The development of ICP-MS methods for the study of biomedical problems particularly those involving nucleic acids
thesisposted on 16.08.2019, 08:21 authored by Peter D. Winship
Inductively coupled plasma mass spectrometry (ICP-MS) is a well established and versatile technique for the elemental analysis of a wide spectrum of samples. For a majority of the elements that can be analysed by ICP-MS limits of detection in the order of sub ng 1 1 levels can be attained. However, a number of these elements have problems associated with them that lead to a restriction of the limits of detection that can be achieved. Phosphorus and Sulphur are two such elements that exhibit poorer limits of detection, the improvement of which would be highly desirable to the ICPMS analyst. Six methods for the measurement of 31p and 32S isotopes have been developed with the aim of avoiding the spectroscopic interferences at the native m/z ratios of 31 and 32 respectively. These approaches have utilised a hexapole collision cell, a 'cold/cool plasma' and an experimental ICP torch bonnet. Via the collision cell and 'cold/cool plasma' approaches the isotopes of interest were either converted to different species for successful measurement at an alternative m/z ratio or interfering species were removed allowing measurement at the native m/z. Limits of detection achieved by these approaches were comparable with those quoted in the literature and by ICP-MS instrument manufacturers. The approach using the torch bonnet was not successful in attenuating spectroscopic interferences; however, it did show potential for continuing as an area of research. The development of these six methods is discussed in Chapter 2. As an application of the successful methods developed for the measurement Of 31p and 328 isotopes, DNA (and its associated components) was selected for study as this biomolecule is comprised of approximately IO % phosphorus. DNA in solution was successfully quantified by these methods and DNA components, studied during polymerase chain reaction processes and in single nucleotide polymorphisms, were qualified. The application of these methods to the study of DNA and its components is discussed in Chapter 3. As part of a collaboration between the Loughborough University Atomic Spectroscopy Research Group and the Cancer Biomarkers and Prevention Group at the University of Leicester, ICP-MS was employed in the investigation of the interactions between two Pt based anti-cancer drugs (cisplatin and oxaliplatin) and their biological target DNA. For this collaboration, DNA was the interest common to both groups. The interaction of each of these drugs with known quantities of DNA was measured by ICP-MS and binding constant data was calculated for use as the basis of a clinical test for drug efficacy in cancer patients. The binding constant data showed that the interaction between drug and target is particularly inefficient. This area of research is discussed in Chapter 4. The potential for ICP-MS interface modification was also explored. Two modified designs are discussed that may prove to be advantageous for the transport of ions between the atmospheric pressure conditions of the ICP ion source and the vacuum conditions of the mass spectrometer. One of these designs was successfully manufactured and produced positive data. Research into this design is being furthered by the Thermo Electron Corporation, the discussion of which is in Chapter 5. A further collaboration was established with both the Biomaterials-related Infection Group of the School of Medical and Surgical Sciences and the Polymer Group of the School of Mechanical, Materials and Manufacturing Engineering at the University of Nottingham. Here ICP-MS was employed in the measurement of silver leaching from a silver nano-particle impregnated polymer material that could be used in the production of catheters. Silver leaching from a catheter is potentially desirable due to its anti-microbial properties. The study of this leaching revealed that significant quantities of silver were being transferred from the polymer into surrounding human serum media over the period of seven days and beyond. For the most part this work was routine ICP-MS measurement, and did not involve research or development, so does not take part in the main body of this thesis. This work is discussed in Appendix 5.