Anal. Chem. 1997, 69, 1265
Correction Quantification of Compound Classes in Complex Mixtures and Fuels Using HPLC with Differential Refractive Index Detection Charles W. Sink and Dennis R. Hardy* (Anal. Chem. 1994, 66, 1334-1338).
Our paper failed to reference one earlier paper by Synovec and Yeung,1 in which an attempt was made to derive a set of equations based on the concept of analyte detection by differential refractive index detection using two different mobile phases and HPLC separation. The equations derived in that work proved to be of very limited use in practice, and we believe that this is due to the incorrect use of molar refractivity as a derivation starting point. In fact, their original equations were empirically modified to give the correct form by Dorschel et al.2 in a review article in 1989 by simply substituting n for n2. Our paper provides the correct derivation based on starting with the bulk property of refractive index of the analyte and leads to the equations shown in the Dorschel review. It should also be noted that our dual-solvent technique was not referenced in the extensive historical background to the problem of compound class quantitation in mid-distillate fuels in a recent publication by Lee et al.3 That paper suggests the use of supercritical fluid chromatography (SFC), followed by hydrogen flame ionization detection, as the method of choice for this analysis. Since no calibration is attempted in the SFC method, it is not surprising that the authors claim absolute errors on the order of 5% too low for the important total aromatics fraction. This should be compared to accuracy errors on the order of less than 1% for fuel samples analyzed by our dual-solvent method when compared to primary gravimetric techniques.4 (1) Synovec, R. E.; Yeung, E. S. Anal. Chem. 1983, 55, 1599-1603. (2) Dorschel, C. A.; Ekmanis, J. L.; Oberhotzer, F. V. W.; Bidlingmeyer, B. A. Anal. Chem. 1989, 61, 951A-960A. (3) Li, W.; Malik, A.; Lee, M. L.; Jones, B. A.; Porter, N. L.; Richter, B. E. Anal. Chem. 1995, 67, 647-654. (4) Sink, C. W.; Hardy, D. R. Anal. Chem. 1994, 66, 1334-1338.
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© 1997 American Chemical Society
Analytical Chemistry, Vol. 69, No. 6, March 15, 1997 1265
