Principles and Practice of Chromatography - The Basic Column Chromatograph > Detector and Detector Electronics > Page 56

Almost all LC columns are packed, although they can vary widely in length and diameter depending of the nature of the sample and the resolution required. They are usually manufactured of stainless steel or titanium (reputed to provide greater stability for labile materials of biological origin) and the connection to the sample valve and detector should be as short as possible and have a very small diameter to reduce extra column dispersion.

Detector and Detector Electronics

There is a wide range of detectors available for both GC and LC each having their own particular areas of application. In general the more catholic the response, the less sensitive the detector and the most sensitive detectors are those that have a specific response. The performance of all detectors should be properly specified so that the user can determine which is most suitable for a specific application. Such specifications are also essential to compare the performance of different detectors supplied by alternative instrument manufactures. Detector specifications should be presented in a standard form and in standard units, so that detectors can be compared that function on widely different principles. The more important detector specifications are summarized in table 2.

Table 1 Detector Specifications

 

Specifications Units
Dynamic Range (DR) g/ml (e.g. 3 x 10-9 to 6 x 10-5 )
Response Index (r) dimensionless
Linear Dynamic Range (DLR) g/ml (e.g. 1 x 10-8 to 2 x 10-5 )
Detector Response (RC) Volts/g or (specific units of measurement/g)
Detector Noise Level (ND) usually in millivolts but may be in specific units (e.g. Refractive Index Units)
Sensitivity or minimum detectable concentration (XD) g/ml (e.g. 3 x 10-8) but may be in specific units (e.g. Absorption Units)
Total Detection System Dispersion () (ml2 often ml2)
Cell Dimensions (length (l), and radius (r)), (cm)
Cell Volume (VD), ml.
Overall Time Constant (sensor and electronics) (TD), seconds (sometimes milliseconds)
Pressure Sensitivity (DP) usually in the USA, p.s.i in Europe MPa
Flow Rate Sensitivity (DQ) usually in ml/min
Temperature Range oC