Liquid Chromatography - The Tridet Multi Functional Detector 2

The UV adsorption system consists of a low pressure mercury lamp (major emission at 254 nm) and a solid state photo cell with quartz windows so it responds to light in the UV region. The cell is 3 mm long and is terminated at on end by a cylindrical quartz window and at the other by a quartz lens. The lens focuses the transmitted light on to the photo cell. There are two stainless steel discs separated by a 1 cm length of Pyrex tube adjacent to the quartz windows. Mobile phase enters and leaves the detector cell through radial holes in the periphery of the stainless steel discs. The steel discs act as the electrodes for conductivity detection. Normal to the Pyrex tube is another photo cell that receives fluorescent light emitted at right angles to the UV excitation light. The output from each sensor is processed by an appropriate amplifier to provide an output that is linearly related solute concentration.

The column eluent is, thus, continuously and simultaneously monitored by UV adsorption, fluorescence and electrical conductivity. This detector is very versatile and, perhaps surprisingly, is relatively inexpensive costing together with a column, sample valve, pump and recorder about $8,000. Chromatograms showing the simultaneous use of all three detector functions are depicted in figure 27.

UV Adsorption

Function

Electrical.Conductivity

Function

Fluorescence

Function

 

The column used was a Pecosphere™ 3 mm in diameter and 3 cm long carrying a C18 stationary phase. The mobile phase was a mixture of methanol(75%) and water (25%) at a flow rate of 2 ml/min. The solutes were 1 benzene, 2 toluene, 3 ethyl benzene, 4 isopropyl benzene, 5 t-butylbenzene, 6 anthracene, and 7 sodium chloride.

Courtesy of Bacharach Inc.

 

Figure 27. Chromatograms Demonstrating the Simultaneous Monitoring of a Mixture by all Three Detector Functions