Linearity The E19 committee suggested an alternative procedure for defining linearity (3). They defined the linear dynamic range as follows,    "the linear dynamic range of a detector is that range of concentration of a test substance over which the response of the detector is linear to within 5%, determined form a linearity curve".   The range should be expressed as a ratio of the highest concentration to the minimum detectable concentration. Although defining linearity by this method ensures an minimum linear performance and, consequently, a reasonable quantitative accuracy, the definition is not sufficiently explicit. Conversely, if the response index is employed, any slight non linearity can be taken into account by correcting the peak height (or the peak area) using the numerical value of the response index. Thus. in effect, the useful linear dynamic range of a detector for quantitative purposes can be significantly extended by employing

The Logarithmic Dilution Method of Linearity Measurement This method of linearity measurement was introduced by Lovelock (2). The procedure requires some special apparatus that is diagramatically represented in figure 3. Figure 3 The Logarithmic  Dilution Apparatus. A known mass of solute is introduced into a well–stirred vessel through which passes a flow of gas. The exit gas is arranged to pass directly into the detector. As a consequence, the mixture is continuously diluted and the concentration of the solute in

and the linear dynamic range and the two range are not synonymous. The dynamic range of a detector is that concentration range over which a concentration dependent output is produced. The minimum of the range will be the concentration at which the output is equivalent to twice the noise level and the maximum that concentration where the detector no longer responds to a concentration increase. The dynamic range is usually given as a concentration ratio and is thus, dimensionless. Detector Linearity The linear dynamic range of a detector is that concentration range over which the detector output is linearly related to solute concentration.         Thus,                           y= Ac           (c) is the concentration of solute in the mobile phase passing    and (A) is a constant

nbsp; The Incremental Method of Linearity Measurement This procedure provides a curve relating detector output to solute concentration over the concentration range of interest employing the associated chromatograph. Replicate sample are placed on the column and the eluted peaks monitored. The sample solution is made up in an appropriate volatile solvent at the maximum concentration of interest and duplicate samples placed sequentially on the column and the eluted peaks monitored. The sample is then diluted by three and the

In practice, no detector has a truly linear response (despite manufacturers claims) but most detectors will have a response approaching that of linear. It is difficult to apply a standard to detector linearity, but the Response Index (1) does help comparisons to be made between one detector with that of another. Providing the response of the detector approaches linearity then its response can be described by the following simple equation,                                        y = Acr     where (r) is the response index and the other symbols have the For a truly linear detector, r=1, and the extent to which (r) deviates from unity would be a measure of its non linearity.

have sensitivities of two to three orders of magnitude less than their GC counterparts and linear dynamic ranges one to two orders of magnitude lower. Only highly specific LC detectors have sensitivities that can approach those of GC detectors. See also the section on detectors in the HPLC supplement. Detector Specifications Detector specifications are like those for GC detectors and are listed as follows, 1. Dynamic Range 2. Response Index or Linearity 3. Linear Dynamic range 4. Detector Response 5. Detector Noise Level 6. Detector Sensitivity or Minimum Detectable Concentration 7. Total System Dispersion 8. Sensor Dimensions 9. Detector Time Constant 10. Pressure Sensitivity 11. Flow Sensitivity 12. Operating Temperature Range In general the