Ion mobility mass spectrometry: an elegant alternative focusing on speciation studies

This work is proposed to demonstrate the Traveling-Wave Ion Mobility Specrometry (TWIMS) coupled to Mass Spectrometry (MS) as an alternative technique for speciation analysis between metals/metalloids and biomolecules. Mobilities of bovine carbonic anhydrase bound to Ba2+, Cu2+, Pb2+, Zn2+, Cr3+, Cr6+, Se4+ and Se6+ were estimated. The metal belonging to the bovine carbonic anhydrase structure, commonly found in the commercially available enzyme, was removed by filtration, using centrifugal filter devices. Then, some metals/metalloids were added to 10.0 mmol L-1 ammonium acetate at pH = 6.8 enzyme solution. Experiments were carried out by direct insertion of the sample at 10 mu L min(-1) flow rate into the ESI source of the instrument. Carbonic anhydrase mobility varied according to the metal bound in its structure, following the order: Zn2+ < Cu2+ < Ba2+ < Pb2+. Metals with higher affinity by the enzyme, such as Zn2+ and Cu2+ had lower mobility, suggesting a higher structural modification, binding itself to the enzyme metallic site. Considering metals with different oxidation states, the enzyme mobility followed the order: Se4+ < Cr6+ < Se6+ < Cr3+.