Bifunctional detector

The problem was solved by the development of multifunctional detectors, where more than one property of the solute is concurrently measured while it is situated in a single sensor cell. This arrangement reduces both the cost of the detector and also the extracolumn dispersion as only one cell is employed and only the normal column detector connection is necessary. The first multifunctional detector was developed by DuPont and was a bifunctional detector that simultaneously measured UV absorption and solute fluorescence. 

In 1984 Baba and Housako (7) described a second bifunctional detector based on the concurrent measurement of UV absorption and electrical conductivity. A diagram of the detector is shown in figure... 

The UV absorption system is very similar to that of the DuPont bifunctional detector. Light from a UV lamp is collimated through the cell by a quartz lens that serves as one end of the sensor cell, and is then focused by another quartz lens at the other end of the cell onto a photodiode. The output from the photodiode is processed electronically in the usual manner to provide an output that changes linearly with solute concentration. The ends of the cell, between the cell body and the quartz lens, where the mobile phase from the column enters the... 

Another bifunctional detector that was developed by Knauer and made commercially available in Europe operated on the simultaneous measurement of UV absorption and refractive index. This detector is particularly interesting as it combines a solute property detector with a bulk property detector and consequently should have a wide field of application. 

More recently (1984), Baba and Housako (7) described another bifunctional detector but this time based on the UV absorption detector combined with the electrical conductivity detector. A diagram of their detector is shown in Figure 2. The UV absorption system is very similar to that of the DuPont bifunctional detector. UV light is collimated through the cell and focussed by a second quartz lens onto a photo diode, the output from which, is processed by suitable electronic circuitry in the usual manner. 

Another bifunctional detector was recently developed by Knauer and has been raade coramercially available in Europe. This bifunctional detector operates on the basis of UV absorption and changes in refractive index. As such, it is particularly interesting as it corabines a solute property detector with a bulk property detector. Consequently, the corabination will cover a very wide field of applications. A diagram of the instrument is shown is Figure 3. 

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. 

The UV absorption system is again very similar to the bifunctional detectors and consisted of a low pressure mercury discharge lamp and a solid state photocell fitted with a quartz... 

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. 

Bronlc acids containing electron-capturing subsitituents were developed by Poole and co-workers. Table 8.19 (451,535,536). In terms of volatility, stability of derivatives, and response to the electron-capture detector the 3,5-bis(trifluoromethyl)benzeneboronic acid, 2,4-dichlorobenzeneboronic acid, and 4-bromo-benzeneboronic acid were recommended for general applications. In particular, the 3,5-bis(trifluoromethyl)benzeneboronate derivatives are remarkably volatile, more so than the benzeneboronates, and are suitable for the analysis of bifunctional compounds of low volatility. All the benzeneboronate derivatives are susceptible to solvolysis which is the primary limitation to their general use for trace analysis. 

The p-dicumyl chloride/BCl3/isobutylene inifer system has been thoroughly investigated. Detailed characterization research including various chemical techniques [3,8,10],1H NMR spectroscopy [1,3,8], GPC equipped by dual RI and UV detectors [1], end-group determination by dehydrochlorination [9], and kinetic studies [8] proved that the structure of the product is as shown by formula I in Scheme I and that the molecule is perfectly bifunctional (Ern = 2.0). 

From the above discussion, it is evident that BR is a bifunctional electronic material [64] it is sensitive to light as well as to ions such as H+, Cl, and Ca. In the motion detector developed by Miyasaka etal, BR is configured as a photon sensor. In the cyclic-GMP cascade, a photon, via its action on rhodopsin, triggers the hydrolysis of cyclic-GMP, and thus in turn regulates the release of energy stored as a Na+ gradient. The hypothetical trigger mechanism based on the surface potential thus works like a field effect transistor (FET), or more precisely, a phototransistor. 

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