HPLC-APCI-MS with calibration based on stable isotope-labelled internal standards for the quantification of carbonyls in air samples

A method for the selective determination of formaldehyde and acetaldehyde in air samples based on HPLC-APCI-MS with calibration using stable isotope-labelled standards was developed. d₂-Formaldehyde-2,4-dinitrophenylhydrazone and d₄-acetaldehyde-2,4-dinitrophenylhydrazone were synthesized from 2,4-dinitrophenylhydrazine and the respective deuterated aldehydes. The labelled derivatives were used as internal calibration standards in the quantification of formaldehyde and acetaldehyde in complex matrices, including automobile exhaust. Co-elution of the labelled and non-labelled derivatives in HPLC provides for identical mass spectrometric conditions, thus significantly reducing the relative standard deviation of the internal calibration approach compared with external calibration with non-labelled derivatives.