Dear Isogeochemists,

Many of us are familiar with the problem of instrument linearity affecting 
the isotopic ratios obtained for a sample or standard as a result of 
varying yields in the gas of interest. Those of us who run samples with a 
Continuous Flow (CF) method are also familiar with the problem of 
chromatography affecting the isotopic composition of a sample or standard. 
 Moreover, those of us who run samples with unknown yields a priori are 
familiar with the struggle of correcting for both linearity and 
chromatography. Finally, there are those among us who run hundreds if not 
thousands of samples with unknown yields in an automated CF mode, creating 
a very complex situation when dealing with the simultaneous correction of 
both linearity and drift, over and above considering chromatography and 
possible memory effects. 

My question is this: would it be better to calculate and correct isotope 
ratios for samples run in CF mode using the peak height (or maximum 
voltage response) rather than the peak area?  Of course, this would only 
apply to the standards and the samples in the run that result in 
chromatographic peaks, not the reference gas peaks, which are flat-topped.

Any feedback is appreciated. 


Daniel H. Doctor
U.S. Geological Survey
Eastern Geology and Paleoclimate Science Center
12201 Sunrise Valley Drive, MS 926A
Reston, VA 20192
tel: 703-648-6027