Liquid Chromatography Detectors - LC Detectors Based on Refractive Index Measurement > The Dielectric Constant Detector > Page 36

Figure 22 The Sensor of a Dielectric Constant Detector

Each cell consisted of a concentric cylinder (inner electrode) inside a larger cylinder (the outer electrode) which formed the outer wall of the cell. Both electrodes were made of stainless steel. The two cylinders were electrically isolated with a cylindrical flow path through the cell. The inner cylindrical electrodes were 1.26 cm in diameter and 0.625 cm long separated from the outer cylinder by about 0.009 cm. The linear dynamic range of the detector was reported to be 3.5 x 104 . The sensitivity was quoted as about 1 x 10-7 g/ml, which would be close to the theoretical limit for bulk property detectors. An example of the use of the dielectric constant detector to monitor a separation of triglycerides is shown in figure 23.

Bulk property detectors have neither the sensitivity nor the linear dynamic range of solute property detectors and are less frequently used in modern LC analyses. None can be used satisfactorily with gradient elution, flow programming or temperature programming and so they restrict the choice of development. They do have certain unique areas of application, some of which have already been mentioned. Their use probably represents less than 5% of all LC analyses.


Figure 23 The Separation of Some Triglycerides Monitored by a Dielectric Constant Detector