Rapidly formed quinalphos complexes with transition metal ions characterized by electrospray ionization mass spectrometry.

RATIONALE

Electrospray ionization tandem mass spectrometry (ESI-MS/MS) offers the unique opportunity to characterize complexes of the organophosphorus pesticide (OP) quinalphos (PA-Q) with transition metal ions immediately formed after contact. This study complements research looking at longer term kinetics of quinalphos hydrolysis in the presence of transition metal ions and gives insights into the structural features of the initial complex formation in solution. (Hydrolysis reaction: PA-Q + H2 O → PA-OH + HQ, where PA-OH is the diethyl phosphate product and HQ is hydroxyquinoxaline.)

METHODS

Low micromolar PA-Q solutions with an approximately 3-fold molar excess of transition metal ions were immediately analyzed after mixing. Fragmentation of the transition metal ion complexes with PA-Q was accomplished in two different ways: first, in-source fragmentation by elevating the declustering potential and second, low-energy collision-induced dissociation (CID).

RESULTS

For Ag(+), the [PA-Q - Ag(+)] and respective Ag(+) -containing degradation product ions are readily observed. For Cu(2+), we observed the [PA-Q + Cu(2+) + NO3(-)] complex ion with weak intensity and strong signals from both the [2PA-Q + Cu(+)] and the [PA-Q + Cu(+)] ions, the latter two attributable to charge-state reduction in the gas phase from Cu(II) to Cu(I), indicating that PA-Q fulfills specific structural requirements of the formed complex for charge-state reduction during transition from solution to the gas phase. For Hg(2+), the [PA-Q + Hg(2+) + (PA-OH - H)(-)] ion was the largest observed species containing one Hg(2+) ion. No 1:1 species ([PA-Q] or other degradation products:Hg(2+)) was observable.

CONCLUSIONS

ESI-MS/MS of complexes formed from PA-Q and transition metal ions is a formidable technique to probe initial formation of these complexes in solution. Previous work from other groups established structural requirements that enable charge-state reduction from Cu(II) to Cu(I) in ligand complexes during transition into the gas phase, and these rules allow us to propose structural features of PA-Q complexes with copper ions in solution.