New tools and methods for CE-MS: Applications in anticancer metallodrug research

Abstract

Capillary electrophoresis (CE) is a separation technique for charged species and ideal for the study of metallodrugs. Despite exceptional analytical advantages, there are concerns regarding CE reproducibility, in combination with unspecific and insensitive detectors. Mass spectrometry (MS) provides sensitive species specific identification, and its incorporation in CE through commercially available CE-MS interface systems can overcome these disadvantages. There are sample introduction incompatibilities when hyphenating the CE to inductively coupled plasma (ICP)-MS, and despite commercially available interfaces, the process remains technically challenging. CE hyphenation to electrospray ionisation (ESI)-mass spectrometry is simple and sensitive with the concentric Agilent CE-ESI-MS sprayer. By designing a PTFE end cap, the Agilent sprayer was connected to the ICP-MS and key nebulisation parameters including, capillary position, sheath liquid and carrier gas flow rate were optimised. Terming the new interface coaxial sheath-flow interface (CSFI)-ICP-MS, compared with the commercially available CEI-100, the CSFI had superior usability, signal-to-noise ratios, and detection limits (0.08 μM Pt) for the study of cisplatin. Run-by-run variability was improved by the development of a robust series of Co(III) internal standards [Co(en)3]Cl3, [Co(acac)3] and K[Co(EDTA)], suitable for a broad range of detection systems, including UV, ESI-MS and ICP-MS. The cobalt internal standards were applied in various applications from the proto-typical cisplatin with guanosine 5'-monophosphate, to complex protein-containing mixtures, and data analyses were improved with up to three times lower detection limits, standardised migration times and peak areas, and simplified species transformation tracking over time. Incorporation of a capillary coating increased serum protein resolution, and metal-protein adduct identification, helping to create an efficient metabolite screening method for the in vitro analysis of the metallodrugs cisplatin and RAPTA-C. Analyses demonstrated that the extracellular speciation behaviour of metals can be correlated to their cellular uptake. All presented techniques and methods have improved CE analyses by enhancing sensitivity and reliability, allowing studies of metal complexes in biological sample matrices to be carried out with high efficiency. The principle criticisms of CE are addressed and the presented solutions are simple, but effective, which can lead to greater inclusion of this instrument in routine analysis for metallodrugs or even other purposes in the future.