Gas Chromatography Detectors - Detector Response > Page 11

Alternative Method for Specifying Detector 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 correction procedures when using the response index.

It should be pointed out that the logarithmic dilution method should not be used if the linearity is to be measured by the method recommended by the E19 committee of the ASTM.

Detector Response

There are two ways of defining detector response, either as detector output (usually in mv) per unit change in solute concentration or as the detector output per unit change in the units of detector measurement (e.g. the sensitivity of a conductivity detector would be defined in terms of detector output per unit change in electrical conductivity). The detector response (RD) is determined by injecting a known mass (m ) onto the column and measuring the peak height (h) in (mv), then,