The Chromatography Detector

The two essential elements of a quantitative chromatographic analysis are that the solutes of interest must be adequately resolved from one another, and that the eluted solutes are monitored by a device with a known function relating mass or concentration of the solute eluted to elapsed time.

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

The former depends on the chosen column and phase system, the latter requires a detector with a known and predictable response and a sensitivity commensurate with the composition and size of the sample. Chromatographic detectors that are commercially available will all be suitable for quantitative analysis, but differ in their performance specifications.

The Dynamic Range of a Detector

The detector dynamic range extends from the minimum detectable concentration (i.e. the sensitivity) to that concentration where the detector no longer responds to any concentration increase. The dynamic range is not pertinent to quantitative chromatographic analysis, but is of interest in preparative chromatography. The dynamic range of a detector (DR) is usually given in the form

DR = 6 x 105

The dynamic range is dimensionless as it is a ratio of concentrations and, thus, independent of the units used.