Gas Chromatography Detectors - Detector Linearity > Determination of Response Index > Page 6

The curves shown in figure 2 appear to closely approximate to a straight line (i.e. are linear). However, if linearity is assumed considerable errors can result as shown in table 2.

 

Table 1 The Analysis of a Two-Component -Mixture Using Detectors Having Different Response Indices

 

Solute r=0.94 r=0.97 r=1.00 r=1.03 r=1.05
1 11.25% 10.6% 10.0% .42% 9.05%
2 88.75% 89.4% 90.0% 90.58% (0.95%

It is seen that the results for the lower level component (10 % w/w) can be as great as 12.5 % (1.25 % absolute) when (r) is a low as 0.94 and 9.5 % (0.95 % absolute) if (r) is a high as 1.05. It follows, that to provide adequate accuracy for concentration ranges of 10 or more then (r) should lie between 0.98 and 1.02.

 

Determination of Response Index

There are two basic methods for measuring the response index of a detector and they are the incremental method and the logarithmic dilution method. The incremental method requires no special apparatus other than the chromatograph itself but the latter does require special equipment but the apparatus is very simple to construct.