Effects of acid treatment on the trace metal content of chromatographic silica: bulk analysis, surface analysis and chromatographic performance of bonded phases

• Published in: Journal of Chromatography A Vol. 905; no. 1; pp. 69 - 83
• Main Authors: Barrett, D.A, Brown, V.A, Watson, R.C, Davies, M.C, Shaw, P.N, Ritchie, H.J, Ross, P
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05.01.2001; Elsevier
• Subjects: Acids; Analytical chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, Liquid - instrumentation; Electron Probe Microanalysis; Exact sciences and technology; Metals - analysis; Other chromatographic methods; Silica; Silicon Dioxide - chemistry; Surface Properties; Weak bases; Acid treatment; Weak bases; Silica; Silanols; Stationary phases, LC; Trace analysis; Performance evaluation; Peak resolution; Weak base; Chromatographic retention; HPLC chromatography; Metal; Surface analysis; Experimental study; Acidic solution; Pyridine derivatives; Ultraviolet detector; Plate efficiency; Chemical treatment; Dilute solution; Silica gel; Pretreatment; Bonded stationary phase
• ISSN: 0021-9673
• DOI: 10.1016/S0021-9673(00)01000-1

A series of studies has been carried out on the effect of refluxing silica chromatography particles for 0.5 h and 18 h in water, dilute hydrochloric acid and dilute hydrofluoric acid. The bulk and surface trace metal concentrations were measured by inductively-coupled plasma atomic emission spectroscopy, static secondary ion mass spectrometry (SSIMS) and X-ray photoelectron spectroscopy. Diffuse reflectance Fourier transform infrared spectroscopy was used to determine changes in “isolated” and “bonded” silanol groups. The chromatographic behaviour of a series of weakly basic analytes was investigated on C 8 and C 18 bonded phases manufactured from the acid-treated silicas. The different reflux treatments all resulted in a reduction in the numbers of isolated silanols compared with the untreated silica and SSIMS analysis suggested that the HF-treated silicas had undergone a more efficient surface rehydroxylation. Bulk trace metals were removed most effectively by the HF treatment, with the multivalent elements (Ti and Al) being the most difficult to remove. Surface specific analysis suggested that trace metals were removed more rapidly from the surface of the silica compared to the bulk matrix and that the acid treatments resulted in halide contamination of the silica surface. Evidence is presented to suggest that the bulk metal content of the silica is not representative of the concentration of metals at the chromatographic surface. The chromatographic investigations showed that the HF-treated silica gave substantially better performance towards weak bases than the HCl-treated silicas.