Surface modification of chromatography adsorbents by low temperature low pressure plasma

• Published in: Journal of Chromatography A 2010-10, Vol.1217 (44), p.6905-6916
• Main Authors: Arpanaei, A., Winther-Jensen, B., Theodosiou, E., Kingshott, P., Hobley, T.J., Thomas, O.R.T.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Analytical, structural and metabolic biochemistry; Anti-fouling; Biological and medical sciences; Chemistry; Chromatographic methods and physical methods associated with chromatography; Dna, deoxyribonucleoproteins; Exact sciences and technology; Expanded bed adsorption; Fundamental and applied biological sciences. Psychology; General aspects, investigation methods; Ion exchange; Non-adsorptive surfaces; Nucleic acids; Other chromatographic methods; Plasma etching/polymerization; Protein and plasmid DNA separation; Proteins; Size exclusion; Support cross-linking
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2010.08.069

In this study we show how low temperature glow discharge plasma can be used to prepare bi-layered chromatography adsorbents with non-adsorptive exteriors. The commercial strong anion exchange expanded bed chromatography matrix, Q HyperZ, was treated with plasmas in one of two general ways. Using a purpose-designed rotating reactor, plasmas were employed to either: (i) remove anion exchange ligands at or close to the exterior surface of Q HyperZ, and replace them with polar oxygen containing functions (‘plasma etching and oxidation’); or (ii) bury the same surface exposed ligands beneath thin polymer coatings (‘plasma polymerization coating’) using appropriate monomers (vinyl acetate, vinyl pyrrolidone, safrole) and argon as the carrier gas. X-ray photoelectron spectroscopy analysis (first ∼10 nm depth) of Q HyperZ before and after the various plasma treatments confirmed that substantial changes to the elemental composition of Q HyperZ's exterior had been inflicted in all cases. The atomic percent changes in carbon, nitrogen, oxygen, yttrium and zirconium observed after being exposed to air plasma etching were entirely consistent with: the removal of pendant Q (trimethylammonium) functions; increased exposure of the underlying yttrium-stabilised zirconia shell; and introduction of hydroxyl and carbonyl functions. Following plasma polymerization treatments (with all three monomers tested), the increased atomic percent levels of carbon and parallel drops in nitrogen, yttrium and zirconium provided clear evidence that thin polymer coats had been created at the exteriors of Q HyperZ adsorbent particles. No changes in adsorbent size and surface morphology, nor any evidence of plasma-induced damage could be discerned from scanning electron micrographs, light micrographs and measurements of particle size distributions following 3 h exposure to air (220 V; 35.8 W L −1) or ‘vinyl acetate/argon’ (170 V; 16.5 W L −1) plasmas. Losses in bulk chloride exchange capacity before and after exposure to plasmas enabled effective modification depths within hydrated Q HyperZ adsorbent particles to be calculated as 0.2–1.2 μm, depending on the conditions applied. The depth of plasma induced alteration was strongly influenced by the power input and size of the treated batch, i.e. dropping the power or increasing the batch size resulted in reduced plasma penetration and therefore shallower modification. The selectivity of ‘surface vs. core’ modification imparted to Q HyperZ by the