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