotine Raman scattering is observed at the electrode surface. The intensity of the SERS signal on a silver electrode is linear with concentration from 10 to 900 ppb, with an estimated detection limit of 7 ppb. The total analysis time per sample is approximately five minutes. This procedure has been used to analyze the extract from a cigarette side-stream smoke sample (environmental tobacco smoke); the SERS results agree well with those of conventional gas chromatographic analysis.
An in situ method for the determination of trichloroethylene (TCE), perchloroethylene (PCE), chloroform (CHCl3), and carbon tetrachloride (CCl4) in aqueous solution is described. The method is based on ESERS—a combination of electrochemical methods and surface-enhanced Raman scattering (SERS). Electrochemistry prepares the surface of a copper electrode for SERS and concentrates the analyte on the surface. The formation of common reaction products for chloroalkanes and for chloroalkenes prevents unequivocal differentiation within a specific class of chlorinated hydrocarbons. However, spectroscopic selectivity between the chloroalkane and chloroalkene classes is excellent, while differences in electrochemical response provide a secondary means for differentiating analyte class. Sensitivity was found to be: <1 ppm for TCE; 15 ppm for PCE; 15 ppm for CHCl3; and 10 ppm for CCl4. Application of the method to groundwater contaminated with TCE has been demonstrated. In combination with a fiber-optic waveguide, the ESERS technique offers potential for remote detection of chlorinated hydrocarbons in groundwater and remediation process streams.
A multiple-mode laser diode is used to supply the primary radiation for atomic absorption spectroscopy (AAS). The multiple wavelength characteristics of the laser allow peak ratio measurements and possible background correction by the monitoring of the absorption spectrum with a diode-array spectrometer. In this demonstration, lithium is used as the analyte and air/acetylene flame is used as the atom reservoir. The detection sensitivity (1% absorption) is 20 ng/mL and the detection limit (2 σ of blank) is 4 ng/mL; these values are comparable to those of the conventional flame AAS with the use of a hollow cathode lamp as the source radiation.
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