SGMS Meeting 2001

Advantages and problems of the analysis of di-carbonyl-DNPH derivatives with HPLC-MSⁿ using APCI(-) ionization

Stephan Brombacher, Michael Oehme and Basil Boesch
Organische Analytische Chemie, Universität Basel, Switzerland

Air sampling combined with transformation to 2,4-dinitrophenylhydrazone derivatives (carbonyl-DNPHs) under acidic conditions and determination with HPLC/UV has become one of the standard methods for carbonyl monitoring. Traditional up to C5 carbonyls are determined in this way. In recent publications long chained carbonyls (up to C12) are measured and mass spectrometers are used as alternative detectors. In our workgroup a Finnigan LCQ ion trap mass spectrometer operated with an atmospheric pressure chemical ionization (APCI) ion source in the negative ion mode is used for the determination of carbonyl-DNPHs.

During real air sample measurements several unknown compounds were detected which are assumed to be dicarbonyls. To gain more information about this molecule class, especially about fragmentation behavior and ionization properties, six dicarbonyl-DNPHs (glyoxal, methylglyoxal, 2,3-butandione, 2,3-pentandione, 2,4-pentandione and 1,5-pentandial) were synthesized and investigated with LC/MSn.

In the first part of the presentation the fragmentation behavior of some dicarbonyl-DNPHs in the ion trap is shown. The MS2-spectra of 2,4-butandione and 1,5-pentandial are compared and several of the fragments and fragmentation pathways are explained.

In the second part the influence of the ion source geometry on the ionization behavior of dicarbonyl-DNPHs is shown for glyoxal-DNPH and methylglyoxal -DNPH. The examples demonstrate that the linearity of the detector as well as the limits of detection (LOD) are strongly linked to the position of the corona needle in the APCI ion source. In contrary to the dicarbonyl-DNPHs the carbonyl-DNPHs like formaldehyde-DNPH are only affected in their LODs but not in their linear behavior in the MS-detector.