Trifunctional detectors

The popularity of the UV detector, the electrical conductivity detector and the fluorescence detector motivated Schmidt and Scott (5,6) to develop a trifunctional detector that detected solutes by all three methods simultaneously in a single low volume cell. 

However, it is not the simultaneous use of all detector functions that makes this detector so useful. The real advantage of the trifunctional detector is that it allows the analyst a choice of the three most useful detector functions in one detecting system. Furthermore, any of the three functions can be chosen at the touch of a switch and without any changes in hardware. 

Trifunctional detectors are the natural extension of the multifunctional concept but, to date, there appears to be only one trifunctional detecting system that has been fully developed and become commercially successful. In fact, there is no reason why four, five or even more sensing devices could not be incorporated together in an effective multifunctional detector. However, it appears that, so far, the TriDet, a trifunctional detector has the maximum number of different sensors of any commercially available detector. 

In 1985 Schmidt and Scott (8, 9) introduced the trifunctional detector, which was in fact, a combination of the bifunctional detectors of DuPont, and Baba and Housako (7) but with a redesigned cell and eluent conduits to minimize cell dispersion. A diagram of their detector, now manufactured by Perkin-Elmer Corporation, is shown in Figure 4. 

Multi-functional detectors monitor the column eluent by the measurement of more than one physical or chemical property simultaneously, employing a single sensing cell. To date, three bifunctional detectors and one trifunctional detector have been described. The three bifunctional detectors have combined UV absorption and fluorescent detection, UV absorption and electrical conductivity detection and UV absorption and refractive index detection. The latter uniquely combines a bulk property detector with a solute property detector producing, at least in theory, the nearest approach to a universal detector. The trifunctional detector incorporates UV absorption, electrical conductivity and fluorescence functions. Multi-functional detection provides detector versatility and a means of confirmir solute identity. Such detectors have to be designed, so that the performance specifications are not seriously compromised, and the cell and eluent conduits do not contribute significantly to peak dispersion. 

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