Page 304 - Tandem Techniques

Page 288

Synopsis

Today the LC/UV tandem systems are basically multi-wavelength detectors. The multi-wavelenght
dispersion detector can only monitor a separation at one wavelength, but has the higher resolution. The
diode array detector monitors UV absorption simultaneously at all wavelengths, but its resolution is
limited by the number of diodes. The tandem LC/UV system is either used to monitor a separation at
the optimum wavelength, test the purity of a peak from its spectrum, or compare the spectrum of a peak
to that of a reference. Tandem systems employing fluorescence spectroscopy help identify eluted
compounds, selectively monitor a specific type of sample, or enhance the sensitivity of the system to a
particular compound. Both excitation spectra and emission spectra can be obtained and in modern
instruments, the change in excitation wavelength and emission wavelength can be programmed to suit
the elution pattern of the eluents. Fluorescent derivatives can be used very effectively to enhance the
sensitivity or render substances that do not naturally fluoresce amenable to fluorescent detection. More
recently the diode array (appropriately cooled to reduce the dark noise) has also been used to monitor
fluorescence spectra.

References

1. M. Yanaguchi, K. Wade, J. Ishida and M. Nakamura, Analyst,117(1992)1859.

2. W. J. Adams, B. E. Bothwell, W. M. Bothwell, G. J. VanGiesen and D. G. Kaiser, Anal. Chem., 59
(11)(1987)1504.

3. K. Soroka, R. S. Vithanage, D. A. Phillips, B. Walker and P. K. Dasgupta, Anal. Chem., 59(4)(1987)
629.

4. K. Tenabe, M. Glick, B. Smith, E, Volgtman and J. D. Winefordner, Anal. Chem., 59(8)(1987)1124.

5. Y. Talmi, Appl. Spectrosc., 36(1982)1.

6. J. Wegrzyn, G. Patonay, M. Ford and I. Warner, Anal. Chem., 62(17)(1990)1754.

7. M. C. Yappert, M. W. Schuyler and J. D. Ingle, Jr. Anal. Chem. 61(1989)593.

8 . M. C. Roach and M. D. Harmony, Anal. Chem., 59(3)(1987)411.

9. M. J. Sepaniak and E. S. Yeung, J Chromatogr., 190(1980)377.

10. R. G. Carlson, K. Scrinivasachar, K. R. S. Givens and B. K. J. Matuszewske,