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

Abstract

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 μL 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⁺.