Application of screening experimental designs to assess chromatographic isotope effect upon isotope-coded derivatization for quantitative liquid chromatography-mass spectrometry.

2 Therefore, the change in the analyte to IS peak area ratios may be significant enough to influence the accuracy of quantitation. 8 − 13 Several approaches have been recommended to overcome caveats associated with the use of d -labeled ISs. 12 − 17 Additional sample preparation steps, the use of shallow gradient profiles to achieve adequate separation of analytes from major matrix components eluting with the solvent front, application of atmospheric pressure chemical ionization (APCI) which is less prone to matrix effect than ESI, 2 or using other than d - (i.e., 13 C-, 15 N-, or 18 O-) labeled ISs are examples of these efforts.

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Since there is an increased chance for false positive decisions using ME and significance was not confirmed by other statistical and graphical interpretation methods, this effect may only be considered as “possibly significant” according to Vander Heyden et al. 26 Nevertheless, the results obtained by our asymmetrical design experiment (Table 2 ) pointed out that neither 13 C nor 15 N labeling had a significant effect on retention time difference; only deuterium isotope substitution ended up as a significant factor.

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